VS Code Copilot Chat freezes when many Claude Code sessions exist in ~/.claude/projects/

Bug Description

VS Code Copilot Chat Extension (v0.37) becomes completely unresponsive (99.99% CPU) when a project has many Claude Code CLI session files (.jsonl) in ~/.claude/projects/<project-slug>/.

Environment

• VS Code: Insiders 1.109.0 (darwin-arm64)
• Copilot Chat Extension: v0.37.2026020404 (pre-release)
• Claude Code: v2.1.31
• OS: macOS Darwin 25.1.0 (arm64)

Root Cause

The Copilot Chat Extension includes a ClaudeCodeSessionService that calls _loadSessionsFromDisk() on startup. This function reads all .jsonl files from ~/.claude/projects/<project-slug>/ synchronously, parsing every line.

In our case:

• 241 session files totaling 287 MB in a single project directory
• The function consumed 99.99% of CPU for 5+ seconds, making the Extension Host completely unresponsive
• The Chat UI appeared functional but could not process any input

CPU Profile Evidence

38844 hits | _loadSessionsFromDisk | extension.js:1442:9616
    3 hits | (program)

Steps to Reproduce

1. Use Claude Code CLI extensively in a project (accumulate 200+ sessions / 250+ MB in ~/.claude/projects/)
2. Open the same project in VS Code with Copilot Chat Extension
3. Open the Copilot Chat panel and try to send a message
4. Chat appears to accept input but never responds

Workaround

Move old .jsonl session files from ~/.claude/projects/<project-slug>/ to an archive directory:

PROJ_DIR="$HOME/.claude/projects/<your-project-slug>"
mkdir -p "$PROJ_DIR/_archived_sessions"
mv "$PROJ_DIR"/*.jsonl "$PROJ_DIR/_archived_sessions/"

Suggested Fix

Consider one or more of:

1. Lazy loading: Only load session metadata on startup, parse full content on demand
2. Pagination: Limit the number of sessions loaded (e.g., most recent 20)
3. Async loading: Use non-blocking I/O to prevent Extension Host freeze
4. Session cleanup: Provide a built-in mechanism to archive/purge old sessions
5. Size limit: Skip files exceeding a certain size threshold