context_compactor.maybe_compact built its summary text with
msg.get('content', '')[:2000], which raised
TypeError: 'NoneType' object is not subscriptable on assistant turns
whose content is None (turns that carried only native tool_calls).
Once a conversation crossed the 85% compaction threshold — reached
after only a few turns on small-context local models plus the large
agent prompt — every subsequent message failed ("send more than three
messages and it stops working").
Flatten message content to text first via a _content_as_text helper
(str passthrough, multimodal list blocks joined, None -> "") and
tolerate a missing role. Adds tests/test_context_compactor.py covering
the helper and a >=4-message conversation that forces compaction with
a None-content tool-call turn (fails before this change, passes after).
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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