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/discover/test_engine.py

@@ -0,0 +1,192 @@
+"""
+Unit tests for discover engine utilities.
+
+Tests I18nString, Metadata, and Component utilities.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+from langbot.pkg.discover.engine import I18nString, Metadata, Component
+
+
+class TestI18nString:
+    """Tests for I18nString Pydantic model."""
+
+    def test_create_with_english_only(self):
+        """Create I18nString with only English."""
+        i18n = I18nString(en_US="Hello")
+
+        assert i18n.en_US == "Hello"
+        assert i18n.zh_Hans is None
+
+    def test_create_with_multiple_languages(self):
+        """Create I18nString with multiple languages."""
+        i18n = I18nString(
+            en_US="Hello",
+            zh_Hans="你好",
+            zh_Hant="你好",
+            ja_JP="こんにちは",
+        )
+
+        assert i18n.en_US == "Hello"
+        assert i18n.zh_Hans == "你好"
+        assert i18n.zh_Hant == "你好"
+        assert i18n.ja_JP == "こんにちは"
+
+    def test_to_dict_with_english_only(self):
+        """to_dict returns only non-None fields."""
+        i18n = I18nString(en_US="Hello")
+
+        result = i18n.to_dict()
+
+        assert result == {"en_US": "Hello"}
+
+    def test_to_dict_with_multiple_languages(self):
+        """to_dict returns all non-None fields."""
+        i18n = I18nString(
+            en_US="Hello",
+            zh_Hans="你好",
+        )
+
+        result = i18n.to_dict()
+
+        assert result == {"en_US": "Hello", "zh_Hans": "你好"}
+
+    def test_to_dict_excludes_none(self):
+        """to_dict excludes None values."""
+        i18n = I18nString(
+            en_US="Hello",
+            zh_Hans=None,
+            ja_JP="こんにちは",
+        )
+
+        result = i18n.to_dict()
+
+        assert "zh_Hans" not in result
+        assert "en_US" in result
+        assert "ja_JP" in result
+
+    def test_to_dict_all_languages(self):
+        """to_dict with all supported languages."""
+        i18n = I18nString(
+            en_US="Hello",
+            zh_Hans="你好",
+            zh_Hant="你好",
+            ja_JP="こんにちは",
+            th_TH="สวัสดี",
+            vi_VN="Xin chào",
+            es_ES="Hola",
+        )
+
+        result = i18n.to_dict()
+
+        assert len(result) == 7
+
+
+class TestMetadata:
+    """Tests for Metadata Pydantic model."""
+
+    def test_create_minimal(self):
+        """Create Metadata with required fields only."""
+        from langbot.pkg.discover.engine import I18nString
+
+        metadata = Metadata(
+            name="test-component",
+            label=I18nString(en_US="Test Component"),
+        )
+
+        assert metadata.name == "test-component"
+        assert metadata.label.en_US == "Test Component"
+
+    def test_create_with_all_fields(self):
+        """Create Metadata with all optional fields."""
+        from langbot.pkg.discover.engine import I18nString
+
+        metadata = Metadata(
+            name="test-component",
+            label=I18nString(en_US="Test"),
+            description=I18nString(en_US="A test component"),
+            version="1.0.0",
+            icon="test-icon",
+            author="Test Author",
+            repository="https://github.com/test/repo",
+        )
+
+        assert metadata.version == "1.0.0"
+        assert metadata.icon == "test-icon"
+        assert metadata.author == "Test Author"
+
+
+class TestComponentManifest:
+    """Tests for Component manifest detection."""
+
+    def test_is_component_manifest_valid(self):
+        """is_component_manifest returns True for valid manifest."""
+        manifest = {
+            'apiVersion': 'v1',
+            'kind': 'Component',
+            'metadata': {'name': 'test'},
+            'spec': {},
+        }
+
+        assert Component.is_component_manifest(manifest) is True
+
+    def test_is_component_manifest_missing_apiversion(self):
+        """is_component_manifest returns False without apiVersion."""
+        manifest = {
+            'kind': 'Component',
+            'metadata': {'name': 'test'},
+            'spec': {},
+        }
+
+        assert Component.is_component_manifest(manifest) is False
+
+    def test_is_component_manifest_missing_kind(self):
+        """is_component_manifest returns False without kind."""
+        manifest = {
+            'apiVersion': 'v1',
+            'metadata': {'name': 'test'},
+            'spec': {},
+        }
+
+        assert Component.is_component_manifest(manifest) is False
+
+    def test_is_component_manifest_missing_metadata(self):
+        """is_component_manifest returns False without metadata."""
+        manifest = {
+            'apiVersion': 'v1',
+            'kind': 'Component',
+            'spec': {},
+        }
+
+        assert Component.is_component_manifest(manifest) is False
+
+    def test_is_component_manifest_missing_spec(self):
+        """is_component_manifest returns False without spec."""
+        manifest = {
+            'apiVersion': 'v1',
+            'kind': 'Component',
+            'metadata': {'name': 'test'},
+        }
+
+        assert Component.is_component_manifest(manifest) is False
+
+    def test_is_component_manifest_empty(self):
+        """is_component_manifest returns False for empty dict."""
+        manifest = {}
+
+        assert Component.is_component_manifest(manifest) is False
+
+    def test_is_component_manifest_extra_fields_ok(self):
+        """is_component_manifest accepts extra fields."""
+        manifest = {
+            'apiVersion': 'v1',
+            'kind': 'Component',
+            'metadata': {'name': 'test'},
+            'spec': {},
+            'extraField': 'ignored',
+        }
+
+        assert Component.is_component_manifest(manifest) is True