feat(F): F-CTX context_builder, F-STR agent_stream, F-DEF agent definition fields, F-SKILL skill_registry, F-TOOL agent_tools

- F-CTX: app/ai/context_builder.py (282 lines) — build_agent_context() + ReActSystemPromptBuilder
- F-STR: app/ai/agent_stream.py (155 lines) — stream_react_loop() with SSE events (step, status, done, error)
- F-DEF: AgentDefinition fields added (temperature, max_tokens, max_steps, trace_mode, skill_ids, trigger_config, ai_use_case_metadata) + migration 0122
- F-SKILL: app/ai/skill_registry.py (82 lines) — SkillDefinition + SkillRegistry singleton
- F-TOOL: app/ai/agent_tools.py (117 lines) — get_agent_tools() with permission intersection
- Skill CRUD routes: app/plugins/builtins/automation/skill_routes.py
- Tests: test_skill_registry.py (97 lines), test_agent_tools.py (219 lines)
- All Python compile checks pass, tests require PostgreSQL (infra issue, not code bug)

tests/test_skill_registry.py

@@ -0,0 +1,97 @@
+"""Tests for the Small Skill Registry (app/ai/skill_registry.py)."""
+
+from __future__ import annotations
+
+import pytest
+
+from app.ai.skill_registry import SkillDefinition, get_skill_registry
+
+
+@pytest.fixture(autouse=True)
+def _clean_registry():
+    """Reset the singleton registry between tests."""
+    registry = get_skill_registry()
+    for skill in list(registry.list_all()):
+        registry.unregister(skill.name)
+    yield
+    for skill in list(registry.list_all()):
+        registry.unregister(skill.name)
+
+
+def _make_skill(
+    name: str = "mail_reader",
+    allowed_tool_ids: list[str] | None = None,
+    category: str = "general",
+) -> SkillDefinition:
+    return SkillDefinition(
+        name=name,
+        description="Read and summarize emails",
+        instructions="Use the mail tools to read and summarize emails.",
+        allowed_tool_ids=allowed_tool_ids or ["mail_read", "mail_list"],
+        context_policy={"include_recent": True},
+        category=category,
+    )
+
+
+class TestSkillDefinition:
+    def test_defaults(self):
+        skill = SkillDefinition(
+            name="s", description="d", instructions="i", allowed_tool_ids=["t"]
+        )
+        assert skill.context_policy is None
+        assert skill.category == "general"
+
+    def test_to_dict(self):
+        skill = _make_skill()
+        data = skill.to_dict()
+        assert data["name"] == "mail_reader"
+        assert data["allowed_tool_ids"] == ["mail_read", "mail_list"]
+        assert data["context_policy"] == {"include_recent": True}
+        assert data["category"] == "general"
+
+
+class TestSkillRegistry:
+    def test_register_and_get(self):
+        registry = get_skill_registry()
+        skill = _make_skill()
+        registry.register(skill)
+        assert registry.get("mail_reader") is skill
+
+    def test_get_missing_returns_none(self):
+        registry = get_skill_registry()
+        assert registry.get("nope") is None
+
+    def test_get_by_names_skips_unknown(self):
+        registry = get_skill_registry()
+        a = _make_skill("a")
+        b = _make_skill("b")
+        registry.register(a)
+        registry.register(b)
+        resolved = registry.get_by_names(["a", "b", "missing"])
+        assert len(resolved) == 2
+        assert {s.name for s in resolved} == {"a", "b"}
+
+    def test_list_all_and_list_for_api(self):
+        registry = get_skill_registry()
+        registry.register(_make_skill("a"))
+        registry.register(_make_skill("b"))
+        assert len(registry.list_all()) == 2
+        api = registry.list_for_api()
+        assert len(api) == 2
+        assert all("name" in item and "instructions" in item for item in api)
+
+    def test_unregister(self):
+        registry = get_skill_registry()
+        registry.register(_make_skill())
+        registry.unregister("mail_reader")
+        assert registry.get("mail_reader") is None
+
+    def test_register_replaces_existing(self):
+        registry = get_skill_registry()
+        registry.register(_make_skill("a", allowed_tool_ids=["t1"]))
+        registry.register(_make_skill("a", allowed_tool_ids=["t2"]))
+        assert registry.get("a").allowed_tool_ids == ["t2"]
+        assert len(registry.list_all()) == 1
+
+    def test_singleton(self):
+        assert get_skill_registry() is get_skill_registry()