Handle deleted PR head refs non-fatally

actions/setup/js/update_pull_request.cjs

@@ -52,7 +52,7 @@ function isNonFatalUpdateBranchError(error) {
     if (status === 403 && (hasWorkflowsPermissionError || hasWorkflowsScopeRequired)) {
       return true;
     }
-    if (status !== 422) {
+    if (status !== 422 && !message.includes("head ref does not exist")) {
       return false;
     }
   }
@@ -62,12 +62,15 @@ function isNonFatalUpdateBranchError(error) {
   // - cannot auto-update due to conflict ("merge conflict between base and head")
   // - stale merged targets where the head branch was deleted ("head ref does not exist")
   // These should not fail safe output processing.
-  // Restrict to status === 422 to avoid silently swallowing the same phrases from proxy/network
-  // errors that lack a numeric status. hasWorkflowsPermissionError / hasWorkflowsScopeRequired
-  // are only checked for errors with no numeric status (status === undefined); the explicit 403
-  // case is already handled by the if-block above.
+  // A deleted head ref is a stale target regardless of which numeric status the API/proxy reports.
+  // Keep requiring some numeric status so transport/proxy failures with no HTTP response still fail.
+  // Restrict the other phrases to status === 422 to avoid silently swallowing proxy/network
+  // errors. hasWorkflowsPermissionError / hasWorkflowsScopeRequired are only checked for errors
+  // with no numeric status (status === undefined); the explicit 403 case is already handled by
+  // the if-block above.
   return (
-    (status === 422 && (message.includes("there are no new commits on the base branch") || message.includes("merge conflict between base and head") || message.includes("head ref does not exist"))) ||
+    (status !== undefined && message.includes("head ref does not exist")) ||
+    (status === 422 && (message.includes("there are no new commits on the base branch") || message.includes("merge conflict between base and head"))) ||
     ((hasWorkflowsPermissionError || hasWorkflowsScopeRequired) && status === undefined)
   );
 }

actions/setup/js/update_pull_request.test.cjs

@@ -960,17 +960,31 @@ describe("update_pull_request.cjs - update_branch behavior", () => {
     expect(mockCore.warning).toHaveBeenCalledWith(expect.stringContaining("branch from base (non-fatal)"));
   });
 
-  it("should treat head-ref-missing as fatal when updateBranch returns a non-422 status", async () => {
+  it("should treat head-ref-missing as non-fatal regardless of updateBranch status", async () => {
     const unexpectedStatusError = new Error("head ref does not exist - https://docs.github.com/rest/pulls/pulls#update-a-pull-request-branch");
     unexpectedStatusError.status = 404;
     mockGithub.rest.pulls.updateBranch.mockRejectedValueOnce(unexpectedStatusError);
 
     const handler = await updatePRModule.main({ update_branch: true });
     const result = await handler({ pull_request_number: 100 });
 
-    expect(result.success).toBe(false);
+    expect(result.success).toBe(true);
     expect(mockGithub.rest.pulls.updateBranch).toHaveBeenCalledTimes(1);
     expect(mockGithub.rest.pulls.update).not.toHaveBeenCalled();
+    expect(mockCore.warning).toHaveBeenCalledWith(expect.stringContaining("branch from base (non-fatal)"));
+  });
+
+  it("should keep head-ref-missing fatal when updateBranch has no numeric status", async () => {
+    const missingStatusError = new Error("head ref does not exist - https://docs.github.com/rest/pulls/pulls#update-a-pull-request-branch");
+    mockGithub.rest.pulls.updateBranch.mockRejectedValueOnce(missingStatusError);
+
+    const handler = await updatePRModule.main({ update_branch: true });
+    const result = await handler({ pull_request_number: 100 });
+
+    expect(result.success).toBe(false);
+    expect(result.error).toContain("update pull request #100 branch from base failed");
+    expect(mockGithub.rest.pulls.updateBranch).toHaveBeenCalledTimes(1);
+    expect(mockCore.warning).toHaveBeenCalledWith(expect.not.stringContaining("(non-fatal)"));
   });
 
   it("should continue title/body updates when updateBranch gets workflows-permission 403", async () => {