Keep stale chat navigation callbacks out of the current view

[Maya-Kid]

Post-merge synchronization (2026-09-22)

Rebased onto dev@7cfeedfeb11c3a1c42d5091c5941a51afaaeb161 after #848, #851, #849, #850 and #852 merged. Current head: bd11c1d9ea61f5015d55ed8bc0f656c1bb2e2717.

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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When conversation A loads slowly and the user selects B, A's late success or failure can replace B's transcript or navigate away. A late identity response from a new chat can likewise pull the user back after they leave.

This gives each view request an identity, including separate visits in A → B → A. History, navigation and initial reattachment callbacks must still own that view before changing it. Existing generation handles continue in the background. Temporary history failures keep the selected URL and offer a retry; missing/inaccessible conversations retain their existing redirect behavior. Route changes also hide the previous transcript before paint.

Validation on dev@ea0557b, fix 0df6d2a:

• The first four browser regressions fail on the original production component, then pass with the fix. All 11 component/browser cases pass: late success/error, repeated visits, late identity, new chat, cross-KB navigation, retry, missing history, StrictMode, late snapshots, and selecting an already-loading conversation. Tests import the real Chat, router, query client and live-answer store; HTTP responses are controlled.
• Frontend 116 module tests and the production build/typecheck/guard pass.
• A separate Chrome run against the actual Linux server and PostgreSQL delayed a real history response while selecting another conversation; the current URL and transcript stayed correct. No history payloads were fabricated in that run.
• Integration tree f7bcd0878bf490d6efb122b71d6f13d379df4709 combines this with Hand off exhausted tool runs to an evidence-only final answer #845 and the other scoped Chat fixes: 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 pass. This integration result is distinct from the standalone branch checks.

The browser harness uses optional Playwright/Chromium, following the repository's existing browser-test pattern; it adds no package dependency. Run node --test tests/chat-view.test.mjs from web, with CHAT_PLAYWRIGHT_PATH and CHAT_CHROMIUM_PATH if needed. This does not introduce server-side cancellation, retries of a generation, or changes to #845's model policy.