feat(strategist) S7: strategist resume / open-round repair

DESIGN_STRATEGIST.md §5. Support resume from a crash mid-strategist-loop.

_resume_strategist_state inspects investigation_rounds for a tail entry
without completed_at — an "open" round, i.e. one that started but never
closed. Two repairs:

  1. Mark the round closed with strategist_action="interrupted_resume"
     so the run history reflects what actually happened.
  2. Walk that round's leads; any still in "assigned" state are
     re-marked as "failed" with failure_reason="interrupted before
     complete". The Retry-failed-leads + Gap-analysis passes that run
     after the strategist loop can pick them up.

Returns max(round_number) + 1 — the round at which to resume the loop.
On a clean graph (no prior rounds) returns 1 and makes no changes.

_phase3_strategist_loop now calls this helper before the main for-loop
and uses its return value as start_round, so a resume run lands at the
right round number rather than restarting from R1.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_optimizations.py

@@ -3407,6 +3407,54 @@ class TestInvestigationRound:
         assert "not in" in result
         assert graph.strategist_complete_requested is False
 
+    @pytest.mark.asyncio
+    async def test_resume_repairs_open_round(self, tmp_path):
+        """Simulate a crash mid-round: half-open InvestigationRound + a
+        lead in 'assigned' state. _resume_strategist_state must close the
+        round and re-mark the lead as failed."""
+        from unittest.mock import AsyncMock
+        from orchestrator import Orchestrator
+        graph = EvidenceGraph()
+        hid = await graph.add_hypothesis("h", "d")
+        rid = await graph.start_investigation_round(1)
+        lid = await graph.add_lead(
+            target_agent="filesystem", description="probe",
+            proposed_by="strategist", motivating_hypothesis=hid,
+            expected_evidence_type="supports", round_number=1,
+        )
+        lead = next(l for l in graph.leads if l.id == lid)
+        lead.status = "assigned"
+
+        llm = AsyncMock()
+        class FakeFactory:
+            def get_or_create_agent(self, name):
+                return AsyncMock()
+        orch = Orchestrator(llm, graph, FakeFactory(), config={})
+        next_round = await orch._resume_strategist_state()
+
+        round_ = graph.get_investigation_round(rid)
+        assert round_.completed_at != ""
+        assert round_.strategist_action == "interrupted_resume"
+        lead2 = next(l for l in graph.leads if l.id == lid)
+        assert lead2.status == "failed"
+        assert "interrupted" in lead2.context.get("failure_reason", "")
+        assert next_round == 2
+
+    @pytest.mark.asyncio
+    async def test_resume_state_is_idempotent_on_clean_graph(self):
+        """No prior rounds → resume returns 1, no changes."""
+        from unittest.mock import AsyncMock
+        from orchestrator import Orchestrator
+        graph = EvidenceGraph()
+        llm = AsyncMock()
+        class FakeFactory:
+            def get_or_create_agent(self, name):
+                return AsyncMock()
+        orch = Orchestrator(llm, graph, FakeFactory(), config={})
+        result = await orch._resume_strategist_state()
+        assert result == 1
+        assert graph.investigation_rounds == []
+
     @pytest.mark.asyncio
     async def test_strategist_loop_exits_on_declare_complete(self):
         """Mock strategist that declares complete in round 1 — orchestrator