Refresh persisted chat history once after an idle reattachment

[Maya-Kid]

Post-merge synchronization (2026-09-22)

Rebased onto dev@7cfeedfeb11c3a1c42d5091c5941a51afaaeb161 after #848, #851, #849, #850 and #852 merged. Current head: ba964f3aaa94ae514f9e585c04329f642708299d.

The UI dependency order remains #854 → #856 → #855. Retained upstream stream-interruption strings alongside the history/pagination keys when resolving i18n conflicts. The complete UI tree is byte-for-byte identical to the previous validated integration tree. Maintainer visual review remains outstanding.

Validation on combined tree d06f4ad0199a382635a6bbf94210b9421cbeba66 (675 tracked Linux inputs hash-matched):

• Rust fmt, strict workspace/all-target Clippy and workspace build passed. Workspace tests: 1018 passed, 0 failed, 5 ignored. The two delivery/process-kill parent tests and busy-deferral test additionally passed on their own exclusive database; crash_child is invoked by its parent. The existing public-network RSS test remains ignored.
• The exact unified Chat CI command listed and executed 47 passing tests, including all 37 introduced tests from Hand off exhausted tool runs to an evidence-only final answer #845/Keep older chat handles from unregistering newer generations #848/Publish citation sources added by document reads #849/Keep fallback retrieval failures distinct from empty results #850/Preserve exact chat outcomes across stream closure and reattachment #851/Do not report fallback chat completion when saving fails #852/Assert a chat turn ends in exactly one earned terminal #858. All four terminal-table rows ran. Seven deliberately omitted groups each produced a green Cargo result but were rejected by the independent executed-test checker (exit 1); the complete run passed (exit 0).
• Frontend: 129 module tests, 27 browser subtests (29 including parent tests) and build/typecheck/guard passed.
• The five actual-backend browser scenarios from the previous validation were not repeated this time: the complete frontend and frozen finalization/LLM implementation are unchanged. This pass reruns the deterministic browser and real-PostgreSQL Rust regressions. No new paid-model accuracy claim is made.

Earlier evidence below refers to its stated historical heads.

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Depends on #854 (view-request ownership). This branch includes that prerequisite so stale refreshes cannot overwrite a later navigation or send. The additional commits for this behavior are cb82751 and 9afbe39; after #854 merges, GitHub's diff will reduce to those changes.

An answer can commit after the browser reads a user-only history but before it reattaches to the live producer. The server then correctly returns idle, while the page remains stuck with the unanswered question. On that initial idle handoff, read the persisted history once and apply it only while the initiating view request still owns the page. If it is still unanswered, display a bounded idle status; a failed read offers an explicit retry. This never re-POSTs the question or recursively reattaches.

Validation, based on dev@ea0557b plus #854, final head 9afbe39:

• Four new history-handoff browser regressions fail before this change while the 11 prerequisite cases pass.
• All 16 browser subtests pass after the fix: the 11 prerequisite cases plus completed-between-reads, bounded user-only history, late refresh after navigation, retry after refresh failure, and a new send taking ownership before the old refresh arrives. The tests render the real Chat/router/query/live-answer implementation with controlled HTTP responses.
• Frontend 116 module tests and build/typecheck/guard pass; the final additional send-race case and typecheck pass as well.
• Chrome with the actual Linux backend and PostgreSQL held reattachment until a locally scripted model's answer had committed and the producer had unregistered. The real idle response caused exactly one extra detail GET, rendered the saved answer, and caused zero chat POSTs.
• Integration tree f7bcd0878bf490d6efb122b71d6f13d379df4709, including Hand off exhausted tool runs to an evidence-only final answer #845 and Preserve exact chat outcomes across stream closure and reattachment #851's strict stream terminal handling, passes Rust fmt, strict workspace Clippy, 1,013 tests (one pre-existing external-HTTPS RSS test ignored), workspace build, 129 frontend module tests, 27 browser subtests and frontend build.

Run node --test tests/chat-view.test.mjs from web, with optional CHAT_PLAYWRIGHT_PATH and CHAT_CHROMIUM_PATH. No new dependency, polling loop, model retry, or server generation policy is introduced. All model integration evidence uses a local scripted endpoint, not a paid model.