fix(claude-code-agent): end the turn on the terminal ResultMessage, not stream EOF

[tmatup]

What

When the SDK stream delivers the terminal ResultMessage of a one-shot query(), communicate() now ends the turn immediately — instead of waiting for stream EOF (i.e. CLI process exit). The subprocess is then reaped with a bounded grace (10 s, so it can flush its session file for resume) followed by SIGKILL.

Why

A successful agent run could be scored 0. If the Claude CLI process lingers after emitting its result — a stray child process holding stdio, a slow shutdown flush — the stream never hits EOF, so the turn watchdog eventually hard-kills it and raises TurnTimeoutError. The task is then recorded final_status=ERROR, score=0 even though the agent finished cleanly.

Observed 3× on live eval sweeps (twice yesterday, once today, all at exactly turn_timeout+4s wall):

05:38:42  final assistant message completes; ResultMessage captured
          (subtype=success, stop_reason=end_turn)
05:47:30  watchdog: Turn timeout (1200s) fired — hard-killing subprocess (pid=77)
          → TurnTimeoutError → task scored 0

~530 s of dead waiting on a process whose result was already in hand.

How

• communicate() message loop: after state.dispatch(message), break when the terminal ResultMessage has been captured (state.sdk_result_summary set). The ResultMessage is by protocol the last message of a one-shot query — nothing follows it but process exit.
• New _reap_transport_after_result(): bounded grace (default 10 s) for the CLI to exit on its own — killing instantly could lose the session-file tail the SDK's own close() protects (see its #625 comment) — then SIGKILL. No-op in the common already-exited case. Breaking alone is not enough: async-generator finalization is GC-scheduled, and the SDK's anyio scopes swallow cooperative cancellation (same reason the watchdog exists).
• test_multiple_assistant_turns reshaped to the real one-shot protocol (single terminal ResultMessage; previously it interleaved two mid-stream ResultMessages, a shape the CLI never produces in one-shot mode).

Tests

• New: test_communicate_ends_turn_on_result_message_when_cli_lingers (the regression: stream yields result then hangs — must return a clean TurnRecord, not TurnTimeoutError), test_reap_after_result_kills_lingering_process (grace-then-kill + no-op paths).
• Full suite: 3313 passed, 10 skipped.

🤖 Generated with Claude Code

https://claude.ai/code/session_01LrwDtggu1dG9WKAsgvxfnq

[github-actions]

Claude finished @tmatup's task in 1m 22s —— View job

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• Read full context of changed files
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[tmatup]

Deployment note for the eval images: the images baked at /opt/coder_eval carry 0.7.1 (5c285d6), not current main — overlaying this branch's file into them fails at import (coder_eval.pricing exists only on newer main). The fix is cherry-picked onto 5c285d6 as branch fix/turn-end-on-result-message-071 (no PR — deployment vehicle only), which is what the flow-v2 measurement images now overlay. Both commits are content-identical to this PR.

[tmatup]

Second commit (0fbed2c): the break exposed a pre-existing misclassification — fixed at its root.

First live run with the turn-end fix truncated every turn that spawned a sub-agent: ~20 s in, zero authored output, empty sandbox. Cause: _is_sdk_result_message duck-types the result as session_id + usage — and the sub-agent lifecycle message TaskProgressMessage carries both. The misread pre-existed (silently corrupting session-id advance and token backfill whenever a sub-agent ran); ending the turn on the "result" merely made it fatal.

The classifier now matches isinstance(message, ResultMessage) positively and rejects the entire SystemMessage family (all task-lifecycle messages subclass it); the duck-typed fallback survives only for non-SDK test mocks. New regression test drives a real TaskProgressMessage through communicate() mid-stream and asserts the turn ends on the true terminal result with the transcript intact. Suite: 3314 passed.

Backport branch fix/turn-end-on-result-message-071 updated with the same commit (050e4ef).