fix: make entity_registry.research() local-only by default (#811)

* fix: make entity_registry.research() local-only by default

research() previously called _wikipedia_lookup() unconditionally,
sending entity names to en.wikipedia.org on every uncached lookup.
This violates the project's local-first and privacy-by-architecture
principles documented in CLAUDE.md.

Changes:
- research() now returns "unknown" for uncached words by default
- New allow_network=True parameter required for Wikipedia lookups
- Wikipedia 404 now returns "unknown" instead of asserting "person"
  with 0.70 confidence, preventing entity registry poisoning
- Added privacy warning docstring to _wikipedia_lookup()
- Added tests for local-only default, opt-in network, 404 handling,
  and cache-not-persisted-on-local-only behaviour

Refs: MemPalace/mempalace#809

* fix: improve research() cache read path and deduplicate test mocks

- Use .get() instead of .setdefault() for cache reads in research()
  so the local-only path never mutates _data unnecessarily
- Move .setdefault() to the network-write path only
- Use result.setdefault() for word/confirmed keys to ensure
  consistent return shape across all _wikipedia_lookup error paths
- Extract duplicated mock_result dict into _MOCK_SAOIRSE_PERSON
  constant shared by 3 test functions

tests/test_entity_registry.py

@@ -8,6 +8,14 @@ from mempalace.entity_registry import (
     EntityRegistry,
 )
 
+# Shared mock result for Wikipedia person lookup tests
+_MOCK_SAOIRSE_PERSON = {
+    "inferred_type": "person",
+    "confidence": 0.80,
+    "wiki_summary": "Saoirse is an Irish given name.",
+    "wiki_title": "Saoirse",
+}
+
 
 # ── COMMON_ENGLISH_WORDS ────────────────────────────────────────────────
 
@@ -213,22 +221,49 @@ def test_lookup_ambiguous_word_as_concept(tmp_path):
     assert result["type"] == "concept"
 
 
-# ── research (Wikipedia) — mocked ──────────────────────────────────────
+# ── research — local-only by default ───────────────────────────────────
 
 
-def test_research_caches_result(tmp_path):
+def test_research_local_only_by_default(tmp_path):
+    """research() must NOT call Wikipedia unless allow_network=True."""
     registry = EntityRegistry.load(config_dir=tmp_path)
     registry.seed(mode="personal", people=[], projects=[])
 
-    mock_result = {
-        "inferred_type": "person",
-        "confidence": 0.80,
-        "wiki_summary": "Saoirse is an Irish given name.",
-        "wiki_title": "Saoirse",
-    }
+    with patch(
+        "mempalace.entity_registry._wikipedia_lookup",
+        side_effect=AssertionError("network call should not happen"),
+    ):
+        result = registry.research("Saoirse")
 
-    with patch("mempalace.entity_registry._wikipedia_lookup", return_value=mock_result):
-        result = registry.research("Saoirse", auto_confirm=True)
+    assert result["inferred_type"] == "unknown"
+    assert result["confidence"] == 0.0
+    assert result["word"] == "Saoirse"
+    assert "network lookup disabled" in result.get("note", "")
+
+
+def test_research_with_allow_network(tmp_path):
+    """research(allow_network=True) calls Wikipedia and caches result."""
+    registry = EntityRegistry.load(config_dir=tmp_path)
+    registry.seed(mode="personal", people=[], projects=[])
+
+    with patch(
+        "mempalace.entity_registry._wikipedia_lookup",
+        return_value=dict(_MOCK_SAOIRSE_PERSON),
+    ):
+        result = registry.research("Saoirse", auto_confirm=True, allow_network=True)
+    assert result["inferred_type"] == "person"
+
+
+def test_research_caches_result(tmp_path):
+    """Once cached via allow_network, subsequent calls use cache without network."""
+    registry = EntityRegistry.load(config_dir=tmp_path)
+    registry.seed(mode="personal", people=[], projects=[])
+
+    with patch(
+        "mempalace.entity_registry._wikipedia_lookup",
+        return_value=dict(_MOCK_SAOIRSE_PERSON),
+    ):
+        result = registry.research("Saoirse", auto_confirm=True, allow_network=True)
     assert result["inferred_type"] == "person"
 
     # Second call should use cache, not call Wikipedia again
@@ -240,24 +275,49 @@ def test_research_caches_result(tmp_path):
     assert cached["inferred_type"] == "person"
 
 
+def test_research_local_only_not_cached(tmp_path):
+    """Local-only result for uncached word should NOT be persisted to cache."""
+    registry = EntityRegistry.load(config_dir=tmp_path)
+    registry.seed(mode="personal", people=[], projects=[])
+
+    registry.research("Xander")  # local-only, no network
+    assert "Xander" not in registry._data.get("wiki_cache", {})
+
+
 def test_confirm_research_adds_to_people(tmp_path):
     registry = EntityRegistry.load(config_dir=tmp_path)
     registry.seed(mode="personal", people=[], projects=[])
 
-    mock_result = {
-        "inferred_type": "person",
-        "confidence": 0.80,
-        "wiki_summary": "Saoirse is a name",
-        "wiki_title": "Saoirse",
-    }
-    with patch("mempalace.entity_registry._wikipedia_lookup", return_value=mock_result):
-        registry.research("Saoirse", auto_confirm=False)
+    with patch(
+        "mempalace.entity_registry._wikipedia_lookup",
+        return_value=dict(_MOCK_SAOIRSE_PERSON),
+    ):
+        registry.research("Saoirse", auto_confirm=False, allow_network=True)
 
     registry.confirm_research("Saoirse", entity_type="person", relationship="friend")
     assert "Saoirse" in registry.people
     assert registry.people["Saoirse"]["source"] == "wiki"
 
 
+def test_wikipedia_404_returns_unknown(tmp_path):
+    """A 404 from Wikipedia should return 'unknown', not assert 'person'."""
+    registry = EntityRegistry.load(config_dir=tmp_path)
+    registry.seed(mode="personal", people=[], projects=[])
+
+    mock_result = {
+        "inferred_type": "unknown",
+        "confidence": 0.3,
+        "wiki_summary": None,
+        "wiki_title": None,
+        "note": "not found in Wikipedia",
+    }
+    with patch("mempalace.entity_registry._wikipedia_lookup", return_value=mock_result):
+        result = registry.research("Zzxqy", auto_confirm=False, allow_network=True)
+
+    assert result["inferred_type"] == "unknown"
+    assert result["confidence"] < 0.5
+
+
 # ── extract_people_from_query ───────────────────────────────────────────