fix: stop codex app-server transcript re-printing streamed reasoning/messages on idle

[dimavedenyapin]

Problem

Codex is still re-printing previous messages after the last message in the agent transcript, even after PR #419.

Root cause (incomplete fix, not a regression)

PR #419 made reconcileCompletedTurn() idempotent for the reconcile-vs-reconcile path (bufferedThreadItemIds + computeThreadItemKey) — it stops the same item being re-buffered across idles. But it never covered the live-stream-vs-reconcile path: on every turn/completed the adapter re-lists the whole thread and re-emits items that were already delivered live during the turn. When the reconcile emission lands under a different part id/type than the live emission, the renderer cannot collapse the two and appends a duplicate below the final message.

The only commit touching this file since #419 is #423 (git metadata roots), which is unrelated to reconcile/buffering — so this is an incomplete fix, not a regression. #419's logic and its regression test still pass.

Two concrete, reproduced paths (investigation subtask confirmed both):

1. Reasoning items — streamed live via item/reasoning/textDelta as part id reasoning-<id> (REASONING). convertThreadItem() had no reasoning branch, so on reconcile the same item routed into the tool branch and was emitted as tool-<id> (TOOL, name reasoning). Different part id and type → the renderer appends a duplicate.
2. Assistant final message when the persisted thread-item id differs from the streaming itemId — live delta emits agent-<streamId>, reconcile emits agent-<persistedId>, both update:false → appended twice. The hasSeenAssistantTextForTurn guard missed it because streaming deltas never call markAssistantTextForTurn() (only convertThreadItem's item/completed branch did), so the text wasn't registered for the turn when reconcile ran.

Fix

Make the reconcile emission reuse the same part identity as the live path:

1. Add a reasoning branch to convertThreadItem() that emits reasoning-<itemId> (REASONING, role: assistant), updating in place when the part was already streamed — so it collapses against the live reasoning part instead of appearing as a separate tool call.
2. Register streamed assistant text for the turn via markAssistantTextForTurn() inside the item/agentMessage/delta handler, so a later reconcile item/completed for the same message (under a different persisted id) is recognized as already-shown and dropped.

Both changes are additive and scoped to the transcript emission path.

Tests

• Added reconciles a reasoning item as a REASONING part, not a duplicate tool part
• Added does not re-print a streamed assistant message when reconcile re-lists it under a different item id

Both new tests fail on main (reproduce the bug) and pass with the fix.

• ✅ pnpm typecheck
• ✅ eslint on changed files
• ✅ Full main project suite: 918 tests passed (24 in the codex adapter, incl. the 2 new)

🤖 Generated with Claude Code

[dimavedenyapin]

Closing as superseded by #427. #427 contains this live-stream-vs-reconcile app-server fix plus the additional AP-task evidence fix for Codex turn_id/thread-level assistant text dedupe.