fix(core): remove orphaned FunctionExecutionResultMessage after mid-list token truncation

[zerafachris (zerafachris)]

Summary

TokenLimitedChatCompletionContext.get_messages() drops messages from the middle of the list to stay within the token budget. When a middle-list AssistantMessage that carries FunctionCall items is removed, its paired FunctionExecutionResultMessage becomes orphaned and will cause an API error.

Root cause

The previous clean-up guard was:

if messages and isinstance(messages[0], FunctionExecutionResultMessage):
    messages = messages[1:]

This only catches the degenerate case where an orphaned result ends up at position 0. Any orphaned result elsewhere in the list passed through silently.

Fix

After the truncation loop, collect the call_ids of every FunctionCall that still exists in a surviving AssistantMessage, then filter out any FunctionExecutionResultMessage whose results reference a call_id that is no longer present (or that has no results at all).

active_call_ids: set[str] = set()
for msg in messages:
    if isinstance(msg, AssistantMessage) and isinstance(msg.content, list):
        for item in msg.content:
            if isinstance(item, FunctionCall):
                active_call_ids.add(item.id)
messages = [
    m
    for m in messages
    if not isinstance(m, FunctionExecutionResultMessage)
    or (m.content and all(r.call_id in active_call_ids for r in m.content))
]

Tests

Added a regression test (test_token_limited_mid_list_orphaned_function_result_is_removed) that:

• Builds a 7-message list with an AssistantMessage(content=[FunctionCall(id="call_1", ...)]) at index 3 and a paired FunctionExecutionResultMessage at index 4.
• Sets token_limit=6 so the truncation loop removes the AssistantMessage, orphaning the result.
• Asserts no FunctionExecutionResultMessage survives in the returned list.

All 10 existing tests in test_model_context.py continue to pass.

Closes #7955.

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Prepared with AI assistance (Claude Code, Anthropic), reviewed for correctness before submission.

[zerafachris (zerafachris)]

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