fix(desktop): stop resurrecting completed stream bubbles

[Dolverin]

Summary

• treat the explicit pending flag as the authority when reconciling local assistant projections
• stop a completed assistant-stream-* bubble from being re-appended after authoritative history has caught up
• add a focused regression test for the completed-stream case

Why

preserveLocalPendingTurnMessages currently considers any assistant message whose ID starts with assistant-stream- to be pending, even after terminal stream paths have explicitly set pending: false.

If such a completed local bubble has no same-ordinal assistant in the refreshed authoritative transcript, the reconciliation step appends it again. This can resurrect an already completed assistant bubble alongside the persisted response.

All live stream constructors set pending: true, while completion, interim sealing, interruption, and error paths set pending: false; the explicit state is therefore the correct authority. This is a separate reconciliation invariant from the upstream stream/final merge work in #70173.

Related: #70108

Verification

• focused regression fails on current origin/main and passes with this patch
• npm exec vitest run -- --project ui src/app/session/hooks/use-session-actions/utils.test.ts — 33 passed
• npm exec vitest run -- --project ui src/app/session/hooks/use-session-actions.test.tsx — 33 passed
• npm run typecheck — passed
• npm exec eslint -- src/app/session/hooks/use-session-actions/utils.ts src/app/session/hooks/use-session-actions/utils.test.ts — passed
• npm exec prettier -- --check src/app/session/hooks/use-session-actions/utils.ts src/app/session/hooks/use-session-actions/utils.test.ts — passed

[alt-glitch]

This was generated by AI during triage.

Related: #70173 deduplicates an interim stream bubble and its final completion; this patch separately prevents an already-completed local stream projection from being re-appended during history reconciliation.

[teknium1]

Thanks for the focused regression fix. Current main still has the reported predicate: apps/desktop/src/app/session/hooks/use-session-actions/utils.ts:403-404 classifies every assistant-stream-* row as pending even when its explicit pending state is false. Terminal stream paths explicitly settle rows with pending: false at apps/desktop/src/app/session/hooks/use-message-stream/index.ts:434, :504, and :634-645; when no same-ordinal authoritative assistant is present, the reconciliation appends that local row at utils.ts:422-437.

The proposed change makes the explicit flag authoritative and adds the missing completed-stream case. The PR is currently conflicting with main, but its two-file change is localized and should be mechanically salvageable without broad rework.

Automated hermes-sweeper review.

[OutThisLife]

Superseded by #77644, with credit — the duplicate settled bubble is real and it's fixed there.

Your diagnosis of the mechanism holds; I took a narrower fix than the predicate change. Keying isPendingAssistant on the explicit pending flag alone also discards a sibling case in the same area: a reply that finished locally before the gateway committed it, where the settled assistant-stream-* row is the only copy that exists. I verified that directly — that row survives on main today and is dropped under this patch. #77644 instead drops a settled stream row only when authoritative history already carries that exact text, so both cases hold at once.

The conflict with main is moot now; no rebase needed on your side.