fix(a2a): add A2A Python SDK as project dependency

Add a2a-sdk>=0.3.0 to [project.dependencies] in pyproject.toml.
The specification mandates that both local (stdio) and server (HTTP)
transports use the A2A Python SDK (ADR-047). Previously the package
was absent from pyproject.toml and uv.lock, making the project
non-compliant with the spec requirement.

Changes:
- Add 'a2a-sdk>=0.3.0' to [project.dependencies] in pyproject.toml
- Regenerate uv.lock to include a2a-sdk 0.3.25 and its transitive deps
- Add Behave scenarios confirming a2a is importable as a project dependency
- Add step definitions for the new TDD scenarios

ISSUES CLOSED: #2922

features/steps/tdd_a2a_sdk_dependency_steps.py

@@ -0,0 +1,87 @@
+"""Step definitions for TDD issue #2922: A2A Python SDK dependency."""
+
+from __future__ import annotations
+
+import importlib
+import tomllib
+from pathlib import Path
+from typing import Any
+
+from behave import given, then, when
+from behave.runner import Context
+
+
+@given('the pyproject.toml file exists at "{path}"')
+def step_pyproject_exists(context: Context, path: str) -> None:
+    """Verify pyproject.toml exists at the given path."""
+    pyproject_path = Path(path)
+    assert pyproject_path.exists(), f"pyproject.toml not found at {path}"
+    context.pyproject_path = pyproject_path
+
+
+@when("I read the project dependencies from pyproject.toml")
+def step_read_project_dependencies(context: Context) -> None:
+    """Read the [project.dependencies] list from pyproject.toml."""
+    content = context.pyproject_path.read_bytes()
+    data: dict[str, Any] = tomllib.loads(content.decode("utf-8"))
+    context.project_dependencies = data.get("project", {}).get("dependencies", [])
+
+
+@then(
+    'the dependency list should include a package that provides the "{module}" module'
+)
+def step_dependency_provides_module(context: Context, module: str) -> None:
+    """Assert that a dependency providing the given module is listed."""
+    deps: list[str] = context.project_dependencies
+    # The a2a-sdk package installs as the 'a2a' module.
+    # Accept either 'a2a-sdk' or 'a2a' as the package name.
+    found = any(
+        dep.lower().startswith("a2a-sdk") or dep.lower().startswith("a2a>=")
+        for dep in deps
+    )
+    assert found, (
+        f"No dependency providing the '{module}' module found in "
+        f"[project.dependencies]. Current deps: {deps}"
+    )
+
+
+@when('I attempt to import the "{module_name}" module')
+def step_attempt_import(context: Context, module_name: str) -> None:
+    """Attempt to import the given module and record the result."""
+    try:
+        context.imported_module = importlib.import_module(module_name)
+        context.import_error = None
+    except ImportError as exc:
+        context.imported_module = None
+        context.import_error = exc
+
+
+@then("the import should succeed without errors")
+def step_import_succeeded(context: Context) -> None:
+    """Assert that the previous import attempt succeeded."""
+    assert context.import_error is None, f"Import failed with: {context.import_error}"
+    assert context.imported_module is not None, "Module was not imported"
+
+
+@when('I import "{module_path}" and access "{attr_name}"')
+def step_import_and_access(context: Context, module_path: str, attr_name: str) -> None:
+    """Import a module and access a named attribute."""
+    try:
+        mod = importlib.import_module(module_path)
+        context.accessed_attr = getattr(mod, attr_name, None)
+        context.access_error = None
+    except ImportError as exc:
+        context.accessed_attr = None
+        context.access_error = exc
+
+
+@then('the "{attr_name}" class should be available')
+def step_class_available(context: Context, attr_name: str) -> None:
+    """Assert that the accessed attribute is a class."""
+    assert context.access_error is None, f"Import failed with: {context.access_error}"
+    assert context.accessed_attr is not None, (
+        f"Attribute '{attr_name}' not found in module"
+    )
+    assert isinstance(context.accessed_attr, type), (
+        f"'{attr_name}' is not a class, got {type(context.accessed_attr)}"
+    )

features/tdd_a2a_sdk_dependency.feature

@@ -0,0 +1,20 @@
+@tdd_issue @tdd_issue_2922
+Feature: A2A Python SDK is a declared project dependency
+  As a CleverAgents developer
+  I want the A2A Python SDK to be listed in pyproject.toml dependencies
+  So that the SDK is always installed and importable in any project environment
+
+  Background:
+    Given the pyproject.toml file exists at "pyproject.toml"
+
+  Scenario: a2a-sdk is listed in project dependencies
+    When I read the project dependencies from pyproject.toml
+    Then the dependency list should include a package that provides the "a2a" module
+
+  Scenario: a2a module is importable as a project dependency
+    When I attempt to import the "a2a" module
+    Then the import should succeed without errors
+
+  Scenario: a2a SDK provides the A2AClient class
+    When I import "a2a.client" and access "A2AClient"
+    Then the "A2AClient" class should be available

pyproject.toml

@@ -48,6 +48,7 @@ dependencies = [
     "tomlkit>=0.13.0",  # TOML writing with comment preservation for config CLI
     "tenacity>=8.2.0",  # Retry framework for service layer resilience
     "aiohttp>=3.13.4",  # CVE-2026-34515 mitigation: open redirect vulnerability
+    "a2a-sdk>=0.3.0",  # A2A Python SDK — required transport for local (stdio) and server (HTTP) modes (ADR-047)
 ]
 
 [project.optional-dependencies]