diff --git a/services/memory/memory_extractor.py b/services/memory/memory_extractor.py
index 32412e6..44a9f1f 100644
--- a/services/memory/memory_extractor.py
+++ b/services/memory/memory_extractor.py
@@ -345,8 +345,17 @@ async def extract_and_store(
                     logger.warning(f"Memory dedup (vector) unavailable, using text fallback: {e}")
                     existing_id = None
                 if existing_id:
-                    logger.debug(f"Memory dedup (vector): '{fact_text[:50]}' matches {existing_id}")
-                    continue
+                    # The vector store is a single shared collection with no
+                    # owner metadata, so find_similar can return ANOTHER
+                    # tenant's memory. Only treat it as a duplicate when the
+                    # match is this user's own (or a legacy unowned) memory —
+                    # otherwise the user's freshly-extracted fact would be
+                    # silently dropped. Mirror the owner predicate used by the
+                    # text dedup below; cross-tenant/stale matches fall through.
+                    _match = next((e for e in existing if e.get("id") == existing_id), None)
+                    if _match is not None and (_match.get("owner") == _owner or _match.get("owner") is None):
+                        logger.debug(f"Memory dedup (vector): '{fact_text[:50]}' matches {existing_id}")
+                        continue
 
             # Text dedup fallback: exact match + fuzzy similarity
             user_existing = [e for e in existing if e.get("owner") == _owner or e.get("owner") is None] if _owner else existing
diff --git a/tests/test_memory_extractor_vector_cross_tenant.py b/tests/test_memory_extractor_vector_cross_tenant.py
new file mode 100644
index 0000000..6b1d243
--- /dev/null
+++ b/tests/test_memory_extractor_vector_cross_tenant.py
@@ -0,0 +1,111 @@
+"""Regression: auto-memory vector dedup must not drop a user's fact because it
+matches ANOTHER tenant's memory.
+
+`extract_and_store` dedups each extracted fact against the vector store first.
+The vector store (`memory_vector`) is a single shared ChromaDB collection with
+no owner in its metadata, so `find_similar` can return a memory_id belonging to
+a different user. The old code `continue`d (skipped storing) on any vector hit
+without checking ownership, so user B's freshly-extracted fact was silently
+dropped when it was merely semantically similar to user A's memory. The text
+dedup fallback right below is already owner-scoped; the vector path must be too.
+"""
+import asyncio
+import importlib.util
+import sys
+import types
+from pathlib import Path
+
+import pytest
+
+ROOT = Path(__file__).resolve().parents[1]
+
+
+def _load_extractor():
+    # Load services/memory/memory_extractor.py directly by path so we don't
+    # trigger services/__init__ (which imports the search stack and its heavy
+    # optional deps). The module's only module-level imports are stdlib; its
+    # src.llm_core / src.event_bus imports are lazy and stubbed/guarded.
+    path = ROOT / "services" / "memory" / "memory_extractor.py"
+    spec = importlib.util.spec_from_file_location("memory_extractor_under_test", path)
+    mod = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(mod)
+    return mod
+
+
+def _install_llm_stub(facts_json):
+    mod = types.ModuleType("src.llm_core")
+
+    async def llm_call_async(*a, **k):
+        return facts_json
+
+    mod.llm_call_async = llm_call_async
+    src_pkg = sys.modules.get("src") or types.ModuleType("src")
+    sys.modules["src"] = src_pkg
+    sys.modules["src.llm_core"] = mod
+
+
+class FakeSession:
+    def __init__(self, owner):
+        self.owner = owner
+
+    def get_context_messages(self):
+        return [
+            {"role": "user", "content": "Tell me where I live."},
+            {"role": "assistant", "content": "Noted."},
+        ]
+
+
+class FakeMemoryManager:
+    def __init__(self, rows):
+        self.rows = list(rows)
+        self._n = 0
+
+    def load_all(self):
+        return list(self.rows)
+
+    def load(self, owner=None):
+        return [r for r in self.rows if r.get("owner") == owner]
+
+    def find_duplicates(self, text, subset):
+        t = text.strip().lower()
+        return [r for r in subset if r.get("text", "").strip().lower() == t]
+
+    def add_entry(self, text, source="auto", category="fact", owner=None):
+        self._n += 1
+        entry = {"id": f"new-{self._n}", "text": text, "owner": owner,
+                 "source": source, "category": category}
+        self.rows.append(entry)
+        return entry
+
+
+class FakeVector:
+    """Healthy vector store whose find_similar always matches user A's memory."""
+    def __init__(self, match_id):
+        self.healthy = True
+        self._match_id = match_id
+
+    def find_similar(self, text, threshold=0.92):
+        return self._match_id
+
+
+def test_vector_match_from_other_tenant_does_not_drop_users_fact(monkeypatch):
+    # User A already owns a semantically-similar memory.
+    mm = FakeMemoryManager([
+        {"id": "a1", "text": "I live in Lisbon", "owner": "userA"},
+    ])
+    # The vector store reports user B's new fact as a near-duplicate of a1.
+    vec = FakeVector(match_id="a1")
+    _install_llm_stub('["My home is in Lisbon"]')
+
+    memory_extractor = _load_extractor()
+
+    asyncio.run(memory_extractor.extract_and_store(
+        FakeSession(owner="userB"), mm, vec,
+        endpoint_url="http://x", model="m",
+    ))
+
+    b_texts = {r["text"] for r in mm.load(owner="userB")}
+    assert "My home is in Lisbon" in b_texts, (
+        "User B's own extracted fact was dropped because the shared vector "
+        "store matched user A's memory (cross-tenant dedup)."
+    )