#168 activity_writer: tolerate Codex notify's appended arg (parse_known_args)

[AlvinShenSSW]

Closes #168.

Bug

The documented Codex integration wires notify to activity_writer.py --tool codex --path ... --state idle. Codex invokes its notify program with its event JSON appended as a trailing argv, which main()'s strict argparse.parse_args rejected (error: unrecognized arguments: {...} → exit 2, nothing written). So following the guide, Codex activity was never recorded — dev_activity saw Codex via process-presence only.

Fix

main() now uses parse_known_args — a fire-and-forget hook/notify shim must tolerate extra args and never break the host's chain. Trade-off (a mistyped flag is silently ignored) is acceptable and documented in a comment.

Changes

• activity_writer.py: parse_args → parse_known_args (+ rationale comment).
• tests/test_activity.py: regression test — main([... , '{"type":"agent-turn-complete"}']) returns 0 and writes the file.
• docs/guides/dev-agent-activity.md: note that the writer ignores Codex's appended payload.

Tests

uv run --locked pytest green; uv lock --check, ruff, ruff format --check, mypy all clean.

Review trail (/afk)

Claude implement + TDD. External gates run automatically: Codex 外门 then Kimi 终审. Leave-open (owner merges).

[AlvinShenSSW]

Review trail (/afk — Claude-driven)

• Codex 外门: CLEAN — "correctly tolerates Codex notify's trailing event argument while preserving existing behavior; test covers the intended scenario; no introduced correctness issues."
• Kimi 终审: VERDICT: PASS. No blocking/major. parse_known_args is the right API; the trade-off (a mistyped optional flag is silently ignored) is proportionate for a fire-and-forget shim whose contract is "never disrupt the host hook/notify chain." One optional informational nit (a test for an unknown flag) — not required; the core regression (trailing JSON argv) is covered.

CI green. Leave-open (owner merges).