[prellr]

Problem

Posting a reply in an annotation thread made the message vanish on Send, then reappear — a flicker, not a data loss.

Root cause

useAddDraftAnnotationMessage optimistically appends a message with a temp id (temp-message-…), then onSettled invalidates the list. But when the reply @-mentions Aye it triggers a turn, so a concurrent draft_annotation:updated WS event arrives mid-flight. onDraftAnnotationUpdated replaced the whole annotation with the WS payload (whose messages are the server's, without the in-flight optimistic reply) → the optimistic message was dropped. The later refetch/echo brought the committed copy back, producing the flicker.

A latent second bug: onDraftAnnotationMessageCreated deduped only by id, but the optimistic temp id ≠ the server id, so the user's own message-created echo would have appended a duplicate.

Fix (frontend-only, packages/core/drafts/)

1. Swap optimistic temp → real on success (useAddDraftAnnotationMessage): new onSuccess replaces the optimistic temp message (matched by the temp id carried in the onMutate context) with the real api.addDraftAnnotationMessage response, so the real id is in the cache promptly. onError rollback unchanged; onSettled invalidate kept as a now-non-flickering safety net.
2. Preserve in-flight optimistic messages across WS annotation rewrites (annotation-ws-updaters.ts): a shared withPreservedTempMessages helper keeps any temp-id messages the incoming WS payload omits, applied in onDraftAnnotationUpdated and the re-match branch of onDraftAnnotationCreated. Adds/exports isTempMessageId (mirrors isTempAnnotationId).
3. Robust message dedupe (onDraftAnnotationMessageCreated): keeps the id dedupe and, for the window before the temp→real swap, replaces an un-swapped temp message with the same author_user_id+body instead of appending a duplicate.

Tests

packages/core/drafts/annotation-ws-updaters.test.ts and annotation-mutations.test.tsx:

• Reproduces the original flicker: post a reply (optimistic temp message in cache) → fire onDraftAnnotationUpdated with a payload that lacks it → assert the optimistic reply survives (this is where it used to disappear).
• Proves no duplicate: then fire onDraftAnnotationMessageCreated with the real row → assert exactly one copy.
• onSuccess swaps temp→real (real id lands in cache); onError rolls back.

Verification

• pnpm --filter @multica/core typecheck ✓ · pnpm --filter @multica/views typecheck ✓ · full pnpm typecheck ✓ (6/6)
• pnpm --filter @multica/core exec vitest run ✓ (42 files, 378 tests) · full pnpm test ✓ (857 views tests, all packages)
• pnpm --filter @multica/core lint ✓ (no new findings)

No backend/schema/daemon change.

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