feat(web): open diff files in external editor

[ipanasenko]

The diff header filename opens the file in T3 Code’s internal viewer, but the header has no explicit way to open that file in the configured external editor.

This adds an external-editor button beside the copy-path action from #2403. The filename keeps its internal-viewer behavior, while the new action resolves the workspace-relative path and routes through the same preferred-editor setting used by the top Open control.

Built with GPT-5.6 Sol in the T3 Code harness.

Note

Add open-in-external-editor action to diff file headers in web UI

• Adds openDiffFileInEditor utility in diffFileActions.ts that resolves a diff path to a workspace-relative target before invoking the editor launcher; returns without action when path resolution fails
• Adds DiffFileHeaderActionButton and DiffFileOpenInEditorButton components in DiffFileHeaderActionButton.tsx and DiffFileOpenInEditorButton.tsx to render a labeled micro button with tooltip in each diff file header
• Wires the new action into DiffPanel in DiffPanel.tsx with a centralized launch callback that opens a remote editor URL or falls back to the existing local editor flow; the new button is disabled until the relevant environment and editor are available
• Refactors DiffFilePathCopyButton in DiffFilePathCopyButton.tsx to use the shared DiffFileHeaderActionButton primitive instead of its own button composition
• Behavioral Change: the existing filename click in diff rows still opens the internal file viewer; the new open-in-editor button is a separate, explicitly labeled action rendered alongside the copy-path button

^{Macroscope summarized 9c10b1c.}

---

Note

Low Risk
Scoped UI and path-resolution changes reusing existing editor and workspace helpers; no auth or data-handling changes.

Overview
Adds an Open in editor control next to the copy-path button on each diff file header, while filename clicks still open the in-app file viewer.

A shared DiffFileHeaderActionButton backs both header actions. openDiffFileInEditor resolves workspace paths (same rules as the primary diff action) and invokes the editor launcher without opening the right-panel viewer. DiffPanel centralizes launching in launchDiffFileInEditor, which uses remote editor URLs when available and otherwise the existing preferred local editor flow; the new button stays disabled until an editor can be resolved.

^{Reviewed by Cursor Bugbot for commit 9c10b1c. Bugbot is set up for automated code reviews on this repo. Configure here.}

[cursor]

Cursor Bugbot has reviewed your changes using default effort and found 2 potential issues.

^{❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

^{Reviewed by Cursor Bugbot for commit 0e98aa1. Configure here.}

[macroscopeapp]

Approvability

Verdict: Not approved

Macroscope's review found this PR not approvable — This PR adds a new diff-header action that launches local or remote external editors and introduces associated path and editor-resolution behavior. The capability is localized and explicitly user-triggered, but its external side effects and shared DiffPanel integration warrant human review.

^{You can add or adjust custom eligibility rules. Learn more.}