fix(load-balancing): add pagination limits and rate-limit detection

Cap pagination at 100 pages (10,000 runners max), detect GitHub API
rate limiting (403/429) with reset time reporting, add 30-second total
timeout for pagination loop. Log clear diagnostic when no runners found
suggesting possible causes (token permissions, runner registration).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/model/orchestrator/services/core/runner-availability-service.test.ts

@@ -43,7 +43,7 @@ describe('RunnerAvailabilityService', () => {
     });
 
     it('should fallback when no runners are registered', async () => {
-      const mockRequest = jest.fn().mockResolvedValue({ data: { runners: [] } });
+      const mockRequest = jest.fn().mockResolvedValue({ status: 200, data: { runners: [] } });
       MockedOctokit.mockImplementation(() => ({ request: mockRequest }) as any);
 
       const result = await RunnerAvailabilityService.checkAvailability('owner', 'repo', 'token', [], 1);
@@ -57,7 +57,7 @@ describe('RunnerAvailabilityService', () => {
         { name: 'runner-1', status: 'online', busy: false, labels: ['self-hosted', 'linux'] },
         { name: 'runner-2', status: 'online', busy: false, labels: ['self-hosted', 'linux'] },
       ]);
-      const mockRequest = jest.fn().mockResolvedValue({ data: { runners } });
+      const mockRequest = jest.fn().mockResolvedValue({ status: 200, data: { runners } });
       MockedOctokit.mockImplementation(() => ({ request: mockRequest }) as any);
 
       const result = await RunnerAvailabilityService.checkAvailability('owner', 'repo', 'token', [], 1);
@@ -71,7 +71,7 @@ describe('RunnerAvailabilityService', () => {
         { name: 'runner-1', status: 'online', busy: true, labels: ['self-hosted'] },
         { name: 'runner-2', status: 'online', busy: true, labels: ['self-hosted'] },
       ]);
-      const mockRequest = jest.fn().mockResolvedValue({ data: { runners } });
+      const mockRequest = jest.fn().mockResolvedValue({ status: 200, data: { runners } });
       MockedOctokit.mockImplementation(() => ({ request: mockRequest }) as any);
 
       const result = await RunnerAvailabilityService.checkAvailability('owner', 'repo', 'token', [], 1);
@@ -84,7 +84,7 @@ describe('RunnerAvailabilityService', () => {
       const runners = createMockRunners([
         { name: 'runner-1', status: 'offline', busy: false, labels: ['self-hosted'] },
       ]);
-      const mockRequest = jest.fn().mockResolvedValue({ data: { runners } });
+      const mockRequest = jest.fn().mockResolvedValue({ status: 200, data: { runners } });
       MockedOctokit.mockImplementation(() => ({ request: mockRequest }) as any);
 
       const result = await RunnerAvailabilityService.checkAvailability('owner', 'repo', 'token', [], 1);
@@ -97,7 +97,7 @@ describe('RunnerAvailabilityService', () => {
         { name: 'linux-runner', status: 'online', busy: false, labels: ['self-hosted', 'linux'] },
         { name: 'windows-runner', status: 'online', busy: false, labels: ['self-hosted', 'windows'] },
       ]);
-      const mockRequest = jest.fn().mockResolvedValue({ data: { runners } });
+      const mockRequest = jest.fn().mockResolvedValue({ status: 200, data: { runners } });
       MockedOctokit.mockImplementation(() => ({ request: mockRequest }) as any);
 
       const result = await RunnerAvailabilityService.checkAvailability(
@@ -118,7 +118,7 @@ describe('RunnerAvailabilityService', () => {
       const runners = createMockRunners([
         { name: 'windows-runner', status: 'online', busy: false, labels: ['self-hosted', 'windows'] },
       ]);
-      const mockRequest = jest.fn().mockResolvedValue({ data: { runners } });
+      const mockRequest = jest.fn().mockResolvedValue({ status: 200, data: { runners } });
       MockedOctokit.mockImplementation(() => ({ request: mockRequest }) as any);
 
       const result = await RunnerAvailabilityService.checkAvailability(
@@ -138,7 +138,7 @@ describe('RunnerAvailabilityService', () => {
       const runners = createMockRunners([
         { name: 'runner-1', status: 'online', busy: false, labels: ['self-hosted'] },
       ]);
-      const mockRequest = jest.fn().mockResolvedValue({ data: { runners } });
+      const mockRequest = jest.fn().mockResolvedValue({ status: 200, data: { runners } });
       MockedOctokit.mockImplementation(() => ({ request: mockRequest }) as any);
 
       // Need 2, have 1 — should fallback
@@ -151,7 +151,7 @@ describe('RunnerAvailabilityService', () => {
       const runners = createMockRunners([
         { name: 'runner-1', status: 'online', busy: false, labels: ['Self-Hosted', 'Linux'] },
       ]);
-      const mockRequest = jest.fn().mockResolvedValue({ data: { runners } });
+      const mockRequest = jest.fn().mockResolvedValue({ status: 200, data: { runners } });
       MockedOctokit.mockImplementation(() => ({ request: mockRequest }) as any);
 
       const result = await RunnerAvailabilityService.checkAvailability(
@@ -180,7 +180,7 @@ describe('RunnerAvailabilityService', () => {
         { name: 'busy', status: 'online', busy: true, labels: ['self-hosted'] },
         { name: 'offline', status: 'offline', busy: false, labels: ['self-hosted'] },
       ]);
-      const mockRequest = jest.fn().mockResolvedValue({ data: { runners } });
+      const mockRequest = jest.fn().mockResolvedValue({ status: 200, data: { runners } });
       MockedOctokit.mockImplementation(() => ({ request: mockRequest }) as any);
 
       const result = await RunnerAvailabilityService.checkAvailability('owner', 'repo', 'token', [], 1);
@@ -190,4 +190,131 @@ describe('RunnerAvailabilityService', () => {
       expect(result.idleRunners).toBe(1);
     });
   });
+
+  describe('pagination limits', () => {
+    it('should stop paginating after reaching the page limit', async () => {
+      // Return full pages (100 runners each) to force continued pagination
+      let callCount = 0;
+      const mockRequest = jest.fn().mockImplementation(() => {
+        callCount++;
+        const runners = createMockRunners(
+          Array.from({ length: 100 }, (_, i) => ({
+            name: `runner-${callCount}-${i}`,
+            status: 'online' as const,
+            busy: false,
+            labels: ['self-hosted'],
+          })),
+        );
+
+        return Promise.resolve({ status: 200, data: { runners } });
+      });
+      MockedOctokit.mockImplementation(() => ({ request: mockRequest }) as any);
+
+      const result = await RunnerAvailabilityService.checkAvailability('owner', 'repo', 'token', [], 1);
+
+      // Should have called at most 100 pages (the MAX_PAGINATION_PAGES limit)
+      expect(mockRequest).toHaveBeenCalledTimes(100);
+      // Should still have runners from the pages it did fetch
+      expect(result.totalRunners).toBe(10000);
+      expect(result.shouldFallback).toBe(false);
+    });
+
+    it('should stop paginating on rate limit (HTTP 403)', async () => {
+      let callCount = 0;
+      const mockRequest = jest.fn().mockImplementation(() => {
+        callCount++;
+        if (callCount === 2) {
+          // Octokit throws for non-2xx responses
+          const error: any = new Error('API rate limit exceeded');
+          error.status = 403;
+          error.response = {
+            status: 403,
+            headers: { 'x-ratelimit-reset': String(Math.floor(Date.now() / 1000) + 3600) },
+          };
+
+          return Promise.reject(error);
+        }
+        const runners = createMockRunners(
+          Array.from({ length: 100 }, (_, i) => ({
+            name: `runner-${i}`,
+            status: 'online' as const,
+            busy: false,
+            labels: ['self-hosted'],
+          })),
+        );
+
+        return Promise.resolve({ status: 200, data: { runners } });
+      });
+      MockedOctokit.mockImplementation(() => ({ request: mockRequest }) as any);
+
+      const result = await RunnerAvailabilityService.checkAvailability('owner', 'repo', 'token', [], 1);
+
+      // Should have stopped at page 2 (rate limited)
+      expect(mockRequest).toHaveBeenCalledTimes(2);
+      // Should use the 100 runners from the first page
+      expect(result.totalRunners).toBe(100);
+      expect(result.shouldFallback).toBe(false);
+    });
+
+    it('should stop paginating on rate limit (HTTP 429)', async () => {
+      let callCount = 0;
+      const mockRequest = jest.fn().mockImplementation(() => {
+        callCount++;
+        if (callCount === 1) {
+          // Octokit throws for non-2xx responses
+          const error: any = new Error('Too Many Requests');
+          error.status = 429;
+          error.response = { status: 429, headers: {} };
+
+          return Promise.reject(error);
+        }
+
+        return Promise.resolve({ status: 200, data: { runners: [] } });
+      });
+      MockedOctokit.mockImplementation(() => ({ request: mockRequest }) as any);
+
+      const result = await RunnerAvailabilityService.checkAvailability('owner', 'repo', 'token', [], 1);
+
+      // Should have stopped at first page (rate limited immediately)
+      expect(mockRequest).toHaveBeenCalledTimes(1);
+      // No runners found — should fallback
+      expect(result.totalRunners).toBe(0);
+      expect(result.shouldFallback).toBe(true);
+    });
+
+    it('should handle pagination timeout gracefully', async () => {
+      // Mock Date.now to simulate timeout
+      const originalDateNow = Date.now;
+      let callCount = 0;
+
+      const mockRequest = jest.fn().mockImplementation(() => {
+        callCount++;
+        // After first call, advance time past the timeout
+        if (callCount >= 2) {
+          Date.now = jest.fn(() => originalDateNow() + 31_000);
+        }
+        const runners = createMockRunners(
+          Array.from({ length: 100 }, (_, i) => ({
+            name: `runner-${callCount}-${i}`,
+            status: 'online' as const,
+            busy: false,
+            labels: ['self-hosted'],
+          })),
+        );
+
+        return Promise.resolve({ status: 200, data: { runners } });
+      });
+      MockedOctokit.mockImplementation(() => ({ request: mockRequest }) as any);
+
+      const result = await RunnerAvailabilityService.checkAvailability('owner', 'repo', 'token', [], 1);
+
+      // Should have stopped after timeout was detected (2 pages: first succeeds, second triggers timeout check)
+      expect(mockRequest.mock.calls.length).toBeLessThanOrEqual(3);
+      // Should have runners from pages fetched before timeout
+      expect(result.totalRunners).toBeGreaterThan(0);
+
+      // Restore
+      Date.now = originalDateNow;
+    });
+  });
 });

src/model/orchestrator/services/core/runner-availability-service.ts

@@ -17,6 +17,18 @@ interface RunnerCheckResult {
   idleRunners: number;
 }
 
+/**
+ * Maximum number of pages to fetch when paginating through GitHub API results.
+ * 100 pages * 100 per page = 10,000 runners maximum.
+ */
+const MAX_PAGINATION_PAGES = 100;
+
+/**
+ * Total timeout in milliseconds for the pagination loop.
+ * Prevents indefinite API calls if GitHub is slow or pagination is unexpectedly deep.
+ */
+const PAGINATION_TIMEOUT_MS = 30_000;
+
 /**
  * Checks GitHub Actions runner availability to support automatic provider fallback.
  *
@@ -102,19 +114,55 @@ export class RunnerAvailabilityService {
 
   /**
    * Fetch all runners for a repository, handling pagination.
+   *
+   * Includes defensive limits:
+   * - Maximum page count (MAX_PAGINATION_PAGES) to prevent infinite loops
+   * - Total timeout (PAGINATION_TIMEOUT_MS) to prevent indefinite API calls
+   * - Rate-limit detection (HTTP 403/429 with X-RateLimit-Remaining header)
    */
   private static async fetchRunners(octokit: Octokit, owner: string, repo: string): Promise<GitHubRunner[]> {
     const allRunners: GitHubRunner[] = [];
     let page = 1;
     const perPage = 100;
+    const startTime = Date.now();
 
-    while (true) {
-      const response = await octokit.request('GET /repos/{owner}/{repo}/actions/runners', {
-        owner,
-        repo,
-        per_page: perPage,
-        page,
-      });
+    while (page <= MAX_PAGINATION_PAGES) {
+      // Check total timeout
+      if (Date.now() - startTime > PAGINATION_TIMEOUT_MS) {
+        OrchestratorLogger.logWarning(
+          `[RunnerAvailability] Pagination timeout reached after ${page - 1} pages and ${Date.now() - startTime}ms. ` +
+            `Using ${allRunners.length} runners found so far.`,
+        );
+        break;
+      }
+
+      let response: any;
+      try {
+        response = await octokit.request('GET /repos/{owner}/{repo}/actions/runners', {
+          owner,
+          repo,
+          per_page: perPage,
+          page,
+        });
+      } catch (requestError: any) {
+        // Octokit throws for non-2xx responses. Check if this is a rate limit error.
+        const status = requestError.status ?? requestError.response?.status;
+        if (status === 403 || status === 429) {
+          const resetTime =
+            requestError.response?.headers?.['x-ratelimit-reset'] ??
+            requestError.headers?.['x-ratelimit-reset'];
+          const resetMessage = resetTime
+            ? ` Resets at ${new Date(Number.parseInt(String(resetTime), 10) * 1000).toISOString()}`
+            : '';
+          OrchestratorLogger.logWarning(
+            `[RunnerAvailability] GitHub API rate limit reached (HTTP ${status}).${resetMessage} ` +
+              `Using ${allRunners.length} runners found so far.`,
+          );
+          break;
+        }
+        // Re-throw non-rate-limit errors to be handled by the outer catch
+        throw requestError;
+      }
 
       const runners = (response.data.runners || []) as GitHubRunner[];
       allRunners.push(...runners);
@@ -123,6 +171,22 @@ export class RunnerAvailabilityService {
       page++;
     }
 
+    if (page > MAX_PAGINATION_PAGES) {
+      OrchestratorLogger.logWarning(
+        `[RunnerAvailability] Maximum pagination limit reached (${MAX_PAGINATION_PAGES} pages). ` +
+          `Using ${allRunners.length} runners found so far.`,
+      );
+    }
+
+    if (allRunners.length === 0) {
+      OrchestratorLogger.log(
+        '[RunnerAvailability] No runners found. Possible causes: ' +
+          'wrong token permissions (needs repo or actions scope), ' +
+          'no self-hosted runners registered, ' +
+          'or runners are registered at the organization level instead of the repository.',
+      );
+    }
+
     return allRunners;
   }