Port pydantic-ai's A2A integration tests + wire CI to run them

.github/workflows/main.yml

@@ -2,11 +2,32 @@ name: CI
 
 on:
   push:
-    branches: ["main"]
+    branches: ["main", "release/**"]
   pull_request:
-    branches: ["main"]
+    branches: ["main", "release/**"]
 
 jobs:
+  # `scripts/check` (ruff, pyright, check-sdist, uv lock) runs once on a fixed
+  # interpreter. pyright must see `pydantic-ai-slim` to resolve the bridge's
+  # `pydantic_ai` imports, and that extra is marker-gated to Python 3.10+, so
+  # this job pins 3.12 — running it across the test matrix would fail on 3.9.
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v4
+        with:
+          python-version: "3.12"
+          enable-cache: true
+
+      - name: Install dependencies
+        run: uv sync --frozen --extra pydantic-ai
+
+      - name: Run linters
+        run: scripts/check
+
   test:
     runs-on: ubuntu-latest
     strategy:
@@ -21,19 +42,20 @@ jobs:
           python-version: ${{ matrix.python-version }}
           enable-cache: true
 
+      # `[pydantic-ai]` is the optional extra that pulls `pydantic-ai-slim` for
+      # the `fasta2a.pydantic_ai` bridge tests. Marker-gated to Python 3.10+, so
+      # on 3.9 it resolves to nothing and the bridge tests skip themselves via
+      # `pytest.importorskip('pydantic_ai')` in `tests/test_pydantic_ai.py`.
       - name: Install dependencies
-        run: uv sync --frozen
-
-      - name: Run linters
-        run: scripts/check
+        run: uv sync --frozen --extra pydantic-ai
 
       - name: Run tests
         run: scripts/test
 
   # https://github.com/marketplace/actions/alls-green#why used for branch protection checks
   check:
     if: always()
-    needs: [test]
+    needs: [lint, test]
     runs-on: ubuntu-latest
     steps:
       - name: Decide whether the needed jobs succeeded or failed

pyproject.toml

@@ -56,8 +56,10 @@ pydantic-ai = ["pydantic-ai-slim>=1.92; python_version >= '3.10'"]
 
 [dependency-groups]
 dev = [
+    "anyio",
     "asgi-lifespan",
     "coverage",
+    "dirty-equals",
     "httpx",
     "inline-snapshot",
     "pytest",