Enforce black formatting and mypy checks in Copilot agentic sessions

.github/copilot-instructions.md

@@ -33,6 +33,7 @@ poetry run pytest -x                 # Stop at first failure
 ```bash
 poetry run black .                   # Format code
 poetry run black --check .           # Check formatting
+poetry run mypy                      # Type checking
 ```
 
 ### Building
@@ -83,3 +84,13 @@ poetry build
 - Update documentation if changing user-facing behavior
 - Ensure all tests pass locally before submitting
 - Run linters and formatters before committing
+
+## Validation Before Finishing
+
+Before completing any task, **always** run the following checks and fix any issues found:
+
+1. **Format with black** — run `poetry run black .` to auto-format, then verify with `poetry run black --check .`
+2. **Type-check with mypy** — run `poetry run mypy` and resolve all reported errors
+3. **Run tests** — run `poetry run pytest` (excluding network tests) to confirm nothing is broken
+
+Do not consider a task done until all three checks pass with no errors.

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

@@ -0,0 +1,34 @@
+name: "Copilot Setup Steps"
+
+on:
+  workflow_dispatch:
+  push:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+  pull_request:
+    paths:
+      - .github/workflows/copilot-setup-steps.yml
+
+jobs:
+  # The job MUST be called `copilot-setup-steps` or it will not be picked up by Copilot.
+  copilot-setup-steps:
+    runs-on: ubuntu-latest
+
+    permissions:
+      contents: read
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v6
+
+      - name: Install Poetry
+        run: pipx install poetry
+
+      - name: Set up Python
+        uses: actions/setup-python@v6
+        with:
+          python-version: "3.13"
+          cache: poetry
+
+      - name: Install dependencies
+        run: poetry install