🤖 perf: debounce stream delta events to reduce markdown streaming lag

[ammar-agent]

Problem

High-frequency streaming events (stream-delta, tool-call-delta, reasoning-delta) were triggering immediate state bumps and React re-renders on every token. This caused noticeable lag during fast streaming of markdown content.

Solution

Add a debounce mechanism (~16ms / 60fps cap) for delta event UI notifications:

• Data integrity preserved: The aggregator is updated immediately on each event - no data is ever lost
• UI updates batched: states.bump() calls are debounced so React only re-renders at most ~60 times per second
• Stream boundaries handled: stream-end and stream-abort flush any pending debounced bumps to ensure final state is visible immediately
• Cleanup on removal: Debounce timers are cleared when workspaces are removed to prevent stale callbacks
• No change for other events: Tool call start/end, reasoning end, etc. still bump immediately since they're lower frequency

Risk Assessment

Risk	Assessment
Data loss	None - aggregator updated immediately
Timer leak	Mitigated - cleaned up on workspace removal
Final state hidden	None - flushed on stream-end/abort
Perceived delay	None - 16ms is sub-perceptual

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