VS Code extension: group session history by project folder (Desktop parity) and allow cross-project session opening

Feature request: session history grouping by project (Desktop parity) and cross-project session opening in the VS Code extension

The gap

Claude Desktop groups the session list by project folder (it keeps per-session metadata including the cwd, and renders one group per folder). The VS Code extension (observed on 2.1.226, still current behavior) does neither:

1. The history panel lists only the open workspace folder's sessions (from ~/.claude/projects/<sanitized-cwd>/) as one flat, mtime-sorted list. Local, worktree, and cloud sessions are merged into that single list with no grouping and no way to see sessions from other projects.
2. There is no way to open a session that belongs to another project folder. The session store is strictly per-folder, so a conversation started in repo A cannot be opened (even read-only) while a window has repo B open. The only workaround is opening a second VS Code window on the other folder.

For anyone working across several repos or git worktrees at once (worktree-based agent workflows make this the norm, not the exception), both limits bite daily: the flat list gets long and unscannable, and resuming "that session from the other repo" means juggling windows.

Asks

1. Grouping in the history panel: group sessions the way Desktop does (by project folder / cwd), with an "all projects" scope toggle so the panel can show either the current folder's sessions or everything, grouped. User-defined groups (as requested in #82641) would compose nicely with this, but plain folder grouping alone would close most of the gap.
2. Cross-project session opening: allow opening a session from another project folder in the current window — ideally fully interactive, but even a read-only transcript view would help.

Related issues

• #82641 (user-defined groups in the left panel)
• #74139 (agent view grouping by repo)
• #74129 (nested sidebar folders)

This request is the Desktop-parity variant of those: grouping keyed on the project folder the sessions already record, plus an escape hatch from the strict per-folder store.