fix: persist rotated compression transcripts

[rayjun]

What does this PR do?

Fixes a rotated-compression persistence gap introduced by the intrinsic _db_persisted marker. When compression rotates into a child session, protected head/tail messages are shallow-copied into the compressed transcript. If those source dictionaries were already persisted in the parent session, the copied _db_persisted marker makes the child-session flush skip them, so the rotated transcript can lose live context.

This strips persistence-only markers from messages copied into a newly compressed transcript, while leaving in-place compaction semantics unchanged.

Related Issue

Fixes #57491

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 🔒 Security fix
• ✅ Tests (adding or improving test coverage)
• ♻️ Refactor (no behavior change)
• 🎯 New skill (bundled or hub)

Changes Made

• agent/context_compressor.py
  • Add a compression-copy helper that removes session-store persistence markers from copied transcript messages.
  • Use the helper when copying protected head and tail messages into a rotated compressed transcript.
• tests/run_agent/test_compression_persistence.py
  • Add a regression test covering already-persisted parent messages copied into a rotated child transcript.
  • Verify the compressed child transcript is flushable and includes the summary row.

How to Test

1. Run python -m pytest tests/run_agent/test_compression_persistence.py tests/agent/test_codex_app_server_persist.py -q
2. Run python -m pytest tests/agent/test_context_compressor.py tests/agent/test_context_compressor_session_end_clears_state.py tests/agent/test_context_compressor_temporal_anchoring.py tests/agent/test_context_compressor_summary_continuity.py tests/agent/test_context_compressor_cross_session_guard.py tests/run_agent/test_compression_persistence.py -q
3. Confirm rotated compression copies no longer carry _db_persisted into the child session and the child session receives the compressed transcript rows.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits (fix(scope):, feat(scope):, etc.)
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature (no unrelated commits)
• I've run pytest tests/ -q and all tests pass
• I've added tests for my changes (required for bug fixes, strongly encouraged for features)
• I've tested on my platform: Ubuntu 24.04

Documentation & Housekeeping

• I've updated relevant documentation (README, docs/, docstrings) — or N/A
• I've updated cli-config.yaml.example if I added/changed config keys — or N/A
• I've updated CONTRIBUTING.md or AGENTS.md if I changed architecture or workflows — or N/A
• I've considered cross-platform impact (Windows, macOS) per the compatibility guide — or N/A
• I've updated tool descriptions/schemas if I changed tool behavior — or N/A

For New Skills

N/A

Screenshots / Logs

$ python -m pytest tests/run_agent/test_compression_persistence.py tests/agent/test_codex_app_server_persist.py -q
.............                                                            [100%]
13 passed in 4.18s

$ python -m pytest tests/agent/test_context_compressor.py tests/agent/test_context_compressor_session_end_clears_state.py tests/agent/test_context_compressor_temporal_anchoring.py tests/agent/test_context_compressor_summary_continuity.py tests/agent/test_context_compressor_cross_session_guard.py tests/run_agent/test_compression_persistence.py -q
........................................................................ [ 43%]
........................................................................ [ 86%]
.......................                                                  [100%]
167 passed in 7.40s

[kshitijk4poor]

Fixed on main via #57574 (commits 3e204bd, e1a1dac).

Your PR and #57531 were independent fixes for the same root cause (shallow .copy() propagating _db_persisted into the rotated child transcript). #57574 landed the fix with a structural terminal-sweep guard on top. Credit to you and @nankingjing for the parallel diagnosis.

Closing as superseded.