fix(tracing): keep initiating /goal objective as turn input when user messages arrive mid-turn

[deepanshupal]

Fixes #110.

Root cause

A turn started by /goal receives its objective as a response_item user message wrapping <codex_internal_context source="goal">, which becomes userInputFallback. A user message sent while that turn is still running arrives as item_completed / UserMessage and sets userInput, and finishTurn() prefers userInput over the fallback - so the later in-flight message replaced the initiating goal as the root input.

Behavior change (both sides)

• Fixed: the initiating input now wins for the whole turn. A user message that arrives mid-turn (via user_message or item_completed/UserMessage) no longer displaces an input already captured from either channel, so a goal-started turn keeps its goal as the root input and later messages stay distinguishable instead of replacing it.
• Changed presentation: for a goal-started turn, the root input is now the <objective> text extracted from the <codex_internal_context source="goal"> wrapper, rather than the raw internal wrapper.

The deliberate "structured UserMessage rescues the prompt from an AGENTS.md-wrapped fallback" behavior is unchanged: in those cases the fallback is rejected (unset), so the gate does not engage, and that existing test suite passes unmodified.

Testing

New parse-goal-attribution.test.ts with the issue's synthetic fixture, covering a goal-started turn with and without a subsequent progress message, plus a guard that the raw wrapper is never exposed as input. On pristine main the first two tests fail (input = "What is the progress?", and the raw wrapper respectively); with the fix all three pass.

Full suite: 124/124 pass (pnpm run build && vitest run; the 3 hook-command tests fail without a prior build on a fresh checkout, on pristine main too - they execute the bundled hook). tsc --noEmit clean, prettier --check clean.

[claude]

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