fix(compaction): filter media parts to prevent API error

[howardpen9]

Summary

When context usage is high (~85%+) and auto-compaction triggers, media content parts (image_url, audio_url, video_url) are included in the compaction request sent to the Kimi API. The API rejects these with:

Error code: 400 - {'error': {'message': "the message at position 1 with role 'user' contains an invalid part type: video_url", 'type': 'invalid_request_error'}}

This PR filters out ImageURLPart, AudioURLPart, and VideoURLPart from the compaction input in SimpleCompaction.prepare(), while preserving media parts in recent (non-compacted) messages.

Root cause: compaction.py:177 only filtered ThinkPart but let all media parts through:

# Before
part for part in msg.content if not isinstance(part, ThinkPart)

# After
part for part in msg.content if not isinstance(part, (ThinkPart, ImageURLPart, AudioURLPart, VideoURLPart))

Changes

• src/kimi_cli/soul/compaction.py — Filter media parts from compaction input (2-line change)
• tests/core/test_simple_compaction.py — Add 2 test cases:
  • test_prepare_filters_out_media_parts — Verifies all 3 media types are stripped
  • test_prepare_preserves_media_parts_in_recent_messages — Verifies preserved messages keep media intact

Reproduction

1. Upload a video file in a conversation
2. Continue chatting until context usage reaches ~85%
3. Auto-compaction triggers → 400 error

Related

• Fixes the message at position 1 with role 'user' contains an invalid part type: video_url #1395
• Fixes error response with video attachment #1390
• Related to fix(compaction): filter media parts to prevent API error at high context usage #802 (same fix direction, rebased on latest main with custom_instruction support)

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 2 additional findings.