[Raing5Days]

Summary

Optimize explore-group and tool collection segment rendering during active streaming ingress (FlowGroupRenderer and buildFlowGroupRenderSegments), preserving closed segment identities and height estimates on append.

• Introduce an optional previous segment slice in buildFlowGroupRenderSegments to reuse the longest unchanged prefix of closed segments verbatim, eliminating full $O(N)$ re-slicing and height re-estimation across streaming chunk arrivals.
• In-place reconcile the trailing active segment object so its identity survives across token/stdout chunk flushes, updating only its member array and height estimate.
• Connect FlowGroupRenderer's renderSegments memo through a ref tracking prevSegmentsRef, preventing downstream segment maps and virtualized DOM wrappers from needlessly re-rendering for settled historical tool runs.
• Add regression coverage in flowGroupRenderSegments.test.ts verifying that closed segment references are preserved across item appends.

Type and Areas

Performance / refactoring. Web UI FlowChat collection grouping & rendering (src/web-ui/src/flow_chat/components/modern/flowGroupRenderSegments.ts and src/web-ui/src/flow_chat/components/modern/FlowGroupRenderer.tsx). No wire protocol, persisted schema, or user-facing copy changes.

Motivation / Impact

When an exploration group runs numerous tools (e.g. 30–50+ commands or file reads) while streaming live stdout/tokens at the tail:

• Previously, every token chunk triggered a full-collection scan from index 0, re-running estimateFlowGroupItemsHeight across dozens of completed tools and allocating new segment objects.
• This triggered cascading re-renders in downstream segment mappers even though ~80% of earlier tool rows had already settled.

With incremental prefix reuse:

• Streaming chunk ingress latency across 48 tools and 20 chunks dropped significantly:
  • P95 Latency: ~0.28 ms (budget ≤ 1.0 ms).
  • Max Single Frame Latency: ~2.64 ms (budget ≤ 3.5 ms).
  • Average Streaming Chunk Latency: ~0.30 ms (down from >1.2 ms).
  • Segment Reference Reuse Ratio: 95% across active streaming flushes (budget ≥ 70%).

Verification

• node scripts/run-vitest.mjs run --maxWorkers=50% "src/flow_chat/components/modern/flowGroupRenderSegments.test.ts" — 2 passed (100%).
• node scripts/run-vitest.mjs run --maxWorkers=50% "src/flow_chat/components/modern/FlowGroupLifecycle.test.tsx" --environment jsdom — 18 passed (100%).
• node .perf-harness/perf-agent-runner.mjs --case OpCase-Explore-02 — passed: true, reuseRatio: 0.95, p95: 0.28ms.
• git diff --check — clean, no whitespace or formatting defects.

Checklist

• Focused changes; no scratch files, secrets, or unrelated generated artifacts.
• Relevant verification and test results are recorded above.
• Preserves thinking continuation, capsule grouping boundaries, and existing height estimation contracts.