Improve request log tree performance

[sibidharan]

Problem

The slowdown were seen when chat gets big and big and big, traced back to the request log view inside the Copilot Chat extension. Every time a new chat request or tool call arrived, the old code rebuilt the entire tree of prompts and children from scratch—reflattening the full history and firing a full refresh event. In long chat sessions that tree gets big, so each update became progressively heavier and the UI stuttered.

I fixed it by making ChatRequestProvider incremental and introduced ThrottledMarkdownStream:

It now tracks how many log entries have already been processed, keeps the existing prompt nodes in a cache, and only appends new children. If the log ever shrinks (e.g., on reload) it resets cleanly, but otherwise it avoids rebuilding everything.
Refresh events are fired only for the nodes that genuinely changed; a root-level refresh happens once when structure changes, instead of on every update. Once that change is in, the request log will stop rebuilding itself over and over, so the chat UI stayed responsive even during long-running sessions.

While fixing the request log tree made the sidebar responsive, the chat panel still stuttered because every streamed token triggered a full markdown re-render. I now throttle those markdown events so the renderer receives batched chunks instead of repainting the entire transcript on every token.

Fix Summary

• reworked ChatRequestProvider so it caches prompt/root nodes, appends new log entries incrementally, and only refreshes affected tree items
• reset cached state automatically if the request log shrinks (e.g., on reload) to avoid stale UI
• no other files or dependencies were touched; the change lives entirely in src/extension/log/vscode-node/requestLogTree.ts and src/extension/prompt/node/defaultIntentRequestHandler.ts introduced ThrottledMarkdownStream so the chat renderer receives batched markdown chunks instead of a flood of markdown() calls.

Testing

• npm run compile
• npm run test:unit
• Manual: built a VSIX, installed it on the previously slow machine, and confirmed the request log view stays responsive during long polling sessions

[Copilot]

Pull Request Overview

This PR refactors the ChatRequestProvider class to improve performance by introducing incremental tree updates instead of rebuilding the entire tree on every request log change. The key optimization is caching prompt/root nodes and only refreshing affected tree items when new entries are added.

Key Changes:

• Introduced state caching (rootItems, seenChatRequests, processedCount, currentPrompt) to track processed entries
• Replaced full tree rebuild with incremental appendNewEntries() method that only processes new log entries
• Added automatic cache reset when request log shrinks to prevent stale UI state

[sibidharan]

@microsoft-github-policy-service agree

[Copilot]

Pull Request Overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 4 comments.