fix: harden JSON misformat handling to prevent infinite loops and crashes

[PaoloC68]

Summary

Fixes the infinite misformat loop that affects 5+ reported issues. The agent's process_tools had a gap where parseable-but-invalid JSON (e.g., dict without tool_name) would raise RepairableException, get swallowed by _50_handle_repairable_exception, and loop forever without hitting the circuit breaker.

Changes

agent.py — Circuit breaker covers both failure modes

• Case A (already worked): json_parse_dirty returns None → misformat counter increments
• Case B (NEW fix): validate_tool_request raises RepairableException → counter now increments via try/except wrapper in process_tools
• Moved counter reset to right after validation passes (format correctness, not tool existence)
• At 5 consecutive failures, raises HandledException to stop the monologue gracefully

helpers/extract_tools.py — Brace-depth JSON extraction (unchanged from v1)

• Replaces buggy rfind('}') with character-by-character brace-depth tracking
• Handles nested braces, string-escaped braces, escaped quotes

prompts/fw.msg_misformat.md — Improved misformat prompt

• Shows attempt countdown (attempt X/5) so model knows it's running out of retries
• Removed contradictory code-fence example (told model "no fences" but showed one)
• Compressed to single-line JSON example

tests/test_misformat_circuit_breaker.py — 73 tests

Suite	Tests	Coverage
TestExtractJsonObjectString	22	Brace-depth tracking, rfind regression, escapes, edge cases
TestJsonParseDirty	12	Parse, dirty JSON, non-string input, arrays
TestValidateToolRequest	14	None guard, RepairableException (not ValueError), all invalid shapes
TestCircuitBreakerCaseA	4	None parse → counter accumulates → breaker at 5
TestCircuitBreakerCaseB	6	Invalid dict → counter accumulates → breaker at 5
TestCircuitBreakerMixed	5	Mixed A+B accumulate, reset, boundary conditions
TestEndToEndPipeline	10	Realistic messages, rfind bug scenario, session reproduction

Root cause analysis

The _50_handle_repairable_exception extension (line 23) sets data["exception"] = None, swallowing the RepairableException and continuing the monologue loop. Meanwhile, the _error_retry plugin explicitly skips RepairableException (line 21). So for Case B, no circuit breaker ever fired — the counter was only in the else branch (Case A).

Workaround for models with frequent misformats

Thinking/reasoning models (e.g., MiniMax M2.5) produce reasoning traces with incidental { characters that confuse the JSON parser. To mitigate, add this to Chat model additional parameters in Agent Zero settings:

response_format={"type": "json_object"}

This forces JSON output at the token generation level. Confirmed supported on OpenRouter for: MiniMax M2.5, DeepSeek V3, Gemini 2.5 Flash, Grok 4.1 Fast, GPT-OSS-120B.

Testing

pytest tests/test_misformat_circuit_breaker.py -v
# 73 passed in 0.26s