Persist Copilot CLI credentials across dev container rebuilds

.devcontainer/devcontainer.json

@@ -5,6 +5,9 @@
     "ghcr.io/devcontainers/features/github-cli:1": {},
     "ghcr.io/devcontainers/features/node:1": {}
   },
+  "mounts": [
+    "source=copilot-cli-credentials,target=/home/vscode/.config/github-copilot,type=volume"
+  ],
   "customizations": {
     "vscode": {
       "extensions": [
@@ -13,5 +16,5 @@
     }
   },
   "onCreateCommand": "pip install pytest && npm install -g @github/copilot",
-  "postStartCommand": "echo '✅ Python, pytest, GitHub CLI, and Copilot CLI are ready. Run: cd samples/book-app-project && python book_app.py help'"
+  "postStartCommand": "bash .devcontainer/startup.sh"
 }

.devcontainer/startup.sh

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+echo '✅ Python, pytest, GitHub CLI, and Copilot CLI are ready. Run: cd samples/book-app-project && python book_app.py help'
+if ls ~/.config/github-copilot/*.json &>/dev/null; then
+  echo '🔑 Copilot CLI credentials found — you are already signed in.'
+else
+  echo '🔑 No credentials found — open the Copilot CLI session (run: copilot) and then type /login to authenticate.'
+fi

00-quick-start/README.md

@@ -121,6 +121,45 @@ After trusting the folder, you can sign in with your GitHub account.
 
 **Tip**: The sign-in persists across sessions. You only need to do this once unless your token expires or you explicitly sign out.
 
+### Persisting Credentials in Dev Containers
+
+When you work inside a **dev container** (locally or via a Codespace), credentials can be lost when the container is rebuilt — because the container's file system starts fresh. Here is how each environment handles this:
+
+| Environment | What happens to credentials |
+|---|---|
+| **Local install** (no container) | Credentials persist in `~/.config/github-copilot/` on your machine |
+| **GitHub Codespace** | Credentials persist within the *same* Codespace; creating a *new* Codespace requires one-time re-authentication |
+| **Local dev container** | Credentials are stored in a named Docker volume (`copilot-cli-credentials`) that survives container rebuilds automatically |
+
+#### How credential persistence works in this repo's dev container
+
+The `.devcontainer/devcontainer.json` in this repo mounts a named Docker volume at the path where Copilot CLI stores its credentials:
+
+```json
+"mounts": [
+  "source=copilot-cli-credentials,target=/home/vscode/.config/github-copilot,type=volume"
+]
+```
+
+**What this means for you:**
+
+- **First time**: Open the dev container, start the Copilot CLI session (`copilot`), and then type `/login` inside the session to authenticate once.
+- **After a rebuild**: Your credentials are loaded automatically from the volume — no need to log in again.
+- **Start fresh**: To reset credentials, delete the named volume from Docker Desktop (Volumes tab) or run `docker volume rm copilot-cli-credentials` in your terminal, then re-authenticate.
+
+> 💡 **Status check at startup**: Each time the container starts, the terminal shows a 🔑 line telling you either that credentials were found (and you are already signed in) or that no credentials were found (and you need to run `/login`).
+
+#### Re-authenticating when needed
+
+If you see an authentication error, or if you created a new Codespace, simply sign in again:
+
+```bash
+copilot
+> /login
+```
+
+Follow the same device-flow steps described above.
+
 ---
 
 ## Verify It Works