perf(web): reuse sessions reference to stop sidebar re-render on streaming deltas - #1113
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Problem
During long streaming replies the web UI's session sidebar re-renders on every single token, contributing to main-thread jank. Profiling attributed ~2.2s/frame to the sidebar computeds (
sessionsForView/workspaceGroups/mergedWorkspaces).Root cause: the event reducer's
cloneState()didsessions: [...s.sessions]on every event, so thesessionsarray reference changed on every high-frequency event (e.g.assistantDelta,toolOutput,taskProgress) even though those events never touch sessions. Since the sidebar computeds depend onrawState.sessions, the changed reference dirtied all of them each token.What changed
cloneState()now reuses the existingsessionsreference for events that do not change sessions. Every session-mutating case in the reducer already builds its own array via[...]/.map/.filter, so sharing the reference is safe — events that genuinely change sessions still produce a new array.This is a small, focused subset of the larger streaming-render work, split out so it can be reviewed and merged on its own. It does not change any rendering or event-routing behavior; it only avoids invalidating the sidebar on unrelated events.
Checklist
reduceAppEvent sessions reference stability: reuses the array when sessions are untouched, produces a new array when sessions change).@moonshot-ai/kimi-code: patch).gen-docsN/A).