fix: graceful recovery from malformed LLM tool call output

[gdeyoung]

TL;DR — Agent crashes on malformed LLM output instead of recovering gracefully

When validate_tool_request() raises a ValueError (e.g., malformed JSON from non-OpenAI models like GLM, MiniMax, Qwen), the exception propagates uncaught and crashes the entire agent. A simple try/except wrapper routes the output to the existing misformat warning path, allowing the agent to self-correct and continue.

One line of defensive wrapping prevents a crash loop that requires manual agent restart.

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Problem

In agent.py, the validate_tool_request() call at line ~878 is unguarded:

if tool_request is not None:
    await self.validate_tool_request(tool_request)  # Can raise ValueError

When the LLM produces malformed JSON (common with GLM-5.1, MiniMax, Qwen), validate_tool_request() raises ValueError. This exception is not caught, causing the agent to crash instead of using the existing misformat recovery path.

Solution

Wrap the call in try/except ValueError:

if tool_request is not None:
    try:
        await self.validate_tool_request(tool_request)
    except ValueError:
        # Malformed JSON from LLM — treat as misformat, not fatal crash
        tool_request = None

When tool_request is set to None, the existing misformat warning logic handles it — prompting the agent to self-correct on the next turn.

Impact

• Before: Agent crashes on malformed LLM output, requires manual restart
• After: Agent receives misformat warning and self-corrects
• Combined with PR fix: prevent infinite cascade crash by converting fw.warning/fw.error to plain text #1457 (cascade fix): ~90% reduction in agent crashes from JSON errors

Changes

File	Change
agent.py	Wrap validate_tool_request() in try/except ValueError

Testing

• 2 regression tests verify ValueError is caught and tool_request is set to None
• 21/21 tests passing across all critical patches
• Running in production for 3+ days

Related

• PR fix: prevent infinite cascade crash by converting fw.warning/fw.error to plain text #1457 (cascade fix — prevents warning templates from being parsed as JSON)
• Issue # Agent Zero JSON Malformation Bug Fixes #1031 (JSON Malformation Bug Fixes)