Stop completed turns from appearing stuck (#2484)

* fix(app): stop completed turns from appearing stuck

Turn activity was inferred from a user-message row flag, so a stale duplicate row could keep the working footer active after the turn ended. Track submission lifecycle separately and route every send path through the shared submission flow.

* fix(app): guard pending message identity

* test(app): measure submission layout independent of scroll

* fix(app): keep submitted messages consistent through reconnects

Track each in-flight send until its own RPC establishes acceptance, and keep canonical timeline placement authoritative. Restore legacy cached rewind IDs during cache deserialization.

* fix(app): close canonical submission races

* test(app): cover canonical submission races in browser

* fix(app): keep replacement submissions authoritative

Keep current pending rows out of legacy cache migration and leave ambiguous terminal lifecycle events to the daemon snapshot. This prevents fabricated rewind identities and stale completion events from marking replacement turns idle.

* fix(app): keep submitted messages stable across sync

Give submission transport and canonical timeline ingestion separate authority. Preserve every unresolved local send across replacement, reconcile provider identity once, and bridge RPC acceptance to authoritative running state without deriving lifecycle from timeline rows.

* fix(app): settle submissions in either acknowledgement order

Complete submission transactions when RPC and provider acknowledgement arrive in either order. Cache only transaction-owned local rows as transient data, preserve canonical ID-less prompts, and invalidate ambiguous legacy display caches instead of inventing provider identity.

* fix(app): keep agent visible during history handoff

Running and terminal updates could clear create continuity before the initial authoritative timeline arrived, leaving a streaming agent behind the loading screen. End the handoff only when authoritative history is applied.

* fix(app): settle attachment-only submissions

Canonical providers can acknowledge image-only prompts with empty text. Reconcile those events by client identity without rendering a blank canonical row.

* fix(agent): settle out-of-band message submissions

Accepted commands that do not allocate a foreground turn previously had no canonical user acknowledgement. Record the command before its handler runs so submission state and reconnect history converge through the normal timeline producer.

* fix(app): settle out-of-band submissions compatibly

* fix(app): preserve canonical prompt order

* test(app): keep workspace status check timing-independent

The workspace-status scenario asserted footer settlement before initial agent creation had necessarily completed. The dedicated draft-handoff coverage owns that lifecycle contract.

docs/timeline-sync.md

@@ -87,14 +87,42 @@ its completion advances `seqEnd`, followed by a merged assistant message. The ap
 remaining page through the existing stream reducer. It must not append full projected text to a
 live prefix.
 
-Optimistic user prompts occupy stable timeline slots. Catch-up never extracts, delays, or reinserts
-them. A canonical user row replaces its matching slot in place; an unmatched prompt stays exactly
-where the user submitted it. Other canonical rows are applied after the already-present timeline
-instead of relocating visible user messages around newly fetched history.
+Every path that sends a message to an agent — composer send, dictation accept-and-send, queued
+send-now, and the automatic queue drain in `HostRuntime` — goes through
+`dispatchComposerAgentMessage` with a submission writer. There is no second transport for the same
+product action: calling `client.sendAgentMessage` directly skips the submitted row and the pending
+footer, and permanently drops attachments because the daemon does not echo them back.
+
+A submitted prompt is one `UserMessageItem` row. That row is the authoritative local presentation:
+its stable identity, text, timestamp, images, and attachments do not change when the provider
+acknowledges it. Submission lifecycle is a separate record keyed by agent, not another row shape or
+a property inferred from message identity. The transaction registry holds every unresolved send and
+records RPC acceptance and provider acknowledgement independently. Provider acknowledgement exists
+solely so a later transport error cannot roll back a prompt already observed canonically.
+
+The daemon's accepted response already waits for the correlated run start, but its response and the
+directory update reach client state separately. An accepted transaction remains active until the
+directory observes that run or canonical ingestion acknowledges the prompt, bridging those ordered
+authorities without inspecting timeline snapshots. Either signal clears only an RPC-accepted
+transaction, regardless of which arrived first; it cannot settle a fresh send.
+Overlapping sends settle independently rather than collapsing to one newest pending message.
 
 Canonical submitted user rows carry the provider's `messageId` and Paseo's optional
-`clientMessageId`. Clients reconcile optimistic prompts by `clientMessageId`. Content matching is
-limited to the dated compatibility path for daemon timelines created before that field existed.
+`clientMessageId`. The user-message producer reconciles them by `clientMessageId`, adds provider
+identity to the existing row, and keeps the local presentation in its original timeline slot.
+Content matching is limited to the dated compatibility path for daemon timelines created before
+that field existed. Canonical ingestion may match only an explicit unreconciled local candidate;
+the draft-create handoff is the one boundary that also permits the legacy canonical twin to have
+arrived first. Generic reducers and consumers do not reimplement message identity matching.
+
+Ordinary bootstrap, same-epoch reset, and catch-up replacement preserve unmatched locally submitted
+rows because a provider may never echo them. A known epoch change or rewind replaces history and
+drops acknowledged local rows omitted by the new canonical epoch; every transaction not yet
+acknowledged by the provider, and no other local row, crosses that destructive boundary.
+
+Canonical replacement owns both timeline lanes. A matching local row keeps its presentation ID and
+payload while taking the canonical row's ordered position. If a live assistant head is the
+canonical assistant prefix, it stays in the head lane. No row may be returned in both lanes.
 
 ## Relevant code