Fix: fall back to default branch when workflow_dispatch trigger missing on PR branch

actions/setup/js/route_slash_command.cjs

@@ -274,9 +274,10 @@ async function addImmediateReaction(reaction) {
  * @param {string} workflowId
  * @param {string} ref
  * @param {Record<string, string>} inputs
+ * @param {string} [fallbackRef]
  * @returns {Promise<boolean>}
  */
-async function dispatchWorkflow(workflowId, ref, inputs) {
+async function dispatchWorkflow(workflowId, ref, inputs, fallbackRef) {
   try {
     await github.rest.actions.createWorkflowDispatch({
       owner: context.repo.owner,
@@ -294,6 +295,10 @@ async function dispatchWorkflow(workflowId, ref, inputs) {
       core.info(`Skipping workflow '${workflowId}' because it is disabled.`);
       return false;
     }
+    if (isMissingWorkflowDispatchTriggerError(error) && fallbackRef && ref !== fallbackRef) {
+      core.info(`Workflow '${workflowId}' not found on ref '${ref}'; retrying on default branch '${fallbackRef}'.`);
+      return dispatchWorkflow(workflowId, fallbackRef, inputs, undefined);
+    }
     throw new Error(`Failed to dispatch workflow '${workflowId}' on ref '${ref}': ${String(error)}`);
   }
 }
@@ -324,6 +329,20 @@ function isDisabledWorkflowDispatchError(error) {
   return message.includes("workflow is disabled") || message.includes("workflow was disabled") || message.includes("disabled workflow");
 }
 
+function isMissingWorkflowDispatchTriggerError(error) {
+  const status = error?.status ?? error?.response?.status;
+  const message = [error?.message, error?.response?.data?.message]
+    .filter(value => typeof value === "string" && value.trim())
+    .join(" ")
+    .toLowerCase();
+
+  if (status !== 422 || !message) {
+    return false;
+  }
+
+  return message.includes("does not have 'workflow_dispatch' trigger");
+}
+
 /**
  * @param {Record<string, Array<{workflow?: unknown, events?: unknown, ai_reaction?: unknown}>>} slashRouteMap
  * @param {string} actualCommand
@@ -367,6 +386,7 @@ async function main() {
   const identifier = eventIdentifier();
   const { buildAwContext } = require("./aw_context.cjs");
   const ref = await resolveDispatchRef();
+  const defaultBranch = normalizeDispatchRef(context.payload?.repository?.default_branch || "main");
   if (isPRClosedAtStart()) {
     core.info("Pull request is closed at workflow start; skipping centralized routing.");
     return;
@@ -404,9 +424,14 @@ async function main() {
         ...(routeReaction ? { desired_ai_reaction: routeReaction } : {}),
       };
       core.info(`Dispatching workflow '${workflowID}' for label '${labelName}'.`);
-      const dispatched = await dispatchWorkflow(workflowID, ref, {
-        aw_context: JSON.stringify(awContext),
-      });
+      const dispatched = await dispatchWorkflow(
+        workflowID,
+        ref,
+        {
+          aw_context: JSON.stringify(awContext),
+        },
+        defaultBranch
+      );
       if (dispatched) {
         core.info(`Dispatched '${workflowID}' for label '${labelName}'`);
       }
@@ -452,9 +477,14 @@ async function main() {
       ...(routeReaction ? { desired_ai_reaction: routeReaction } : {}),
     };
     core.info(`Dispatching workflow '${workflowID}' for '/${commandName}'.`);
-    const dispatched = await dispatchWorkflow(workflowID, ref, {
-      aw_context: JSON.stringify(awContext),
-    });
+    const dispatched = await dispatchWorkflow(
+      workflowID,
+      ref,
+      {
+        aw_context: JSON.stringify(awContext),
+      },
+      defaultBranch
+    );
     if (dispatched) {
       core.info(`Dispatched '${workflowID}' for '/${commandName}'`);
     }

actions/setup/js/route_slash_command.test.cjs

@@ -440,6 +440,62 @@ describe("route_slash_command", () => {
     expect(globals.core.info).toHaveBeenCalledWith(expect.stringContaining("Completed decentralized label routing for 'smoke'."));
   });
 
+  it("falls back to default branch for slash commands when workflow_dispatch trigger is missing on PR branch", async () => {
+    globals.github.rest.actions.createWorkflowDispatch = vi.fn(async params => {
+      if (params.ref === "refs/heads/copilot/some-feature-branch") {
+        throw Object.assign(new Error("Workflow does not have 'workflow_dispatch' trigger"), {
+          status: 422,
+          response: { status: 422, data: { message: "Workflow does not have 'workflow_dispatch' trigger" } },
+        });
+      }
+      dispatchCalls.push(params);
+    });
+    globals.context.payload = {
+      issue: { number: 42, pull_request: {} },
+      comment: { id: 99, body: "/archie do the thing" },
+    };
+    globals.github.rest.pulls.get = vi.fn(async () => ({
+      data: { number: 42, head: { ref: "copilot/some-feature-branch" } },
+    }));
+    globals.context.payload.repository = { default_branch: "main" };
+
+    await main();
+
+    expect(dispatchCalls).toHaveLength(1);
+    expect(dispatchCalls[0].workflow_id).toBe("archie.lock.yml");
+    expect(dispatchCalls[0].ref).toBe("refs/heads/main");
+    expect(globals.core.info).toHaveBeenCalledWith(expect.stringContaining("Workflow 'archie.lock.yml' not found on ref 'refs/heads/copilot/some-feature-branch'; retrying on default branch 'refs/heads/main'."));
+  });
+
+  it("falls back to default branch for label routes when workflow_dispatch trigger is missing on PR branch", async () => {
+    globals.github.rest.actions.createWorkflowDispatch = vi.fn(async params => {
+      if (params.ref === "refs/heads/copilot/some-feature-branch") {
+        throw Object.assign(new Error("Workflow does not have 'workflow_dispatch' trigger"), {
+          status: 422,
+          response: { status: 422, data: { message: "Workflow does not have 'workflow_dispatch' trigger" } },
+        });
+      }
+      dispatchCalls.push(params);
+    });
+    globals.context.eventName = "pull_request";
+    globals.context.payload = {
+      action: "labeled",
+      label: { name: "ci-doctor" },
+      pull_request: { number: 42, head: { ref: "copilot/some-feature-branch" }, state: "open" },
+      repository: { default_branch: "main" },
+    };
+    process.env.GH_AW_LABEL_ROUTING = JSON.stringify({
+      "ci-doctor": [{ workflow: "ci-doctor", events: ["pull_request"], ai_reaction: "eyes" }],
+    });
+
+    await main();
+
+    expect(dispatchCalls).toHaveLength(1);
+    expect(dispatchCalls[0].workflow_id).toBe("ci-doctor.lock.yml");
+    expect(dispatchCalls[0].ref).toBe("refs/heads/main");
+    expect(globals.core.info).toHaveBeenCalledWith(expect.stringContaining("Workflow 'ci-doctor.lock.yml' not found on ref 'refs/heads/copilot/some-feature-branch'; retrying on default branch 'refs/heads/main'."));
+  });
+
   it("skips centralized routing when PR is closed at workflow start", async () => {
     globals.context.eventName = "pull_request";
     globals.context.payload = { action: "ready_for_review", pull_request: { number: 12, state: "closed" } };