test: add issue regression test infrastructure and issue OpenRouterTeam#194 test (OpenRouterTeam#379)

* test: add e2e/issues directory with issue OpenRouterTeam#194 regression test

- Create e2e/issues/ directory for issue-specific regression tests
- Add regression test for issue OpenRouterTeam#194 (Grok 4 Fast Invalid JSON response)
- Document the e2e/issues/ pattern in CONTRIBUTING.md

The test verifies that Grok 4 Fast works correctly with:
- generateText (non-streaming)
- streamText (streaming)
- Tool calls

Issue: OpenRouterTeam#194
Co-Authored-By: Robert Yeakel <robert.yeakel@openrouter.ai>

* fix: remove internal repo reference from test comment

Co-Authored-By: Robert Yeakel <robert.yeakel@openrouter.ai>

* feat: separate issue regression tests from main e2e suite

- Exclude e2e/issues/ from vitest.e2e.config.ts
- Add vitest.issues.config.ts for issue-specific tests
- Add pnpm test:issues script to package.json
- Update CONTRIBUTING.md with test:issues documentation

Issue regression tests are now run separately to avoid slowing down
the main e2e suite with potentially slow/rate-limited API calls.

Co-Authored-By: Robert Yeakel <robert.yeakel@openrouter.ai>

* refactor: remove speculative root cause from test comments

- Update test comment to only include known facts (error message, model)
- Update CONTRIBUTING.md template to clarify only known facts should be included
- Add note about not including speculative root cause analysis

Co-Authored-By: Robert Yeakel <robert.yeakel@openrouter.ai>

---------

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: robert-j-y

CONTRIBUTING.md

@@ -113,11 +113,10 @@ pnpm test:issues
  * Regression test for GitHub issue #{number}
  * https://github.com/OpenRouterTeam/ai-sdk-provider/issues/{number}
  *
- * Issue: {brief description of the issue}
+ * Reported error: {exact error message from the issue}
+ * Model: {model ID if applicable}
  *
- * Root cause: {explanation of what caused the issue}
- *
- * This test verifies that {what the test checks}
+ * This test verifies that {what the test checks}.
  */
 import { ... } from 'ai';
 import { describe, expect, it, vi } from 'vitest';
@@ -128,6 +127,8 @@ describe('Issue #{number}: {brief description}', () => {
 });
 ```
 
+> **Note:** Only include known facts from the issue report (error message, model, SDK version). Do not include speculative root cause analysis.
+
 **When to add issue regression tests:**
 - Bug fixes that have a clear reproduction case
 - Issues that could potentially regress

e2e/issues/issue-194-grok-invalid-json.test.ts

@@ -2,16 +2,10 @@
  * Regression test for GitHub issue #194
  * https://github.com/OpenRouterTeam/ai-sdk-provider/issues/194
  *
- * Issue: "Can not use grok 4 fast" - AI_APICallError: Invalid JSON response
+ * Reported error: "AI_APICallError: Invalid JSON response"
+ * Model: x-ai/grok-4-fast
  *
- * Root cause: Early Grok 4 Fast API instability (model was only 11 days old
- * when the issue was reported on September 30, 2025). Multiple API-side fixes
- * were deployed after the issue was reported.
- *
- * This test verifies that Grok 4 Fast works correctly with the SDK:
- * - doGenerate returns valid JSON responses
- * - doStream returns valid streaming responses
- * - Tool calls work correctly
+ * This test verifies that Grok 4 Fast works correctly with the SDK.
  */
 import { generateText, streamText, tool } from 'ai';
 import { describe, expect, it, vi } from 'vitest';