fix(session-recovery): add thinking_block_modified error detection and recovery

[omer-koren]

Problem

• Amazon Bedrock can return thinking / redacted_thinking signature errors after compaction corrupts the latest assistant thinking block signatures.
• Session recovery already handles thinking block ordering and thinking-disabled violations, but it did not recognize this corruption case.
• Users with experimental.auto_resume: true were left without an automatic recovery path when the provider rejected the modified thinking blocks.

Solution

• add a thinking_block_modified recovery error type and detect the Bedrock thinking blocks cannot be modified failure pattern
• wire the new error type into the session recovery hook with dedicated toast messaging
• reuse recoverThinkingDisabledViolation to strip corrupted thinking blocks, then auto-resume the session when enabled
• add regression tests for the full Bedrock error message and a simpler variant

Testing

• bun run typecheck
• bun test src/hooks/session-recovery/
• bun run build

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Summary by cubic

Detects and recovers from Bedrock “thinking block modified” errors caused by compaction, restoring auto-resume when enabled and preventing stuck sessions.

• Bug Fixes
  • Added thinking_block_modified recovery type; detects Bedrock “thinking … cannot be modified” errors (full and simple variants).
  • Integrated with session recovery: shows dedicated toast, strips corrupted thinking blocks using existing logic, and auto-resumes when experimental.auto_resume is enabled; added regression tests.

^{Written for commit b6ad494. Summary will update on new commits.}

[github-actions]

All contributors have signed the CLA. Thank you! ✅
_{Posted by the CLA Assistant Lite bot.}

[cubic-dev-ai]

No issues found across 3 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Auto-approved: Safely adds detection and recovery for Bedrock thinking block errors by reusing existing logic; includes regression tests and is isolated from other error handling paths.}

[omer-koren]

I have read the CLA Document and I hereby sign the CLA