From 4fd4e48425097d9e5b504fede268eea7fcf9db7a Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Tue, 24 Mar 2026 17:41:35 +0900
Subject: [PATCH 01/43] wip: add mergeReportsLabel

---
 packages/vitest/src/node/cli/cli-config.ts      |  5 +++++
 .../vitest/src/node/config/resolveConfig.ts     |  6 ++++++
 packages/vitest/src/node/reporters/blob.ts      | 17 ++++++++++++++---
 packages/vitest/src/node/types/config.ts        |  8 ++++++++
 4 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/packages/vitest/src/node/cli/cli-config.ts b/packages/vitest/src/node/cli/cli-config.ts
index f1cb5cc3ee06..4fade97dfe15 100644
--- a/packages/vitest/src/node/cli/cli-config.ts
+++ b/packages/vitest/src/node/cli/cli-config.ts
@@ -827,6 +827,11 @@ export const cliOptionsConfig: VitestCLIOptions = {
       return value
     },
   },
+  mergeReportsLabel: {
+    description:
+      'Label for this test run\'s environment (e.g., "linux", "node-22"). Suffixes the project name so blobs from different environments are distinct during merge',
+    argument: '<label>',
+  },
   listTags: {
     description: 'List all available tags instead of running tests. `--list-tags=json` will output tags in JSON format, unless there are no tags.',
     argument: '[type]',
diff --git a/packages/vitest/src/node/config/resolveConfig.ts b/packages/vitest/src/node/config/resolveConfig.ts
index 78964c1829c7..45fda87edf43 100644
--- a/packages/vitest/src/node/config/resolveConfig.ts
+++ b/packages/vitest/src/node/config/resolveConfig.ts
@@ -226,6 +226,12 @@ export function resolveConfig(
     ? options.name
     : (options.name?.label || '')
 
+  if (resolved.mergeReportsLabel) {
+    resolved.name = resolved.name
+      ? `${resolved.name} [${resolved.mergeReportsLabel}]`
+      : resolved.mergeReportsLabel
+  }
+
   resolved.color = typeof options.name !== 'string' ? options.name?.color : undefined
 
   if (resolved.environment === 'browser') {
diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index 32dd65948bd7..466c8d92eec8 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -50,9 +50,20 @@ export class BlobReporter implements Reporter {
       = this.options.outputFile ?? getOutputFile(this.ctx.config, 'blob')
     if (!outputFile) {
       const shard = this.ctx.config.shard
-      outputFile = shard
-        ? `.vitest-reports/blob-${shard.index}-${shard.count}.json`
-        : '.vitest-reports/blob.json'
+      const label = this.ctx.config.mergeReportsLabel
+      // TODO: join
+      if (shard && label) {
+        outputFile = `.vitest-reports/blob-${label}-${shard.index}-${shard.count}.json`
+      }
+      else if (shard) {
+        outputFile = `.vitest-reports/blob-${shard.index}-${shard.count}.json`
+      }
+      else if (label) {
+        outputFile = `.vitest-reports/blob-${label}.json`
+      }
+      else {
+        outputFile = '.vitest-reports/blob.json'
+      }
     }
 
     const environmentModules: MergeReportEnvironmentModules = {}
diff --git a/packages/vitest/src/node/types/config.ts b/packages/vitest/src/node/types/config.ts
index 3f6ec9ece2db..ba9d187b3f5e 100644
--- a/packages/vitest/src/node/types/config.ts
+++ b/packages/vitest/src/node/types/config.ts
@@ -1091,6 +1091,14 @@ export interface UserConfig extends InlineConfig {
    */
   mergeReports?: string
 
+  // TODO: rename
+  /**
+   * Label for this test run's environment (e.g., "linux", "node-22").
+   * Suffixes the project name so that blobs from different environments
+   * are treated as distinct projects during merge.
+   */
+  mergeReportsLabel?: string
+
   /**
    * Delete all Vitest caches, including `experimental.fsModuleCache`.
    * @experimental

From 31c89a099d1650b81e428b7d5e69825b013101c4 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Tue, 24 Mar 2026 17:42:51 +0900
Subject: [PATCH 02/43] fix: append label to projects

---
 packages/vitest/src/node/project.ts | 1 +
 1 file changed, 1 insertion(+)

diff --git a/packages/vitest/src/node/project.ts b/packages/vitest/src/node/project.ts
index b6f687db692e..970eed9239c6 100644
--- a/packages/vitest/src/node/project.ts
+++ b/packages/vitest/src/node/project.ts
@@ -547,6 +547,7 @@ export class TestProject {
       {
         ...options,
         coverage: this.vitest.config.coverage,
+        mergeReportsLabel: this.vitest.config.mergeReportsLabel,
       },
       server.config,
     )

From 8753200a314676ac7039a8a84d1973c9088008cc Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Tue, 24 Mar 2026 18:14:14 +0900
Subject: [PATCH 03/43] wip: mergeReportsLabels?: string[]

---
 packages/vitest/src/node/cli/cli-config.ts | 6 ++++++
 packages/vitest/src/node/types/config.ts   | 7 +++++++
 2 files changed, 13 insertions(+)

diff --git a/packages/vitest/src/node/cli/cli-config.ts b/packages/vitest/src/node/cli/cli-config.ts
index 4fade97dfe15..fc4e7abdad80 100644
--- a/packages/vitest/src/node/cli/cli-config.ts
+++ b/packages/vitest/src/node/cli/cli-config.ts
@@ -832,6 +832,12 @@ export const cliOptionsConfig: VitestCLIOptions = {
       'Label for this test run\'s environment (e.g., "linux", "node-22"). Suffixes the project name so blobs from different environments are distinct during merge',
     argument: '<label>',
   },
+  mergeReportsLabels: {
+    description:
+      'Expected labels when merging reports from multiple environments. Repeat the flag for multiple labels',
+    argument: '<label>',
+    array: true,
+  },
   listTags: {
     description: 'List all available tags instead of running tests. `--list-tags=json` will output tags in JSON format, unless there are no tags.',
     argument: '[type]',
diff --git a/packages/vitest/src/node/types/config.ts b/packages/vitest/src/node/types/config.ts
index ba9d187b3f5e..7b97bf73c819 100644
--- a/packages/vitest/src/node/types/config.ts
+++ b/packages/vitest/src/node/types/config.ts
@@ -1099,6 +1099,13 @@ export interface UserConfig extends InlineConfig {
    */
   mergeReportsLabel?: string
 
+  /**
+   * Labels expected when merging reports from multiple environments.
+   * These will later be used to synthesize distinct project identities
+   * during merge.
+   */
+  mergeReportsLabels?: string[]
+
   /**
    * Delete all Vitest caches, including `experimental.fsModuleCache`.
    * @experimental

From cf6df38cdd28bfac459e201a312e08f9a6546692 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Tue, 24 Mar 2026 18:59:11 +0900
Subject: [PATCH 04/43] wip: cloneProject

---
 packages/vitest/src/node/core.ts              |  5 +-
 packages/vitest/src/node/project.ts           |  9 ++-
 .../src/node/projects/resolveProjects.ts      | 69 ++++++++++++++++++-
 test/cli/test/projects.test.ts                | 61 ++++++++++++++++
 4 files changed, 140 insertions(+), 4 deletions(-)

diff --git a/packages/vitest/src/node/core.ts b/packages/vitest/src/node/core.ts
index 60ce250c24bb..bb47063a4ea7 100644
--- a/packages/vitest/src/node/core.ts
+++ b/packages/vitest/src/node/core.ts
@@ -43,7 +43,7 @@ import { collectModuleDurationsDiagnostic, collectSourceModulesLocations } from
 import { VitestPackageInstaller } from './packageInstaller'
 import { createPool } from './pool'
 import { TestProject } from './project'
-import { getDefaultTestProject, resolveBrowserProjects, resolveProjects } from './projects/resolveProjects'
+import { getDefaultTestProject, resolveBrowserProjects, resolveMergeReportProjects, resolveProjects } from './projects/resolveProjects'
 import { BlobReporter, readBlobs } from './reporters/blob'
 import { HangingProcessReporter } from './reporters/hanging-process'
 import { createBenchmarkReporters, createReporters } from './reporters/utils'
@@ -558,7 +558,8 @@ export class Vitest {
     if (!project) {
       return []
     }
-    return resolveBrowserProjects(this, new Set([project.name]), [project])
+    const browserProjects = await resolveBrowserProjects(this, new Set([project.name]), [project])
+    return resolveMergeReportProjects(this, new Set(browserProjects.map(project => project.name)), browserProjects)
   }
 
   /**
diff --git a/packages/vitest/src/node/project.ts b/packages/vitest/src/node/project.ts
index 970eed9239c6..e8a3dfec8320 100644
--- a/packages/vitest/src/node/project.ts
+++ b/packages/vitest/src/node/project.ts
@@ -728,7 +728,7 @@ export class TestProject {
   }
 
   /** @internal */
-  static _cloneBrowserProject(parent: TestProject, config: ResolvedConfig): TestProject {
+  static _cloneProject(parent: TestProject, config: ResolvedConfig): TestProject {
     const clone = new TestProject(parent.vitest, undefined, parent.tmpDir)
     clone.runner = parent.runner
     clone._vite = parent._vite
@@ -741,6 +741,13 @@ export class TestProject {
     clone._provideObject(config.provide)
     return clone
   }
+
+  /** @internal */
+  static _cloneBrowserProject(parent: TestProject, config: ResolvedConfig): TestProject {
+    const clone = TestProject._cloneProject(parent, config)
+    clone._parent = parent
+    return clone
+  }
 }
 
 function deduped<T extends (...args: any[]) => Promise<void>>(cb: T): T {
diff --git a/packages/vitest/src/node/projects/resolveProjects.ts b/packages/vitest/src/node/projects/resolveProjects.ts
index bd69651a5510..55e0d9cea7b0 100644
--- a/packages/vitest/src/node/projects/resolveProjects.ts
+++ b/packages/vitest/src/node/projects/resolveProjects.ts
@@ -197,7 +197,8 @@ export async function resolveProjects(
     names.add(name)
   }
 
-  return resolveBrowserProjects(vitest, names, resolvedProjects)
+  const browserProjects = await resolveBrowserProjects(vitest, names, resolvedProjects)
+  return resolveMergeReportProjects(vitest, names, browserProjects)
 }
 
 export async function resolveBrowserProjects(
@@ -269,6 +270,61 @@ export async function resolveBrowserProjects(
   return resolvedProjects.filter(project => !removeProjects.has(project))
 }
 
+// TODO: review
+export function resolveMergeReportProjects(
+  vitest: Vitest,
+  names: Set<string>,
+  resolvedProjects: TestProject[],
+): TestProject[] {
+  const labels = vitest.config.mergeReportsLabels
+  if (!labels?.length) {
+    return resolvedProjects
+  }
+
+  const removeProjects = new Set<TestProject>()
+
+  resolvedProjects.forEach((project) => {
+    const originalName = project.name
+    const filteredLabels = vitest.matchesProjectFilter(originalName)
+      ? labels
+      : labels.filter((label) => {
+          const nextName = originalName
+            ? `${originalName} [${label}]`
+            : label
+          return vitest.matchesProjectFilter(nextName)
+        })
+
+    if (!filteredLabels.length) {
+      removeProjects.add(project)
+      return
+    }
+
+    filteredLabels.forEach((label) => {
+      const name = originalName
+        ? `${originalName} [${label}]`
+        : label
+
+      if (names.has(name)) {
+        throw new Error(
+          `Project name "${name}" is not unique. All projects should have unique names. Make sure your configuration is correct.`,
+        )
+      }
+
+      names.add(name)
+      resolvedProjects.push(
+        TestProject._cloneProject(
+          project,
+          cloneMergeReportProjectConfig(project, label, name),
+        ),
+      )
+    })
+
+    removeProjects.add(project)
+  })
+
+  return resolvedProjects.filter(project => !removeProjects.has(project))
+}
+
 function cloneConfig(project: TestProject, { browser, ...config }: BrowserInstanceOption) {
   const {
     locators,
@@ -313,6 +369,17 @@ function cloneConfig(project: TestProject, { browser, ...config }: BrowserInstan
   } satisfies ResolvedConfig, overrideConfig) as ResolvedConfig
 }
 
+function cloneMergeReportProjectConfig(
+  project: TestProject,
+  label: string,
+  name: string,
+): ResolvedConfig {
+  const clonedConfig = deepClone(project.config)
+  clonedConfig.mergeReportsLabel = label
+  clonedConfig.name = name
+  return clonedConfig
+}
+
 async function resolveTestProjectConfigs(
   vitest: Vitest,
   workspaceConfigPath: string | undefined,
diff --git a/test/cli/test/projects.test.ts b/test/cli/test/projects.test.ts
index 0495ca4a1c48..777a3ac32f5c 100644
--- a/test/cli/test/projects.test.ts
+++ b/test/cli/test/projects.test.ts
@@ -110,6 +110,67 @@ it('can define inline workspace config programmatically', async () => {
   expect(stdout).toContain('3 passed')
 })
 
+// TODO: more cases
+// - single browser instance
+// - multiple browser instances
+// - multiple browser instances with multiple projects
+it('duplicates the default project for mergeReportsLabels', async () => {
+  const { ctx, stderr, exitCode } = await runInlineTests({
+    'basic.test.js': `
+      import { expect, test } from 'vitest'
+
+      test('works', () => {
+        expect(1).toBe(1)
+      })
+    `,
+  }, {
+    name: 'base',
+    mergeReportsLabels: ['linux', 'macos'],
+  })
+
+  expect(exitCode).toBe(0)
+  expect(stderr).toBe('')
+  expect(ctx?.projects.map(project => project.name).sort()).toEqual([
+    'base [linux]',
+    'base [macos]',
+  ])
+})
+
+it('duplicates configured projects for mergeReportsLabels', async () => {
+  const { ctx, stderr, exitCode } = await runInlineTests({
+    'basic.test.js': `
+      import { expect, test } from 'vitest'
+
+      test('works', () => {
+        expect(1).toBe(1)
+      })
+    `,
+  }, {
+    mergeReportsLabels: ['linux', 'macos'],
+    projects: [
+      {
+        test: {
+          name: 'server',
+        },
+      },
+      {
+        test: {
+          name: 'client',
+        },
+      },
+    ],
+  })
+
+  expect(exitCode).toBe(0)
+  expect(stderr).toBe('')
+  expect(ctx?.projects.map(project => project.name).sort()).toEqual([
+    'client [linux]',
+    'client [macos]',
+    'server [linux]',
+    'server [macos]',
+  ])
+})
+
 it('correctly inherits the root config', async () => {
   const { stderr, stdout } = await runVitest({
     root: 'fixtures/workspace/config-extends',

From 15ca046d22ec97207a2afa32d19951fe4033d1bd Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 10:52:57 +0900
Subject: [PATCH 05/43] wip: slop

---
 packages/vitest/src/node/core.ts              | 19 +++++++-
 .../src/node/projects/resolveProjects.ts      |  2 +-
 packages/vitest/src/node/reporters/blob.ts    | 38 ++++++++++++++++
 test/cli/test/reporters/merge-reports.test.ts | 45 ++++++++++++++++++-
 4 files changed, 100 insertions(+), 4 deletions(-)

diff --git a/packages/vitest/src/node/core.ts b/packages/vitest/src/node/core.ts
index bb47063a4ea7..a656c4048f5d 100644
--- a/packages/vitest/src/node/core.ts
+++ b/packages/vitest/src/node/core.ts
@@ -44,7 +44,7 @@ import { VitestPackageInstaller } from './packageInstaller'
 import { createPool } from './pool'
 import { TestProject } from './project'
 import { getDefaultTestProject, resolveBrowserProjects, resolveMergeReportProjects, resolveProjects } from './projects/resolveProjects'
-import { BlobReporter, readBlobs } from './reporters/blob'
+import { BlobReporter, discoverMergeReportLabels, readBlobs } from './reporters/blob'
 import { HangingProcessReporter } from './reporters/hanging-process'
 import { createBenchmarkReporters, createReporters } from './reporters/utils'
 import { VitestResolver } from './resolver'
@@ -606,7 +606,22 @@ export class Vitest {
         throw new Error('Cannot merge reports when `--reporter=blob` is used. Remove blob reporter from the config first.')
       }
 
-      const { files, errors, coverages, executionTimes } = await readBlobs(this.version, directory || this.config.mergeReports, this.projects)
+      // TODO: move projects duplication inside `readBlobs(ctx: Vitest, ...)`
+      // TODO: auto-discover labels from blob content not filename.
+      const reportsDirectory = directory || this.config.mergeReports
+      if (!this.config.mergeReportsLabels?.length) {
+        const labels = await discoverMergeReportLabels(reportsDirectory)
+        if (labels?.length) {
+          this.projects = resolveMergeReportProjects(
+            this,
+            new Set(this.projects.map(project => project.name)),
+            this.projects,
+            labels,
+          )
+        }
+      }
+
+      const { files, errors, coverages, executionTimes } = await readBlobs(this.version, reportsDirectory, this.projects)
       this.state.blobs = { files, errors, coverages, executionTimes }
 
       await this.report('onInit', this)
diff --git a/packages/vitest/src/node/projects/resolveProjects.ts b/packages/vitest/src/node/projects/resolveProjects.ts
index 55e0d9cea7b0..beb9877a67f8 100644
--- a/packages/vitest/src/node/projects/resolveProjects.ts
+++ b/packages/vitest/src/node/projects/resolveProjects.ts
@@ -275,8 +275,8 @@ export function resolveMergeReportProjects(
   vitest: Vitest,
   names: Set<string>,
   resolvedProjects: TestProject[],
+  labels: string[] = vitest.config.mergeReportsLabels,
 ): TestProject[] {
-  const labels = vitest.config.mergeReportsLabels
   if (!labels?.length) {
     return resolvedProjects
   }
diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index 466c8d92eec8..d7a40582e116 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -222,6 +222,26 @@ export async function readBlobs(
   }
 }
 
+export async function discoverMergeReportLabels(blobsDirectory: string): Promise<string[] | undefined> {
+  // using process.cwd() because --merge-reports can only be used in CLI
+  const resolvedDir = resolve(process.cwd(), blobsDirectory)
+  const blobsFiles = await readdir(resolvedDir)
+  const labels = new Set<string>()
+
+  for (const filename of blobsFiles) {
+    const label = getBlobFilenameLabel(filename)
+    if (label) {
+      labels.add(label)
+    }
+  }
+
+  if (!labels.size) {
+    return undefined
+  }
+
+  return [...labels]
+}
+
 export interface MergedBlobs {
   files: File[]
   errors: unknown[]
@@ -238,6 +258,24 @@ type MergeReport = [
   environmentModules: MergeReportEnvironmentModules,
 ]
 
+function getBlobFilenameLabel(filename: string): string | undefined {
+  const match = filename.match(/^blob-(.+?)(?:-(\d+)-(\d+))?\.json$/)
+  if (!match) {
+    return undefined
+  }
+
+  const [, label, shardIndex, shardCount] = match
+  if (shardIndex && shardCount) {
+    return label
+  }
+
+  if (label.match(/^\d+-\d+$/)) {
+    return undefined
+  }
+
+  return label
+}
+
 interface MergeReportEnvironmentModules {
   [projectName: string]: {
     environments: {
diff --git a/test/cli/test/reporters/merge-reports.test.ts b/test/cli/test/reporters/merge-reports.test.ts
index 2f445b5c20f9..448949b60b93 100644
--- a/test/cli/test/reporters/merge-reports.test.ts
+++ b/test/cli/test/reporters/merge-reports.test.ts
@@ -2,7 +2,7 @@ import type { File, Test } from '@vitest/runner/types'
 import type { TestUserConfig, Vitest } from 'vitest/node'
 import { rmSync } from 'node:fs'
 import { resolve } from 'node:path'
-import { runVitest } from '#test-utils'
+import { runInlineTests, runVitest } from '#test-utils'
 import { playwright } from '@vitest/browser-playwright'
 import { createFileTask } from '@vitest/runner/utils'
 import { beforeEach, expect, test } from 'vitest'
@@ -246,6 +246,49 @@ test('merge reports', async () => {
   `)
 })
 
+// TODO
+test('auto-discovers merge report labels from default blob filenames', async () => {
+  // const { root } = await runInlineTests({
+  //   'basic.test.ts': `
+  //     import { expect, test } from 'vitest'
+
+  //     test('works', () => {
+  //       expect(1).toBe(1)
+  //     })
+  //   `,
+  // }, {
+  //   name: 'base',
+  // })
+
+  // await runVitest({
+  //   root,
+  //   name: 'base',
+  //   reporters: ['blob'],
+  //   mergeReportsLabel: 'linux',
+  // })
+
+  // await runVitest({
+  //   root,
+  //   name: 'base',
+  //   reporters: ['blob'],
+  //   mergeReportsLabel: 'macos',
+  // })
+
+  // const result = await runVitest({
+  //   root,
+  //   name: 'base',
+  //   mergeReports: resolve(root, '.vitest-reports'),
+  //   reporters: [['default', { isTTY: false }]],
+  // })
+
+  // expect(exitCode).toBe(0)
+  // expect(stderr).toBe('')
+  // expect(ctx?.projects.map(project => project.name).sort()).toEqual([
+  //   'base [linux]',
+  //   'base [macos]',
+  // ])
+})
+
 test('total and merged execution times are shown', async () => {
   for (const [_index, name] of ['first.test.ts', 'second.test.ts'].entries()) {
     const index = 1 + _index

From 42a977953bd61e71a1be7ba5325567521a17e331 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 10:55:27 +0900
Subject: [PATCH 06/43] wip: no slop

---
 packages/vitest/src/node/core.ts              | 3 +--
 test/cli/test/reporters/merge-reports.test.ts | 2 +-
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/packages/vitest/src/node/core.ts b/packages/vitest/src/node/core.ts
index a656c4048f5d..06267e3052d4 100644
--- a/packages/vitest/src/node/core.ts
+++ b/packages/vitest/src/node/core.ts
@@ -558,8 +558,7 @@ export class Vitest {
     if (!project) {
       return []
     }
-    const browserProjects = await resolveBrowserProjects(this, new Set([project.name]), [project])
-    return resolveMergeReportProjects(this, new Set(browserProjects.map(project => project.name)), browserProjects)
+    return resolveBrowserProjects(this, new Set([project.name]), [project])
   }
 
   /**
diff --git a/test/cli/test/reporters/merge-reports.test.ts b/test/cli/test/reporters/merge-reports.test.ts
index 448949b60b93..5a68f5422399 100644
--- a/test/cli/test/reporters/merge-reports.test.ts
+++ b/test/cli/test/reporters/merge-reports.test.ts
@@ -2,7 +2,7 @@ import type { File, Test } from '@vitest/runner/types'
 import type { TestUserConfig, Vitest } from 'vitest/node'
 import { rmSync } from 'node:fs'
 import { resolve } from 'node:path'
-import { runInlineTests, runVitest } from '#test-utils'
+import { runVitest } from '#test-utils'
 import { playwright } from '@vitest/browser-playwright'
 import { createFileTask } from '@vitest/runner/utils'
 import { beforeEach, expect, test } from 'vitest'

From 19c1e0242d22a7c85f45cb81dfc90bab7ea20b17 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 10:58:26 +0900
Subject: [PATCH 07/43] chore: no slop

---
 .../vitest/src/node/config/resolveConfig.ts   |  1 +
 packages/vitest/src/node/types/config.ts      |  2 +-
 test/cli/test/projects.test.ts                | 61 -----------------
 test/cli/test/reporters/merge-reports.test.ts | 65 ++++++++++++++++++-
 4 files changed, 65 insertions(+), 64 deletions(-)

diff --git a/packages/vitest/src/node/config/resolveConfig.ts b/packages/vitest/src/node/config/resolveConfig.ts
index 45fda87edf43..bbea71cdf03a 100644
--- a/packages/vitest/src/node/config/resolveConfig.ts
+++ b/packages/vitest/src/node/config/resolveConfig.ts
@@ -227,6 +227,7 @@ export function resolveConfig(
     : (options.name?.label || '')
 
   if (resolved.mergeReportsLabel) {
+    // TODO: can we move project mutation only at blob report stage?
     resolved.name = resolved.name
       ? `${resolved.name} [${resolved.mergeReportsLabel}]`
       : resolved.mergeReportsLabel
diff --git a/packages/vitest/src/node/types/config.ts b/packages/vitest/src/node/types/config.ts
index 7b97bf73c819..6debc1d5c051 100644
--- a/packages/vitest/src/node/types/config.ts
+++ b/packages/vitest/src/node/types/config.ts
@@ -1091,7 +1091,7 @@ export interface UserConfig extends InlineConfig {
    */
   mergeReports?: string
 
-  // TODO: rename
+  // TODO: remove
   /**
    * Label for this test run's environment (e.g., "linux", "node-22").
    * Suffixes the project name so that blobs from different environments
diff --git a/test/cli/test/projects.test.ts b/test/cli/test/projects.test.ts
index 777a3ac32f5c..0495ca4a1c48 100644
--- a/test/cli/test/projects.test.ts
+++ b/test/cli/test/projects.test.ts
@@ -110,67 +110,6 @@ it('can define inline workspace config programmatically', async () => {
   expect(stdout).toContain('3 passed')
 })
 
-// TODO: more cases
-// - single browser instance
-// - multiple browser instances
-// - multiple browser instances with multiple projects
-it('duplicates the default project for mergeReportsLabels', async () => {
-  const { ctx, stderr, exitCode } = await runInlineTests({
-    'basic.test.js': `
-      import { expect, test } from 'vitest'
-
-      test('works', () => {
-        expect(1).toBe(1)
-      })
-    `,
-  }, {
-    name: 'base',
-    mergeReportsLabels: ['linux', 'macos'],
-  })
-
-  expect(exitCode).toBe(0)
-  expect(stderr).toBe('')
-  expect(ctx?.projects.map(project => project.name).sort()).toEqual([
-    'base [linux]',
-    'base [macos]',
-  ])
-})
-
-it('duplicates configured projects for mergeReportsLabels', async () => {
-  const { ctx, stderr, exitCode } = await runInlineTests({
-    'basic.test.js': `
-      import { expect, test } from 'vitest'
-
-      test('works', () => {
-        expect(1).toBe(1)
-      })
-    `,
-  }, {
-    mergeReportsLabels: ['linux', 'macos'],
-    projects: [
-      {
-        test: {
-          name: 'server',
-        },
-      },
-      {
-        test: {
-          name: 'client',
-        },
-      },
-    ],
-  })
-
-  expect(exitCode).toBe(0)
-  expect(stderr).toBe('')
-  expect(ctx?.projects.map(project => project.name).sort()).toEqual([
-    'client [linux]',
-    'client [macos]',
-    'server [linux]',
-    'server [macos]',
-  ])
-})
-
 it('correctly inherits the root config', async () => {
   const { stderr, stdout } = await runVitest({
     root: 'fixtures/workspace/config-extends',
diff --git a/test/cli/test/reporters/merge-reports.test.ts b/test/cli/test/reporters/merge-reports.test.ts
index 5a68f5422399..63c74811e37e 100644
--- a/test/cli/test/reporters/merge-reports.test.ts
+++ b/test/cli/test/reporters/merge-reports.test.ts
@@ -2,7 +2,7 @@ import type { File, Test } from '@vitest/runner/types'
 import type { TestUserConfig, Vitest } from 'vitest/node'
 import { rmSync } from 'node:fs'
 import { resolve } from 'node:path'
-import { runVitest } from '#test-utils'
+import { runInlineTests, runVitest } from '#test-utils'
 import { playwright } from '@vitest/browser-playwright'
 import { createFileTask } from '@vitest/runner/utils'
 import { beforeEach, expect, test } from 'vitest'
@@ -246,7 +246,68 @@ test('merge reports', async () => {
   `)
 })
 
-// TODO
+
+// TODO: more cases
+// - single browser instance
+// - multiple browser instances
+// - multiple browser instances with multiple projects
+test('duplicates the default project for mergeReportsLabels', async () => {
+  const { ctx, stderr, exitCode } = await runInlineTests({
+    'basic.test.js': `
+      import { expect, test } from 'vitest'
+
+      test('works', () => {
+        expect(1).toBe(1)
+      })
+    `,
+  }, {
+    name: 'base',
+    mergeReportsLabels: ['linux', 'macos'],
+  })
+
+  expect(exitCode).toBe(0)
+  expect(stderr).toBe('')
+  expect(ctx?.projects.map(project => project.name).sort()).toEqual([
+    'base [linux]',
+    'base [macos]',
+  ])
+})
+
+test('duplicates configured projects for mergeReportsLabels', async () => {
+  const { ctx, stderr, exitCode } = await runInlineTests({
+    'basic.test.js': `
+      import { expect, test } from 'vitest'
+
+      test('works', () => {
+        expect(1).toBe(1)
+      })
+    `,
+  }, {
+    mergeReportsLabels: ['linux', 'macos'],
+    projects: [
+      {
+        test: {
+          name: 'server',
+        },
+      },
+      {
+        test: {
+          name: 'client',
+        },
+      },
+    ],
+  })
+
+  expect(exitCode).toBe(0)
+  expect(stderr).toBe('')
+  expect(ctx?.projects.map(project => project.name).sort()).toEqual([
+    'client [linux]',
+    'client [macos]',
+    'server [linux]',
+    'server [macos]',
+  ])
+})
+
 test('auto-discovers merge report labels from default blob filenames', async () => {
   // const { root } = await runInlineTests({
   //   'basic.test.ts': `

From a236b02deecdbfcd6f2eb1069671a6225fa80cc0 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 11:03:40 +0900
Subject: [PATCH 08/43] wip: TODO BlobOptions.label

---
 packages/vitest/src/node/reporters/blob.ts | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index d7a40582e116..91c797d7692a 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -13,6 +13,8 @@ import { getOutputFile } from '../../utils/config-helpers'
 
 export interface BlobOptions {
   outputFile?: string
+  // TODO:
+  // label?: string
 }
 
 export class BlobReporter implements Reporter {

From d4014bde355c193449b03f4f22ec846a1fd7e9e5 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 11:12:02 +0900
Subject: [PATCH 09/43] test: wip

---
 test/cli/test/reporters/merge-reports.test.ts | 172 +++++++-----------
 1 file changed, 67 insertions(+), 105 deletions(-)

diff --git a/test/cli/test/reporters/merge-reports.test.ts b/test/cli/test/reporters/merge-reports.test.ts
index 63c74811e37e..037461ec05bc 100644
--- a/test/cli/test/reporters/merge-reports.test.ts
+++ b/test/cli/test/reporters/merge-reports.test.ts
@@ -2,7 +2,7 @@ import type { File, Test } from '@vitest/runner/types'
 import type { TestUserConfig, Vitest } from 'vitest/node'
 import { rmSync } from 'node:fs'
 import { resolve } from 'node:path'
-import { runInlineTests, runVitest } from '#test-utils'
+import { runVitest } from '#test-utils'
 import { playwright } from '@vitest/browser-playwright'
 import { createFileTask } from '@vitest/runner/utils'
 import { beforeEach, expect, test } from 'vitest'
@@ -246,110 +246,6 @@ test('merge reports', async () => {
   `)
 })
 
-
-// TODO: more cases
-// - single browser instance
-// - multiple browser instances
-// - multiple browser instances with multiple projects
-test('duplicates the default project for mergeReportsLabels', async () => {
-  const { ctx, stderr, exitCode } = await runInlineTests({
-    'basic.test.js': `
-      import { expect, test } from 'vitest'
-
-      test('works', () => {
-        expect(1).toBe(1)
-      })
-    `,
-  }, {
-    name: 'base',
-    mergeReportsLabels: ['linux', 'macos'],
-  })
-
-  expect(exitCode).toBe(0)
-  expect(stderr).toBe('')
-  expect(ctx?.projects.map(project => project.name).sort()).toEqual([
-    'base [linux]',
-    'base [macos]',
-  ])
-})
-
-test('duplicates configured projects for mergeReportsLabels', async () => {
-  const { ctx, stderr, exitCode } = await runInlineTests({
-    'basic.test.js': `
-      import { expect, test } from 'vitest'
-
-      test('works', () => {
-        expect(1).toBe(1)
-      })
-    `,
-  }, {
-    mergeReportsLabels: ['linux', 'macos'],
-    projects: [
-      {
-        test: {
-          name: 'server',
-        },
-      },
-      {
-        test: {
-          name: 'client',
-        },
-      },
-    ],
-  })
-
-  expect(exitCode).toBe(0)
-  expect(stderr).toBe('')
-  expect(ctx?.projects.map(project => project.name).sort()).toEqual([
-    'client [linux]',
-    'client [macos]',
-    'server [linux]',
-    'server [macos]',
-  ])
-})
-
-test('auto-discovers merge report labels from default blob filenames', async () => {
-  // const { root } = await runInlineTests({
-  //   'basic.test.ts': `
-  //     import { expect, test } from 'vitest'
-
-  //     test('works', () => {
-  //       expect(1).toBe(1)
-  //     })
-  //   `,
-  // }, {
-  //   name: 'base',
-  // })
-
-  // await runVitest({
-  //   root,
-  //   name: 'base',
-  //   reporters: ['blob'],
-  //   mergeReportsLabel: 'linux',
-  // })
-
-  // await runVitest({
-  //   root,
-  //   name: 'base',
-  //   reporters: ['blob'],
-  //   mergeReportsLabel: 'macos',
-  // })
-
-  // const result = await runVitest({
-  //   root,
-  //   name: 'base',
-  //   mergeReports: resolve(root, '.vitest-reports'),
-  //   reporters: [['default', { isTTY: false }]],
-  // })
-
-  // expect(exitCode).toBe(0)
-  // expect(stderr).toBe('')
-  // expect(ctx?.projects.map(project => project.name).sort()).toEqual([
-  //   'base [linux]',
-  //   'base [macos]',
-  // ])
-})
-
 test('total and merged execution times are shown', async () => {
   for (const [_index, name] of ['first.test.ts', 'second.test.ts'].entries()) {
     const index = 1 + _index
@@ -585,3 +481,69 @@ function createTest(name: string, file: File): Test {
     context: {} as any,
   }
 }
+
+// TODO: more tests
+// - single browser instance
+// - multiple browser instances
+// - multiple browser instances with multiple projects
+test('merge report with labels', async () => {
+  await runVitest({
+    root: './fixtures/reporters/merge-reports',
+    reporters: ['blob'],
+    mergeReportsLabel: 'linux',
+    // TODO
+    // reporters: [['blob', { label: 'linux' }]],
+  })
+
+  await runVitest({
+    root: './fixtures/reporters/merge-reports',
+    reporters: ['blob'],
+    mergeReportsLabel: 'macos',
+    // TODO
+    // reporters: [['blob', { label: 'macos' }]],
+  })
+
+  const result = await runVitest({
+    root: './fixtures/reporters/merge-reports',
+    mergeReports: reportsDir,
+    reporters: [['default', { isTTY: false }]],
+  })
+  expect(result.errorTree({ project: true })).toMatchInlineSnapshot(`
+    {
+      "linux": {
+        "first.test.ts": {
+          "test 1-1": "passed",
+          "test 1-2": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+        "second.test.ts": {
+          "group": {
+            "test 2-2": "passed",
+            "test 2-3": "passed",
+          },
+          "test 2-1": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+      "macos": {
+        "first.test.ts": {
+          "test 1-1": "passed",
+          "test 1-2": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+        "second.test.ts": {
+          "group": {
+            "test 2-2": "passed",
+            "test 2-3": "passed",
+          },
+          "test 2-1": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+    }
+  `)
+})

From 8b55122baec3a9d3029934b22a75a554d68ada27 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 11:17:55 +0900
Subject: [PATCH 10/43] test: wip

---
 test/cli/test/reporters/merge-reports.test.ts | 96 ++++++++++++++++++-
 1 file changed, 93 insertions(+), 3 deletions(-)

diff --git a/test/cli/test/reporters/merge-reports.test.ts b/test/cli/test/reporters/merge-reports.test.ts
index 037461ec05bc..ef5801b6823d 100644
--- a/test/cli/test/reporters/merge-reports.test.ts
+++ b/test/cli/test/reporters/merge-reports.test.ts
@@ -1,3 +1,4 @@
+import type { RunVitestConfig } from '#test-utils'
 import type { File, Test } from '@vitest/runner/types'
 import type { TestUserConfig, Vitest } from 'vitest/node'
 import { rmSync } from 'node:fs'
@@ -486,9 +487,13 @@ function createTest(name: string, file: File): Test {
 // - single browser instance
 // - multiple browser instances
 // - multiple browser instances with multiple projects
+// - coverage
 test('merge report with labels', async () => {
-  await runVitest({
+  const baseConfig: RunVitestConfig = {
     root: './fixtures/reporters/merge-reports',
+  }
+  await runVitest({
+    ...baseConfig,
     reporters: ['blob'],
     mergeReportsLabel: 'linux',
     // TODO
@@ -496,7 +501,7 @@ test('merge report with labels', async () => {
   })
 
   await runVitest({
-    root: './fixtures/reporters/merge-reports',
+    ...baseConfig,
     reporters: ['blob'],
     mergeReportsLabel: 'macos',
     // TODO
@@ -504,7 +509,7 @@ test('merge report with labels', async () => {
   })
 
   const result = await runVitest({
-    root: './fixtures/reporters/merge-reports',
+    ...baseConfig,
     mergeReports: reportsDir,
     reporters: [['default', { isTTY: false }]],
   })
@@ -547,3 +552,88 @@ test('merge report with labels', async () => {
     }
   `)
 })
+
+test('merge report with labels and projects', async () => {
+  const baseConfig: RunVitestConfig = {
+    root: './fixtures/reporters/merge-reports',
+    projects: [
+      {
+        extends: true,
+        test: {
+          name: 'first',
+          include: ['**/first.test.ts'],
+        },
+      },
+      {
+        extends: true,
+        test: {
+          name: 'second',
+          include: ['**/second.test.ts'],
+        },
+      },
+    ],
+  }
+  await runVitest({
+    ...baseConfig,
+    reporters: ['blob'],
+    mergeReportsLabel: 'linux',
+    // TODO
+    // reporters: [['blob', { label: 'linux' }]],
+  })
+
+  await runVitest({
+    ...baseConfig,
+    reporters: ['blob'],
+    mergeReportsLabel: 'macos',
+    // TODO
+    // reporters: [['blob', { label: 'macos' }]],
+  })
+
+  const result = await runVitest({
+    ...baseConfig,
+    mergeReports: reportsDir,
+    reporters: [['default', { isTTY: false }]],
+  })
+  expect(result.errorTree({ project: true })).toMatchInlineSnapshot(`
+    {
+      "first [linux]": {
+        "first.test.ts": {
+          "test 1-1": "passed",
+          "test 1-2": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+      "first [macos]": {
+        "first.test.ts": {
+          "test 1-1": "passed",
+          "test 1-2": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+      "second [linux]": {
+        "second.test.ts": {
+          "group": {
+            "test 2-2": "passed",
+            "test 2-3": "passed",
+          },
+          "test 2-1": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+      "second [macos]": {
+        "second.test.ts": {
+          "group": {
+            "test 2-2": "passed",
+            "test 2-3": "passed",
+          },
+          "test 2-1": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+    }
+  `)
+})

From 50c32c32c24fd68383ba8bfb61ba9d9ddf1f9957 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 11:30:58 +0900
Subject: [PATCH 11/43] refactor: do more on readBlobs

---
 packages/vitest/src/node/core.ts           | 21 +++------------
 packages/vitest/src/node/reporters/blob.ts | 31 +++++++++++++++-------
 2 files changed, 24 insertions(+), 28 deletions(-)

diff --git a/packages/vitest/src/node/core.ts b/packages/vitest/src/node/core.ts
index 06267e3052d4..4ae72a5b5576 100644
--- a/packages/vitest/src/node/core.ts
+++ b/packages/vitest/src/node/core.ts
@@ -43,8 +43,8 @@ import { collectModuleDurationsDiagnostic, collectSourceModulesLocations } from
 import { VitestPackageInstaller } from './packageInstaller'
 import { createPool } from './pool'
 import { TestProject } from './project'
-import { getDefaultTestProject, resolveBrowserProjects, resolveMergeReportProjects, resolveProjects } from './projects/resolveProjects'
-import { BlobReporter, discoverMergeReportLabels, readBlobs } from './reporters/blob'
+import { getDefaultTestProject, resolveBrowserProjects, resolveProjects } from './projects/resolveProjects'
+import { BlobReporter, readBlobs } from './reporters/blob'
 import { HangingProcessReporter } from './reporters/hanging-process'
 import { createBenchmarkReporters, createReporters } from './reporters/utils'
 import { VitestResolver } from './resolver'
@@ -605,22 +605,7 @@ export class Vitest {
         throw new Error('Cannot merge reports when `--reporter=blob` is used. Remove blob reporter from the config first.')
       }
 
-      // TODO: move projects duplication inside `readBlobs(ctx: Vitest, ...)`
-      // TODO: auto-discover labels from blob content not filename.
-      const reportsDirectory = directory || this.config.mergeReports
-      if (!this.config.mergeReportsLabels?.length) {
-        const labels = await discoverMergeReportLabels(reportsDirectory)
-        if (labels?.length) {
-          this.projects = resolveMergeReportProjects(
-            this,
-            new Set(this.projects.map(project => project.name)),
-            this.projects,
-            labels,
-          )
-        }
-      }
-
-      const { files, errors, coverages, executionTimes } = await readBlobs(this.version, reportsDirectory, this.projects)
+      const { files, errors, coverages, executionTimes } = await readBlobs(this, directory || this.config.mergeReports)
       this.state.blobs = { files, errors, coverages, executionTimes }
 
       await this.report('onInit', this)
diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index 91c797d7692a..2efad43c2aba 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -10,6 +10,7 @@ import { mkdir, readdir, readFile, stat, writeFile } from 'node:fs/promises'
 import { parse, stringify } from 'flatted'
 import { dirname, resolve } from 'pathe'
 import { getOutputFile } from '../../utils/config-helpers'
+import { resolveMergeReportProjects } from '../projects/resolveProjects'
 
 export interface BlobOptions {
   outputFile?: string
@@ -123,9 +124,8 @@ export async function writeBlob(content: MergeReport, filename: string): Promise
 }
 
 export async function readBlobs(
-  currentVersion: string,
+  ctx: Vitest,
   blobsDirectory: string,
-  projectsArray: TestProject[],
 ): Promise<MergedBlobs> {
   // using process.cwd() because --merge-reports can only be used in CLI
   const resolvedDir = resolve(process.cwd(), blobsDirectory)
@@ -164,13 +164,27 @@ export async function readBlobs(
     )
   }
 
-  if (!versions.has(currentVersion)) {
+  if (!versions.has(ctx.version)) {
     throw new Error(
-      `the blobs in "${blobsDirectory}" were generated by a different version of Vitest. Expected v${currentVersion}, but received v${blobs[0].version}`,
+      `the blobs in "${blobsDirectory}" were generated by a different version of Vitest. Expected v${ctx.version}, but received v${blobs[0].version}`,
     )
   }
 
+  // Auto-discover labels and duplicate projects if needed
+  if (!ctx.config.mergeReportsLabels?.length) {
+    const labels = discoverMergeReportLabels(blobs)
+    if (labels?.length) {
+      ctx.projects = resolveMergeReportProjects(
+        ctx,
+        new Set(ctx.projects.map(project => project.name)),
+        ctx.projects,
+        labels,
+      )
+    }
+  }
+
   // Restore module graph
+  const projectsArray = ctx.projects
   const projects = Object.fromEntries(
     projectsArray.map(p => [p.name, p]),
   )
@@ -224,14 +238,11 @@ export async function readBlobs(
   }
 }
 
-export async function discoverMergeReportLabels(blobsDirectory: string): Promise<string[] | undefined> {
-  // using process.cwd() because --merge-reports can only be used in CLI
-  const resolvedDir = resolve(process.cwd(), blobsDirectory)
-  const blobsFiles = await readdir(resolvedDir)
+function discoverMergeReportLabels(blobs: { file: string }[]): string[] | undefined {
   const labels = new Set<string>()
 
-  for (const filename of blobsFiles) {
-    const label = getBlobFilenameLabel(filename)
+  for (const blob of blobs) {
+    const label = getBlobFilenameLabel(blob.file)
     if (label) {
       labels.add(label)
     }

From 490b4d28b98cd0a877d7503545f771b0a7a70dfc Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 11:33:10 +0900
Subject: [PATCH 12/43] refactor: remove mergeReportsLabels

---
 packages/vitest/LICENSE.md                    |  2 +-
 packages/vitest/src/node/cli/cli-config.ts    |  6 ------
 .../src/node/projects/resolveProjects.ts      |  5 ++---
 packages/vitest/src/node/reporters/blob.ts    | 19 ++++++++-----------
 packages/vitest/src/node/types/config.ts      |  7 -------
 5 files changed, 11 insertions(+), 28 deletions(-)

diff --git a/packages/vitest/LICENSE.md b/packages/vitest/LICENSE.md
index d2883c9b3d11..409eaa16026d 100644
--- a/packages/vitest/LICENSE.md
+++ b/packages/vitest/LICENSE.md
@@ -363,7 +363,7 @@ Repository: lydell/js-tokens
 
 > The MIT License (MIT)
 >
-> Copyright (c) 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023 Simon Lydell
+> Copyright (c) 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024 Simon Lydell
 >
 > Permission is hereby granted, free of charge, to any person obtaining a copy
 > of this software and associated documentation files (the "Software"), to deal
diff --git a/packages/vitest/src/node/cli/cli-config.ts b/packages/vitest/src/node/cli/cli-config.ts
index fc4e7abdad80..4fade97dfe15 100644
--- a/packages/vitest/src/node/cli/cli-config.ts
+++ b/packages/vitest/src/node/cli/cli-config.ts
@@ -832,12 +832,6 @@ export const cliOptionsConfig: VitestCLIOptions = {
       'Label for this test run\'s environment (e.g., "linux", "node-22"). Suffixes the project name so blobs from different environments are distinct during merge',
     argument: '<label>',
   },
-  mergeReportsLabels: {
-    description:
-      'Expected labels when merging reports from multiple environments. Repeat the flag for multiple labels',
-    argument: '<label>',
-    array: true,
-  },
   listTags: {
     description: 'List all available tags instead of running tests. `--list-tags=json` will output tags in JSON format, unless there are no tags.',
     argument: '[type]',
diff --git a/packages/vitest/src/node/projects/resolveProjects.ts b/packages/vitest/src/node/projects/resolveProjects.ts
index beb9877a67f8..e10afa79d493 100644
--- a/packages/vitest/src/node/projects/resolveProjects.ts
+++ b/packages/vitest/src/node/projects/resolveProjects.ts
@@ -197,8 +197,7 @@ export async function resolveProjects(
     names.add(name)
   }
 
-  const browserProjects = await resolveBrowserProjects(vitest, names, resolvedProjects)
-  return resolveMergeReportProjects(vitest, names, browserProjects)
+  return resolveBrowserProjects(vitest, names, resolvedProjects)
 }
 
 export async function resolveBrowserProjects(
@@ -275,7 +274,7 @@ export function resolveMergeReportProjects(
   vitest: Vitest,
   names: Set<string>,
   resolvedProjects: TestProject[],
-  labels: string[] = vitest.config.mergeReportsLabels,
+  labels: string[],
 ): TestProject[] {
   if (!labels?.length) {
     return resolvedProjects
diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index 2efad43c2aba..70791416eca5 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -2,7 +2,6 @@ import type { File } from '@vitest/runner'
 import type { SerializedError } from '@vitest/utils'
 import type { DevEnvironment, EnvironmentModuleNode } from 'vite'
 import type { Vitest } from '../core'
-import type { TestProject } from '../project'
 import type { Reporter } from '../types/reporter'
 import type { TestModule } from './reported-tasks'
 import { existsSync } from 'node:fs'
@@ -171,16 +170,14 @@ export async function readBlobs(
   }
 
   // Auto-discover labels and duplicate projects if needed
-  if (!ctx.config.mergeReportsLabels?.length) {
-    const labels = discoverMergeReportLabels(blobs)
-    if (labels?.length) {
-      ctx.projects = resolveMergeReportProjects(
-        ctx,
-        new Set(ctx.projects.map(project => project.name)),
-        ctx.projects,
-        labels,
-      )
-    }
+  const labels = discoverMergeReportLabels(blobs)
+  if (labels?.length) {
+    ctx.projects = resolveMergeReportProjects(
+      ctx,
+      new Set(ctx.projects.map(project => project.name)),
+      ctx.projects,
+      labels,
+    )
   }
 
   // Restore module graph
diff --git a/packages/vitest/src/node/types/config.ts b/packages/vitest/src/node/types/config.ts
index 6debc1d5c051..4f2c5a9ae889 100644
--- a/packages/vitest/src/node/types/config.ts
+++ b/packages/vitest/src/node/types/config.ts
@@ -1099,13 +1099,6 @@ export interface UserConfig extends InlineConfig {
    */
   mergeReportsLabel?: string
 
-  /**
-   * Labels expected when merging reports from multiple environments.
-   * These will later be used to synthesize distinct project identities
-   * during merge.
-   */
-  mergeReportsLabels?: string[]
-
   /**
    * Delete all Vitest caches, including `experimental.fsModuleCache`.
    * @experimental

From 5428417399614a5698bf8e8925127bbcab7895de Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 11:41:44 +0900
Subject: [PATCH 13/43] refactor: slop

---
 .../src/node/projects/resolveProjects.ts      | 57 ++++---------------
 1 file changed, 11 insertions(+), 46 deletions(-)

diff --git a/packages/vitest/src/node/projects/resolveProjects.ts b/packages/vitest/src/node/projects/resolveProjects.ts
index e10afa79d493..4baac174a731 100644
--- a/packages/vitest/src/node/projects/resolveProjects.ts
+++ b/packages/vitest/src/node/projects/resolveProjects.ts
@@ -276,31 +276,12 @@ export function resolveMergeReportProjects(
   resolvedProjects: TestProject[],
   labels: string[],
 ): TestProject[] {
-  if (!labels?.length) {
-    return resolvedProjects
-  }
-
-  const removeProjects = new Set<TestProject>()
-
-  resolvedProjects.forEach((project) => {
-    const originalName = project.name
-    const filteredLabels = vitest.matchesProjectFilter(originalName)
-      ? labels
-      : labels.filter((label) => {
-          const nextName = originalName
-            ? `${originalName} [${label}]`
-            : label
-          return vitest.matchesProjectFilter(nextName)
-        })
+  const clonedProjects: TestProject[] = []
 
-    if (!filteredLabels.length) {
-      removeProjects.add(project)
-      return
-    }
-
-    filteredLabels.forEach((label) => {
-      const name = originalName
-        ? `${originalName} [${label}]`
+  for (const project of resolvedProjects) {
+    for (const label of labels) {
+      const name = project.name
+        ? `${project.name} [${label}]`
         : label
 
       if (names.has(name)) {
@@ -310,18 +291,13 @@ export function resolveMergeReportProjects(
       }
 
       names.add(name)
-      resolvedProjects.push(
-        TestProject._cloneProject(
-          project,
-          cloneMergeReportProjectConfig(project, label, name),
-        ),
-      )
-    })
-
-    removeProjects.add(project)
-  })
+      const config = deepClone(project.config)
+      config.name = name
+      clonedProjects.push(TestProject._cloneProject(project, config))
+    }
+  }
 
-  return resolvedProjects.filter(project => !removeProjects.has(project))
+  return clonedProjects
 }
 
 function cloneConfig(project: TestProject, { browser, ...config }: BrowserInstanceOption) {
@@ -368,17 +344,6 @@ function cloneConfig(project: TestProject, { browser, ...config }: BrowserInstan
   } satisfies ResolvedConfig, overrideConfig) as ResolvedConfig
 }
 
-function cloneMergeReportProjectConfig(
-  project: TestProject,
-  label: string,
-  name: string,
-): ResolvedConfig {
-  const clonedConfig = deepClone(project.config)
-  clonedConfig.mergeReportsLabel = label
-  clonedConfig.name = name
-  return clonedConfig
-}
-
 async function resolveTestProjectConfigs(
   vitest: Vitest,
   workspaceConfigPath: string | undefined,

From 065a347c621efd7ff4aec92445f6c9ddda1d2e08 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 11:51:12 +0900
Subject: [PATCH 14/43] wip: move to BlobOptions.label

---
 packages/vitest/src/node/cli/cli-config.ts    |  5 --
 .../vitest/src/node/config/resolveConfig.ts   |  7 --
 packages/vitest/src/node/project.ts           |  1 -
 packages/vitest/src/node/reporters/blob.ts    | 66 +++++++++++--------
 packages/vitest/src/node/types/config.ts      |  8 ---
 test/cli/test/reporters/merge-reports.test.ts | 20 ++----
 6 files changed, 44 insertions(+), 63 deletions(-)

diff --git a/packages/vitest/src/node/cli/cli-config.ts b/packages/vitest/src/node/cli/cli-config.ts
index 4fade97dfe15..f1cb5cc3ee06 100644
--- a/packages/vitest/src/node/cli/cli-config.ts
+++ b/packages/vitest/src/node/cli/cli-config.ts
@@ -827,11 +827,6 @@ export const cliOptionsConfig: VitestCLIOptions = {
       return value
     },
   },
-  mergeReportsLabel: {
-    description:
-      'Label for this test run\'s environment (e.g., "linux", "node-22"). Suffixes the project name so blobs from different environments are distinct during merge',
-    argument: '<label>',
-  },
   listTags: {
     description: 'List all available tags instead of running tests. `--list-tags=json` will output tags in JSON format, unless there are no tags.',
     argument: '[type]',
diff --git a/packages/vitest/src/node/config/resolveConfig.ts b/packages/vitest/src/node/config/resolveConfig.ts
index 8dbd75d179a6..472d15c13715 100644
--- a/packages/vitest/src/node/config/resolveConfig.ts
+++ b/packages/vitest/src/node/config/resolveConfig.ts
@@ -235,13 +235,6 @@ export function resolveConfig(
     ? options.name
     : (options.name?.label || '')
 
-  if (resolved.mergeReportsLabel) {
-    // TODO: can we move project mutation only at blob report stage?
-    resolved.name = resolved.name
-      ? `${resolved.name} [${resolved.mergeReportsLabel}]`
-      : resolved.mergeReportsLabel
-  }
-
   resolved.color = typeof options.name !== 'string' ? options.name?.color : undefined
 
   if (resolved.environment === 'browser') {
diff --git a/packages/vitest/src/node/project.ts b/packages/vitest/src/node/project.ts
index e8a3dfec8320..ed6e1664b48a 100644
--- a/packages/vitest/src/node/project.ts
+++ b/packages/vitest/src/node/project.ts
@@ -547,7 +547,6 @@ export class TestProject {
       {
         ...options,
         coverage: this.vitest.config.coverage,
-        mergeReportsLabel: this.vitest.config.mergeReportsLabel,
       },
       server.config,
     )
diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index 70791416eca5..238d3b73af80 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -6,6 +6,7 @@ import type { Reporter } from '../types/reporter'
 import type { TestModule } from './reported-tasks'
 import { existsSync } from 'node:fs'
 import { mkdir, readdir, readFile, stat, writeFile } from 'node:fs/promises'
+import { calculateSuiteHash, generateFileHash } from '@vitest/runner/utils'
 import { parse, stringify } from 'flatted'
 import { dirname, resolve } from 'pathe'
 import { getOutputFile } from '../../utils/config-helpers'
@@ -13,8 +14,7 @@ import { resolveMergeReportProjects } from '../projects/resolveProjects'
 
 export interface BlobOptions {
   outputFile?: string
-  // TODO:
-  // label?: string
+  label?: string
 }
 
 export class BlobReporter implements Reporter {
@@ -48,12 +48,13 @@ export class BlobReporter implements Reporter {
     const errors = [...unhandledErrors]
     const coverage = this.coverage
 
+    const label = this.options.label
+
     let outputFile
       = this.options.outputFile ?? getOutputFile(this.ctx.config, 'blob')
     if (!outputFile) {
       const shard = this.ctx.config.shard
-      const label = this.ctx.config.mergeReportsLabel
-      // TODO: join
+      // TODO: join("-")
       if (shard && label) {
         outputFile = `.vitest-reports/blob-${label}-${shard.index}-${shard.count}.json`
       }
@@ -95,6 +96,8 @@ export class BlobReporter implements Reporter {
       environmentModules[project.name] = serializedProject
     })
 
+    const metadata: MergeReportMetadata | undefined = label ? { label } : undefined
+
     const report = [
       this.ctx.version,
       files,
@@ -102,6 +105,7 @@ export class BlobReporter implements Reporter {
       coverage,
       executionTime,
       environmentModules,
+      metadata,
     ] satisfies MergeReport
 
     const reportFile = resolve(this.ctx.config.root, outputFile)
@@ -138,7 +142,7 @@ export async function readBlobs(
       )
     }
     const content = await readFile(fullPath, 'utf-8')
-    const [version, files, errors, coverage, executionTime, environmentModules] = parse(
+    const [version, files, errors, coverage, executionTime, environmentModules, metadata] = parse(
       content,
     ) as MergeReport
     if (!version) {
@@ -146,7 +150,7 @@ export async function readBlobs(
         `vitest.mergeReports() expects all paths in "${blobsDirectory}" to be files generated by the blob reporter, but "${filename}" is not a valid blob file`,
       )
     }
-    return { version, files, errors, coverage, file: filename, executionTime, environmentModules }
+    return { version, files, errors, coverage, file: filename, executionTime, environmentModules, metadata }
   })
   const blobs = await Promise.all(promises)
 
@@ -180,6 +184,25 @@ export async function readBlobs(
     )
   }
 
+  // TODO: review
+  // Rewrite file projectName/IDs and environmentModules keys for labeled blobs
+  for (const blob of blobs) {
+    const label = blob.metadata?.label
+    if (!label) {
+      continue
+    }
+    for (const file of blob.files) {
+      file.projectName = suffixProjectName(file.projectName, label)
+      file.id = generateFileHash(file.name, file.projectName)
+      calculateSuiteHash(file)
+    }
+    const rewritten: MergeReportEnvironmentModules = {}
+    for (const [projectName, modules] of Object.entries(blob.environmentModules)) {
+      rewritten[suffixProjectName(projectName, label)] = modules
+    }
+    blob.environmentModules = rewritten
+  }
+
   // Restore module graph
   const projectsArray = ctx.projects
   const projects = Object.fromEntries(
@@ -235,13 +258,17 @@ export async function readBlobs(
   }
 }
 
-function discoverMergeReportLabels(blobs: { file: string }[]): string[] | undefined {
+function suffixProjectName(originalName: string | undefined, label: string): string {
+  return originalName ? `${originalName} [${label}]` : label
+}
+
+// TODO: do we support some blob has label but some doesn't?
+function discoverMergeReportLabels(blobs: { metadata?: MergeReportMetadata }[]): string[] | undefined {
   const labels = new Set<string>()
 
   for (const blob of blobs) {
-    const label = getBlobFilenameLabel(blob.file)
-    if (label) {
-      labels.add(label)
+    if (blob.metadata?.label) {
+      labels.add(blob.metadata.label)
     }
   }
 
@@ -266,24 +293,11 @@ type MergeReport = [
   coverage: unknown,
   executionTime: number,
   environmentModules: MergeReportEnvironmentModules,
+  metadata?: MergeReportMetadata,
 ]
 
-function getBlobFilenameLabel(filename: string): string | undefined {
-  const match = filename.match(/^blob-(.+?)(?:-(\d+)-(\d+))?\.json$/)
-  if (!match) {
-    return undefined
-  }
-
-  const [, label, shardIndex, shardCount] = match
-  if (shardIndex && shardCount) {
-    return label
-  }
-
-  if (label.match(/^\d+-\d+$/)) {
-    return undefined
-  }
-
-  return label
+interface MergeReportMetadata {
+  label?: string
 }
 
 interface MergeReportEnvironmentModules {
diff --git a/packages/vitest/src/node/types/config.ts b/packages/vitest/src/node/types/config.ts
index 4f2c5a9ae889..3f6ec9ece2db 100644
--- a/packages/vitest/src/node/types/config.ts
+++ b/packages/vitest/src/node/types/config.ts
@@ -1091,14 +1091,6 @@ export interface UserConfig extends InlineConfig {
    */
   mergeReports?: string
 
-  // TODO: remove
-  /**
-   * Label for this test run's environment (e.g., "linux", "node-22").
-   * Suffixes the project name so that blobs from different environments
-   * are treated as distinct projects during merge.
-   */
-  mergeReportsLabel?: string
-
   /**
    * Delete all Vitest caches, including `experimental.fsModuleCache`.
    * @experimental
diff --git a/test/cli/test/reporters/merge-reports.test.ts b/test/cli/test/reporters/merge-reports.test.ts
index ef5801b6823d..e3d01b9b8f66 100644
--- a/test/cli/test/reporters/merge-reports.test.ts
+++ b/test/cli/test/reporters/merge-reports.test.ts
@@ -494,18 +494,12 @@ test('merge report with labels', async () => {
   }
   await runVitest({
     ...baseConfig,
-    reporters: ['blob'],
-    mergeReportsLabel: 'linux',
-    // TODO
-    // reporters: [['blob', { label: 'linux' }]],
+    reporters: [['blob', { label: 'linux' }]],
   })
 
   await runVitest({
     ...baseConfig,
-    reporters: ['blob'],
-    mergeReportsLabel: 'macos',
-    // TODO
-    // reporters: [['blob', { label: 'macos' }]],
+    reporters: [['blob', { label: 'macos' }]],
   })
 
   const result = await runVitest({
@@ -575,18 +569,12 @@ test('merge report with labels and projects', async () => {
   }
   await runVitest({
     ...baseConfig,
-    reporters: ['blob'],
-    mergeReportsLabel: 'linux',
-    // TODO
-    // reporters: [['blob', { label: 'linux' }]],
+    reporters: [['blob', { label: 'linux' }]],
   })
 
   await runVitest({
     ...baseConfig,
-    reporters: ['blob'],
-    mergeReportsLabel: 'macos',
-    // TODO
-    // reporters: [['blob', { label: 'macos' }]],
+    reporters: [['blob', { label: 'macos' }]],
   })
 
   const result = await runVitest({

From f4838d5d4f550880eed77579d0faf440b0a8d4ad Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 11:59:17 +0900
Subject: [PATCH 15/43] fix: require all blobs to have labels when any blob has
 one

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 packages/vitest/src/node/reporters/blob.ts | 23 ++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index 238d3b73af80..70459b518838 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -14,6 +14,7 @@ import { resolveMergeReportProjects } from '../projects/resolveProjects'
 
 export interface BlobOptions {
   outputFile?: string
+  // TOOD: support via environemnt variable?
   label?: string
 }
 
@@ -175,7 +176,7 @@ export async function readBlobs(
 
   // Auto-discover labels and duplicate projects if needed
   const labels = discoverMergeReportLabels(blobs)
-  if (labels?.length) {
+  if (labels) {
     ctx.projects = resolveMergeReportProjects(
       ctx,
       new Set(ctx.projects.map(project => project.name)),
@@ -262,20 +263,22 @@ function suffixProjectName(originalName: string | undefined, label: string): str
   return originalName ? `${originalName} [${label}]` : label
 }
 
-// TODO: do we support some blob has label but some doesn't?
-function discoverMergeReportLabels(blobs: { metadata?: MergeReportMetadata }[]): string[] | undefined {
-  const labels = new Set<string>()
+function discoverMergeReportLabels(blobs: { file: string, metadata?: MergeReportMetadata }[]): string[] | undefined {
+  const labeled = blobs.filter(b => b.metadata?.label)
 
-  for (const blob of blobs) {
-    if (blob.metadata?.label) {
-      labels.add(blob.metadata.label)
-    }
+  if (!labeled.length) {
+    return undefined
   }
 
-  if (!labels.size) {
-    return undefined
+  const unlabeled = blobs.filter(b => !b.metadata?.label)
+  if (unlabeled.length) {
+    throw new Error(
+      `vitest.mergeReports() requires all blob files to have a label when any blob has one. `
+      + `Missing label in: ${unlabeled.map(b => `"${b.file}"`).join(', ')}`,
+    )
   }
 
+  const labels = new Set(labeled.map(b => b.metadata!.label!))
   return [...labels]
 }
 

From 64959b951e456a7e02c844d9a90682fc01c5d206 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 12:01:53 +0900
Subject: [PATCH 16/43] refactor: move resolveMergeReportProjects to blob.ts

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 .../src/node/projects/resolveProjects.ts      | 31 -------------------
 packages/vitest/src/node/reporters/blob.ts    | 31 ++++++++++++++++++-
 2 files changed, 30 insertions(+), 32 deletions(-)

diff --git a/packages/vitest/src/node/projects/resolveProjects.ts b/packages/vitest/src/node/projects/resolveProjects.ts
index 4baac174a731..bd69651a5510 100644
--- a/packages/vitest/src/node/projects/resolveProjects.ts
+++ b/packages/vitest/src/node/projects/resolveProjects.ts
@@ -269,37 +269,6 @@ export async function resolveBrowserProjects(
   return resolvedProjects.filter(project => !removeProjects.has(project))
 }
 
-// TODO: review
-export function resolveMergeReportProjects(
-  vitest: Vitest,
-  names: Set<string>,
-  resolvedProjects: TestProject[],
-  labels: string[],
-): TestProject[] {
-  const clonedProjects: TestProject[] = []
-
-  for (const project of resolvedProjects) {
-    for (const label of labels) {
-      const name = project.name
-        ? `${project.name} [${label}]`
-        : label
-
-      if (names.has(name)) {
-        throw new Error(
-          `Project name "${name}" is not unique. All projects should have unique names. Make sure your configuration is correct.`,
-        )
-      }
-
-      names.add(name)
-      const config = deepClone(project.config)
-      config.name = name
-      clonedProjects.push(TestProject._cloneProject(project, config))
-    }
-  }
-
-  return clonedProjects
-}
-
 function cloneConfig(project: TestProject, { browser, ...config }: BrowserInstanceOption) {
   const {
     locators,
diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index 70459b518838..dbd049de68b5 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -9,8 +9,9 @@ import { mkdir, readdir, readFile, stat, writeFile } from 'node:fs/promises'
 import { calculateSuiteHash, generateFileHash } from '@vitest/runner/utils'
 import { parse, stringify } from 'flatted'
 import { dirname, resolve } from 'pathe'
+import { deepClone } from '@vitest/utils/helpers'
 import { getOutputFile } from '../../utils/config-helpers'
-import { resolveMergeReportProjects } from '../projects/resolveProjects'
+import { TestProject } from '../project'
 
 export interface BlobOptions {
   outputFile?: string
@@ -263,6 +264,34 @@ function suffixProjectName(originalName: string | undefined, label: string): str
   return originalName ? `${originalName} [${label}]` : label
 }
 
+function resolveMergeReportProjects(
+  vitest: Vitest,
+  names: Set<string>,
+  resolvedProjects: TestProject[],
+  labels: string[],
+): TestProject[] {
+  const clonedProjects: TestProject[] = []
+
+  for (const project of resolvedProjects) {
+    for (const label of labels) {
+      const name = suffixProjectName(project.name || undefined, label)
+
+      if (names.has(name)) {
+        throw new Error(
+          `Project name "${name}" is not unique. All projects should have unique names. Make sure your configuration is correct.`,
+        )
+      }
+
+      names.add(name)
+      const config = deepClone(project.config)
+      config.name = name
+      clonedProjects.push(TestProject._cloneProject(project, config))
+    }
+  }
+
+  return clonedProjects
+}
+
 function discoverMergeReportLabels(blobs: { file: string, metadata?: MergeReportMetadata }[]): string[] | undefined {
   const labeled = blobs.filter(b => b.metadata?.label)
 

From dd283984ac6fed623ea5fb029132a19eacd2a599 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 12:04:29 +0900
Subject: [PATCH 17/43] refactor: slop

---
 packages/vitest/src/node/reporters/blob.ts | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index dbd049de68b5..8669f090a1c1 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -7,9 +7,9 @@ import type { TestModule } from './reported-tasks'
 import { existsSync } from 'node:fs'
 import { mkdir, readdir, readFile, stat, writeFile } from 'node:fs/promises'
 import { calculateSuiteHash, generateFileHash } from '@vitest/runner/utils'
+import { deepClone } from '@vitest/utils/helpers'
 import { parse, stringify } from 'flatted'
 import { dirname, resolve } from 'pathe'
-import { deepClone } from '@vitest/utils/helpers'
 import { getOutputFile } from '../../utils/config-helpers'
 import { TestProject } from '../project'
 
@@ -179,8 +179,6 @@ export async function readBlobs(
   const labels = discoverMergeReportLabels(blobs)
   if (labels) {
     ctx.projects = resolveMergeReportProjects(
-      ctx,
-      new Set(ctx.projects.map(project => project.name)),
       ctx.projects,
       labels,
     )
@@ -265,14 +263,13 @@ function suffixProjectName(originalName: string | undefined, label: string): str
 }
 
 function resolveMergeReportProjects(
-  vitest: Vitest,
-  names: Set<string>,
-  resolvedProjects: TestProject[],
+  projects: TestProject[],
   labels: string[],
 ): TestProject[] {
+  const names = new Set(projects.map(p => p.name))
   const clonedProjects: TestProject[] = []
 
-  for (const project of resolvedProjects) {
+  for (const project of projects) {
     for (const label of labels) {
       const name = suffixProjectName(project.name || undefined, label)
 
@@ -292,7 +289,7 @@ function resolveMergeReportProjects(
   return clonedProjects
 }
 
-function discoverMergeReportLabels(blobs: { file: string, metadata?: MergeReportMetadata }[]): string[] | undefined {
+function discoverMergeReportLabels(blobs: { file: string; metadata?: MergeReportMetadata }[]): string[] | undefined {
   const labeled = blobs.filter(b => b.metadata?.label)
 
   if (!labeled.length) {

From cddd750e63eed4c1506d2be257b6f392f5f58a1c Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 12:08:09 +0900
Subject: [PATCH 18/43] refactor: simple tuple

---
 packages/vitest/src/node/reporters/blob.ts | 24 ++++++++--------------
 1 file changed, 9 insertions(+), 15 deletions(-)

diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index 8669f090a1c1..cb8306be9f6a 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -98,8 +98,6 @@ export class BlobReporter implements Reporter {
       environmentModules[project.name] = serializedProject
     })
 
-    const metadata: MergeReportMetadata | undefined = label ? { label } : undefined
-
     const report = [
       this.ctx.version,
       files,
@@ -107,7 +105,7 @@ export class BlobReporter implements Reporter {
       coverage,
       executionTime,
       environmentModules,
-      metadata,
+      label,
     ] satisfies MergeReport
 
     const reportFile = resolve(this.ctx.config.root, outputFile)
@@ -144,7 +142,7 @@ export async function readBlobs(
       )
     }
     const content = await readFile(fullPath, 'utf-8')
-    const [version, files, errors, coverage, executionTime, environmentModules, metadata] = parse(
+    const [version, files, errors, coverage, executionTime, environmentModules, label] = parse(
       content,
     ) as MergeReport
     if (!version) {
@@ -152,7 +150,7 @@ export async function readBlobs(
         `vitest.mergeReports() expects all paths in "${blobsDirectory}" to be files generated by the blob reporter, but "${filename}" is not a valid blob file`,
       )
     }
-    return { version, files, errors, coverage, file: filename, executionTime, environmentModules, metadata }
+    return { version, label, files, errors, coverage, file: filename, executionTime, environmentModules }
   })
   const blobs = await Promise.all(promises)
 
@@ -187,7 +185,7 @@ export async function readBlobs(
   // TODO: review
   // Rewrite file projectName/IDs and environmentModules keys for labeled blobs
   for (const blob of blobs) {
-    const label = blob.metadata?.label
+    const label = blob.label
     if (!label) {
       continue
     }
@@ -289,14 +287,14 @@ function resolveMergeReportProjects(
   return clonedProjects
 }
 
-function discoverMergeReportLabels(blobs: { file: string; metadata?: MergeReportMetadata }[]): string[] | undefined {
-  const labeled = blobs.filter(b => b.metadata?.label)
+function discoverMergeReportLabels(blobs: { file: string; label?: string }[]): string[] | undefined {
+  const labeled = blobs.filter(b => b.label)
 
   if (!labeled.length) {
     return undefined
   }
 
-  const unlabeled = blobs.filter(b => !b.metadata?.label)
+  const unlabeled = blobs.filter(b => !b.label)
   if (unlabeled.length) {
     throw new Error(
       `vitest.mergeReports() requires all blob files to have a label when any blob has one. `
@@ -304,7 +302,7 @@ function discoverMergeReportLabels(blobs: { file: string; metadata?: MergeReport
     )
   }
 
-  const labels = new Set(labeled.map(b => b.metadata!.label!))
+  const labels = new Set(labeled.map(b => b.label!))
   return [...labels]
 }
 
@@ -322,13 +320,9 @@ type MergeReport = [
   coverage: unknown,
   executionTime: number,
   environmentModules: MergeReportEnvironmentModules,
-  metadata?: MergeReportMetadata,
+  label?: string,
 ]
 
-interface MergeReportMetadata {
-  label?: string
-}
-
 interface MergeReportEnvironmentModules {
   [projectName: string]: {
     environments: {

From 6490840c85a71cda81fde04509f1dbc9191150e4 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 12:12:35 +0900
Subject: [PATCH 19/43] refactor: simplify blob filename construction and
 flatten MergeReport label

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 packages/vitest/src/node/reporters/blob.ts | 15 ++-------------
 1 file changed, 2 insertions(+), 13 deletions(-)

diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index cb8306be9f6a..c352bb2b5e6d 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -56,19 +56,8 @@ export class BlobReporter implements Reporter {
       = this.options.outputFile ?? getOutputFile(this.ctx.config, 'blob')
     if (!outputFile) {
       const shard = this.ctx.config.shard
-      // TODO: join("-")
-      if (shard && label) {
-        outputFile = `.vitest-reports/blob-${label}-${shard.index}-${shard.count}.json`
-      }
-      else if (shard) {
-        outputFile = `.vitest-reports/blob-${shard.index}-${shard.count}.json`
-      }
-      else if (label) {
-        outputFile = `.vitest-reports/blob-${label}.json`
-      }
-      else {
-        outputFile = '.vitest-reports/blob.json'
-      }
+      const suffix = [label, shard && `${shard.index}-${shard.count}`].filter(Boolean).join('-')
+      outputFile = suffix ? `.vitest-reports/blob-${suffix}.json` : '.vitest-reports/blob.json'
     }
 
     const environmentModules: MergeReportEnvironmentModules = {}

From f5fb52e197ee507bd0c69f8ba1aa1ef842d5eb55 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 12:12:58 +0900
Subject: [PATCH 20/43] chore: todo

---
 test/cli/test/reporters/merge-reports.test.ts | 1 +
 1 file changed, 1 insertion(+)

diff --git a/test/cli/test/reporters/merge-reports.test.ts b/test/cli/test/reporters/merge-reports.test.ts
index e3d01b9b8f66..1f867095b4a2 100644
--- a/test/cli/test/reporters/merge-reports.test.ts
+++ b/test/cli/test/reporters/merge-reports.test.ts
@@ -487,6 +487,7 @@ function createTest(name: string, file: File): Test {
 // - single browser instance
 // - multiple browser instances
 // - multiple browser instances with multiple projects
+// - shards
 // - coverage
 test('merge report with labels', async () => {
   const baseConfig: RunVitestConfig = {

From 52f1927ec1442dec54a336e8f86da11a65d0d792 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 12:15:49 +0900
Subject: [PATCH 21/43] chore: todo

---
 packages/vitest/src/node/reporters/blob.ts | 1 +
 1 file changed, 1 insertion(+)

diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index c352bb2b5e6d..64727f6d0a90 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -283,6 +283,7 @@ function discoverMergeReportLabels(blobs: { file: string; label?: string }[]): s
     return undefined
   }
 
+  // TODO: support mix of labeled and unlabeled blobs?
   const unlabeled = blobs.filter(b => !b.label)
   if (unlabeled.length) {
     throw new Error(

From 5d9407675648d5df8e45654057304c6169248b1c Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 12:28:15 +0900
Subject: [PATCH 22/43] wip: support VITEST_BLOB_LABEL

---
 docs/guide/cli.md                          |  2 +-
 docs/guide/improving-performance.md        | 92 ++++++++++++++++++++++
 docs/guide/reporters.md                    |  9 ++-
 packages/vitest/src/node/reporters/blob.ts |  7 +-
 4 files changed, 105 insertions(+), 5 deletions(-)

diff --git a/docs/guide/cli.md b/docs/guide/cli.md
index e1a16c45193b..64b9bc4782b8 100644
--- a/docs/guide/cli.md
+++ b/docs/guide/cli.md
@@ -225,7 +225,7 @@ You cannot use this option with `--watch` enabled (enabled in dev by default).
 :::
 
 ::: tip
-If `--reporter=blob` is used without an output file, the default path will include the current shard config to avoid collisions with other Vitest processes.
+If `--reporter=blob` is used without an output file, the default path will include the current shard config and [label](/guide/reporters#labels) to avoid collisions with other Vitest processes.
 :::
 
 ### merge-reports
diff --git a/docs/guide/improving-performance.md b/docs/guide/improving-performance.md
index efbbc804d3ac..e22776b46b80 100644
--- a/docs/guide/improving-performance.md
+++ b/docs/guide/improving-performance.md
@@ -221,6 +221,98 @@ If your tests create file-based attachments (for example via `context.annotate`
 
 :::
 
+## Merging Reports from Multiple Environments
+
+If you run the same test suite across multiple platforms or environments in CI (e.g., linux/macos/windows, or node 20/22), you can use the blob reporter's [`label`](/guide/reporters#labels) option to merge results into a unified report.
+
+Unlike [sharding](#sharding) where test files are split with no overlap, cross-environment runs execute the same tests in each environment. The label tells Vitest which environment produced each blob, so results appear as separate projects in the merged output.
+
+```sh
+# On each environment
+VITEST_BLOB_LABEL=linux vitest run --reporter=blob
+VITEST_BLOB_LABEL=macos vitest run --reporter=blob
+```
+
+Then merge:
+
+```sh
+vitest run --merge-reports
+```
+
+::: details GitHub Actions example
+
+```yaml
+name: Tests
+on:
+  push:
+    branches:
+      - main
+jobs:
+  tests:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+
+      - name: Install pnpm
+        uses: pnpm/action-setup@a7487c7e89a18df4991f7f222e4898a00d66ddda # v4.1.0
+
+      - name: Install dependencies
+        run: pnpm i
+
+      - name: Run tests
+        run: pnpm run test --reporter=blob
+        env:
+          VITEST_BLOB_LABEL: ${{ matrix.os }}
+
+      - name: Upload blob report to GitHub Actions Artifacts
+        if: ${{ !cancelled() }}
+        uses: actions/upload-artifact@v4
+        with:
+          name: blob-report-${{ matrix.os }}
+          path: .vitest-reports/*
+          include-hidden-files: true
+          retention-days: 1
+
+  merge-reports:
+    if: ${{ !cancelled() }}
+    needs: [tests]
+
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+
+      - name: Install pnpm
+        uses: pnpm/action-setup@a7487c7e89a18df4991f7f222e4898a00d66ddda # v4.1.0
+
+      - name: Install dependencies
+        run: pnpm i
+
+      - name: Download blob reports from GitHub Actions Artifacts
+        uses: actions/download-artifact@v4
+        with:
+          path: .vitest-reports
+          pattern: blob-report-*
+          merge-multiple: true
+
+      - name: Merge reports
+        run: npx vitest --merge-reports
+```
+
+:::
+
+:::tip
+Labels can be combined with sharding. For example, you can shard tests within each platform. The blob filename will include both the label and shard index (e.g., `blob-linux-1-3.json`).
+:::
+
 :::tip
 Test sharding can also become useful on high CPU-count machines.
 
diff --git a/docs/guide/reporters.md b/docs/guide/reporters.md
index 95612f070208..53a05efe5ce2 100644
--- a/docs/guide/reporters.md
+++ b/docs/guide/reporters.md
@@ -670,13 +670,18 @@ By default, stores all results in `.vitest-reports` folder, but can be overridde
 npx vitest --reporter=blob --outputFile=reports/blob-1.json
 ```
 
-We recommend using this reporter if you are running Vitest on different machines with the [`--shard`](/guide/cli#shard) flag.
-All blob reports can be merged into any report by using `--merge-reports` command at the end of your CI pipeline:
+We recommend using this reporter if you are running Vitest on different machines with the [`--shard`](/guide/cli#shard) flag or across multiple environments (e.g., linux/macos/windows). All blob reports can be merged into any report by using `--merge-reports` command at the end of your CI pipeline:
 
 ```bash
 npx vitest --merge-reports=reports --reporter=json --reporter=default
 ```
 
+When running the same tests across multiple environments, set the `label` option (or `VITEST_BLOB_LABEL` environment variable) to distinguish each environment's blob. Vitest reads labels at merge time and creates separate project entries automatically (e.g., `myproject [linux]`, `myproject [macos]`). See [Merging Reports from Multiple Environments](/guide/improving-performance#merging-reports-from-multiple-environments) for a full CI example.
+
+```bash
+VITEST_BLOB_LABEL=linux vitest run --reporter=blob
+```
+
 Blob reporter output doesn't include file-based [attachments](/api/advanced/artifacts.html#testattachment).
 Make sure to merge [`attachmentsDir`](/config/attachmentsdir) separately alongside blob reports on CI when using this feature.
 
diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index 64727f6d0a90..a8b89090b993 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -15,7 +15,10 @@ import { TestProject } from '../project'
 
 export interface BlobOptions {
   outputFile?: string
-  // TOOD: support via environemnt variable?
+  /**
+   * Label for this environment's blob report (e.g., "linux", "node-22").
+   * Can also be set via `VITEST_BLOB_LABEL` environment variable.
+   */
   label?: string
 }
 
@@ -50,7 +53,7 @@ export class BlobReporter implements Reporter {
     const errors = [...unhandledErrors]
     const coverage = this.coverage
 
-    const label = this.options.label
+    const label = this.options.label ?? process.env.VITEST_BLOB_LABEL
 
     let outputFile
       = this.options.outputFile ?? getOutputFile(this.ctx.config, 'blob')

From a5f6c56d2c7c8988ade1ecd7b4988219ecf83290 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 12:36:27 +0900
Subject: [PATCH 23/43] docs: add blob reporter label and cross-platform merge
 docs

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 docs/guide/improving-performance.md | 101 ++--------------------------
 docs/guide/reporters.md             |   2 +-
 2 files changed, 7 insertions(+), 96 deletions(-)

diff --git a/docs/guide/improving-performance.md b/docs/guide/improving-performance.md
index e22776b46b80..85370a22b8a4 100644
--- a/docs/guide/improving-performance.md
+++ b/docs/guide/improving-performance.md
@@ -144,9 +144,10 @@ on:
       - main
 jobs:
   tests:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
     strategy:
       matrix:
+        os: [ubuntu-latest, macos-latest]
         shardIndex: [1, 2, 3, 4]
         shardTotal: [4]
     steps:
@@ -163,12 +164,14 @@ jobs:
 
       - name: Run tests
         run: pnpm run test --reporter=blob --shard=${{ matrix.shardIndex }}/${{ matrix.shardTotal }}
+        env:
+          VITEST_BLOB_LABEL: ${{ matrix.os }}
 
       - name: Upload blob report to GitHub Actions Artifacts
         if: ${{ !cancelled() }}
         uses: actions/upload-artifact@v4
         with:
-          name: blob-report-${{ matrix.shardIndex }}
+          name: blob-report-${{ matrix.os }}-${{ matrix.shardIndex }}
           path: .vitest-reports/*
           include-hidden-files: true
           retention-days: 1
@@ -177,7 +180,7 @@ jobs:
         if: ${{ !cancelled() }}
         uses: actions/upload-artifact@v4
         with:
-          name: blob-attachments-${{ matrix.shardIndex }}
+          name: blob-attachments-${{ matrix.os }}-${{ matrix.shardIndex }}
           path: .vitest-attachments/**
           include-hidden-files: true
           retention-days: 1
@@ -221,98 +224,6 @@ If your tests create file-based attachments (for example via `context.annotate`
 
 :::
 
-## Merging Reports from Multiple Environments
-
-If you run the same test suite across multiple platforms or environments in CI (e.g., linux/macos/windows, or node 20/22), you can use the blob reporter's [`label`](/guide/reporters#labels) option to merge results into a unified report.
-
-Unlike [sharding](#sharding) where test files are split with no overlap, cross-environment runs execute the same tests in each environment. The label tells Vitest which environment produced each blob, so results appear as separate projects in the merged output.
-
-```sh
-# On each environment
-VITEST_BLOB_LABEL=linux vitest run --reporter=blob
-VITEST_BLOB_LABEL=macos vitest run --reporter=blob
-```
-
-Then merge:
-
-```sh
-vitest run --merge-reports
-```
-
-::: details GitHub Actions example
-
-```yaml
-name: Tests
-on:
-  push:
-    branches:
-      - main
-jobs:
-  tests:
-    strategy:
-      matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
-    runs-on: ${{ matrix.os }}
-    steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-node@v4
-        with:
-          node-version: 20
-
-      - name: Install pnpm
-        uses: pnpm/action-setup@a7487c7e89a18df4991f7f222e4898a00d66ddda # v4.1.0
-
-      - name: Install dependencies
-        run: pnpm i
-
-      - name: Run tests
-        run: pnpm run test --reporter=blob
-        env:
-          VITEST_BLOB_LABEL: ${{ matrix.os }}
-
-      - name: Upload blob report to GitHub Actions Artifacts
-        if: ${{ !cancelled() }}
-        uses: actions/upload-artifact@v4
-        with:
-          name: blob-report-${{ matrix.os }}
-          path: .vitest-reports/*
-          include-hidden-files: true
-          retention-days: 1
-
-  merge-reports:
-    if: ${{ !cancelled() }}
-    needs: [tests]
-
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-node@v4
-        with:
-          node-version: 20
-
-      - name: Install pnpm
-        uses: pnpm/action-setup@a7487c7e89a18df4991f7f222e4898a00d66ddda # v4.1.0
-
-      - name: Install dependencies
-        run: pnpm i
-
-      - name: Download blob reports from GitHub Actions Artifacts
-        uses: actions/download-artifact@v4
-        with:
-          path: .vitest-reports
-          pattern: blob-report-*
-          merge-multiple: true
-
-      - name: Merge reports
-        run: npx vitest --merge-reports
-```
-
-:::
-
-:::tip
-Labels can be combined with sharding. For example, you can shard tests within each platform. The blob filename will include both the label and shard index (e.g., `blob-linux-1-3.json`).
-:::
-
 :::tip
 Test sharding can also become useful on high CPU-count machines.
 
diff --git a/docs/guide/reporters.md b/docs/guide/reporters.md
index 53a05efe5ce2..f59854fdeb37 100644
--- a/docs/guide/reporters.md
+++ b/docs/guide/reporters.md
@@ -676,7 +676,7 @@ We recommend using this reporter if you are running Vitest on different machines
 npx vitest --merge-reports=reports --reporter=json --reporter=default
 ```
 
-When running the same tests across multiple environments, set the `label` option (or `VITEST_BLOB_LABEL` environment variable) to distinguish each environment's blob. Vitest reads labels at merge time and creates separate project entries automatically (e.g., `myproject [linux]`, `myproject [macos]`). See [Merging Reports from Multiple Environments](/guide/improving-performance#merging-reports-from-multiple-environments) for a full CI example.
+When running the same tests across multiple environments, set the `label` option (or `VITEST_BLOB_LABEL` environment variable) to distinguish each environment's blob. Vitest reads labels at merge time and creates separate project entries automatically (e.g., `myproject [linux]`, `myproject [macos]`).
 
 ```bash
 VITEST_BLOB_LABEL=linux vitest run --reporter=blob

From 8d318a38e93065e15d073b9ff50295cdd2ba7d3c Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 12:47:52 +0900
Subject: [PATCH 24/43] test: move workers-option unit test to test/core

The unit test with vi.mock for node:os breaks in test/cli (isolate: false)
when other tests cause node:os to be cached before the mock applies.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 test/cli/test/workers-option.test.ts  | 25 +------------------------
 test/core/test/workers-option.test.ts | 24 ++++++++++++++++++++++++
 2 files changed, 25 insertions(+), 24 deletions(-)
 create mode 100644 test/core/test/workers-option.test.ts

diff --git a/test/cli/test/workers-option.test.ts b/test/cli/test/workers-option.test.ts
index 00372a6cd23c..304d433d6fb6 100644
--- a/test/cli/test/workers-option.test.ts
+++ b/test/cli/test/workers-option.test.ts
@@ -1,28 +1,5 @@
 import * as testUtils from '#test-utils'
-import { describe, expect, test, vi } from 'vitest'
-import { getWorkersCountByPercentage } from 'vitest/src/utils/workers.js'
-
-vi.mock(import('node:os'), async importOriginal => ({
-  ...(await importOriginal()),
-  default: {
-    ...(await importOriginal()).default,
-    availableParallelism: () => 10,
-  },
-}))
-
-describe('workers util', () => {
-  test('percent=50% should return 5', () => {
-    expect(getWorkersCountByPercentage('50%')).toBe(5)
-  })
-
-  test('percent=-10% should return 1', () => {
-    expect(getWorkersCountByPercentage('-10%')).toBe(1)
-  })
-
-  test('percent=110% should return 10', () => {
-    expect(getWorkersCountByPercentage('110%')).toBe(10)
-  })
-})
+import { expect, test } from 'vitest'
 
 test.each([
   { pool: 'threads' },
diff --git a/test/core/test/workers-option.test.ts b/test/core/test/workers-option.test.ts
new file mode 100644
index 000000000000..0b95fb1c08d1
--- /dev/null
+++ b/test/core/test/workers-option.test.ts
@@ -0,0 +1,24 @@
+import { describe, expect, test, vi } from 'vitest'
+import { getWorkersCountByPercentage } from 'vitest/src/utils/workers.js'
+
+vi.mock(import('node:os'), async importOriginal => ({
+  ...(await importOriginal()),
+  default: {
+    ...(await importOriginal()).default,
+    availableParallelism: () => 10,
+  },
+}))
+
+describe('workers util', () => {
+  test('percent=50% should return 5', () => {
+    expect(getWorkersCountByPercentage('50%')).toBe(5)
+  })
+
+  test('percent=-10% should return 1', () => {
+    expect(getWorkersCountByPercentage('-10%')).toBe(1)
+  })
+
+  test('percent=110% should return 10', () => {
+    expect(getWorkersCountByPercentage('110%')).toBe(10)
+  })
+})

From fd30d079d754858ee47db6e3ae430efeba48e8e8 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 12:56:01 +0900
Subject: [PATCH 25/43] test: silly but for now

---
 packages/vitest/src/node/reporters/blob.ts | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index a8b89090b993..7358c774edc5 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -2,6 +2,7 @@ import type { File } from '@vitest/runner'
 import type { SerializedError } from '@vitest/utils'
 import type { DevEnvironment, EnvironmentModuleNode } from 'vite'
 import type { Vitest } from '../core'
+import type { TestProject } from '../project'
 import type { Reporter } from '../types/reporter'
 import type { TestModule } from './reported-tasks'
 import { existsSync } from 'node:fs'
@@ -11,7 +12,6 @@ import { deepClone } from '@vitest/utils/helpers'
 import { parse, stringify } from 'flatted'
 import { dirname, resolve } from 'pathe'
 import { getOutputFile } from '../../utils/config-helpers'
-import { TestProject } from '../project'
 
 export interface BlobOptions {
   outputFile?: string
@@ -272,7 +272,8 @@ function resolveMergeReportProjects(
       names.add(name)
       const config = deepClone(project.config)
       config.name = name
-      clonedProjects.push(TestProject._cloneProject(project, config))
+      // TODO: importing `import "../project"` breaks some tests
+      clonedProjects.push((project.constructor as typeof TestProject)._cloneProject(project, config))
     }
   }
 

From 44e2721217e491621dadebb6e3074739ef224965 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 13:25:17 +0900
Subject: [PATCH 26/43] chore: lint

---
 packages/vitest/LICENSE.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/vitest/LICENSE.md b/packages/vitest/LICENSE.md
index 409eaa16026d..d2883c9b3d11 100644
--- a/packages/vitest/LICENSE.md
+++ b/packages/vitest/LICENSE.md
@@ -363,7 +363,7 @@ Repository: lydell/js-tokens
 
 > The MIT License (MIT)
 >
-> Copyright (c) 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024 Simon Lydell
+> Copyright (c) 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023 Simon Lydell
 >
 > Permission is hereby granted, free of charge, to any person obtaining a copy
 > of this software and associated documentation files (the "Software"), to deal

From 747cf0fe582f4f31f97a2043aac9b36f213952bd Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 13:47:34 +0900
Subject: [PATCH 27/43] refactor: minor

---
 packages/vitest/src/node/project.ts                  | 7 -------
 packages/vitest/src/node/projects/resolveProjects.ts | 2 +-
 2 files changed, 1 insertion(+), 8 deletions(-)

diff --git a/packages/vitest/src/node/project.ts b/packages/vitest/src/node/project.ts
index ed6e1664b48a..b67c5be939d7 100644
--- a/packages/vitest/src/node/project.ts
+++ b/packages/vitest/src/node/project.ts
@@ -740,13 +740,6 @@ export class TestProject {
     clone._provideObject(config.provide)
     return clone
   }
-
-  /** @internal */
-  static _cloneBrowserProject(parent: TestProject, config: ResolvedConfig): TestProject {
-    const clone = TestProject._cloneProject(parent, config)
-    clone._parent = parent
-    return clone
-  }
 }
 
 function deduped<T extends (...args: any[]) => Promise<void>>(cb: T): T {
diff --git a/packages/vitest/src/node/projects/resolveProjects.ts b/packages/vitest/src/node/projects/resolveProjects.ts
index bd69651a5510..103dee52ff1d 100644
--- a/packages/vitest/src/node/projects/resolveProjects.ts
+++ b/packages/vitest/src/node/projects/resolveProjects.ts
@@ -259,7 +259,7 @@ export async function resolveBrowserProjects(
       names.add(name)
       const clonedConfig = cloneConfig(project, config)
       clonedConfig.name = name
-      const clone = TestProject._cloneBrowserProject(project, clonedConfig)
+      const clone = TestProject._cloneProject(project, clonedConfig)
       resolvedProjects.push(clone)
     })
 

From 31a6a049483f7c5bdd972cf67bff432ec91f77b2 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 13:54:49 +0900
Subject: [PATCH 28/43] test: more

---
 test/cli/test/reporters/merge-reports.test.ts | 281 +++++++++++++++++-
 1 file changed, 276 insertions(+), 5 deletions(-)

diff --git a/test/cli/test/reporters/merge-reports.test.ts b/test/cli/test/reporters/merge-reports.test.ts
index 1f867095b4a2..35be6e221790 100644
--- a/test/cli/test/reporters/merge-reports.test.ts
+++ b/test/cli/test/reporters/merge-reports.test.ts
@@ -484,9 +484,6 @@ function createTest(name: string, file: File): Test {
 }
 
 // TODO: more tests
-// - single browser instance
-// - multiple browser instances
-// - multiple browser instances with multiple projects
 // - shards
 // - coverage
 test('merge report with labels', async () => {
@@ -506,7 +503,6 @@ test('merge report with labels', async () => {
   const result = await runVitest({
     ...baseConfig,
     mergeReports: reportsDir,
-    reporters: [['default', { isTTY: false }]],
   })
   expect(result.errorTree({ project: true })).toMatchInlineSnapshot(`
     {
@@ -581,7 +577,6 @@ test('merge report with labels and projects', async () => {
   const result = await runVitest({
     ...baseConfig,
     mergeReports: reportsDir,
-    reporters: [['default', { isTTY: false }]],
   })
   expect(result.errorTree({ project: true })).toMatchInlineSnapshot(`
     {
@@ -626,3 +621,279 @@ test('merge report with labels and projects', async () => {
     }
   `)
 })
+
+test('merge report with labels and single browser', async () => {
+  const baseConfig: RunVitestConfig = {
+    root: './fixtures/reporters/merge-reports',
+    browser: {
+      enabled: true,
+      provider: playwright(),
+      instances: [{ browser: 'chromium' }],
+      headless: true,
+    },
+  }
+  await runVitest({
+    ...baseConfig,
+    reporters: [['blob', { label: 'linux' }]],
+  })
+
+  await runVitest({
+    ...baseConfig,
+    reporters: [['blob', { label: 'macos' }]],
+  })
+
+  const result = await runVitest({
+    ...baseConfig,
+    mergeReports: reportsDir,
+  })
+  expect(result.errorTree({ project: true })).toMatchInlineSnapshot(`
+    {
+      "chromium [linux]": {
+        "first.test.ts": {
+          "test 1-1": "passed",
+          "test 1-2": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+        "second.test.ts": {
+          "group": {
+            "test 2-2": "passed",
+            "test 2-3": "passed",
+          },
+          "test 2-1": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+      "chromium [macos]": {
+        "first.test.ts": {
+          "test 1-1": "passed",
+          "test 1-2": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+        "second.test.ts": {
+          "group": {
+            "test 2-2": "passed",
+            "test 2-3": "passed",
+          },
+          "test 2-1": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+    }
+  `)
+})
+
+test('merge report with labels and multiple browsers', async () => {
+  const baseConfig: RunVitestConfig = {
+    root: './fixtures/reporters/merge-reports',
+    browser: {
+      enabled: true,
+      provider: playwright(),
+      instances: [
+        { name: 'chrome1', browser: 'chromium' },
+        { name: 'chrome2', browser: 'chromium' },
+      ],
+      headless: true,
+    },
+  }
+  await runVitest({
+    ...baseConfig,
+    reporters: [['blob', { label: 'linux' }]],
+  })
+
+  await runVitest({
+    ...baseConfig,
+    reporters: [['blob', { label: 'macos' }]],
+  })
+
+  const result = await runVitest({
+    ...baseConfig,
+    mergeReports: reportsDir,
+  })
+  expect(result.errorTree({ project: true })).toMatchInlineSnapshot(`
+    {
+      "chrome1 [linux]": {
+        "first.test.ts": {
+          "test 1-1": "passed",
+          "test 1-2": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+        "second.test.ts": {
+          "group": {
+            "test 2-2": "passed",
+            "test 2-3": "passed",
+          },
+          "test 2-1": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+      "chrome1 [macos]": {
+        "first.test.ts": {
+          "test 1-1": "passed",
+          "test 1-2": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+        "second.test.ts": {
+          "group": {
+            "test 2-2": "passed",
+            "test 2-3": "passed",
+          },
+          "test 2-1": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+      "chrome2 [linux]": {
+        "first.test.ts": {
+          "test 1-1": "passed",
+          "test 1-2": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+        "second.test.ts": {
+          "group": {
+            "test 2-2": "passed",
+            "test 2-3": "passed",
+          },
+          "test 2-1": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+      "chrome2 [macos]": {
+        "first.test.ts": {
+          "test 1-1": "passed",
+          "test 1-2": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+        "second.test.ts": {
+          "group": {
+            "test 2-2": "passed",
+            "test 2-3": "passed",
+          },
+          "test 2-1": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+    }
+  `)
+})
+
+test('merge report with labels and multiple browser projects', async () => {
+  const baseConfig: RunVitestConfig = {
+    root: './fixtures/reporters/merge-reports',
+    projects: [
+      {
+        extends: true,
+        test: {
+          name: 'first',
+          include: ['**/first.test.ts'],
+          browser: {
+            enabled: true,
+            provider: playwright(),
+            instances: [
+              { name: 'chrome1', browser: 'chromium' },
+              { name: 'chrome2', browser: 'chromium' },
+            ],
+            headless: true,
+          },
+        },
+      },
+      {
+        extends: true,
+        test: {
+          name: 'second',
+          include: ['**/second.test.ts'],
+          browser: {
+            enabled: true,
+            provider: playwright(),
+            instances: [
+              { browser: 'chromium' },
+            ],
+            headless: true,
+          },
+        },
+      },
+    ],
+  }
+  await runVitest({
+    ...baseConfig,
+    reporters: [['blob', { label: 'linux' }]],
+  })
+
+  await runVitest({
+    ...baseConfig,
+    reporters: [['blob', { label: 'macos' }]],
+  })
+
+  const result = await runVitest({
+    ...baseConfig,
+    mergeReports: reportsDir,
+  })
+  expect(result.errorTree({ project: true })).toMatchInlineSnapshot(`
+    {
+      "chrome1 [linux]": {
+        "first.test.ts": {
+          "test 1-1": "passed",
+          "test 1-2": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+      "chrome1 [macos]": {
+        "first.test.ts": {
+          "test 1-1": "passed",
+          "test 1-2": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+      "chrome2 [linux]": {
+        "first.test.ts": {
+          "test 1-1": "passed",
+          "test 1-2": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+      "chrome2 [macos]": {
+        "first.test.ts": {
+          "test 1-1": "passed",
+          "test 1-2": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+      "second (chromium) [linux]": {
+        "second.test.ts": {
+          "group": {
+            "test 2-2": "passed",
+            "test 2-3": "passed",
+          },
+          "test 2-1": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+      "second (chromium) [macos]": {
+        "second.test.ts": {
+          "group": {
+            "test 2-2": "passed",
+            "test 2-3": "passed",
+          },
+          "test 2-1": [
+            "expected 1 to be 2 // Object.is equality",
+          ],
+        },
+      },
+    }
+  `)
+})

From 0503fd926781af1e82aaf63f91a95d7d770e8e19 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 14:02:38 +0900
Subject: [PATCH 29/43] chore: cleanup

---
 test/cli/test/reporters/merge-reports.test.ts | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/test/cli/test/reporters/merge-reports.test.ts b/test/cli/test/reporters/merge-reports.test.ts
index 35be6e221790..c3f2d1c079ee 100644
--- a/test/cli/test/reporters/merge-reports.test.ts
+++ b/test/cli/test/reporters/merge-reports.test.ts
@@ -483,9 +483,6 @@ function createTest(name: string, file: File): Test {
   }
 }
 
-// TODO: more tests
-// - shards
-// - coverage
 test('merge report with labels', async () => {
   const baseConfig: RunVitestConfig = {
     root: './fixtures/reporters/merge-reports',

From 7d89db06870fd17e9a3c674bc1df38eba2b9026d Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 14:07:12 +0900
Subject: [PATCH 30/43] chore: cleanup

---
 packages/vitest/src/node/reporters/blob.ts | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/packages/vitest/src/node/reporters/blob.ts b/packages/vitest/src/node/reporters/blob.ts
index 7358c774edc5..bd4ebe60f60f 100644
--- a/packages/vitest/src/node/reporters/blob.ts
+++ b/packages/vitest/src/node/reporters/blob.ts
@@ -174,8 +174,7 @@ export async function readBlobs(
     )
   }
 
-  // TODO: review
-  // Rewrite file projectName/IDs and environmentModules keys for labeled blobs
+  // Rewrite blob data so they get attached to duplicated projects based on labels
   for (const blob of blobs) {
     const label = blob.label
     if (!label) {

From fe175fb9a7a17cc844fd1aad52cfa2eed8716ac9 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Wed, 25 Mar 2026 14:14:33 +0900
Subject: [PATCH 31/43] test: assert blob output

---
 test/cli/test/reporters/merge-reports.test.ts | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/test/cli/test/reporters/merge-reports.test.ts b/test/cli/test/reporters/merge-reports.test.ts
index c3f2d1c079ee..1224a8cc1088 100644
--- a/test/cli/test/reporters/merge-reports.test.ts
+++ b/test/cli/test/reporters/merge-reports.test.ts
@@ -6,6 +6,7 @@ import { resolve } from 'node:path'
 import { runVitest } from '#test-utils'
 import { playwright } from '@vitest/browser-playwright'
 import { createFileTask } from '@vitest/runner/utils'
+import { globSync } from 'tinyglobby'
 import { beforeEach, expect, test } from 'vitest'
 import { version } from 'vitest/package.json'
 import { writeBlob } from 'vitest/src/node/reporters/blob.js'
@@ -575,6 +576,12 @@ test('merge report with labels and projects', async () => {
     ...baseConfig,
     mergeReports: reportsDir,
   })
+  expect(globSync('*', { cwd: reportsDir }).sort()).toMatchInlineSnapshot(`
+    [
+      "blob-linux.json",
+      "blob-macos.json",
+    ]
+  `)
   expect(result.errorTree({ project: true })).toMatchInlineSnapshot(`
     {
       "first [linux]": {

From 0137190f5db43429b97ecca1b91abe34377174d2 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Thu, 26 Mar 2026 09:13:37 +0900
Subject: [PATCH 32/43] ci: dogfood blob label

---
 .github/workflows/ci.yml | 41 ++++++++++++++++++++++++++++++++++++++++
 test/core/vite.config.ts | 11 ++++++++---
 2 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6ef6d0538d0b..e9966102262e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -116,6 +116,8 @@ jobs:
 
       - name: Test
         run: pnpm run test:ci
+        env:
+          VITEST_BLOB_LABEL_DOGFOOD: ${{ matrix.os }}-node-${{ matrix.node_version }}
 
       - name: Test Examples
         run: pnpm run test:examples
@@ -127,6 +129,13 @@ jobs:
           path: test/ui/test-results/
           retention-days: 30
 
+      - uses: actions/upload-artifact@v7
+        if: ${{ !cancelled() }}
+        with:
+          name: vitest-blob-core-${{ matrix.os }}-node-${{ matrix.node_version }}
+          path: test/core/.vitest-reports/
+          retention-days: 1
+
   test-cached:
     needs: changed
     name: 'Cache&Test: node-${{ matrix.node_version }}, ${{ matrix.os }}'
@@ -248,3 +257,35 @@ jobs:
           name: playwright-report-rolldown
           path: rolldown/test/ui/test-results/
           retention-days: 30
+
+  merge-reports:
+    needs: test
+    if: ${{ !cancelled() }}
+    runs-on: ubuntu-latest
+    name: Merge Reports
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@v6
+
+      - uses: ./.github/actions/setup-and-cache
+
+      - name: Install
+        run: pnpm i
+
+      - name: Build
+        run: pnpm run build
+
+      - uses: actions/download-artifact@v4
+        with:
+          pattern: vitest-blob-core-*
+          path: test/core/.vitest-reports/
+          merge-multiple: true
+
+      - name: Merge test/core reports
+        run: pnpm -C test/core vitest --run --merge-reports --reporter=html
+
+      - uses: actions/upload-artifact@v7
+        with:
+          name: vitest-core-html
+          path: test/core/html/
+          retention-days: 30
diff --git a/test/core/vite.config.ts b/test/core/vite.config.ts
index ab7e3aad425a..2d1184bf2082 100644
--- a/test/core/vite.config.ts
+++ b/test/core/vite.config.ts
@@ -125,9 +125,14 @@ export default defineConfig({
       },
     },
     includeTaskLocation: true,
-    reporters: process.env.GITHUB_ACTIONS
-      ? ['default', ['github-actions', { displayAnnotations: false }]]
-      : [['default', { summary: true }], 'hanging-process'],
+    reporters: [
+      ...(process.env.GITHUB_ACTIONS
+        ? [['default'], ['github-actions', { displayAnnotations: false }] as any]
+        : [['default', { summary: true }], ['hanging-process']]),
+      ...(process.env.VITEST_BLOB_LABEL_DOGFOOD
+        ? [['blob', { label: process.env.VITEST_BLOB_LABEL_DOGFOOD }]]
+        : []),
+    ],
     testNamePattern: '^((?!does not include test that).)*$',
     coverage: {
       provider: 'istanbul',

From fb4e8bcbe3c4e69ee412a0669cc7ec6cbe8e7718 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Thu, 26 Mar 2026 09:14:38 +0900
Subject: [PATCH 33/43] ci: dogfood

---
 .github/workflows/ci.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e9966102262e..134ef40c7069 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -288,4 +288,4 @@ jobs:
         with:
           name: vitest-core-html
           path: test/core/html/
-          retention-days: 30
+          retention-days: 7

From fde6ace38216c1c586e7cbc033748fe0bacfd992 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Thu, 26 Mar 2026 09:25:26 +0900
Subject: [PATCH 34/43] ci: test/cli too

---
 .github/workflows/ci.yml  | 22 ++++++++++++++++++++++
 test/cli/vitest.config.ts |  7 ++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 134ef40c7069..2b7aa12aff6c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -136,6 +136,13 @@ jobs:
           path: test/core/.vitest-reports/
           retention-days: 1
 
+      - uses: actions/upload-artifact@v7
+        if: ${{ !cancelled() }}
+        with:
+          name: vitest-blob-cli-${{ matrix.os }}-node-${{ matrix.node_version }}
+          path: test/cli/.vitest-reports/
+          retention-days: 1
+
   test-cached:
     needs: changed
     name: 'Cache&Test: node-${{ matrix.node_version }}, ${{ matrix.os }}'
@@ -289,3 +296,18 @@ jobs:
           name: vitest-core-html
           path: test/core/html/
           retention-days: 7
+
+      - uses: actions/download-artifact@v4
+        with:
+          pattern: vitest-blob-cli-*
+          path: test/cli/.vitest-reports/
+          merge-multiple: true
+
+      - name: Merge test/cli reports
+        run: pnpm -C test/cli vitest --run --merge-reports --reporter=html
+
+      - uses: actions/upload-artifact@v7
+        with:
+          name: vitest-cli-html
+          path: test/cli/html/
+          retention-days: 7
diff --git a/test/cli/vitest.config.ts b/test/cli/vitest.config.ts
index 52442d43a4b2..f312b9fb4a8b 100644
--- a/test/cli/vitest.config.ts
+++ b/test/cli/vitest.config.ts
@@ -4,7 +4,12 @@ export default defineConfig({
   test: {
     include: ['test/**/**.{test,spec}.ts'],
     includeTaskLocation: true,
-    reporters: ['verbose'],
+    reporters: [
+      'verbose',
+      ...(process.env.VITEST_BLOB_LABEL_DOGFOOD
+        ? [['blob', { label: process.env.VITEST_BLOB_LABEL_DOGFOOD }]] as any
+        : []),
+    ],
     testTimeout: 60_000,
     isolate: false,
     fileParallelism: false,

From da49e6e8e4237288b03707911bfec7509e96878b Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Thu, 26 Mar 2026 09:30:21 +0900
Subject: [PATCH 35/43] ci: simplify upload and download artifacts

---
 .github/workflows/ci.yml | 35 ++++++++++-------------------------
 1 file changed, 10 insertions(+), 25 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2b7aa12aff6c..bda6379235c0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -132,15 +132,11 @@ jobs:
       - uses: actions/upload-artifact@v7
         if: ${{ !cancelled() }}
         with:
-          name: vitest-blob-core-${{ matrix.os }}-node-${{ matrix.node_version }}
-          path: test/core/.vitest-reports/
-          retention-days: 1
-
-      - uses: actions/upload-artifact@v7
-        if: ${{ !cancelled() }}
-        with:
-          name: vitest-blob-cli-${{ matrix.os }}-node-${{ matrix.node_version }}
-          path: test/cli/.vitest-reports/
+          name: vitest-blob-${{ matrix.os }}-node-${{ matrix.node_version }}
+          path: |
+            README.md
+            test/core/.vitest-reports/
+            test/cli/.vitest-reports/
           retention-days: 1
 
   test-cached:
@@ -284,30 +280,19 @@ jobs:
 
       - uses: actions/download-artifact@v4
         with:
-          pattern: vitest-blob-core-*
-          path: test/core/.vitest-reports/
+          pattern: vitest-blob-*
           merge-multiple: true
 
       - name: Merge test/core reports
         run: pnpm -C test/core vitest --run --merge-reports --reporter=html
 
-      - uses: actions/upload-artifact@v7
-        with:
-          name: vitest-core-html
-          path: test/core/html/
-          retention-days: 7
-
-      - uses: actions/download-artifact@v4
-        with:
-          pattern: vitest-blob-cli-*
-          path: test/cli/.vitest-reports/
-          merge-multiple: true
-
       - name: Merge test/cli reports
         run: pnpm -C test/cli vitest --run --merge-reports --reporter=html
 
       - uses: actions/upload-artifact@v7
         with:
-          name: vitest-cli-html
-          path: test/cli/html/
+          name: vitest-merge-html
+          path: |
+            test/core/html/
+            test/cli/html/
           retention-days: 7

From 369b469f816089d38853b0ec1ad0788d2146d822 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Thu, 26 Mar 2026 09:33:41 +0900
Subject: [PATCH 36/43] ci: fix merge reports

---
 .github/workflows/ci.yml | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index bda6379235c0..a81b9313c6d6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -284,15 +284,19 @@ jobs:
           merge-multiple: true
 
       - name: Merge test/core reports
-        run: pnpm -C test/core vitest --run --merge-reports --reporter=html
+        if: ${{ !cancelled() }}
+        run: pnpm -C test/core test --run --merge-reports --reporter=html
 
       - name: Merge test/cli reports
-        run: pnpm -C test/cli vitest --run --merge-reports --reporter=html
+        if: ${{ !cancelled() }}
+        run: pnpm -C test/cli test --run --merge-reports --reporter=html
 
       - uses: actions/upload-artifact@v7
+        if: ${{ !cancelled() }}
         with:
-          name: vitest-merge-html
+          name: vitest-merge-reports
           path: |
+            README.md
             test/core/html/
             test/cli/html/
           retention-days: 7

From 87d65388bee783c4b7fa6942dcc8c4e4573eabcf Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Thu, 26 Mar 2026 09:49:46 +0900
Subject: [PATCH 37/43] ci: merge merge reports

---
 .github/workflows/ci.yml | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index a81b9313c6d6..d2aa8d1dd0a3 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -283,13 +283,8 @@ jobs:
           pattern: vitest-blob-*
           merge-multiple: true
 
-      - name: Merge test/core reports
-        if: ${{ !cancelled() }}
-        run: pnpm -C test/core test --run --merge-reports --reporter=html
-
-      - name: Merge test/cli reports
-        if: ${{ !cancelled() }}
-        run: pnpm -C test/cli test --run --merge-reports --reporter=html
+      - name: Merge reports
+        run: pnpm --filter=./test/core --filter=./test/cli --no-bail --sequential test --merge-reports --reporter=html
 
       - uses: actions/upload-artifact@v7
         if: ${{ !cancelled() }}

From 36051a7bc17cf1050fb5813ca74b50d9b04bc0e1 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Thu, 26 Mar 2026 09:55:38 +0900
Subject: [PATCH 38/43] ci: fix upload

---
 .github/workflows/ci.yml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d2aa8d1dd0a3..feb1f2f1cfc0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -135,8 +135,8 @@ jobs:
           name: vitest-blob-${{ matrix.os }}-node-${{ matrix.node_version }}
           path: |
             README.md
-            test/core/.vitest-reports/
-            test/cli/.vitest-reports/
+            test/core/.vitest-reports/*
+            test/cli/.vitest-reports/*
           retention-days: 1
 
   test-cached:

From 7be50d98b61c28661973f3ab94780632bd33a434 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Thu, 26 Mar 2026 10:01:44 +0900
Subject: [PATCH 39/43] ci: more glob

---
 .github/workflows/ci.yml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index feb1f2f1cfc0..d4eadc4790e8 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -292,6 +292,6 @@ jobs:
           name: vitest-merge-reports
           path: |
             README.md
-            test/core/html/
-            test/cli/html/
+            test/core/html/*
+            test/cli/html/*
           retention-days: 7

From 88b50091517d1fab35dd91b27af55a383ee282c6 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Thu, 26 Mar 2026 10:27:24 +0900
Subject: [PATCH 40/43] test: more realistic test

---
 test/cli/test/reporters/merge-reports.test.ts | 103 +++++++++++++++++-
 1 file changed, 102 insertions(+), 1 deletion(-)

diff --git a/test/cli/test/reporters/merge-reports.test.ts b/test/cli/test/reporters/merge-reports.test.ts
index 1224a8cc1088..90536ebebfd5 100644
--- a/test/cli/test/reporters/merge-reports.test.ts
+++ b/test/cli/test/reporters/merge-reports.test.ts
@@ -3,7 +3,7 @@ import type { File, Test } from '@vitest/runner/types'
 import type { TestUserConfig, Vitest } from 'vitest/node'
 import { rmSync } from 'node:fs'
 import { resolve } from 'node:path'
-import { runVitest } from '#test-utils'
+import { runVitest, useFS } from '#test-utils'
 import { playwright } from '@vitest/browser-playwright'
 import { createFileTask } from '@vitest/runner/utils'
 import { globSync } from 'tinyglobby'
@@ -542,6 +542,107 @@ test('merge report with labels', async () => {
   `)
 })
 
+test('merge reports of different results with labels', async () => {
+  const root = resolve(process.cwd(), `vitest-test-${crypto.randomUUID()}`)
+  useFS(root, {
+    'first.test.ts': `
+test("always good", () => {})
+
+test("works on linux", () => {
+  expect(process.env.TEST_LABEL_ENV === 'linux').toBe(true)
+})
+
+test("works on macos", () => {
+  expect(process.env.TEST_LABEL_ENV === 'macos').toBe(true)
+})
+`,
+    'second.test.ts': `
+test("linux only", () => {})
+`,
+    'third.test.ts': `
+test("macos only", () => {})
+`,
+  })
+  process.env.TEST_LABEL_ENV = 'linux'
+  const result1 = await runVitest({
+    root,
+    globals: true,
+    reporters: [['blob', { label: 'linux' }]],
+  }, ['first', 'second'])
+  expect(result1.stderr).toMatchInlineSnapshot(`""`);
+  expect(result1.errorTree({ project: true })).toMatchInlineSnapshot(`
+    {
+      "": {
+        "first.test.ts": {
+          "always good": "passed",
+          "works on linux": "passed",
+          "works on macos": [
+            "expected false to be true // Object.is equality",
+          ],
+        },
+        "second.test.ts": {
+          "linux only": "passed",
+        },
+      },
+    }
+  `)
+  process.env.TEST_LABEL_ENV = 'macos'
+  const result2 = await runVitest({
+    root,
+    globals: true,
+    reporters: [['blob', { label: 'macos' }]],
+  }, ['first', 'third'])
+  expect(result2.stderr).toMatchInlineSnapshot(`""`);
+  expect(result2.errorTree({ project: true })).toMatchInlineSnapshot(`
+    {
+      "": {
+        "first.test.ts": {
+          "always good": "passed",
+          "works on linux": [
+            "expected false to be true // Object.is equality",
+          ],
+          "works on macos": "passed",
+        },
+        "third.test.ts": {
+          "macos only": "passed",
+        },
+      },
+    }
+  `)
+  const result = await runVitest({
+    root,
+    mergeReports: resolve(root, '.vitest-reports'),
+  })
+  expect(result.errorTree({ project: true })).toMatchInlineSnapshot(`
+    {
+      "linux": {
+        "first.test.ts": {
+          "always good": "passed",
+          "works on linux": "passed",
+          "works on macos": [
+            "expected false to be true // Object.is equality",
+          ],
+        },
+        "second.test.ts": {
+          "linux only": "passed",
+        },
+      },
+      "macos": {
+        "first.test.ts": {
+          "always good": "passed",
+          "works on linux": [
+            "expected false to be true // Object.is equality",
+          ],
+          "works on macos": "passed",
+        },
+        "third.test.ts": {
+          "macos only": "passed",
+        },
+      },
+    }
+  `)
+})
+
 test('merge report with labels and projects', async () => {
   const baseConfig: RunVitestConfig = {
     root: './fixtures/reporters/merge-reports',

From 8569516db1e97171f945b5a118d8f0f699b1c0c8 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Thu, 26 Mar 2026 10:34:41 +0900
Subject: [PATCH 41/43] ci: ugh include-hidden-files

---
 .github/workflows/ci.yml | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d4eadc4790e8..89272ff776fe 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -135,9 +135,10 @@ jobs:
           name: vitest-blob-${{ matrix.os }}-node-${{ matrix.node_version }}
           path: |
             README.md
-            test/core/.vitest-reports/*
-            test/cli/.vitest-reports/*
+            test/core/.vitest-reports
+            test/cli/.vitest-reports
           retention-days: 1
+          include-hidden-files: true
 
   test-cached:
     needs: changed
@@ -292,6 +293,6 @@ jobs:
           name: vitest-merge-reports
           path: |
             README.md
-            test/core/html/*
-            test/cli/html/*
+            test/core/html
+            test/cli/html
           retention-days: 7

From cc6543ae4aa4477aaaeb694383c62e6eaf0c8d85 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Thu, 26 Mar 2026 10:44:36 +0900
Subject: [PATCH 42/43] chore: lint

---
 test/cli/test/reporters/merge-reports.test.ts | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/test/cli/test/reporters/merge-reports.test.ts b/test/cli/test/reporters/merge-reports.test.ts
index 90536ebebfd5..745df54db036 100644
--- a/test/cli/test/reporters/merge-reports.test.ts
+++ b/test/cli/test/reporters/merge-reports.test.ts
@@ -569,7 +569,7 @@ test("macos only", () => {})
     globals: true,
     reporters: [['blob', { label: 'linux' }]],
   }, ['first', 'second'])
-  expect(result1.stderr).toMatchInlineSnapshot(`""`);
+  expect(result1.stderr).toMatchInlineSnapshot(`""`)
   expect(result1.errorTree({ project: true })).toMatchInlineSnapshot(`
     {
       "": {
@@ -592,7 +592,7 @@ test("macos only", () => {})
     globals: true,
     reporters: [['blob', { label: 'macos' }]],
   }, ['first', 'third'])
-  expect(result2.stderr).toMatchInlineSnapshot(`""`);
+  expect(result2.stderr).toMatchInlineSnapshot(`""`)
   expect(result2.errorTree({ project: true })).toMatchInlineSnapshot(`
     {
       "": {

From 3dbbf7203916a3e9045eac1b485b34879559b0d0 Mon Sep 17 00:00:00 2001
From: Hiroshi Ogawa <hi.ogawa.zz@gmail.com>
Date: Thu, 26 Mar 2026 11:54:43 +0900
Subject: [PATCH 43/43] ci: merge-reports shouldn't be red

---
 .github/workflows/ci.yml | 1 +
 1 file changed, 1 insertion(+)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 89272ff776fe..6d5cf0f849ab 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -285,6 +285,7 @@ jobs:
           merge-multiple: true
 
       - name: Merge reports
+        continue-on-error: true
         run: pnpm --filter=./test/core --filter=./test/cli --no-bail --sequential test --merge-reports --reporter=html
 
       - uses: actions/upload-artifact@v7