feat: skip action gracefully for workflow validation errors (#460)

* feat: skip action gracefully for workflow validation errors

Handle workflow_not_found_on_default_branch and workflow_content_mismatch
errors by skipping the action with a warning instead of failing. This
improves user experience when adding Claude Code workflows to new
repositories or making workflow changes in PRs.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* Update src/github/token.ts

---------

Co-authored-by: Claude <noreply@anthropic.com>

action.yml

@@ -286,7 +286,7 @@ runs:
         fi
 
     - name: Revoke app token
-      if: always() && inputs.github_token == ''
+      if: always() && inputs.github_token == '' && steps.prepare.outputs.skipped_due_to_workflow_validation_mismatch != 'true'
       shell: bash
       run: |
         curl -L \

src/github/token.ts

@@ -31,8 +31,33 @@ async function exchangeForAppToken(oidcToken: string): Promise<string> {
     const responseJson = (await response.json()) as {
       error?: {
         message?: string;
+        details?: {
+          error_code?: string;
         };
       };
+      type?: string;
+      message?: string;
+    };
+
+    // Check for specific workflow validation error codes that should skip the action
+    const errorCode = responseJson.error?.details?.error_code;
+
+    if (
+      errorCode === "workflow_not_found_on_default_branch" ||
+      errorCode === "workflow_content_mismatch"
+    ) {
+      const message =
+        responseJson.message ??
+        responseJson.error?.message ??
+        "Workflow validation failed";
+      core.warning(`Skipping action due to workflow validation: ${message}`);
+      console.log(
+        "Action skipped due to workflow validation error. This is expected when adding Claude Code workflows to new repositories or on PRs with workflow changes.",
+      );
+      core.setOutput("skipped_due_to_workflow_validation_mismatch", "true");
+      process.exit(0);
+    }
+
     console.error(
       `App token exchange failed: ${response.status} ${response.statusText} - ${responseJson?.error?.message ?? "Unknown error"}`,
     );
@@ -77,6 +102,7 @@ export async function setupGitHubToken(): Promise<string> {
     core.setOutput("GITHUB_TOKEN", appToken);
     return appToken;
   } catch (error) {
+    // Only set failed if we get here - workflow validation errors will exit(0) before this
     core.setFailed(
       `Failed to setup GitHub token: ${error}\n\nIf you instead wish to use this action with a custom GitHub token or custom GitHub app, provide a \`github_token\` in the \`uses\` section of the app in your workflow yml file.`,
     );