Refresh Cloud transcript bindings when chat reconnects

[azooz2003-bit]

When a Cloud Agent Chat page reconnects, the server previously reused its cached transcript session without consulting the current terminal hook record. If the agent resumed in another pane or its transcript path moved, Focus Terminal targeted the old pane and the page could keep tailing the old file.

Subscriptions now re-resolve terminal sessions first, refresh changed terminal bindings, reattach changed transcript paths, and fall back to cached history when the hook store is temporarily unavailable.

Depends on #16069 and targets fix/cloud-transcript-terminal-rebind.

Validation

• Regression commit: 485660de8d3de3a416cf35a3afeba4c9f8f8c03c.
• Fix head: 7285635d7dbc0426b602f743d1225a3138a37e63.
• From agent-chat, bun test/transcript-reconnect.test.ts: red before the fix because reconnect Focus Terminal used OLD-SURFACE; green after the fix. Covers Claude and Codex, same-path binding refresh, changed transcript paths, new event delivery, and cached-history fallback during hook-store misses.
• bun run check: passed (typecheck, 28 scripts, 44 tests across 13 bun:test files).
• Production browser bundles for src/main.tsx and src/gallery-main.tsx: passed.
• git diff --check 25677e569383a99a9fd3a898328b19b85b069797..HEAD: passed.

No live Cloud instance or browser validation.

Changelog

Fixed: Cloud Agent Chat reconnects now follow the agent's current terminal and transcript.

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Summary by cubic

Fixes Cloud Agent Chat reconnects so Focus Terminal and transcripts follow the agent's current terminal instead of a stale cached session. Previously the server reused its cached transcript session without consulting the terminal hook record; if the agent resumed in another pane or its transcript path moved, the page kept tailing the old file.

Subscriptions now re-resolve terminal sessions first, refresh changed terminal bindings, reattach changed transcript paths, and fall back to cached history only when the hook store is temporarily unavailable.

• Swaps the session lookup order in the subscribe handler so the current hook record wins over the session cache.
• Adds a regression test covering Claude and Codex, same-path rebinds, transcript path changes, new event delivery, and cached-history fallback.

Depends on #16069.

^{Written for commit 7285635. Summary will update on new commits.}

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Migrated from #16070 after correcting the PR author identity. The original head commit 7285635 is preserved.

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