fix(server): keep Claude rewind when fork history length changes

[maria-rcks]

claude rewind could reject a valid fork when system notices or compaction metadata changed the transcript's raw length. this aligns retained user/assistant messages from the truncated end and remaps native turn ids. it verifies retained message bodies before accepting that alignment, so restored steering messages or changed replies cannot silently shift a turn boundary.

verification: 137 claude adapter tests and server typechecking passed on blacksmith. coverage includes omitted/extra system messages, compact prefixes, tool results, steering, single/multi-turn rewind, reset-all, and invalid retained history. the two new mismatch cases failed on the original pr head and pass with the body validation.

live claude sonnet 5 verification through the web client covered repeated last-turn rewind, tool calls with a queued follow-up, multi-turn rewind, reset-all, and subsequent messages. ordinary cases passed before and after. the specific metadata-length failure was not reproduced organically; its variants are covered by adapter tests. desktop/mobile use this server adapter but were not separately exercised.

before: original adapter at 3efdcc5296, including last-turn rewind, tools/queued follow-up, multi-turn rewind, and reset-all.

after: the same interaction categories with retained-history validation. the multi-turn examples remove different numbers of turns; these are functional checks, not timing benchmarks.

reviewed and updated with gpt-6-astra in codex.

[macroscopeapp]

Approvability

Verdict: Approved at 3f9057d

Macroscope's review found this PR approvable — This is a localized Claude rollback bug fix with comprehensive tests, preserving valid rewinds while rejecting forks that do not preserve retained conversation content. It does not alter schemas, defaults, deployment configuration, or security-sensitive behavior.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.6 KiB	13.6 KiB	+29 B (+0.2%)	15.1 KiB	✅
Codex	Thread snapshot wire	7.1 KiB	7.1 KiB	−6 B (−0.1%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.5 KiB	6.6 KiB	+35 B (+0.5%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.0 KiB	57.1 KiB	+44 B (+0.1%)	66.4 KiB	✅
Codex	Live turn messages	9	10	+1 (+11.1%)	21	✅
Claude	Total thread wire	13.6 KiB	13.6 KiB	−12 B (−0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	7.1 KiB	7.1 KiB	+1 B (+0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.6 KiB	6.6 KiB	−13 B (−0.2%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	57.9 KiB	57.9 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	10	10	0 (0.0%)	21	✅

Baseline: 3efdcc5 · PR result: 3f9057d · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 113.9 KiB
• Claude decoded thread snapshot: 114.6 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

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📥 Commits

Reviewing files that changed from the base of the PR and between 8e2e05a and 3f9057d.

📒 Files selected for processing (1)

• apps/server/src/provider/Layers/ClaudeAdapter.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• apps/server/src/provider/Layers/ClaudeAdapter.ts

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📝 Walkthrough

Walkthrough

Claude rollback now aligns retained conversation messages across fork histories with different system-message layouts. It validates message types and bodies before remapping boundaries. Tests cover supported histories, rewinds, resets, tool results, steering, and invalid forks.

Changes

Claude rollback handling

Layer / File(s)	Summary
Fork boundary remapping apps/server/src/provider/Layers/ClaudeAdapter.ts	Validates conversation offsets, retained message types, and message bodies before remapping fork message IDs. Rollback uses this validated alignment and preserves the existing error when boundaries cannot be preserved.
Rollback validation apps/server/src/provider/Layers/ClaudeAdapter.ts, apps/server/src/provider/Layers/ClaudeAdapter.test.ts	Adds tests for omitted or extra system messages, compacted prefixes, tool results, steering, multi-turn rewinds, full resets, missing retained turns, inserted messages, and changed assistant content.

Priority: ⬇️ Low

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Bug fix

Merge Risk: ⚪ Minimal · up to 3f905

The rollback update preserves valid forked conversations and safely rejects incompatible fork histories, with focused tests covering supported and rejected history variants. No actionable merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly describes the primary change: preserving Claude rewind when fork history length changes.
Description check	✅ Passed	The description explains what changed, why it was needed, test coverage, live verification, and UI evidence. It does not use the template headings or include the checklist, but it contains the require…

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✨ Finishing Touches 💡 1

📝 Generate docstrings 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/claude-rewind-fork-boundaries

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Dismissing prior approval to re-evaluate 8e2e05a

Dismissing prior approval to re-evaluate 3f9057d