jspg masking system installed

GEMINI.md

@@ -31,6 +31,17 @@ Loads and compiles the entire schema registry into the session's memory, atomica
     *   Compiles schemas into validators.
 *   **Returns**: `{"response": "success"}` or an error object.
 
+### `mask_json_schema(schema_id text, instance jsonb) -> jsonb`
+
+Validates a JSON instance and returns a new JSON object with unknown properties removed (pruned) based on the schema.
+
+*   **Inputs**:
+    *   `schema_id`: The `$id` of the schema to mask against.
+    *   `instance`: The JSON data to mask.
+*   **Returns**:
+    *   On success: A `Drop` containing the **masked data**.
+    *   On failure: A `Drop` containing validation errors.
+
 ### `validate_json_schema(schema_id text, instance jsonb) -> jsonb`
 
 Validates a JSON instance against a pre-compiled schema.
@@ -83,6 +94,16 @@ JSPG enforces a "Secure by Default" philosophy. All schemas are treated as if `u
 ### 4. Format Leniency for Empty Strings
 To simplify frontend form logic, the format validators for `uuid`, `date-time`, and `email` explicitly allow empty strings (`""`). This treats an empty string as "present but unset" rather than "invalid format".
 
+### 5. Masking (Constructive Validation)
+JSPG supports a "Constructive Validation" mode via `mask_json_schema`. This is designed for high-performance API responses where the schema dictates the exact shape of the returned data.
+
+*   **Mechanism**: The validator traverses the instance against the schema.
+*   **Valid Fields**: Kept in the output.
+*   **Unknown/Extra Fields**: Silently removed (pruned) if `extensible: false` (default).
+*   **Invalid Fields**: Still trigger standard validation errors.
+
+This allows the database to return "raw" joined rows (e.g. `SELECT * FROM person JOIN organization ...`) and have JSPG automatically shape the result into the expected API response, removing any internal or unrelated columns not defined in the schema.
+
 ## 🏗️ Architecture
 
 The extension is written in Rust using `pgrx` and structures its schema parser to mirror the Punc Generator's design: