[BingCHuanJ]

Summary

Fixes mobile web session model selection so switching sessions restores the model and reasoning settings saved by the selected host session instead of reusing a browser-wide preference.

• Keep model and reasoning settings scoped to the selected session.
• Prevent delayed, timed-out, or cancelled remote writes from overwriting another session.
• Preserve compatibility with legacy hosts.
• Add browser and Rust regression coverage.

Type and Areas

Type: bug fix

Areas: mobile web, remote connect, Rust core, desktop/CLI adapters, CI

Motivation / Impact

When a user changed the model in one remote session and then switched to another session in mobile web, the selected model could remain from the previous session instead of following the target session's saved configuration.

This change makes mobile web follow the same per-session behavior as the main application.

Verification

• pnpm --dir src/mobile-web run test:session-model-browser — 56/56 passed
• Remote model fence tests — 5/5 passed
• Remote Connect contract tests — 75/75 passed
• cargo check --offline --locked -p openbitfun-cli --bin openbitfun — passed
• pnpm --dir src/mobile-web exec vite build — passed
• pnpm run i18n:audit — passed
• pnpm run check:core-boundaries — passed
• pnpm run check:repo-hygiene — passed

Reviewer Notes

Browser coverage uses an isolated Chromium profile and covers modern and legacy hosts, session switching, stale responses, timed-out writes, cancellation, device changes, account isolation, and narrow layouts.

The local full Desktop check was blocked before Rust compilation by the missing generated file src/apps/extension-host/dist/extension-host.js. No related feature test failed.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above.
• User-facing strings and locales are updated where applicable.