Export COPILOT_GITHUB_TOKEN in copilot-setup-steps for E2E tests

Set COPILOT_GITHUB_TOKEN in GITHUB_ENV during setup so all Copilot
Coding Agent sessions (and agentic workflows) can run E2E tests and
examples with the same token. Also document this in copilot-instructions.md.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: krukow

.github/copilot-instructions.md

@@ -70,6 +70,15 @@ bb test
 COPILOT_E2E_TESTS=true bb test
 ```
 
+**Copilot Coding Agent**: When running as a Copilot Coding Agent, `COPILOT_GITHUB_TOKEN` is set
+by `copilot-setup-steps.yml`. Use it to authenticate E2E tests and examples:
+
+```bash
+export COPILOT_GITHUB_TOKEN="${COPILOT_GITHUB_TOKEN:-$GITHUB_TOKEN}"
+COPILOT_E2E_TESTS=true bb test
+./run-all-examples.sh
+```
+
 ### Instrumented Testing
 
 All public API functions have `clojure.spec` fdefs defined in `instrument.clj`.

.github/workflows/copilot-setup-steps.yml

@@ -73,6 +73,12 @@ jobs:
           # /root/ paths, so bb finds them regardless of $HOME.
           # Ensure deps directories are readable by any user
           chmod -R a+rX ~/.m2/repository ~/.deps.clj 2>/dev/null || true
+      - name: Export Copilot token for SDK E2E tests
+        run: |
+          # Make the GitHub token available as COPILOT_GITHUB_TOKEN so the
+          # Copilot SDK E2E tests and examples can authenticate with the
+          # same token the Copilot Coding Agent uses.
+          echo "COPILOT_GITHUB_TOKEN=${COPILOT_GITHUB_TOKEN:-$GITHUB_TOKEN}" >> "$GITHUB_ENV"
       - name: Install gh-aw extension
         uses: github/gh-aw/actions/setup-cli@v0.48.1
         with: