fix(agent-loop): recover malformed tool arguments

[imMamdouhaboammar]

Problem

agent_runner_loop() parses model tool-call arguments before dispatch. Malformed JSON raised JSONDecodeError and terminated the task before GenericAgent could ask the model to correct the call.

A second edge case exists even when the JSON syntax is valid: null, arrays, strings, numbers, and booleans decode successfully but violate GenericAgent's tool contract, which expects an argument object. Those values later crash _compact_tool_args() or BaseHandler.dispatch() instead of entering the retry flow.

Review also identified a reliability edge: echoing the entire malformed argument payload into the retry prompt lets a very large invalid tool call inflate the next model request.

Fix

• parse each tool call individually
• require the decoded value to be a JSON object (dict)
• route malformed JSON and valid non-object JSON through the existing bad_json recovery path
• include the tool name plus a bounded 800-character preview of the raw arguments
• when truncation occurs, include the original total character count
• keep valid object tool calls unchanged

Verification

TDD and review-driven regression work was performed before rebuilding this clean branch:

1. Regression-only run 31165097818 failed with the exact JSONDecodeError at agent_loop.py:70 before dispatch
2. The initial malformed-JSON recovery fix passed run 31165170657
3. CodeRabbit identified the valid-but-non-object JSON case. Regression-only run 31165565545 failed for all five targeted values: null, [], string, number, and boolean, while malformed-JSON recovery still passed
4. The object-only validation passed run 31165676777: compile, malformed JSON coverage, all five non-object subcases, and git diff --check
5. Qodo identified the unbounded raw-arguments echo. RED run 31167984365 kept the existing recovery tests green and failed only because a ~20k malformed payload produced a 20,112-character retry prompt
6. GREEN run 31168074147 passed compile, all three regression methods, and git diff --check with a bounded preview that retains total length metadata
7. This contribution branch was rebuilt directly from current main as one clean commit using the exact production/test blobs from the last GREEN validation

Scope

• 1 core production file modified
• 1 focused regression-test file added
• 1 clean commit on top of current main
• no dependency or configuration changes