feat(synthesis): Lead/Provenance model + grounded leads + conjecture generator

- codex/synthesis.py: Lead/Provenance dataclasses, find_connections/gaps/improvements,
  propose_conjectures (status=unverified, quarantined in leads/conjectures/),
  write_leads (grounded→leads/grounded/, conjectures→leads/conjectures/ HARD invariant)
- codex/cli.py: synthesis leads/conjectures/report command group
- codex/config.py: F-13 settings (leads_dir, synthesis_llm_*, synthesis_top_k,
  synthesis_min_grounded_ratio, synthesis_gap_min_coverage)
- tests/synthesis/: 42 tests covering model, grounding, conjecture invariant, quarantine, CLI
- spike/: F-13 spike script + output (live run attempted)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/synthesis/test_grounded.py

@@ -0,0 +1,175 @@
+"""Tests for grounded leads (connection / gap / improvement).
+
+The Grounding-Guard is re-used from :mod:`codex.wiki` (F-12). These tests
+verify that ungrounded claims are either dropped or annotated with ⚠,
+and that grounded statements survive intact.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+from codex.synthesis import (
+    _finalise_grounded_lead,
+    _mark_ungrounded,
+    find_connections,
+    find_gaps,
+)
+from tests.synthesis.conftest import StubLLM
+
+_GROUNDED_CONNECTION = (
+    "Both papers build hyperbolic volumes from the Lobachevsky function.\n"
+    "For an ideal tetrahedron with dihedral angles the hyperbolic volume is "
+    "V = L(gamma1) + L(gamma2) + L(gamma3). [Springborn2008 #chunk 16]\n"
+    "A discrete conformal map is defined by logarithmic scale factors u_i at "
+    "each vertex such that the edge lengths satisfy a compatibility condition. "
+    "[BobenkoPinkallSpringborn2015 #chunk 3]\n"
+)
+
+_UNGROUNDED_CONNECTION = (
+    "Both papers prove the Riemann hypothesis via the Lobachevsky function. "
+    "[Springborn2008 #chunk 99]\n"
+)
+
+
+def test_finalise_grounded_lead_returns_none_without_claims(
+    fixture_chunks: list[dict[str, object]],
+) -> None:
+    """Body with no inline citations yields no grounded lead."""
+    lead = _finalise_grounded_lead(
+        seq=1,
+        kind="connection",
+        title="t",
+        body="A plain statement with no citation marker.",
+        chunks=fixture_chunks,
+        min_grounded_ratio=0.5,
+    )
+    assert lead is None
+
+
+def test_finalise_grounded_lead_drops_when_ratio_below_floor(
+    fixture_chunks: list[dict[str, object]],
+) -> None:
+    """All-ungrounded body → None (not silently promoted)."""
+    lead = _finalise_grounded_lead(
+        seq=1,
+        kind="connection",
+        title="t",
+        body=_UNGROUNDED_CONNECTION,
+        chunks=fixture_chunks,
+        min_grounded_ratio=0.5,
+    )
+    assert lead is None
+
+
+def test_finalise_grounded_lead_succeeds_when_grounded(
+    fixture_chunks: list[dict[str, object]],
+) -> None:
+    """Grounded body passes the floor and returns a populated Lead."""
+    lead = _finalise_grounded_lead(
+        seq=1,
+        kind="connection",
+        title="Both papers share a building block",
+        body=_GROUNDED_CONNECTION,
+        chunks=fixture_chunks,
+        min_grounded_ratio=0.5,
+    )
+    assert lead is not None
+    assert lead.kind == "connection"
+    assert lead.id == "L-0001"
+    assert lead.confidence >= 0.5
+    assert lead.status == "unverified"
+    assert lead.suggested_validation == ""
+    # All claims should be grounded
+    assert all(c.grounded for c in lead.claims)
+
+
+def test_mark_ungrounded_prefixes_warning() -> None:
+    """_mark_ungrounded prefixes ⚠ to the matching claim text once."""
+    from codex.wiki import Claim
+
+    body = "Some fact. [X2020 #c 1]\nOther fact. [Y2021 #c 2]\n"
+    claims = [
+        Claim(text="Some fact", bibkey="X2020", locator="c 1", grounded=False),
+        Claim(text="Other fact", bibkey="Y2021", locator="c 2", grounded=True),
+    ]
+    out = _mark_ungrounded(body, claims)
+    assert "⚠ Some fact" in out
+    # Grounded claim is not annotated
+    assert "⚠ Other fact" not in out
+
+
+def test_find_connections_emits_grounded_lead(
+    mock_retrieve: None,
+    mock_paper_titles: None,
+    mock_settings: Path,
+) -> None:
+    """End-to-end: with a grounded LLM response, a connection lead is produced."""
+    llm = StubLLM(_GROUNDED_CONNECTION)
+    leads = find_connections(top_k=6, llm=llm)
+    assert len(leads) >= 1
+    lead = leads[0]
+    assert lead.kind == "connection"
+    assert lead.provenance, "grounded lead must carry provenance"
+    # No ⚠ should appear because all claims grounded
+    assert "⚠" not in lead.body
+
+
+def test_find_connections_drops_ungrounded_response(
+    mock_retrieve: None,
+    mock_paper_titles: None,
+    mock_settings: Path,
+) -> None:
+    """Ungrounded LLM responses are dropped, not emitted with ⚠."""
+    llm = StubLLM(_UNGROUNDED_CONNECTION)
+    leads = find_connections(top_k=6, llm=llm)
+    assert leads == []
+
+
+def test_find_connections_handles_llm_failure(
+    mock_retrieve: None,
+    mock_paper_titles: None,
+    mock_settings: Path,
+) -> None:
+    """LLM raising → returns [] (mirrors F-12 graceful degradation)."""
+
+    class FailingLLM:
+        def generate(self, prompt: str, model: str) -> str:
+            raise ConnectionError("ollama unreachable")
+
+    leads = find_connections(top_k=6, llm=FailingLLM())
+    assert leads == []
+
+
+def test_find_gaps_topic_with_no_chunks(
+    monkeypatch,
+    mock_paper_titles: None,
+    mock_settings: Path,
+) -> None:
+    """When retrieval returns no chunks, a gap lead is emitted directly."""
+    monkeypatch.setattr("codex.synthesis._retrieve_chunks", lambda queries, top_k: [])
+    leads = find_gaps(llm=StubLLM(""))
+    assert len(leads) >= 1
+    assert all(lead.kind == "gap" for lead in leads)
+    # Direct gap leads carry a validation hint (re-ingest)
+    assert all(lead.suggested_validation for lead in leads)
+
+
+def test_find_gaps_well_covered_topic_skipped(
+    monkeypatch,
+    mock_paper_titles: None,
+    mock_settings: Path,
+    fixture_chunks: list[dict[str, object]],
+) -> None:
+    """Topics covered by enough bibkeys are NOT emitted as gaps.
+
+    Three distinct bibkeys in the fixture > synthesis_gap_min_coverage=2,
+    so every topic is well-covered and gets skipped.
+    """
+    monkeypatch.setattr(
+        "codex.synthesis._retrieve_chunks",
+        lambda queries, top_k: [dict(c) for c in fixture_chunks],
+    )
+    leads = find_gaps(llm=StubLLM(""))
+    # All probes well-covered → no gap leads
+    assert leads == []