Addresses the 2nd PR #138 review (test debt + the Variant-B architecture ask).
The new→persisted chat id lifecycle (mount key, both adoption paths, the
history-load latch, the render-phase reconciler, onTurnFinished) is moved out of
the 768-line window into a new useChatSession hook driven by a pure
threadSessionReducer (reconcile/adopt), so adopt-vs-switch is one explicit
dispatch point and the scattering the review flagged is gone (window: 768→~620).
Tests (the blockers):
- use-chat-session.test.tsx — hook-level locks incl. the #137 regression
(adopts the authoritative streamed id 'A', NOT chats.items[0]='B' — fails on
the old heuristic), the error-path fallback (arm/adopt/ambiguous/add+delete),
the disarm-on-reconcile lock (a fallback armed then switched away must not be
adopted by a late refetch), in-place-adopt-keeps-key vs external-switch-remount,
and the waitingForHistory latch.
- extractServerChatId (reading message.metadata.chatId) and newlyAddedChatIds
extracted as pure helpers with unit tests; threadSessionReducer tested.
Cleanups: single canonical #137 explanation in adopt-chat-id.ts (other sites
reference it); fallback effect computes the set diff once; invalidate callbacks
memoized; redundant invariant tests folded.
Behavior preserved — re-verified live (z.ai glm-5.2): new-chat adopt + 2nd turn
in the same row, no mid-conversation remount, two-tab race leak-free, switch to
an existing chat reseeds full history, reload restores history.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Addresses the PR #138 review's architecture note (the deferred 'non-blocking'
item). The brand-new -> persisted chat identity was spread across two separate
useState slots (threadKey + liveThreadChatId) plus a render-phase guard, so the
mount key and the live thread's chat id could in principle diverge.
Consolidate them into ONE atomic state object { key, chatId } with pure,
unit-tested transitions in thread-identity.ts:
- newThread(newKey) — a brand-new id-less chat (fresh session key);
- switchThread(chatId) — switch to an existing chat (key := chat id) -> remount;
- adoptThread(prev, id) — a new chat learns its real id IN PLACE (key unchanged
-> no remount, live useChat store preserved).
The 'key vs chatId diverged' state is now unrepresentable. The render-phase
reconciliation stays (the atom is also set externally, e.g. page-history's
history-item opening a referenced chat), but adoption vs switch is now explicit.
Behavior is unchanged; verified live: new-chat adopt + 2nd turn in the same row,
no mid-conversation remount, the two-tab race stays leak-free, switch-to-existing
remounts + reseeds, and reload restores full history. Adds thread-identity.test.ts.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
