[FEATURE] Add command to resume a specific session by ID in VS Code panel

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

Problem
The Claude Code VS Code extension only shows the last ~10 sessions in the session picker (clock icon). Older sessions are still saved on disk as .jsonl files in ~/.claude/projects/, but there's no way to access them from the chat panel.

The only way to resume older sessions is through the terminal CLI with claude --resume <UUID>, which works but doesn't open in the native VS Code chat panel.

Proposed Solution

Expose a VS Code command like:

claude-vscode.resumeSession
That accepts a session ID (UUID) as an argument and opens that conversation in the VS Code chat panel.

This would enable:

Third-party extensions to integrate with Claude Code (e.g., session manager extensions)
URI handler support — vscode://anthropic.claude-code/resume/<UUID> links that open conversations directly
Access to all sessions, not just the most recent ones shown in the picker
Additional Context
All session data is already on disk (~/.claude/projects/<project>/<UUID>.jsonl)
The CLI already supports claude --resume <UUID> — this just needs a VS Code panel equivalent
I built a session manager extension that lists all sessions in a sidebar, but it can only resume sessions in the terminal because no such command exists
The session picker UI should also be updated to show all sessions, not just the most recent ~10
Current Workarounds
Use claude --resume <UUID> in the integrated terminal (works but not in the native panel)
Manually type /resume in the panel and hope the session appears in the limited picker

Alternative Solutions

1. Show all sessions in the existing picker — Instead of limiting the clock icon session picker to ~10 sessions, show all sessions stored on disk with search/filter support
2. Accept session ID in /resume command — Allow /resume <UUID> to work directly in the chat panel input box (currently it only opens the limited picker and ignores the UUID)
3. URI handler — Register vscode://anthropic.claude-code/resume/<UUID> so clicking a link from anywhere opens that conversation in the VS Code panel

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

As a developer, I have 15+ Claude conversations saved on disk. I want to:

• Go back to a conversation from yesterday where Claude helped me set up my MCP servers
• Save a link/bookmark to an important conversation so I can continue it later
• Build workflow automations that resume specific sessions

Currently, after ~10 new conversations, older ones disappear from the picker and become inaccessible from the chat panel. The only way to reach them is through the terminal CLI (claude --resume <UUID>), which works but loses the native VS Code panel experience.

Additional Context

• VS Code extension version: 2.1.86
• All sessions are stored on disk at ~/.claude/projects/<project-hash>/<UUID>.jsonl and never deleted
• The CLI already fully supports resuming any session by UUID — this feature just needs to be exposed in the VS Code extension
• The existing extension already exposes commands like claude-vscode.editor.open, claude-vscode.newConversation — a similar claude-vscode.resumeSession command would fit naturally
• I built a third-party session manager extension as a workaround, but it can only open sessions in the terminal, not the native panel