[FEATURE] add chat history panel to VS Code extension

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

No way to browse or resume past chat sessions from the VS Code extension.
As a Claude Code user in VS Code, I have no way to view, search, or resume my previous chat sessions from within the editor. Session history is only accessible via the CLI (claude --resume) or by manually navigating to .jsonl files buried in ~/.claude/projects/.

This means:

I lose context from previous conversations unless I remember to resume from the terminal
I can't quickly reference what I discussed or decided in a prior session
Switching between sessions requires leaving the IDE or using file open dialogs with long paths
The experience is significantly worse than competing tools (e.g., GitHub Copilot) which provide a visible session history list directly in the sidebar
Expected behavior: A chat history panel in the VS Code extension sidebar that lists past sessions (with timestamps and previews), allowing users to browse, search, and resume any previous conversation with one click.

Proposed Solution

Session History Panel — Add a new view in the VS Code sidebar (under the Claude Code extension) that lists all past sessions for the current workspace, sorted by most recent. Each entry shows:

Timestamp (e.g., "Sep 11, 2:42 PM")
First message or a short summary as a preview
Session duration or message count
One-click resume — Clicking a session opens it in the Claude Code chat panel with full conversation history loaded, ready to continue.

Search & filter — A search bar at the top of the panel to filter sessions by keyword, date range, or topic.

Session management — Right-click context menu with options to:

Rename a session (add a custom label)
Delete a session
Export as Markdown
Cross-workspace access (optional/stretch) — A global history view that shows sessions across all projects, grouped by workspace.

Implementation notes:

Session data already exists as .jsonl files in ~/.claude/projects/ — this is primarily a UI/UX feature, not a backend change
Could leverage VS Code's TreeView API for the sidebar panel
Session preview text could be extracted from the first user message in each .jsonl file

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

Other

Use Case Example

1. Resuming yesterday's debugging session

I spent 30 minutes yesterday working with Claude to debug a race condition in our message queue. Today I want to continue where I left off, but I can't remember the session ID. With Copilot, I'd just click on yesterday's chat in the sidebar. With Claude Code, I have to open a terminal, run claude --history, or manually dig through .jsonl files in a hidden directory.

1. Referencing a past architectural decision

Last week Claude and I discussed whether to use Redis or Kafka for our event pipeline. We made a decision with good reasoning. Now a teammate is questioning it and I want to pull up that conversation. I have no way to find it without searching raw JSON files.

1. Switching between tasks mid-day

I'm working on feature A in the morning, switch to a bug fix after standup, then want to return to feature A after lunch. Each context switch means losing my Claude conversation unless I proactively copy session IDs or use the CLI. A history panel would let me jump between sessions the same way I jump between editor tabs.

1. Onboarding a teammate

A new team member joins and I want to share the Claude session where I explored how our auth middleware works. Currently there's no easy way to find or share that session — I'd have to locate the .jsonl file and send them raw JSON.

Additional Context

_No response_