fix: fall back to the liveness probe when the identity probe is denied

scripts/lib/process.mjs

@@ -155,10 +155,18 @@ export function getProcessIdentity(pid) {
   }
 }
 
-export function validateProcessIdentity(pid, expectedIdentity) {
+export function validateProcessIdentity(pid, expectedIdentity, options = {}) {
+  const identityImpl = options.identityImpl ?? getProcessIdentity;
   try {
-    return getProcessIdentity(pid) === expectedIdentity;
-  } catch {
+    return identityImpl(pid) === expectedIdentity;
+  } catch (error) {
+    // A denied probe (sandboxed `ps`, unreadable /proc entry) means the identity
+    // cannot be established, not that the process is gone. Fall back to the
+    // zero-signal liveness probe, which still reports ESRCH for a dead PID.
+    // PID-reuse detection is only given up when identity is unknowable at all.
+    if (error?.code === "EPERM" || error?.code === "EACCES") {
+      return isProcessAlive(pid, options);
+    }
     return false;
   }
 }

tests/process.test.mjs

@@ -387,4 +387,42 @@ describe("validateProcessIdentity", () => {
   it("returns false for non-existent PID", () => {
     assert.equal(validateProcessIdentity(99999999, "any"), false);
   });
+
+  it("falls back to the liveness probe when the identity probe is denied", () => {
+    const deniedIdentity = () => {
+      throw Object.assign(new Error("spawnSync ps EPERM"), { code: "EPERM" });
+    };
+
+    assert.equal(
+      validateProcessIdentity(12345, "recorded-identity", {
+        identityImpl: deniedIdentity,
+        killImpl: () => {
+          throw Object.assign(new Error("operation not permitted"), { code: "EPERM" });
+        },
+      }),
+      true,
+    );
+
+    assert.equal(
+      validateProcessIdentity(12345, "recorded-identity", {
+        identityImpl: deniedIdentity,
+        killImpl: () => {
+          throw Object.assign(new Error("no such process"), { code: "ESRCH" });
+        },
+      }),
+      false,
+    );
+  });
+
+  it("keeps a failed identity probe that is not a denial classified as dead", () => {
+    assert.equal(
+      validateProcessIdentity(12345, "recorded-identity", {
+        identityImpl: () => {
+          throw new Error("ps: exit=1");
+        },
+        killImpl: () => true,
+      }),
+      false,
+    );
+  });
 });