Phase 1: tabbed workspaces

Each tab is an independent tile tree; PTYs in non-active tabs keep
running (render-all-panes with visibility:hidden on inactive layers
so xterm.js's fit() still sees valid dimensions and the existing
per-pane resize dedupe absorbs no-op SIGWINCHes).

workspace.json shape goes from a bare TreeNode to
`{ version: 2, workspaces: [{ id, name, tree }] }` with a legacy v1
auto-wrap migration (the old single tree becomes one tab named
"Default").

App.tsx wraps the old single-tree state in workspace-aware state
but keeps `tree` / `setTree` / `activeLeafId` / `setActiveLeafId` as
identity-stable derived wrappers (reading currentWorkspaceId from a
ref), so the bulk of App.tsx stays unchanged.

XtermPane's initial term.focus() now checks `visibility !== "hidden"`
on the container so a pane mounting inside a hidden tab on app boot
doesn't yank focus away from the active tab. The focus poller is
scoped to the active workspace layer for the same reason.

Shortcuts: Ctrl+T new tab, Ctrl+Shift+T close current (window.confirm
when there are live panes), Ctrl+PageDown/PageUp navigate, Ctrl+1..9
switch to tab N. README + help overlay auto-generated from
shortcuts.ts.

79/79 vitest pass (7 new envelope-migration cases). tsc -b clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -38,6 +38,15 @@ A Windows desktop app for running and arranging many WSL terminals at once. Buil
 | `Ctrl+Shift+W` | Close active pane |
 | `Ctrl+Shift+P` | Promote active pane out one level (turns a nested pane into a full row/column; self-inverse) |
 
+**Tabs**
+
+| Key | Action |
+|---|---|
+| `Ctrl+T` | New tab (blank workspace, one pane) |
+| `Ctrl+Shift+T` | Close current tab (confirms when the tab has live panes) |
+| `Ctrl+PageDown / Ctrl+PageUp` | Switch to next / previous tab |
+| `Ctrl+1 … Ctrl+9` | Switch to tab 1 … 9 |
+
 **Navigation**
 
 | Key | Action |
@@ -79,6 +88,7 @@ A Windows desktop app for running and arranging many WSL terminals at once. Buil
 - **Clickable links** — http and https URLs in terminal output get underlined and open in your default browser on click.
 - **Drag pane headers to swap** — Grab a pane's title bar and drag it onto another pane to swap their tree positions. Useful for reorganizing without keyboard.
 - **Workspace persistence** — Layout, labels, distro choices, and SSH hosts auto-save to %APPDATA%/com.megaproxy.tiletopia (debounced 500ms). Closed panes don't come back — only the structure is restored, shells spawn fresh on next launch.
+- **Tabs (workspaces)** — Each tab is an independent tile layout — useful for keeping one tab per project. PTYs in non-active tabs keep running (a Claude session in tab A keeps going while you work in tab B). New tab starts with one default-shell pane; close confirms when the tab has live panes. Tabs auto-save to the same workspace.json.
 - **MCP server (let Claude drive the workspace)** — Titlebar 🤖 opens the MCP control panel. Start the server, then for Claude Desktop click 'Download .mcpb' and drag the file into Settings → Extensions — zero-config because the bundle reads your bearer token from %APPDATA% at launch (no copy-paste, survives token rotation). For Claude Code (terminal CLI) use the fallback snippet in the panel: it wires npx mcp-remote as a stdio shim because Claude Code's HTTP-MCP client ignores static bearer auth and tries OAuth instead. URL + token persist across restarts; Regenerate the token in the panel if it leaks. Default-deny per pane: toggle 🤖 on each pane's toolbar to expose it to MCP.
 
 <!-- SHORTCUTS:END -->