test(V2): migrazione test common/

Copiati e aggiornati i test da services/common/tests/ a tests/unit/common/.
Import aggiornati da mcp_common a cerbero_mcp.common. Eliminati test di
funzionalità V1-only (app_factory, environment, auth/Principal, server_base).
Refactored test_audit.py (principal→actor str) e test_mcp_bridge.py
(TokenStore→valid_tokens set). 71/71 test passano.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/unit/common/test_http.py

@@ -0,0 +1,72 @@
+from __future__ import annotations
+
+import asyncio
+
+import httpx
+import pytest
+from cerbero_mcp.common.http import async_client, call_with_retry
+
+
+def test_async_client_uses_retry_transport():
+    c = async_client(retries=5)
+    assert isinstance(c._transport, httpx.AsyncHTTPTransport)
+    # internal _retries on transport
+    assert c._transport._pool._retries == 5
+
+
+@pytest.mark.asyncio
+async def test_call_with_retry_succeeds_first_try():
+    calls = 0
+
+    async def fn():
+        nonlocal calls
+        calls += 1
+        return "ok"
+
+    result = await call_with_retry(fn)
+    assert result == "ok"
+    assert calls == 1
+
+
+@pytest.mark.asyncio
+async def test_call_with_retry_recovers_after_transient(monkeypatch):
+    monkeypatch.setattr(asyncio, "sleep", asyncio.coroutine(lambda *_: None) if False else _no_sleep)
+    calls = 0
+
+    async def fn():
+        nonlocal calls
+        calls += 1
+        if calls < 3:
+            raise httpx.ConnectError("boom")
+        return "ok"
+
+    result = await call_with_retry(fn, max_attempts=5, base_delay=0.0)
+    assert result == "ok"
+    assert calls == 3
+
+
+async def _no_sleep(_):
+    return None
+
+
+@pytest.mark.asyncio
+async def test_call_with_retry_gives_up_after_max():
+    calls = 0
+
+    async def fn():
+        nonlocal calls
+        calls += 1
+        raise httpx.TimeoutException("slow")
+
+    with pytest.raises(httpx.TimeoutException):
+        await call_with_retry(fn, max_attempts=3, base_delay=0.0)
+    assert calls == 3
+
+
+@pytest.mark.asyncio
+async def test_call_with_retry_does_not_catch_unexpected():
+    async def fn():
+        raise ValueError("not transient")
+
+    with pytest.raises(ValueError):
+        await call_with_retry(fn, max_attempts=5, base_delay=0.0)