fix(claude): safely resume unsigned thinking transcripts

[acedatacloud-dev]

Summary

• detect native Claude transcripts containing assistant thinking blocks without valid signatures before Agent SDK resume
• create an atomic, deterministic recovery fork that removes only invalid thinking blocks while preserving text, tool calls, tool results, UUID links, and the original transcript
• route the SDK resume to the repaired session ID and cover healthy, malformed, repeated, and provider-wiring cases

Root cause evidence

Production trace 824abe10a69544808b31aeff9c5fe6a2 reached the local node and returned Missing required field in assistant message: signature. Structural inspection of session 631c4ebb-0837-4539-86d1-7382ff15bf92 found 234 unsigned thinking blocks. This confirms the direct resume failure; it does not prove which earlier Claude response/serialization path originally wrote those blocks.

Verification

• uv run pytest tests/test_claude_transcript.py tests/test_claude_entrypoint.py tests/test_resume_guard.py tests/test_edit_fork.py tests/test_session.py tests/test_connection.py — 73 passed
• uv run ruff check . — passed
• production-transcript copy validation — source unchanged, 0 unsigned thinking blocks in repaired fork, all 148 signed thinking blocks retained, session IDs consistent
• full suite — 616 passed, with 2 pre-existing/environmental failures: stale Codex max-effort assertion and portal bad-host timeout

🤖 Generated with Claude Code