🤖 perf: reduce memory pressure from streaming message aggregation #1151
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Prevent unnecessary re-renders by only updating the Set when contents actually change. Previously, every subscription event created a new Set reference, invalidating React Compiler's auto-memoization for the entire message list. Also added React Compiler guidance to AGENTS.md.
Replace O(n²) string concatenation with array accumulation and join() to avoid creating millions of V8 "cons strings" during streaming. Heap analysis showed 30M+ concatenated strings (582MB) from the repeated `lastMerged.text + part.text` pattern in getDisplayedMessages(). The new approach collects text fragments in arrays and joins once at the end, which V8 optimizes much better. --- _Generated with `mux` • Model: `claude-sonnet-4-20250514` • Thinking: `low`_
Two related improvements: 1. Compact parts when streaming ends - converts thousands of delta parts into merged strings immediately, reducing memory from O(deltas) to O(content_types). This prevents accumulation of 30M+ small objects observed in heap timeline (582MB of concatenated strings). 2. Extract `mergeAdjacentParts()` helper to deduplicate the merge logic between compactMessageParts() and getDisplayedMessages(). --- _Generated with `mux` • Model: `claude-sonnet-4-20250514` • Thinking: `low`_
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Summary
Performance optimizations to reduce memory pressure and GC pauses caused by inefficient string handling during streaming.
Problem
Heap analysis revealed:
+concatenation creating O(n²) intermediate stringsChanges
1. Stabilize
foregroundToolCallIdsSet referenceAvoid invalidating React Compiler memoization by checking content equality before creating new Set instances.
2. Use
array.join()for message part mergingReplace O(n²) string concatenation with array accumulation. V8 optimizes
join()much better than repeated+.3. Compact message parts on stream end
When streaming completes, merge thousands of delta parts into single strings immediately. This converts memory from O(deltas) small objects to O(content_types) merged objects, preventing accumulation.
4. Extract
mergeAdjacentParts()helperDeduplicate the merge logic between
compactMessageParts()andgetDisplayedMessages().Validation
make static-checkpassesmake typecheckpassesGenerated with
mux• Model:claude-sonnet-4-20250514• Thinking:low