fix: detect $bunfs virtual paths for daemon autostart in Bun binaries (#86)

* fix: detect $bunfs virtual paths for daemon autostart in Bun binaries

The previous fix (PR #84) assumed argv[0] was the real binary and
execPath was the embedded Bun runtime, but it's the opposite: Bun
compiled binaries report argv as ["bun", "/$bunfs/root/<name>", ...]
with execPath pointing to the real binary on disk. The old code matched
the $bunfs virtual path against SCRIPT_ENTRYPOINT_PATTERN (because it
contains "/"), spawning `bun /$bunfs/root/hunk mcp serve` — a path
that doesn't exist outside the binary.

Fix: detect the /$bunfs/ prefix in argv[1] and use execPath directly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* style: format daemon launcher test

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: benvinegar

src/mcp/daemonLauncher.ts

@@ -10,31 +10,33 @@ export interface DaemonLaunchCommand {
   args: string[];
 }
 
+/** Detect Bun's virtual filesystem prefix used inside compiled single-file executables. */
+const BUNFS_PREFIX = "/$bunfs/";
+
 /** Resolve how the current Hunk process should launch a sibling `hunk mcp serve` daemon. */
 export function resolveDaemonLaunchCommand(
   argv = process.argv,
   execPath = process.execPath,
 ): DaemonLaunchCommand {
   const entrypoint = argv[1];
 
-  // Running from source or a JS wrapper (bun src/main.tsx, node bin/hunk.cjs):
-  // reuse the runtime + script entrypoint.
-  if (entrypoint && !entrypoint.startsWith("-") && SCRIPT_ENTRYPOINT_PATTERN.test(entrypoint)) {
+  // Bun-compiled single-file executables report argv as
+  //   ["bun", "/$bunfs/root/<name>", ...userArgs]
+  // with execPath pointing to the real binary on disk.
+  // Detect the virtual $bunfs path and use execPath directly.
+  if (entrypoint && entrypoint.startsWith(BUNFS_PREFIX)) {
     return {
       command: execPath,
-      args: [entrypoint, "mcp", "serve"],
+      args: ["mcp", "serve"],
     };
   }
 
-  // Bun-compiled single-file executables set process.execPath to the Bun
-  // runtime embedded inside the binary, not the binary itself.  When
-  // argv[0] differs from execPath, it is the actual compiled binary the
-  // user invoked — use that to spawn the daemon.
-  const invokedBinary = argv[0];
-  if (invokedBinary && invokedBinary !== execPath) {
+  // Running from source or a JS wrapper (bun src/main.tsx, node bin/hunk.cjs):
+  // reuse the runtime + script entrypoint.
+  if (entrypoint && !entrypoint.startsWith("-") && SCRIPT_ENTRYPOINT_PATTERN.test(entrypoint)) {
     return {
-      command: invokedBinary,
-      args: ["mcp", "serve"],
+      command: execPath,
+      args: [entrypoint, "mcp", "serve"],
     };
   }
 

test/daemon-launcher.test.ts

@@ -26,16 +26,13 @@ describe("MCP daemon launcher", () => {
     });
   });
 
-  test("uses argv[0] for Bun-compiled binaries where execPath is the embedded runtime", () => {
-    // In Bun single-file executables, process.execPath is the Bun runtime
-    // inside the binary, while argv[0] is the actual compiled binary path.
+  test("uses execPath for Bun-compiled binaries where argv contains $bunfs virtual paths", () => {
+    // In Bun single-file executables, argv is ["bun", "/$bunfs/root/<name>", ...userArgs]
+    // and execPath is the real binary on disk.
     expect(
       resolveDaemonLaunchCommand(
-        [
-          "/usr/local/lib/node_modules/hunkdiff/node_modules/hunkdiff-darwin-arm64/bin/hunk",
-          "show",
-        ],
-        "/usr/local/lib/node_modules/hunkdiff/node_modules/hunkdiff-darwin-arm64/bin/hunk___bun",
+        ["bun", "/$bunfs/root/hunk", "show"],
+        "/usr/local/lib/node_modules/hunkdiff/node_modules/hunkdiff-darwin-arm64/bin/hunk",
       ),
     ).toEqual({
       command: "/usr/local/lib/node_modules/hunkdiff/node_modules/hunkdiff-darwin-arm64/bin/hunk",