@remotion/studio: Support custom editors

[JonnyBurger]

Summary

• accept custom editor definitions in Config.setDefaultEditor()
• resolve and launch custom executables server-side without a shell
• expose only an opaque editor ID and display name to Studio
• document placeholders, platform behavior, and the security model

Test plan

• bun test packages/cli/src/test/config-reset.test.ts packages/cli/src/test/config-reload.test.ts packages/studio-server/src/test/custom-editor.test.ts packages/studio-server/src/test/editor-registry.test.ts packages/studio-server/src/test/default-editor-route.test.ts
• bun run build
• bun run stylecheck
• bunx turbo run prewarm-twoslash --filter=docs --no-update-notifier

Stack

• Depends on @remotion/studio: Add default editor menu #9935

Closes #9342

[vercel]

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Project	Deployment	Actions	Updated (UTC)
bugs	Ready	Preview	Jul 30, 2026 5:22pm
remotion	Ready	Preview	Jul 30, 2026 5:22pm

[pullfrog]

✅ No new issues found.

Reviewed changes

• CustomEditor type and option validation — adds CustomEditor type with type, name, executable, and arguments fields; validates placeholders (%TARGET_PATH% required), argument types, and empty-name checks in default-editor.tsx. Renames the old DefaultEditor to BuiltInEditor and makes the new DefaultEditor = BuiltInEditor | CustomEditor.
• Server-side resolution and launching — resolveCustomEditorExecutable searches PATH, handles absolute paths, Mac .app bundles (via open -a), Windows .exe/.com filtering, and symlinks. launchCustomEditor spawns with shell: false, detached: true, stdio: 'ignore' — no shell injection surface.
• WSL path normalization — normalizeCustomEditorTargetPath converts absolute /mnt/ paths to relative paths when running under WSL, mirroring the existing behavior in launchEditor for built-in editors.
• Sanitized API surface — GetDefaultEditorInfoResponse and UpdateDefaultEditorRequest use EditorPickerId = BuiltInEditor | 'custom'. The browser never sees the custom editor's executable path, arguments, or config object — only the opaque 'custom' ID and display name. updateDefaultEditorHandler rejects any custom editor payload sent from the browser and preserves the server-side config as-is when 'custom' is selected.
• Test coverage — custom-editor.test.ts validates resolution on Linux/Windows/macOS, placeholder expansion, WSL normalization, and a full end-to-end spawn. default-editor-route.test.ts covers info-exposure, config preservation on 'custom' select, and browser-submitted rejection. editor-registry.test.ts covers custom editor resolution, fallback on missing executable, and warning deduplication.
• Docs and UI — new docs/studio/open-in-editor.mdx page documents custom editor config, placeholders, platform support, and security model. ConfigureDefaultEditorModal shows the custom editor with an icon in the dropdown.

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