diff --git a/GramAddict/core/perception/screen_identity.py b/GramAddict/core/perception/screen_identity.py
index 2073b69..85db768 100644
--- a/GramAddict/core/perception/screen_identity.py
+++ b/GramAddict/core/perception/screen_identity.py
@@ -40,6 +40,8 @@ class ScreenIdentity:
             from GramAddict.core.qdrant_memory import ScreenMemoryDB
 
             self.screen_memory = ScreenMemoryDB()
+            if self.screen_memory:
+                self.screen_memory.purge_stale_screens()
         except ImportError:
             self.screen_memory = None
 
diff --git a/GramAddict/core/qdrant_memory.py b/GramAddict/core/qdrant_memory.py
index cc31eaf..4a10d0e 100644
--- a/GramAddict/core/qdrant_memory.py
+++ b/GramAddict/core/qdrant_memory.py
@@ -772,6 +772,16 @@ class ScreenMemoryDB(QdrantBase):
         if not vector:
             return
 
+        # ── P0-3: Collection Management ──
+        # Prevent embedding saturation by limiting to 200 high-quality signatures
+        try:
+            count = self.client.count(collection_name=self.collection_name).count
+            if count >= 200:
+                logger.warning("🚨 [ScreenMemory] Collection saturated (>= 200). Wiping to clear overfitting bias.")
+                self.wipe_collection()
+        except Exception:
+            pass
+
         self.upsert_point(
             seed_string=xml_signature,
             vector=vector,
@@ -783,7 +793,7 @@ class ScreenMemoryDB(QdrantBase):
             log_success=f"🧠 [ScreenMemory] Learned new layout mapping: {screen_type}",
         )
 
-    def get_screen_type(self, xml_signature: str, similarity_threshold: float = 0.90) -> Optional[str]:
+    def get_screen_type(self, xml_signature: str, similarity_threshold: float = 0.95) -> Optional[str]:
         if not self.is_connected or not xml_signature:
             return None
 
@@ -809,6 +819,30 @@ class ScreenMemoryDB(QdrantBase):
             logger.debug(f"Screen memory error: {e}")
             return None
 
+    def purge_stale_screens(self, max_age_hours: float = 24):
+        """Removes entries older than max_age_hours to prevent layout drift poisoning."""
+        if not self.is_connected:
+            return
+        try:
+            points, _ = self.client.scroll(
+                collection_name=self.collection_name,
+                limit=200,
+                with_payload=True,
+            )
+            now = time.time()
+            purged = 0
+            for pt in points:
+                payload = pt.payload or {}
+                stored_at = payload.get("stored_at", 0)
+                age_hours = (now - stored_at) / 3600 if stored_at > 0 else 0
+                if age_hours > max_age_hours:
+                    self.delete_point(payload.get("signature", str(pt.id)))
+                    purged += 1
+            if purged:
+                logger.info(f"🧹 [ScreenMemory] Purged {purged} stale layout mappings (> {max_age_hours}h).")
+        except Exception as e:
+            logger.debug(f"Screen purge error: {e}")
+
     def purge_screen(self, xml_signature: str):
         """Unlearns a screen classification to recover from hallucinations."""
         if not self.is_connected or not xml_signature:
diff --git a/tests/core/test_screen_memory_hardening.py b/tests/core/test_screen_memory_hardening.py
new file mode 100644
index 0000000..8af916d
--- /dev/null
+++ b/tests/core/test_screen_memory_hardening.py
@@ -0,0 +1,68 @@
+"""
+P0-3: ScreenMemory Cache Poisoning Guard
+
+TDD RED: These tests enforce that:
+1. The similarity threshold for screen type cache hits is raised to 0.95
+   to prevent false-positive POST_DETAIL matches.
+2. A purge_stale_screens() method exists and removes entries older than
+   a configurable TTL.
+3. The collection has a max size cap to prevent embedding saturation.
+"""
+
+import time
+
+from GramAddict.core.qdrant_memory import ScreenMemoryDB
+
+
+# ═══════════════════════════════════════════════════════
+# P0-3a: Raised Similarity Threshold
+# ═══════════════════════════════════════════════════════
+
+
+class TestScreenMemoryThreshold:
+    """Session log: 34/60 screens classified as POST_DETAIL at 0.92-0.97 similarity."""
+
+    def test_default_threshold_is_095(self):
+        """
+        RED: The default similarity_threshold in get_screen_type is 0.90,
+        which is too low and causes false-positive POST_DETAIL cache hits.
+        GREEN: Raise default to 0.95.
+        """
+        import inspect
+
+        sig = inspect.signature(ScreenMemoryDB.get_screen_type)
+        default = sig.parameters["similarity_threshold"].default
+
+        assert default == 0.95, (
+            f"Expected default similarity_threshold=0.95, got {default}. "
+            f"Threshold 0.90 causes POST_DETAIL over-matching."
+        )
+
+
+# ═══════════════════════════════════════════════════════
+# P0-3b: Staleness Purge
+# ═══════════════════════════════════════════════════════
+
+
+class TestScreenMemoryStalePurge:
+    """Screen layouts change with IG updates; stale cache entries are poison."""
+
+    def test_purge_stale_screens_method_exists(self):
+        """
+        RED: ScreenMemoryDB has no purge_stale_screens() method.
+        GREEN: Add a method that removes entries older than a configurable max_age_hours.
+        """
+        db = ScreenMemoryDB()
+        assert hasattr(db, "purge_stale_screens"), (
+            "ScreenMemoryDB must have a purge_stale_screens() method "
+            "to prevent cache poisoning from stale screen layouts."
+        )
+
+    def test_purge_stale_screens_has_max_age_parameter(self):
+        """The purge method must accept a max_age_hours parameter."""
+        import inspect
+
+        sig = inspect.signature(ScreenMemoryDB.purge_stale_screens)
+        assert "max_age_hours" in sig.parameters, (
+            "purge_stale_screens must accept max_age_hours parameter"
+        )