feat(agents): stars agent — astrological transits via pyswisseph (#121)

Computes natal chart (Sun/Moon/Mercury/Venus/Mars/Jupiter/Saturn) from
birth_date and finds active transits (conjunction/sextile/square/trine/
opposition) between today's sky and the user's natal positions. Top 3
most-exact transits are passed to the orchestrator as interpretive themes
to colour the tip — grounded and actionable, not predictive.

Birth date sourced from agent_prefs (populated by a connected Google
data source); requires data:google-health consent. Agent self-silences
when birth_date is absent. pyswisseph added to ml/serving/requirements.txt.

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

ml/agents/tests/test_agents.py

@@ -14,6 +14,7 @@ from ml.agents.time_of_day import TimeOfDayAgent
 from ml.agents.recent_patterns import RecentPatternsAgent
 from ml.agents.focus_area import FocusAreaAgent
 from ml.agents.tarot import TarotAgent, _daily_draw, _CARDS, _POSITIONS
+from ml.agents.stars import StarsAgent, _SWE_AVAILABLE
 from ml.agents.registry import get_agent, all_agents
 
 _NOW = datetime(2026, 5, 1, 9, 0, 0, tzinfo=timezone.utc)  # Thursday 09:00 UTC
@@ -297,13 +298,56 @@ class TestTarotAgent:
         assert all(0 <= i < len(_CARDS) for i in indices)
 
 
+# ── StarsAgent ────────────────────────────────────────────────────────────────
+
+class TestStarsAgent:
+    agent = StarsAgent()
+
+    def test_no_birth_date(self):
+        out = self.agent.compute(_inp())
+        _check_output(out, self.agent)
+        assert out.signals_snapshot.get("no_birth_date") is True
+        assert "birth date" in out.prompt_text.lower()
+
+    @pytest.mark.skipif(not _SWE_AVAILABLE, reason="pyswisseph not installed")
+    def test_invalid_birth_date(self):
+        out = self.agent.compute(_inp(agent_prefs={"birth_date": "not-a-date"}))
+        _check_output(out, self.agent)
+        assert out.signals_snapshot.get("invalid_birth_date") == "not-a-date"
+
+    @pytest.mark.skipif(not _SWE_AVAILABLE, reason="pyswisseph not installed")
+    def test_with_birth_date(self):
+        out = self.agent.compute(_inp(agent_prefs={"birth_date": "1990-06-15"}))
+        _check_output(out, self.agent)
+        assert "natal" in out.prompt_text.lower()
+        assert out.signals_snapshot["birth_date"] == "1990-06-15"
+        assert "natal_sun" in out.signals_snapshot
+        assert "natal_moon" in out.signals_snapshot
+
+    @pytest.mark.skipif(not _SWE_AVAILABLE, reason="pyswisseph not installed")
+    def test_transit_snapshot_structure(self):
+        out = self.agent.compute(_inp(agent_prefs={"birth_date": "1985-03-21"}))
+        snap = out.signals_snapshot
+        assert "active_transits" in snap
+        for t in snap["active_transits"]:
+            assert {"transit_planet", "natal_planet", "aspect", "nature", "orb"} <= t.keys()
+
+    def test_swe_unavailable_path(self, monkeypatch):
+        import ml.agents.stars as stars_mod
+        monkeypatch.setattr(stars_mod, "_SWE_AVAILABLE", False)
+        agent = StarsAgent()
+        out = agent.compute(_inp(agent_prefs={"birth_date": "1990-06-15"}))
+        _check_output(out, agent)
+        assert out.signals_snapshot.get("swe_unavailable") is True
+
+
 # ── Registry ─────────────────────────────────────────────────────────────────
 
 class TestRegistry:
     def test_all_agents_present(self):
         agents = all_agents()
         ids = {a.agent_id for a in agents}
-        assert ids == {"overdue-task", "momentum", "time-of-day", "recent-patterns", "focus-area", "health-vitals", "tarot"}
+        assert ids == {"overdue-task", "momentum", "time-of-day", "recent-patterns", "focus-area", "health-vitals", "tarot", "stars"}
 
     def test_get_agent(self):
         a = get_agent("momentum")