fix(providers): reject unsupported rewind before restoring files

[aaditagrawal]

Adapters that cannot rewind native conversations previously failed only after checkpoint restoration could change workspace files. Explicitly declares unsupported conversation rollback for Amp, Copilot, Cursor, Droid, Gemini and standard ACP adapters. Cursor now rejects rewind instead of only trimming local history while reporting success.

Validation: six real adapter suites passed (48 tests, two existing skips at this stack layer); checkpoint/provider service suites passed (97 tests). Workspace check/typecheck passed at the integrated tip.

[aaditagrawal]

• sync: finish upstream alignment through bc8584bf8e #273
• fix(providers): preserve custom model descriptors and restore Copilot startup #272
• refactor(web): remove unused legacy client modules #271
• perf(cursor): retain compact turn summaries instead of SDK streams #270
• fix(providers): reject unsupported rewind before restoring files #269 👈 (View in Graphite)
• sync: complete upstream alignment through 7a089b2b24 #268
• sync: adopt upstream streaming and persistence performance work #267
• sync: integrate remaining upstream commits through 09d13de43 #266
• sync: integrate upstream wave 4 (settings reorg, usage limits, compaction) #265
• sync: integrate upstream wave 3 (Antigravity + cookie import) #264
• sync: integrate upstream wave 2 through 652515a34 #263
• sync: integrate upstream wave 1 through 355fbd96d #262
• main

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ No successful main baseline artifact is available yet. This run establishes the initial measurement.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	—	13.6 KiB	—	15.1 KiB	✅
Codex	Thread snapshot wire	—	7.0 KiB	—	7.3 KiB	✅
Codex	Live turn WebSocket wire	—	6.5 KiB	—	7.8 KiB	✅
Codex	Live turn WebSocket decoded	—	57.0 KiB	—	66.4 KiB	✅
Codex	Live turn messages	—	9	—	21	✅
Claude	Total thread wire	—	13.4 KiB	—	15.1 KiB	✅
Claude	Thread snapshot wire	—	7.0 KiB	—	7.3 KiB	✅
Claude	Live turn WebSocket wire	—	6.4 KiB	—	7.8 KiB	✅
Claude	Live turn WebSocket decoded	—	56.9 KiB	—	66.4 KiB	✅
Claude	Live turn messages	—	7	—	21	✅

Baseline: unavailable · PR result: bb8837f · 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.

[aaditagrawal]

Merge activity

• Sep 5, 7:41 AM UTC: A user started a stack merge that includes this pull request via Graphite.
• Sep 5, 7:43 AM UTC: Graphite couldn't merge this pull request because a downstack PR sync: integrate upstream wave 2 through 652515a34 #263 failed to merge.