[BUG] Groq 400 json_validate_failed causes silent fallback failure in code-generation

[koydas]

🎯 Goal

Fix the code-generation job so that a Groq json_validate_failed error is detected, logged, and correctly falls through to the Anthropic provider instead of crashing the run.

📍 Context

• Repo: autonomous-dev-loop
• Component: scripts/lib/groq_client.mjs, scripts/lib/error_taxonomy.mjs, scripts/lib/llm_client.mjs
• Environment: GitHub Actions — code-generation job

❗ Observed problem

When Groq's JSON mode cannot constrain a large structured output (large file_content strings in the changes array), it returns HTTP 400 with code: "json_validate_failed". The pipeline crashes with:

{"level":"error","msg":"Fatal error","error":"All providers failed: groq: Groq API HTTP error 400: {\"error\":{\"code\":\"json_validate_failed\",...}}"}

Root cause: classifyError('400') in error_taxonomy.mjs returns 'UNKNOWN' (400 is not in the PERMANENT or TRANSIENT lists). In groq_client.mjs, retryable is false for 400 so no retry happens. In llm_client.mjs, UNKNOWN does not trigger a break, so the loop should continue to Anthropic — but the final error message only reports the Groq failure, indicating the Anthropic fallback also fails silently without surfacing its own error clearly.

🔁 Steps to reproduce

1. Trigger the code-generation workflow on an issue requiring multi-file changes (≥ 3 large files).
2. Observe the Groq provider returning HTTP 400 with json_validate_failed.
3. The job exits with code 1 — "All providers failed".

Example: run 26795257405, job 78990103447 (run ID issue-134)

✅ Expected behavior

When Groq returns json_validate_failed, the system:

1. Immediately stops retrying Groq (already the case — retryable: false).
2. Logs the Groq failure with its error code for traceability.
3. Falls through to Anthropic and succeeds (or reports the Anthropic failure clearly if it also fails).

🧪 Acceptance criteria

• When Groq returns HTTP 400 with code: "json_validate_failed", groq_client.mjs attaches err.code = 'json_validate_failed' to the thrown error so downstream handlers can inspect it.
• llm_client.mjs logs { provider: 'groq', error_type: 'json_validate_failed', status: 400 } before moving to the next provider.
• When Groq fails with json_validate_failed and Anthropic is available, the callLLM function returns the Anthropic response successfully (no crash).
• When Groq fails with json_validate_failed and Anthropic also fails, the error message includes both failures (e.g. "All providers failed: groq: ..., anthropic: ...") so the actual Anthropic error is visible.
• Unit test in scripts/tests/llm_client.test.mjs: mocking Groq to throw a json_validate_failed 400 error verifies that Anthropic is called as fallback.
• Unit test in scripts/tests/groq_client.test.mjs: a mocked 400 response with json_validate_failed body results in an error with err.code === 'json_validate_failed' and err.retryable === false.

⚠️ Constraints

• Do not change the retry behavior for other 400 errors (e.g. malformed payloads unrelated to JSON mode).
• The PERMANENT break in llm_client.mjs stops all providers — do not reclassify json_validate_failed as PERMANENT; the fallback to Anthropic must remain active.
• Backward compatible: existing error handling for 401, 403, 429, 5xx must be unaffected.

[github-actions]

✅ Issue Validation Report

Field	Value
Status	VALID — ready for development
Score	100/100 [██████████]

💡 Suggested Acceptance Criteria

Copy the block below and paste it into the issue description, then save. Saving will re-trigger validation automatically.

## Acceptance Criteria

- [ ] When Groq returns HTTP 400 with `code: 'json_validate_failed'`, the thrown error must have `err.code === 'json_validate_failed'` and `err.retryable === false`
- [ ] In `llm_client.mjs`, the error log must include `{ provider: 'groq', error_type: 'json_validate_failed', status: 400 }` before proceeding to the next provider
- [ ] A unit test in `scripts/tests/llm_client.test.mjs` must verify that after a mocked Groq `json_validate_failed` error, the Anthropic provider is invoked as fallback
- [ ] When both Groq and Anthropic fail, the final error message must explicitly include both providers' errors (e.g., `All providers failed: groq: ..., anthropic: ...`)
- [ ] In `scripts/tests/groq_client.test.mjs`, a mocked 400 response with `json_validate_failed` must produce an error object with `err.code === 'json_validate_failed'` and `err.retryable === false`