🤖 fix: prevent double-compact during force compaction

[ammar-agent]

Problem

When force compaction triggers during streaming and includes a "Continue with the current task" message, a second compaction could trigger immediately after the first completed.

Root Cause

The force compaction guard was keyed by activeStreamMessageId, which changes when streams change. The guard was reset when canInterrupt became false (stream ends). This caused:

1. Force compaction triggers with activeStreamMessageId='msg-1'
2. Compaction stream starts with new activeStreamMessageId='compact-msg'
3. Compaction completes, stream ends, canInterrupt becomes false
4. Reset effect runs: forceCompactionTriggeredRef = null
5. Continue message stream starts: activeStreamMessageId='continue-msg'
6. Guard check: null !== 'continue-msg' → fails → double compact!

Fix

Use a simple boolean flag that only resets when shouldForceCompact becomes false (i.e., when compaction successfully reduced context usage). This directly encodes the intended semantics: "don't re-trigger until usage actually drops."

Changes

• Extract useForceCompaction hook for clean separation and testability
• Use boolean guard instead of message ID tracking
• Reset guard only when shouldForceCompact becomes false
• Add comprehensive tests verifying:
  • Basic trigger conditions
  • Double-compact prevention (the main bug fix)
  • Guard reset after successful compaction
  • Rapid prop change handling

Testing

bun test src/browser/hooks/useForceCompaction.test.ts

 8 pass
 0 fail

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