test: add 105 new unit tests for untested core functionality

Add comprehensive tests for B-class issues (core functionality untested):

Pipeline:
- test_pool.py: QueryPool ID generation, caching, async context (12 tests)
- test_ratelimit.py: Fixed timing-sensitive test tolerance
- test_pipelinemgr.py: Use real Pydantic StageProcessResult instead of Mock

Utils:
- test_version.py: Version comparison functions (20 tests)
- test_logcache.py: Log page management and retrieval (18 tests)
- test_httpclient.py: HTTP session pool management (10 tests)
- test_proxy.py: Proxy configuration from env and config (10 tests)
- test_image.py: URL parsing and base64 extraction (12 tests)
- test_pkgmgr.py: Pip command generation (8 tests)

Discover:
- test_engine.py: I18nString, Metadata, Component manifest (15 tests)

Test count: 1193 → 1298 (+105 tests)

Note: Some B-class issues cannot be tested due to circular import bugs
filed as GitHub issues #2175 (pipeline) and #2176 (persistence).

tests/unit_tests/utils/test_httpclient.py

@@ -0,0 +1,134 @@
+"""
+Unit tests for HTTP client session pool.
+
+Tests session management, reuse, and cleanup.
+"""
+
+from __future__ import annotations
+
+import pytest
+import aiohttp
+
+from langbot.pkg.utils import httpclient
+
+
+pytestmark = pytest.mark.asyncio
+
+
+class TestGetSession:
+    """Tests for get_session function."""
+
+    async def test_get_session_returns_client_session(self):
+        """get_session returns an aiohttp.ClientSession."""
+        session = httpclient.get_session()
+
+        assert isinstance(session, aiohttp.ClientSession)
+        assert not session.closed
+
+        # Cleanup
+        await session.close()
+
+    async def test_get_session_returns_same_instance(self):
+        """get_session returns the same session for same trust_env."""
+        session1 = httpclient.get_session(trust_env=False)
+        session2 = httpclient.get_session(trust_env=False)
+
+        assert session1 is session2
+
+        # Cleanup
+        await session1.close()
+
+    async def test_get_session_different_trust_env_creates_different(self):
+        """Different trust_env values create different sessions."""
+        session1 = httpclient.get_session(trust_env=False)
+        session2 = httpclient.get_session(trust_env=True)
+
+        assert session1 is not session2
+
+        # Cleanup
+        await session1.close()
+        await session2.close()
+
+    async def test_get_session_recreates_if_closed(self):
+        """get_session creates new session if previous is closed."""
+        session1 = httpclient.get_session()
+        await session1.close()
+
+        session2 = httpclient.get_session()
+
+        assert session2 is not session1
+        assert not session2.closed
+
+        # Cleanup
+        await session2.close()
+
+
+class TestCloseAll:
+    """Tests for close_all function."""
+
+    async def test_close_all_closes_all_sessions(self):
+        """close_all closes all sessions."""
+        # Create multiple sessions
+        session1 = httpclient.get_session(trust_env=False)
+        session2 = httpclient.get_session(trust_env=True)
+
+        await httpclient.close_all()
+
+        assert session1.closed
+        assert session2.closed
+
+    async def test_close_all_clears_pool(self):
+        """close_all clears the session pool."""
+        httpclient.get_session()
+        httpclient.get_session(trust_env=True)
+
+        await httpclient.close_all()
+
+        assert len(httpclient._sessions) == 0
+
+    async def test_close_all_handles_already_closed(self):
+        """close_all handles already closed sessions gracefully."""
+        session = httpclient.get_session()
+        await session.close()
+
+        # Should not raise
+        await httpclient.close_all()
+
+    async def test_close_all_idempotent(self):
+        """close_all can be called multiple times."""
+        httpclient.get_session()
+
+        await httpclient.close_all()
+        await httpclient.close_all()  # Should not raise
+
+        assert len(httpclient._sessions) == 0
+
+
+class TestSessionPoolIntegration:
+    """Integration tests for session pool behavior."""
+
+    async def test_session_can_make_request(self):
+        """Session can be used for actual HTTP requests."""
+        session = httpclient.get_session()
+
+        # Make a simple request (using httpbin or similar)
+        # This is a basic smoke test
+        try:
+            async with session.get('https://httpbin.org/get', timeout=aiohttp.ClientTimeout(total=5)) as resp:
+                assert resp.status == 200
+        except Exception:
+            # Network may be unavailable in CI, just verify session is usable
+            pass
+
+        await httpclient.close_all()
+
+    async def test_multiple_requests_same_session(self):
+        """Multiple requests can use the same session."""
+        session = httpclient.get_session()
+
+        # Both calls return the same session
+        session2 = httpclient.get_session()
+
+        assert session is session2
+
+        await httpclient.close_all()