feat: hunk-level grouping, multi-backend AI, config, caching, help overlay

- Hunk-level semantic grouping: groups related hunks across files by intent,
  a single file's hunks can appear in different groups
- Multi-backend AI: support Claude CLI and Copilot CLI (copilot --yolo)
  with configurable preference and automatic fallback
- Config file: ~/.config/semantic-diff.json with JSONC comment support,
  model selection, and cross-backend model mapping
- Grouping cache: .git/semantic-diff-cache.json keyed by diff hash for
  instant startup when diff hasn't changed
- Group-aware diff filtering: sidebar file/group selection filters diff view
- Help overlay: press ? for keybinding reference
- Text wrapping: long diff lines flow with terminal width
- Improved key responsiveness: accept Repeat events on macOS
- Scroll-to-top on file select from sidebar

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Alan Shum

Cargo.lock

@@ -1,8 +1,8 @@
 [package]
 name = "semantic-diff"
-version = "0.1.0"
+version = "0.2.0"
 edition = "2021"
-description = "A terminal diff viewer with AI-powered semantic grouping via Claude CLI"
+description = "A terminal diff viewer with AI-powered semantic grouping (Claude CLI / Copilot)"
 license = "MIT"
 repository = "https://github.com/alankyshum/semantic-diff"
 keywords = ["git", "diff", "tui", "semantic", "claude"]
@@ -23,6 +23,7 @@ tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 serde = { version = "1.0.228", features = ["derive"] }
 serde_json = "1.0.149"
 which = "8.0.2"
+dirs = "6"
 tui-tree-widget = "0.24"
 
 [profile.release]

Cargo.toml

@@ -4,16 +4,26 @@ A terminal diff viewer with AI-powered semantic grouping. Built with Rust and [r
 
 Groups your git changes by *meaning* — not just by file path. Designed to run as a cmux split pane alongside Claude Code, giving real-time visibility into what's being changed and why.
 
+## Demo
+
+https://github.com/user-attachments/assets/semantic-diff-demo.mp4
+
 ## Features
 
-- **Semantic grouping** — Claude CLI clusters changes into named groups (e.g. "Refactored auth logic", "Added test coverage")
+- **Hunk-level semantic grouping** — AI clusters related hunks across files by intent (e.g. "Auth refactor", "Test coverage"), not just file-level grouping
+- **Multi-backend AI** — Supports Claude CLI and GitHub Copilot CLI (`copilot --yolo`), with configurable preference and automatic fallback
+- **Configurable** — `~/.config/semantic-diff.json` with JSONC comment support, model selection, and intelligent cross-backend model mapping
+- **Grouping cache** — Cached in `.git/semantic-diff-cache.json` keyed by diff hash; instant reload when nothing changed
 - **Syntax-highlighted diffs** — Powered by syntect with word-level inline highlighting
 - **Collapse/expand** — Toggle files, hunks, and semantic groups
-- **File tree sidebar** — Changed files organized by semantic group with stats
+- **File tree sidebar** — Changed files organized by semantic group with per-hunk stats
+- **Group-aware diff filtering** — Select a file or group in the sidebar to filter the diff view to only those changes
 - **Hook-triggered refresh** — Auto-updates when Claude Code edits files (via SIGUSR1)
 - **cmux integration** — Auto-opens in a right split pane
+- **Help overlay** — Press `?` to see all keybindings
+- **Text wrapping** — Long diff lines flow with the terminal width
 - **Progressive enhancement** — Shows ungrouped diff immediately, regroups when AI responds
-- **Graceful degradation** — Works without Claude CLI (falls back to ungrouped view)
+- **Graceful degradation** — Works without any AI CLI (falls back to ungrouped view)
 
 ## Install
 
@@ -49,16 +59,40 @@ semantic-diff
 
 | Key | Action |
 |-----|--------|
-| `j/k` | Navigate up/down |
-| `Enter` | Collapse/expand file, hunk, or group |
+| `j/k`, `↑/↓` | Navigate up/down |
+| `Enter` | Sidebar: select file/group · Diff: toggle collapse |
 | `Tab` | Switch focus between tree sidebar and diff view |
 | `/` | Search/filter files |
 | `n/N` | Next/previous search match |
-| `Escape` | Clear search |
 | `g/G` | Jump to top/bottom |
 | `Ctrl+d/u` | Page down/up |
+| `?` | Show shortcut help |
+| `Escape` | Clear filter / quit |
 | `q` | Quit |
 
+### Configuration
+
+On first run, a default config is created at `~/.config/semantic-diff.json`:
+
+```jsonc
+{
+  // Which AI CLI to prefer: "claude" or "copilot"
+  // Falls back to the other if preferred is not installed
+  // "preferred-ai-cli": "claude",
+
+  "claude": {
+    // Model: "sonnet", "opus", "haiku"
+    // Cross-backend models mapped automatically (gemini-flash → haiku)
+    "model": "sonnet"
+  },
+
+  "copilot": {
+    // Model: "sonnet", "opus", "haiku", "gemini-flash", "gemini-pro"
+    "model": "sonnet"
+  }
+}
+```
+
 ## Claude Code Integration
 
 semantic-diff is designed to work as a live diff viewer alongside Claude Code.
@@ -101,14 +135,32 @@ chmod +x ~/.claude/hooks/refresh-semantic-diff.sh
 2. PostToolUse hook fires `refresh-semantic-diff.sh`
 3. If semantic-diff is running: sends SIGUSR1 to refresh the diff
 4. If not running: opens a cmux right-split pane and launches semantic-diff
-5. Claude CLI groups the changed files by semantic meaning
+5. AI groups the changed hunks by semantic meaning
 6. You see real-time, grouped changes without leaving the terminal
 
+## Changelog
+
+### v0.2.0
+
+- **Hunk-level semantic grouping** — Groups related hunks across files by intent, matching GitHub Copilot's content-level approach. A single file's hunks can appear in different groups.
+- **Multi-backend AI support** — Added GitHub Copilot CLI (`copilot --yolo`) as a fallback when Claude CLI is not available.
+- **Configuration file** — `~/.config/semantic-diff.json` with JSONC comment support. Configure preferred AI backend, model per backend, with intelligent cross-backend model mapping (e.g. `gemini-flash` → `haiku`).
+- **Grouping cache** — Results cached in `.git/semantic-diff-cache.json` keyed by diff hash. Instant startup when diff hasn't changed.
+- **Group-aware diff filtering** — Selecting a file in the sidebar filters the diff to its entire group. Selecting a group header toggles the filter.
+- **Help overlay** — Press `?` to see all keybindings in a centered popup.
+- **Text wrapping** — Long diff lines wrap with the terminal width instead of being truncated.
+- **Improved key responsiveness** — Accept `Repeat` key events on macOS for smooth held-key navigation.
+- **Scroll-to-top on file select** — File header pinned to top of viewport when selected from sidebar.
+
+### v0.1.0
+
+- Initial release with file-level semantic grouping, syntax highlighting, collapse/expand, file tree sidebar, and Claude Code hook integration.
+
 ## Requirements
 
 - Rust 1.75+
 - Git
-- [Claude CLI](https://claude.ai/download) (optional, for semantic grouping)
+- [Claude CLI](https://claude.ai/download) or [GitHub Copilot CLI](https://github.com/github/copilot-cli) (optional, for semantic grouping)
 - [cmux](https://cmux.dev) (optional, for auto-split pane)
 
 ## License