implement file association support

[tsconfigdotjson]

Summary

Fixes #304 — double-clicking a file associated with an Electrobun app now delivers it as a file:// URL through the existing open-url event.

• Config: adds app.fileAssociations to electrobun.config.ts for declaring document types.
• Build: the CLI generates CFBundleDocumentTypes with LSItemContentTypes and UTExportedTypeDeclarations in Info.plist for proper Launch Services integration on modern macOS. UTI identifiers are derived from the app identifier (e.g., com.example.app.myext). Icon files are copied to the bundle with build-time existence checks. Validation strips leading dots from extensions and skips entries with missing ext/name.
• macOS: files opened via Finder arrive as file:// URLs through the existing application:openURLs: handler — no new native code needed.
• Cold-launch fix: fixes a pre-existing race where URLs arriving before the Bun Worker registered its handler were dropped. They are now buffered with a mutex and flushed on registration.

Usage

// electrobun.config.ts
app: {
  fileAssociations: [{
    ext: ["myext"],
    name: "My Document",
    role: "Viewer",
    icon: "assets/doc-icon.icns",
  }],
}

// src/bun/index.ts — files arrive as file:// URLs via open-url
Electrobun.events.on("open-url", (e) => {
  if (e.data.url.startsWith("file://")) {
    console.log("Opened file:", e.data.url);
  }
});

Files changed (3)

Layer	Files
Config	ElectrobunConfig.ts — fileAssociations type + docs
CLI/build	cli/index.ts — generateDocumentTypes (CFBundleDocumentTypes + UTExportedTypeDeclarations), icon copy + validation
Native (macOS)	nativeWrapper.mm — URL cold-launch buffering with mutex

🤖 Generated with Claude Code

[tsconfigdotjson]

@YoavCodes pretty big one to be able to support file assocations, have your agents PR

[tsconfigdotjson]

Clean Room Validation

Tested end-to-end by creating a standalone project in /tmp/electrobun-file-assoc-test/ (completely outside the repo) that links to the local electrobun package. The project declares three file associations to exercise different code paths:

fileAssociations: [
  { ext: ["ebtest"], name: "Electrobun Test Document", role: "Viewer" },
  { ext: ["ebtest2", "ebtest3"], name: "Electrobun Multi-Ext Document", role: "Editor" },
  { ext: [".ebdot"], name: "Dot-Prefix Test", role: "Viewer" },
]

What was validated

1. Info.plist generation — All three CFBundleDocumentTypes entries generated correctly with LSItemContentTypes referencing UTIs derived from the app identifier (e.g., dev.electrobun.fileassoctest.ebtest).

2. UTExportedTypeDeclarations — One UTI exported per extension, each with UTTypeIdentifier, UTTypeDescription, UTTypeConformsTo (public.data), and UTTypeTagSpecification mapping the extension. Multi-ext associations correctly generate separate UTIs.

3. Leading dot stripping — .ebdot stripped to ebdot with a build-time warning.

4. File open delivery — open -a FileAssocTest-dev.app /tmp/test-document.ebtest delivers file:///private/tmp/test-document.ebtest via the existing open-url event.

5. No spurious events — No empty events on cold launch.

6. Cold-launch race — URL buffering + mutex flush delivers file URLs correctly after handler registration.

7. Typecheck — bunx tsc --noEmit passes on the package.

8. Unit tests — All 48 unit tests pass.