fix(memory): bound invalid-target error and restore recovery hint

Route the model-supplied target through _bound_error_text so a huge
bogus target can't bloat context, and restore the "Use 'memory' or
'user'" hint. Follow-up to HexLab98's review note on the salvage.

tests/agent/test_builtin_memory_disabled_surface.py

@@ -220,6 +220,26 @@ class TestIndependentStoreWriteGates:
         assert result["success"] is False
         assert result["target"] == "memory"
 
+    def test_invalid_target_error_is_bounded_and_carries_recovery_hint(self, hermes_home):
+        """Model-supplied target is interpolated into the error: it must stay
+        capped at the shared tool_error bound and keep the recovery hint."""
+        from tools.memory_tool import memory_tool
+        from tools.registry import _MAX_TOOL_ERROR_CHARS
+
+        store = self._store(memory_enabled=True, user_profile_enabled=True)
+        result = json.loads(
+            memory_tool(action="add", target="x" * 10_000, content="fact", store=store)
+        )
+
+        assert result["success"] is False
+        assert len(result["error"]) <= _MAX_TOOL_ERROR_CHARS + 32
+
+        short = json.loads(
+            memory_tool(action="add", target="bogus", content="fact", store=store)
+        )
+        assert short["success"] is False
+        assert "Use 'memory' or 'user'" in short["error"]
+
 
 class TestExternalProviderSurvivesBuiltinDisable:
     """Dropping the built-in tool must not drop the external provider's tools.

tools/memory_tool.py

@@ -1216,7 +1216,14 @@ def check_memory_requirements() -> bool:
 def _memory_target_error(store: "MemoryStore", target: str) -> Optional[Dict[str, Any]]:
     """Return a shared validation error for an invalid or disabled target."""
     if target not in {"memory", "user"}:
-        return {"success": False, "error": f"Invalid memory target '{target}'."}
+        from tools.registry import _bound_error_text
+
+        return {
+            "success": False,
+            "error": _bound_error_text(
+                f"Invalid memory target '{target}'. Use 'memory' or 'user'."
+            ),
+        }
     if store.target_enabled(target):
         return None
     label = "USER.md" if target == "user" else "MEMORY.md"