feat(graph): cross-wing tunnels by shared topics (#1180)

When two wings have one or more confirmed TOPIC labels in common, the
miner now drops a symmetric tunnel between them at mine time so the
palace graph reflects shared themes (frameworks, vendors, recurring
concepts).

- llm_refine: TOPIC label routes to a dedicated `topics` bucket so the
  signal survives confirmation instead of getting collapsed into
  `uncertain` and dropped.
- entity_detector / project_scanner: bucket plumbed through the
  detection pipeline; `confirm_entities` returns confirmed topics
  alongside people/projects.
- miner.add_to_known_entities: optional `wing` parameter records the
  confirmed topics under `topics_by_wing` in
  `~/.mempalace/known_entities.json`. Wing names do NOT leak into the
  flat known-name set used by drawer-tagging.
- palace_graph: `compute_topic_tunnels` and `topic_tunnels_for_wing`
  create symmetric tunnels via the existing `create_tunnel` API so they
  share dedup and persistence with explicit tunnels.
- miner.mine: post-file-loop pass calls `topic_tunnels_for_wing` for
  the freshly-mined wing. Failures are logged but never abort the mine.
- config: `topic_tunnel_min_count` knob (env
  `MEMPALACE_TOPIC_TUNNEL_MIN_COUNT` or `~/.mempalace/config.json`),
  default 1.

Tests cover topic persistence through init->mine, tunnel creation when
wings share a topic, no tunnel below threshold, cross-wing tunnel
retrieval via `list_tunnels`, dedup on recompute, case-insensitive
overlap, and the end-to-end mine-time wiring.

Out of scope for this PR (called out in the PR body): manifest-
dependency overlap, per-topic allow/deny lists, search-result surfacing.

tests/test_known_entities_registry.py

@@ -206,3 +206,71 @@ def test_populated_registry_improves_miner_recall(temp_registry):
     # All four registered entities should land in the metadata string
     for expected in ("Julia Grib", "Kevin Heifner", "hyperion-history", "mempalace"):
         assert expected in tagged, f"expected '{expected}' in metadata {tagged!r}"
+
+
+# ── topics_by_wing — cross-wing tunnel signal source (issue #1180) ──
+
+
+def test_topics_persisted_under_topics_by_wing(temp_registry):
+    miner.add_to_known_entities(
+        {"people": ["Alice"], "topics": ["Angular", "OpenAPI"]},
+        wing="wing_alpha",
+    )
+    data = json.loads(temp_registry.read_text())
+    # Topics also stored as a flat list (existing-style aggregate).
+    assert "Angular" in data["topics"]
+    # And recorded by wing for tunnel computation.
+    assert data["topics_by_wing"]["wing_alpha"] == ["Angular", "OpenAPI"]
+
+
+def test_topics_by_wing_replaces_on_reinit(temp_registry):
+    """Re-running init for the same wing should reflect the latest list,
+    not accumulate stale topics indefinitely."""
+    miner.add_to_known_entities({"topics": ["Angular", "OpenAPI"]}, wing="wing_alpha")
+    miner.add_to_known_entities({"topics": ["OpenAPI", "Postgres"]}, wing="wing_alpha")
+    data = json.loads(temp_registry.read_text())
+    assert data["topics_by_wing"]["wing_alpha"] == ["OpenAPI", "Postgres"]
+
+
+def test_topics_by_wing_multiple_wings_coexist(temp_registry):
+    miner.add_to_known_entities({"topics": ["foo"]}, wing="wing_a")
+    miner.add_to_known_entities({"topics": ["foo", "bar"]}, wing="wing_b")
+    data = json.loads(temp_registry.read_text())
+    assert data["topics_by_wing"] == {"wing_a": ["foo"], "wing_b": ["foo", "bar"]}
+
+
+def test_topics_by_wing_skipped_without_wing(temp_registry):
+    miner.add_to_known_entities({"topics": ["foo"]})
+    data = json.loads(temp_registry.read_text())
+    # No wing → no topics_by_wing entry, but topics list still saved.
+    assert "topics_by_wing" not in data
+    assert data["topics"] == ["foo"]
+
+
+def test_topics_by_wing_dedupes_case_insensitive(temp_registry):
+    miner.add_to_known_entities({"topics": ["OpenAPI", "openapi", "OPENAPI"]}, wing="wing_a")
+    data = json.loads(temp_registry.read_text())
+    # Only one entry, casing of the first observed name preserved.
+    assert data["topics_by_wing"]["wing_a"] == ["OpenAPI"]
+
+
+def test_get_topics_by_wing_reads_registry(temp_registry):
+    miner.add_to_known_entities({"topics": ["foo"]}, wing="wing_a")
+    miner.add_to_known_entities({"topics": ["foo", "bar"]}, wing="wing_b")
+    result = miner.get_topics_by_wing()
+    assert result == {"wing_a": ["foo"], "wing_b": ["foo", "bar"]}
+
+
+def test_get_topics_by_wing_empty_when_missing(temp_registry):
+    miner.add_to_known_entities({"people": ["Alice"]})
+    assert miner.get_topics_by_wing() == {}
+
+
+def test_topics_by_wing_does_not_pollute_known_names(temp_registry):
+    """Wing names in topics_by_wing must NOT leak into the flat known-names
+    set used by ``_extract_entities_for_metadata`` — only the topic strings
+    themselves should be recognized."""
+    miner.add_to_known_entities({"topics": ["Angular"]}, wing="wing_super_secret_project")
+    known = miner._load_known_entities()
+    assert "Angular" in known
+    assert "wing_super_secret_project" not in known