fix(launcher): honor OPENCODEX_BUN_PATH

Author: luvs01

bin/ocx.mjs

@@ -292,13 +292,22 @@ function bunBinDir() {
 // the ~450-byte stub in place, which is NOT executable (ENOEXEC). A size gate
 // cleanly distinguishes the stub from a real binary on every platform.
 const REAL_BUN_MIN_BYTES = 1_000_000;
+const BUN_OVERRIDE_ENV = "OPENCODEX_BUN_PATH";
+
+function isRealBunBinary(path) {
+  try {
+    return existsSync(path) && statSync(path).size >= REAL_BUN_MIN_BYTES;
+  } catch {
+    return false;
+  }
+}
 
 function findBunBinary(bunDir) {
   // The npm `bun` package ships the binary as bin/bun.exe on every platform;
   // probe bin/bun too for forward compatibility.
   for (const name of ["bun.exe", "bun"]) {
     const p = join(bunDir, "bin", name);
-    if (existsSync(p) && statSync(p).size >= REAL_BUN_MIN_BYTES) return p;
+    if (isRealBunBinary(p)) return p;
   }
   return null;
 }
@@ -317,6 +326,11 @@ function fail(msg) {
 }
 
 function resolveBun() {
+  // Keep direct npm-launcher starts aligned with durable service/shim installs:
+  // a valid explicit runtime must win even when the bundled dependency exists.
+  const override = process.env[BUN_OVERRIDE_ENV]?.trim();
+  if (override && isRealBunBinary(override)) return override;
+
   let bunDir;
   try {
     bunDir = bunBinDir();

tests/ocx-launcher-source.test.ts

@@ -22,4 +22,21 @@ describe("ocx.mjs npm launcher (source invariants)", () => {
     expect(source).toContain('if (explicit === "preview" || explicit === "latest") return explicit;');
     expect(source).not.toMatch(/if \(tagIndex !== -1 && process\.argv\[tagIndex \+ 1\]\) return process\.argv/);
   });
+
+  test("valid Bun overrides are selected before the bundled runtime", () => {
+    expect(source).toContain('const BUN_OVERRIDE_ENV = "OPENCODEX_BUN_PATH";');
+    expect(source).toContain("if (override && isRealBunBinary(override)) return override;");
+
+    const resolveStart = source.indexOf("function resolveBun() {");
+    const overrideCheck = source.indexOf("process.env[BUN_OVERRIDE_ENV]?.trim()", resolveStart);
+    const bundledLookup = source.indexOf("bunDir = bunBinDir()", resolveStart);
+    expect(resolveStart).toBeGreaterThanOrEqual(0);
+    expect(overrideCheck).toBeGreaterThan(resolveStart);
+    expect(bundledLookup).toBeGreaterThan(overrideCheck);
+  });
+
+  test("invalid Bun overrides fall back without throwing", () => {
+    expect(source).toContain("function isRealBunBinary(path) {");
+    expect(source).toMatch(/function isRealBunBinary\(path\) \{[\s\S]*?try \{[\s\S]*?statSync\(path\)[\s\S]*?catch \{[\s\S]*?return false;/);
+  });
 });