Extends _sanitize_messages_for_api() with a two-pass approach:
1. Collect all tool_call_ids declared in assistant messages (handles
both OpenAI 'id' and Anthropic 'call_id' field names).
2. Drop any tool-role messages whose tool_call_id was not declared
by a preceding assistant message.
Strictly-conformant providers (Mercury-2/Inception, newer OpenAI
models) reject histories with orphaned tool results with a 400 error:
'Message has tool role, but there was no previous assistant message
with a tool call.' This can happen when histories are edited, when
switching between providers, or when partial messages are stored.
Adds 13 regression tests covering: valid roundtrip preservation,
multiple tool calls, partial orphan filtering, Anthropic call_id,
edge cases (None tool_calls, missing tool_call_id, non-dict entries).
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