finding(app-shell): toUIMessages' tool-result merge rewrites state to output-available, so a rehydrated approval-requested never reaches the chat from the ModelMessage path

[os-tesla]

Found while implementing objectui#8442 (PR #9229), as the end-to-end reading that card explicitly asked the next taker to verify rather than inherit. ⛔ Not claimed.

What

packages/app-shell/src/hooks/useChatConversation.ts, mergeToolResultsInto (called from toUIMessages), measured on origin/main @ b775500af.

The server persists conversations in ModelMessage format: a tool CALL lives on the assistant row, its RESULT on a separate tool row. mergeToolResultsInto merges the result back onto the call part — and, whenever it merges anything, it also overwrites the part's state:

target.state = isError ? 'output-error' : 'output-available';

unconditionally, for every merged result. There is no arm for the approval states.

⇒ On this sub-path a pending approval can never reach hydratedMessagesToChatMessages as approval-requested. The state is rewritten before the mapper ever sees the part, so the mapper's own pass-through of that state — pinned, and deliberately kept — is unreachable from here.

Why it matters, stated at the confidence it was measured at

This is the second half of objectui#8442's consequence 2, which that card reported at reading confidence and flagged as not verified end to end. Now read at the source, on both sides:

• useHitlInChat keys its index purely on pendingActionId, so after PR feat(types,app-shell): carry the tool approval envelope through hydration #9229 the invocation is indexed on this sub-path and decide() has a real id to POST. That half works.
• The awaiting-approval affordance in ChatbotEnhanced is gated on state === 'approval-requested' (isAwaitingApproval, and hidePendingPayload beside it). With the state rewritten to output-available, the card does not render, so there is no button to press even though the wiring behind it is now live.

So the honest answer to objectui#8442's open question is: the operator gets neither a working nor a dead Approve/Reject on this sub-path — they get no approval card at all. The AI-SDK-shaped sub-path (persisted UIMessage parts, no separate tool row to merge) is unaffected and does render.

PR #9229 pins today's reading as a reading, in AiChatPage.hydration.test.ts, so whoever changes this turns that line red instead of finding a stale sentence.

What a fix has to be careful about

⛔ Not "stop rewriting the state". The rewrite is load-bearing: it is how a dangling input-streaming / input-available becomes Completed instead of spinning forever, which is the incident the promotion logic in partToolState and in the live mapper both exist for. The narrow statement is that a merged result must not rewrite an approval state — the live mapper already models this correctly, promoting to approval-requested when it detects the pending envelope, and this merge step is the one place that has no such arm.

⚠️ Sequencing: objectui#8426 owns the authoring state union narrowing under the same ruling. This card is NOT blocked by it — the two touch different files and neither needs the other — but a seat taking both should read them together.

Confidence

Read from the source, not exercised in a browser. Measured: the unconditional assignment; the two gate expressions in ChatbotEnhanced; the useHitlInChat index predicate. NOT measured: the live /conversations endpoint's actual persistence shape, i.e. how much real traffic takes the ModelMessage sub-path versus the UIMessage-parts one. That ratio decides this card's priority and someone with a running backend should read it before costing a fix.

Dedup

REST /search/* is refused for this session by the egress proxy; one targeted search_issues call was used instead and is declared here. 6 hits, all read — objectui#8442 (the control, and the card this splits off from), objectui#5553, objectui#2829, objectui#2762, objectui#2698, objectui#4437. None names this merge step or the state rewrite.

Related

objectui#8442 · objectui#8426 · PR #9229

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