fix(ui): wrap fork dialog with PlatformProvider context

[Protocol-zero-0]

Issue for this PR

Closes #18250

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Clicking the Fork button crashes with Platform context must be used within a context provider because dialog.show() uses createRoot() to render the dialog, which creates a new SolidJS root that doesn't inherit parent context providers.

The fix wraps <DialogFork /> with <PlatformProvider> in the fork command's onSelect handler, passing the current platform value from the parent scope. This is the same pattern used elsewhere in the codebase when rendering components in isolated roots.

How did you verify your code works?

• Confirmed dialog.show() uses createRoot() which creates an isolated context
• Verified PlatformProvider / usePlatform follow the createSimpleContext pattern
• Change is minimal (8 lines) and follows existing patterns in the codebase

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

Made with Cursor

[Copilot]

Pull request overview

Fixes a crash when invoking the “Fork” session command by ensuring the fork dialog is rendered with the required Platform context, even when dialog.show() mounts content in an isolated Solid root.

Changes:

• Import usePlatform and capture the current platform value in useSessionCommands.
• Wrap DialogFork with PlatformProvider inside the session.fork command’s onSelect handler.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

There’s currently no e2e coverage for the session.fork slash command / fork dialog path (unlike undo/redo/share). Consider adding a Playwright spec that opens the slash palette, selects session.fork, and asserts the dialog renders (and ideally that selecting an item navigates to the forked session) to prevent regressions of this context-related crash.