Fix infinite loop in fix_message_list with multiple tool_calls

[juliosuas]

Summary

• Fixes an infinite loop in fix_message_list() (src/cai/util.py) that occurs when an assistant message has multiple tool_calls and the tool responses arrive out of order
• The validity check now walks backward past sibling tool messages to find the parent assistant, instead of only checking the immediately preceding message

Root Cause

The second pass of fix_message_list ensures tool messages follow their parent assistant message. The check at line 1250 only compared against processed_messages[i - 1], but when an assistant has two tool calls (call_1, call_2), the tool response at index 2 sees a sibling tool response at index 1 — not the assistant — and incorrectly moves it. This creates an infinite ping-pong between the two tool responses.

Fix

Walk backward from the current position past any sibling tool messages to locate the nearest assistant message, then check if it owns the current tool response. This correctly handles N tool responses following a single assistant message.

Reproduction

from cai.util import fix_message_list

messages = [
    {"role": "user", "content": "Validate alert"},
    {"role": "assistant", "tool_calls": [
        {"id": "call_1", "type": "function", "function": {"name": "verify_wiz", "arguments": "{}"}},
        {"id": "call_2", "type": "function", "function": {"name": "verify_github", "arguments": "{}"}}
    ]},
    {"role": "tool", "tool_call_id": "call_2", "content": "GitHub result"},
    {"role": "tool", "tool_call_id": "call_1", "content": "Wiz result"},
]

fix_message_list(messages)  # Previously hangs forever, now returns correctly

Fixes #410

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