ci: add a smoke test running outside of the default virtual env (#899)

- Adds a CI workflow that builds and installs `a2a-sdk` with only base
dependencies (no extras or `dev` group) and verifies all core public API
modules import successfully.
- Prevents regressions like #865 (fixed in #897) where `packaging` was
used in core modules but missing from `[project.dependencies]`. Since
`packaging` is a transitive dependency of several dev tools, it was
always available in CI but not for end-users doing `pip install
a2a-sdk`.

Added a workflow which:
1. Builds the package wheel.
1. Creates a clean venv and installs **only** the wheel.
1. Runs the import smoke test script against that clean venv.

Tested:
- Reverting `packaging` from #897 gives [expected
failure](https://github.com/a2aproject/a2a-python/actions/runs/23543503483/job/68537073219).
- #883:
[failed](https://github.com/a2aproject/a2a-python/actions/runs/23545238185/job/68543460859?pr=899),
fix: #898.

Author: ishymko

.github/workflows/minimal-install.yml

@@ -0,0 +1,41 @@
+---
+name: Minimal Install Smoke Test
+on:
+  push:
+    branches: [main, 1.0-dev]
+  pull_request:
+permissions:
+  contents: read
+
+jobs:
+  minimal-install:
+    name: Verify base-only install
+    runs-on: ubuntu-latest
+    if: github.repository == 'a2aproject/a2a-python'
+    strategy:
+      matrix:
+        python-version: ['3.10', '3.11', '3.12', '3.13', '3.14']
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v6
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v7
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Build package
+        run: uv build --wheel
+
+      - name: Install with base dependencies only
+        run: |
+          uv venv .venv-minimal
+          # Install only the built wheel -- no extras, no dev deps.
+          # This simulates what an end-user gets with `pip install a2a-sdk`.
+          VIRTUAL_ENV=.venv-minimal uv pip install dist/*.whl
+
+      - name: List installed packages
+        run: VIRTUAL_ENV=.venv-minimal uv pip list
+
+      - name: Run import smoke test
+        run: .venv-minimal/bin/python scripts/test_minimal_install.py

scripts/test_minimal_install.py

@@ -0,0 +1,90 @@
+#!/usr/bin/env python3
+"""Smoke test for minimal (base-only) installation of a2a-sdk.
+
+This script verifies that all core public API modules can be imported
+when only the base dependencies are installed (no optional extras).
+
+It is designed to run WITHOUT pytest or any dev dependencies -- just
+a clean venv with `pip install a2a-sdk`.
+
+Usage:
+    python scripts/test_minimal_install.py
+
+Exit codes:
+    0 - All core imports succeeded
+    1 - One or more core imports failed
+"""
+
+from __future__ import annotations
+
+import importlib
+import sys
+
+
+# Core modules that MUST be importable with only base dependencies.
+# These are the public API surface that every user gets with
+# `pip install a2a-sdk` (no extras).
+#
+# Do NOT add modules here that require optional extras (grpc,
+# http-server, sql, signing, telemetry, vertex, etc.).
+# Those modules are expected to fail without their extras installed
+# and should use try/except ImportError guards internally.
+CORE_MODULES = [
+    'a2a',
+    'a2a.client',
+    'a2a.client.auth',
+    'a2a.client.base_client',
+    'a2a.client.card_resolver',
+    'a2a.client.client',
+    'a2a.client.client_factory',
+    'a2a.client.errors',
+    'a2a.client.helpers',
+    'a2a.client.interceptors',
+    'a2a.client.optionals',
+    'a2a.client.transports',
+    'a2a.server',
+    'a2a.server.agent_execution',
+    'a2a.server.context',
+    'a2a.server.events',
+    'a2a.server.request_handlers',
+    'a2a.server.tasks',
+    'a2a.types',
+    'a2a.utils',
+    'a2a.utils.artifact',
+    'a2a.utils.constants',
+    'a2a.utils.error_handlers',
+    'a2a.utils.helpers',
+    'a2a.utils.message',
+    'a2a.utils.parts',
+    'a2a.utils.proto_utils',
+    'a2a.utils.task',
+]
+
+
+def main() -> int:
+    failures: list[str] = []
+    successes: list[str] = []
+
+    for module_name in CORE_MODULES:
+        try:
+            importlib.import_module(module_name)
+            successes.append(module_name)
+        except Exception as e:  # noqa: BLE001, PERF203
+            failures.append(f'{module_name}: {e}')
+
+    print(f'Tested {len(CORE_MODULES)} core modules')
+    print(f'  Passed: {len(successes)}')
+    print(f'  Failed: {len(failures)}')
+
+    if failures:
+        print('\nFAILED imports:')
+        for failure in failures:
+            print(f'  - {failure}')
+        return 1
+
+    print('\nAll core modules imported successfully.')
+    return 0
+
+
+if __name__ == '__main__':
+    sys.exit(main())