Show compaction status in CLI code agent UI

[youknowriad]

Related issues

• Related to context window management in studio code

How AI was used in this PR

AI was used to investigate how the Claude Agent SDK handles context compaction, identify the gap in the UI layer, and write the fix.

Proposed Changes

• Handle system message type in AiChatUI.handleMessage() — previously only assistant, user, and result were handled
• Show a loader ("Compacting conversation history...") when the SDK begins auto-compaction
• Show an info message ("Conversation history compacted") when compaction completes

The Claude Agent SDK automatically compacts conversation history when the context window fills up, emitting SDKStatusMessage (status: compacting) and SDKCompactBoundaryMessage (subtype: compact_boundary). These system messages were silently dropped, leaving users with an unexplained pause during long conversations.

Testing Instructions

• Run studio code and have a long conversation that fills the context window
• Verify that a "Compacting conversation history..." loader appears during compaction
• Verify that a "Conversation history compacted" info message appears after

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[wpmobilebot]

📊 Performance Test Results

Comparing 8e39e71 vs trunk

app-size

Metric	trunk	8e39e71	Diff	Change
App Size (Mac)	1282.03 MB	1282.03 MB	+0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	8e39e71	Diff	Change
load	1561 ms	1817 ms	+256 ms	🔴 16.4%

site-startup

Metric	trunk	8e39e71	Diff	Change
siteCreation	8101 ms	9131 ms	+1030 ms	🔴 12.7%
siteStartup	4325 ms	4950 ms	+625 ms	🔴 14.5%

---

Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)

[epeicher]

Thanks @youknowriad! I have tested it, and I can see the new statuses. Changes also LGTM!

Compacting	Compacted