docs(workbench): rewrite welcome.md to match #161 reality (one click, not auto-open)

.devcontainer/welcome.md

@@ -1,35 +1,44 @@
 # 👋 locus workbench — welcome
 
-You've just clicked the **Launch workbench** button. While this VS Code
-window finishes booting, a **separate browser tab** is opening with the
-workbench UI itself.
+You've just clicked **Launch workbench**. The three workbench tiers
+(FastAPI runner + Node BFF + Vite web) are starting in the
+`workbench` terminal panel right now.
 
-## Where's the workbench?
+## How to open the workbench UI
 
-Look for a new tab in your browser at:
+When the `workbench` terminal banner says `🚀 locus workbench is ready`,
+**one click gets you to the playground**. Use whichever you prefer:
 
-> `https://<this-codespace>-5173.app.github.dev`
+1. **⌘-click the URL** in the workbench terminal panel — opens the
+   workbench in a new browser tab.
+2. **Click the `Workbench` row** in the **PORTS** panel (bottom of
+   VS Code) → **Preview in Editor** — opens the workbench as a
+   Simple Browser tab right inside VS Code.
+3. **Cmd-Shift-P** → "Simple Browser: Show" → paste the URL — same
+   thing, manually.
 
-The actual URL is printed in the terminal panel below (look for the
-🚀 banner). **⌘-click** that URL to open it.
+We **wanted** the Simple Browser tab to auto-open with no clicks, and
+the devcontainer does try (via `portsAttributes.5173.onAutoForward:
+"openPreview"` and a `code --open-url` call from
+`workbench-attach.sh`), but Codespaces VS Code Web doesn't reliably
+honor either mechanism from a shell context. So one manual click is
+the documented path.
 
-If your browser blocks the auto-popup, just click the URL from the
-terminal. Same destination.
+## Two-click run flow once the workbench is open
 
-## Two-click flow
-
-1. Open the workbench tab (above).
-2. **Provider settings** → paste an OpenAI or Anthropic API key →
+1. **Provider settings** → paste an OpenAI or Anthropic API key →
    pick a tutorial in the sidebar → **Run**.
 
 OCI options in **Provider settings** won't work here — they need a
-local `~/.oci/config` that doesn't exist in this Codespace. Use OpenAI
-or Anthropic for the in-browser path. (For OCI, clone the repo and run
-the workbench locally; see [`docs/workbench.md`](../docs/workbench.md).)
+local `~/.oci/config` that doesn't exist in this Codespace. Use
+OpenAI or Anthropic for the in-browser path. (For OCI, clone the
+repo and run the workbench locally; see
+[`docs/workbench.md`](../docs/workbench.md).)
 
 ## What's running
 
-Three tiers are auto-started by `postStart.sh`:
+Three tiers auto-started by `.devcontainer/workbench-attach.sh` in
+the `workbench` terminal panel:
 
 | Tier | Port | Process |
 |---|---|---|
@@ -38,18 +47,21 @@ Three tiers are auto-started by `postStart.sh`:
 | Vite dev server (web UI) | 5173 | `vite` in `workbench/web/` |
 
 Logs at `/tmp/wb-backend.log`, `/tmp/wb-bff.log`, `/tmp/wb-web.log` —
-the banner terminal panel tails all three.
+the `workbench` terminal panel tails all three.
 
 ## Restarting tiers (if they die)
 
 ```bash
-# Manually re-fire the lifecycle scripts:
-bash .devcontainer/postStart.sh
+bash .devcontainer/workbench-attach.sh
 ```
 
+The script is idempotent — any tier already listening on its port
+is left alone; only crashed tiers get relaunched.
+
 ## Further reading
 
-- [`docs/workbench.md`](../docs/workbench.md) — the public workbench page
+- [`docs/workbench.md`](../docs/workbench.md) — the public workbench
+  page
 - [`docs/index.md`](../docs/index.md) — locus SDK landing page
 - [`workbench/README.md`](../workbench/README.md) — three-tier
   architecture explained