fix: guard session_diff with Array.isArray() + WIP browser panel

[pvldmitriev]

Summary

• Fix crash: TypeError: e.diffs.map is not a function — replaced ?? [] with Array.isArray() guards across all session_diff consumers (5 files). Root cause: SolidJS reconcile() can return {} instead of [] for non-wrappable initial state, and ?? [] doesn't catch truthy non-arrays.
• WIP browser panel: Tauri webview child commands (create, close, navigate, resize, back/forward/reload), browser UI panel with tabs, platform API bridge, layout integration.
• Rust fixes: Fixed type errors in browser.rs (or_else closures), removed unimplemented get_browser_url from specta commands.

Files changed

Crash fix (Array.isArray guards)

• packages/app/src/components/prompt-input.tsx
• packages/app/src/context/global-sync/event-reducer.ts
• packages/app/src/pages/session.tsx
• packages/app/src/pages/session/session-side-panel.tsx
• packages/app/src/pages/session/use-session-commands.tsx

WIP browser panel

• packages/app/src/components/browser/native-browser.tsx (new)
• packages/app/src/pages/session/browser-panel.tsx (new)
• packages/desktop/src-tauri/src/browser.rs (new)
• packages/desktop/src-tauri/src/lib.rs
• packages/desktop/src/index.tsx
• packages/desktop/src/bindings.ts
• packages/app/src/context/layout.tsx
• packages/app/src/context/platform.tsx

Test plan

• bun typecheck — 13/13 packages pass
• bun run test:unit (packages/app) — 299 pass, 0 fail
• Desktop app launches without diffs.map crash
• CI checks pass on self-hosted runner

🤖 Generated with Claude Code

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Found potentially related PRs:

1. PR fix: add defensive checks for undefined values in diff handling #19261: "fix: add defensive checks for undefined values in diff handling"

   • fix: add defensive checks for undefined values in diff handling #19261
   • Related to similar defensive checks for diff handling issues

2. PR fix(web): harden session diffs handling and support local asset override #19266: "fix(web): harden session diffs handling and support local asset override"

   • fix(web): harden session diffs handling and support local asset override #19266
   • Also addresses session diffs handling robustness

These PRs may address overlapping issues with session diff handling and type safety, though they appear to be from an earlier phase. Your current PR (21094) appears to be the latest comprehensive fix with Array.isArray guards.