fix: handle non-user actors (e.g. Copilot) in permission and actor checks (#1144)

GitHub Apps like Copilot SWE Agent set GITHUB_ACTOR to a value (e.g.
"Copilot") that is neither a valid GitHub user nor ends with "[bot]".
This caused two independent crashes:

1. checkWritePermissions (permissions.ts): called the collaborator
   permission API which returns 404 "is not a user" for non-user actors.
2. checkHumanActor (actor.ts): called the Users API first, which 404s,
   before ever reaching the allowed_bots check.

Fix both by:
- Checking allowed_bots BEFORE making API calls, so known bots skip the
  API entirely.
- In permissions.ts, catching "is not a user" 404 errors and falling
  back to the allowed_bots list instead of crashing.
- In actor.ts, catching 404 errors and providing a clear error message
  telling the user to add the bot to allowed_bots.

Closes #900, #903, #1018, #1133

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

test/actor.test.ts

@@ -93,4 +93,78 @@ describe("checkHumanActor", () => {
       "Workflow initiated by non-human actor: other-bot (type: Bot). Add bot to allowed_bots list or use '*' to allow all bots.",
     );
   });
+
+  describe("non-[bot] actors (e.g. GitHub Copilot)", () => {
+    // GitHub Copilot SWE Agent sets GITHUB_ACTOR="Copilot" which is not a
+    // valid GitHub user and doesn't end with [bot], causing 404 on the
+    // Users API. These tests verify the fix handles this gracefully.
+
+    function createMockOctokitThat404s(): Octokit {
+      return {
+        users: {
+          getByUsername: async () => {
+            const err = new Error("Not Found");
+            (err as any).status = 404;
+            throw err;
+          },
+        },
+      } as unknown as Octokit;
+    }
+
+    test("should pass for non-[bot] actor when in allowed_bots list", async () => {
+      const mockOctokit = createMockOctokitThat404s();
+      const context = createMockContext();
+      context.actor = "Copilot";
+      context.inputs.allowedBots = "copilot,cursor";
+
+      // Should not even call the API — allowed_bots check happens first
+      await expect(
+        checkHumanActor(mockOctokit, context),
+      ).resolves.toBeUndefined();
+    });
+
+    test("should pass for non-[bot] actor when all bots are allowed", async () => {
+      const mockOctokit = createMockOctokitThat404s();
+      const context = createMockContext();
+      context.actor = "Copilot";
+      context.inputs.allowedBots = "*";
+
+      await expect(
+        checkHumanActor(mockOctokit, context),
+      ).resolves.toBeUndefined();
+    });
+
+    test("should throw with clear message for non-[bot] actor that 404s and is not in allowed list", async () => {
+      const mockOctokit = createMockOctokitThat404s();
+      const context = createMockContext();
+      context.actor = "Copilot";
+      context.inputs.allowedBots = "cursor";
+
+      await expect(checkHumanActor(mockOctokit, context)).rejects.toThrow(
+        "Workflow initiated by non-human actor: copilot (actor not found on GitHub). Add bot to allowed_bots list or use '*' to allow all bots.",
+      );
+    });
+
+    test("should throw with clear message for non-[bot] actor that 404s and allowed_bots is empty", async () => {
+      const mockOctokit = createMockOctokitThat404s();
+      const context = createMockContext();
+      context.actor = "Copilot";
+      context.inputs.allowedBots = "";
+
+      await expect(checkHumanActor(mockOctokit, context)).rejects.toThrow(
+        "Workflow initiated by non-human actor: copilot (actor not found on GitHub). Add bot to allowed_bots list or use '*' to allow all bots.",
+      );
+    });
+
+    test("should match allowed_bots case-insensitively for non-[bot] actors", async () => {
+      const mockOctokit = createMockOctokitThat404s();
+      const context = createMockContext();
+      context.actor = "Copilot";
+      context.inputs.allowedBots = "COPILOT";
+
+      await expect(
+        checkHumanActor(mockOctokit, context),
+      ).resolves.toBeUndefined();
+    });
+  });
 });