fix(memory): skip usage for empty sessions

[Hughhhhcoder]

Fixes #4821

Bug

AdvancedSQLiteSession.store_run_usage() could insert a turn_usage row for user turn 0 when the current branch had no conversation turn. This made an empty session report usage and total_turns: 1 even though it contained no items. The same could happen after all turns on a branch were popped.

Root cause

_capture_current_turn() correctly returned turn_anchor=None when no message_structure row existed, but store_run_usage() still passed current_turn=0 to the write path. The write path only guarded anchored stale writes, so it inserted the phantom row.

Fix

Return without writing when the captured turn has no anchor. This preserves the existing stale-write protection and prevents usage from being attributed to a nonexistent turn.

Validation

• PYTHONPATH=src .../python -m pytest -q tests/extensions/memory/test_advanced_sqlite_session.py (130 passed)
• ruff check src/agents/extensions/memory/advanced_sqlite_session.py tests/extensions/memory/test_advanced_sqlite_session.py
• ruff format --check src/agents/extensions/memory/advanced_sqlite_session.py tests/extensions/memory/test_advanced_sqlite_session.py
• PYTHONPATH=src .../python -m mypy src/agents/extensions/memory/advanced_sqlite_session.py

The regression tests cover both an initially empty session and a branch whose only turn has been popped.

[Hughhhhcoder]

@codex review

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-03T10:45:11.739502Z	a1baa2a	Manual request
🔒 Security Review	✅ Completed 2026-09-03T10:45:36.513287Z	a1baa2a	Manual request

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[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. More of your lovely PRs please.

Reviewed commit: a1baa2aa97

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[chatgpt-codex-connector]

Security review completed. No security issues were found in this pull request.

Reviewed commit: a1baa2aa97

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