fix(coding-agent): keep bun/npm routing for regular-file entries on Windows

Bun's global bin entry on Windows is a regular-file .exe shim, not a
symlink, so the standalone-binary override would have rerouted a
legitimate bun-managed install to in-place binary replacement and
clobbered the shim. Gate the override on POSIX, where package-manager
bin entries are always symlinks; add a regression test.

packages/coding-agent/src/cli/update-cli.ts

@@ -239,12 +239,16 @@ function resolveUpdateMethod(
 	if (miseDataDir && isPathInDirectory(ompPath, path.join(miseDataDir, "shims"))) return "mise";
 	// A plain executable file in a package-manager bin dir is the standalone
 	// binary the installer placed there, not an npm/bun-managed install (those
-	// symlink into node_modules). When the global bin dir overlaps the
+	// symlink into node_modules on POSIX). When the global bin dir overlaps the
 	// installer's default (~/.local/bin), classifying by directory alone routes
 	// a binary install through npm/bun, whose reinstall then collides with the
 	// existing file (npm EEXIST). Fall through to binary replacement instead.
-	if (bunBinDir && isPathInDirectory(ompPath, bunBinDir) && !ompIsRegularFile) return "bun";
-	if ((npmBinDir && isPathInDirectory(ompPath, npmBinDir) && !ompIsRegularFile) || isWindowsScriptLauncher)
+	// Windows is excluded: there package managers write regular-file shims
+	// (bun's .exe launcher, npm's .cmd/.ps1), so a regular file is NOT evidence
+	// of a standalone install and the override would hijack managed installs.
+	const isStandaloneRegularFile = ompIsRegularFile && process.platform !== "win32";
+	if (bunBinDir && isPathInDirectory(ompPath, bunBinDir) && !isStandaloneRegularFile) return "bun";
+	if ((npmBinDir && isPathInDirectory(ompPath, npmBinDir) && !isStandaloneRegularFile) || isWindowsScriptLauncher)
 		return "npm";
 	return "binary";
 }

packages/coding-agent/test/update-cli.test.ts

@@ -111,6 +111,26 @@ describe("update-cli install target detection", () => {
 		expect(method).toBe("binary");
 	});
 
+	it("keeps bun update for regular-file entries in the bun global bin dir on Windows, where bun writes .exe shims", () => {
+		// On Windows a bun-managed global install is a regular-file .exe
+		// launcher, not a symlink, so the standalone-binary override must not
+		// apply there — it would clobber the shim with a raw binary. Paths use
+		// forward slashes so the lexical containment check works on the POSIX
+		// host running this suite; the platform gate is what is under test.
+		const platformDescriptor = Object.getOwnPropertyDescriptor(process, "platform");
+		if (!platformDescriptor) throw new Error("process.platform descriptor missing");
+		Object.defineProperty(process, "platform", { ...platformDescriptor, value: "win32" });
+		try {
+			const method = resolveUpdateMethodForTest("C:/Users/test/.bun/bin/omp.exe", "C:/Users/test/.bun/bin", {
+				ompIsRegularFile: true,
+			});
+
+			expect(method).toBe("bun");
+		} finally {
+			Object.defineProperty(process, "platform", platformDescriptor);
+		}
+	});
+
 	it("still uses npm update when the npm global bin entry is a package-manager symlink, not a plain file", () => {
 		const method = resolveUpdateMethodForTest("/home/u/.local/bin/omp", undefined, {
 			npmBinDir: "/home/u/.local/bin",