perf(client): keep latestTurn and checkpoint refs stable while streaming

[leoisadev1]

Problem

Every assistant streaming delta rebuilt latestTurn as a new object even when nothing in it changed. Selectors and memos keyed on that record reran for no reason during a reply.

Adaptation

reuseLatestTurn returns the previous object when turn identity, state, timestamps, assistant message id, request/responding-bot ids, and proposed-plan ids all match. thread.message-sent and thread.session-set go through that helper. Checkpoints already kept the input array when no rebind was needed. Same-turn recomputes also keep an existing sourceProposedPlan so Akeru plan links are not dropped.

Messages still get a new array on each delta, as they must.

Upstream credits

Reviewed adaptation of T3 Code #9145.

Scope

Client reducer reference stability only. Server replay, subscription lifetime, config bootstrap, and static caching are separate PRs.

Verification

Head e3f241faad09c6547413bcc1322cf822335ed559 on leoisadev1/t3-port-thread-ref-stability. Isolated home /tmp/akeru-227-verify.QyRxU8 (populated fixture plus a second bot, Crew group, bound checkpoints, and later live Mastra turns). Web on this branch only. #216 stills were not reused.

• vp test run packages/client-runtime/src/state/threadReducer.test.ts: 36 passed, including streaming-reference and first-bind cases
• vp run --filter @t3tools/client-runtime typecheck passed
• Targeted lint on the two changed files passed

Integrated web pass on BotThreadLanding and GroupThreadLanding:

• First bind after pairing loaded Scout, Ranger, and Crew. Scout's latest chat was the streaming fixture thread.
• Sending "Ping the reconnect path." started a live Mastra turn. The roster showed a working dot and the chat showed "Scout is working", then settled to the fallback "I could not complete that request."
• Reload of /bots/ui-scout kept both user lines and the fallback reply. No re-pair.
• Crew accepted "Crew ping for reconnect." Scout answered with the same fallback. Retry after a group reload restored that transcript.

What this did not prove

• Provider streaming of a real assistant delta. The isolated home has no provider credentials. Both live turns are mastra-turn-* in error with no new checkpoint_ref.
• Checkpoint UI. Snapshots for ui-thread-0 and ui-group-thread-0 return bound checkpointRef + README.md files, and the live threads still carry the seeded checkpoint row. Bot/group landing does not mount DiffPanel. Ctrl+D did nothing there.
• Command palette conversation search. "Make remote coding" returned no matches. Projection fixture chats are not in that index.

Group reload crash (not this diff)

A full reload of /groups/ui-crew hit "This view failed to load": Rendered more hooks than during the previous render from useReplyPlaybackThread in GroupThreadLanding. Retry restored the chat. useReplyPlaybackThread runs after if (!group) return null, so the first paint with a missing group uses fewer hooks than the next one. This PR only changes threadReducer.ts. Scout reload did not hit it.

vp run dev --share failed with tailscale serve permission denied, so there is no tailnet pairing URL from this run.

Grok 4.6 High in Grok Build via Orca.

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1 Skipped Deployment

Project	Deployment	Actions	Updated
akeru-bot-landing	Skipped		Sep 10, 2026 6:00pm UTC

[greptile-apps]

Greptile Summary

This update keeps latest-turn state stable during assistant streaming while preserving request-message, responding-bot, and proposed-plan metadata. The reducer now reuses the prior object only when all relevant turn fields match.

Confidence Score: 5/5

Safe to merge.

No outstanding findings remain. The previously reported stale turn-identity behavior is fully fixed: same-turn recomputation preserves request-message, responding-bot, and proposed-plan identities, and latest-turn reuse compares those fields.

_{Reviews (3): Last reviewed commit: "Merge branch 'main' into leoisadev1/t3-p..." | Re-trigger Greptile}