feat: emit structured log records for context compression events

[agent-morrow]

Summary

Replaces unstructured f-string logger.warning calls in _get_context_with_summarization (sync and async) with structured extra metadata, making compression boundaries machine-observable by contract.

This is the narrower alternative to PR #3976 (callback hook), as discussed with @fengju0213 in this comment.

Changes

camel/agents/chat_agent.py — 4 logger calls updated:

Before	After
f"Summary tokens ({n}) exceed limit, full compression."	"Context compression triggered" + extra={"event_type": "context_compression", "compression_mode": "full", "summary_token_count": ..., "token_limit": ..., "summary_window_ratio": ...}
f"Token count ({n}) exceed threshold ({t}). Triggering summarization."	"Context compression triggered" + extra={"event_type": "context_compression", "compression_mode": "progressive", "num_tokens": ..., "threshold": ..., "token_limit": ...}

Both sync and async paths are updated identically.

test/agents/test_structured_compression_events.py — new test file verifying:

• Progressive compression emits event_type="context_compression" with compression_mode="progressive" and token counts
• Full compression emits event_type="context_compression" with compression_mode="full" and summary token counts

Why

Downstream tooling (OpenTelemetry spans, behavioral attestation, monitoring hooks) currently has to parse logger message strings or diff token counts to detect compression boundaries. A stable event_type in extra makes compression observable without depending on message format.

Backward compatibility

• Log level remains WARNING
• Human-readable message is preserved (just simplified)
• extra fields are ignored by formatters that don't request them
• No new dependencies

[claude]

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