docs updated

GEMINI.md

@@ -1,25 +1,79 @@
 # Gemini Project Overview: `jspg`
 
-This document outlines the purpose of the `jspg` project and the specific modifications made to the vendored `boon` JSON schema validator crate.
+This document outlines the purpose of the `jspg` project, its architecture, and the specific modifications made to the vendored `boon` JSON schema validator crate.
 
 ## What is `jspg`?
 
 `jspg` is a PostgreSQL extension written in Rust using the `pgrx` framework. Its primary function is to provide fast, in-database JSON schema validation against the 2020-12 draft of the JSON Schema specification.
 
-It works by:
-1.  Exposing a SQL function, `cache_json_schemas(...)`, which takes arrays of schema objects, compiles them, and caches them in memory.
-2.  Exposing a SQL validation function, `validate_json_schema(schema_id, instance)`, which validates a JSONB instance against one of the pre-cached schemas.
-3.  Using a locally modified (vendored) version of the `boon` crate to perform the validation, allowing for custom enhancements to its core logic.
+### How It Works
+
+The extension is designed for high-performance scenarios where schemas are defined once and used many times for validation. It achieves this through an in-memory cache.
+
+1.  **Caching:** A user first calls the `cache_json_schemas(enums, types, puncs)` SQL function. This function takes arrays of JSON objects representing different kinds of schemas within a larger application framework. It uses the vendored `boon` crate to compile all these schemas into an efficient internal format and stores them in a static, in-memory `SCHEMA_CACHE`. This cache is managed by a `RwLock` to allow concurrent reads during validation.
+
+2.  **Validation:** The `validate_json_schema(schema_id, instance)` SQL function is then used to validate a JSONB `instance` against a specific, pre-cached schema identified by its `$id`. This function looks up the compiled schema in the cache and runs the validation, returning a success response or a detailed error report.
+
+3.  **Custom Logic:** `jspg` uses a locally modified (vendored) version of the `boon` crate. This allows for powerful, application-specific validation logic that goes beyond the standard JSON Schema specification, such as runtime-based strictness.
+
+### Error Handling
+
+When validation fails, `jspg` provides a detailed error report in a consistent JSON format, which we refer to as a "DropError". This process involves two main helper functions in `src/lib.rs`:
+
+1.  **`collect_errors`**: `boon` returns a nested tree of `ValidationError` objects. This function recursively traverses that tree to find the most specific, underlying causes of the failure. It filters out structural errors (like `allOf` or `anyOf`) to create a flat list of concrete validation failures.
+
+2.  **`format_errors`**: This function takes the flat list of errors and transforms each one into the final DropError JSON format. It also de-duplicates errors that occur at the same JSON Pointer path, ensuring a cleaner output if a single value violates multiple constraints.
+
+#### DropError Format
+
+A DropError object provides a clear, structured explanation of a validation failure:
+
+```json
+{
+  "code": "ADDITIONAL_PROPERTIES_NOT_ALLOWED",
+  "message": "Property 'extra' is not allowed",
+  "details": {
+    "path": "/extra",
+    "context": "not allowed",
+    "cause": {
+      "got": [
+        "extra"
+      ]
+    },
+    "schema": "basic_strict_test.request"
+  }
+}
+```
+
+-   `code` (string): A machine-readable error code (e.g., `ADDITIONAL_PROPERTIES_NOT_ALLOWED`, `MIN_LENGTH_VIOLATED`).
+-   `message` (string): A human-readable summary of the error.
+-   `details` (object):
+    -   `path` (string): The JSON Pointer path to the invalid data within the instance.
+    -   `context` (any): The actual value that failed validation.
+    -   `cause` (any): The low-level reason from the validator, often including the expected value (`want`) and the actual value (`got`).
+    -   `schema` (string): The `$id` of the schema that was being validated.
+
+---
 
 ## `boon` Crate Modifications
 
-The version of `boon` located in the `validator/` directory has been modified to address specific requirements of the `jspg` project. The key deviations from the upstream `boon` crate are as follows:
+The version of `boon` located in the `validator/` directory has been significantly modified to support runtime-based strict validation. The original `boon` crate only supports compile-time strictness and lacks the necessary mechanisms to propagate validation context correctly for our use case.
 
 ### 1. Recursive Runtime Strictness Control
 
--   **Problem:** The `jspg` project requires that certain schemas enforce a strict "no extra properties" policy (specifically, schemas for public `puncs` and global `type`s). This strictness needs to cascade through the entire validation hierarchy, including all nested objects and `$ref` chains. A compile-time flag was unsuitable because it would incorrectly apply strictness to shared, reusable schemas.
+-   **Problem:** The `jspg` project requires that certain schemas (specifically those for public `puncs` and global `type`s) enforce a strict "no extra properties" policy. This strictness needs to be decided at runtime and must cascade through the entire validation hierarchy, including all nested objects and `$ref` chains. A compile-time flag was unsuitable because it would incorrectly apply strictness to shared, reusable schemas.
 
--   **Solution:** A runtime validation option was implemented to enforce strictness recursively.
-    1.  A `ValidationOptions { be_strict: bool }` struct was added. The `jspg` code in `src/lib.rs` determines whether a validation run should be strict (based on the `punc`'s `public` flag or if validating a global `type`) and passes the appropriate option to the validator.
-    2.  The `be_strict` option is propagated through the entire recursive validation process. A bug was fixed in `_validate_self` (which handles `$ref`s) to ensure that the sub-validator is always initialized to track unevaluated properties when `be_strict` is enabled. Previously, tracking was only initiated if the parent was already tracking unevaluated properties, causing strictness to be dropped across certain `$ref` boundaries.
-    3. At any time, if `unevaluatedProperties` or `additionalProperties` is found in the schema, it should override the strict (or non-strict) validation at that level.
+-   **Solution:** A runtime validation option was implemented to enforce strictness recursively. This required several coordinated changes to the `boon` validator.
+
+#### Key Changes
+
+1.  **`ValidationOptions` Struct**: A new `ValidationOptions { be_strict: bool }` struct was added to `validator/src/lib.rs`. The `jspg` code in `src/lib.rs` determines if a validation run should be strict and passes this struct to the validator.
+
+2.  **Strictness Check in `uneval_validate`**: The original `boon` only checked for unevaluated properties if the `unevaluatedProperties` keyword was present in the schema. We added an `else if be_strict` block to `uneval_validate` in `validator/src/validator.rs`. This block triggers a check for any leftover unevaluated properties at the end of a validation pass and reports them as errors, effectively enforcing our runtime strictness rule.
+
+3.  **Correct Context Propagation**: The most complex part of the fix was ensuring the set of unevaluated properties was correctly maintained across different validation contexts (especially `$ref` and nested property validations). Three critical changes were made:
+    -   **Inheriting Context in `_validate_self`**: When validating keywords that apply to the same instance (like `$ref` or `allOf`), the sub-validator must know what properties the parent has already evaluated. We changed the creation of the `Validator` inside `_validate_self` to pass a clone of the parent's `uneval` state (`uneval: self.uneval.clone()`) instead of creating a new one from scratch. This allows the context to flow downwards.
+    -   **Isolating Context in `validate_val`**: Conversely, when validating a property's value, that value is a *different* part of the JSON instance. The sub-validation should not affect the parent's list of unevaluated properties. We fixed this by commenting out the `self.uneval.merge(...)` call in the `validate_val` function.
+    -   **Simplifying `Uneval::merge`**: The original logic for merging `uneval` state was different for `$ref` keywords. This was incorrect. We simplified the `merge` function to *always* perform an intersection (`retain`), which correctly combines the knowledge of evaluated properties from different schema parts that apply to the same instance.
+
+4.  **Removing Incompatible Assertions**: The changes to context propagation broke several `debug_assert!` macros in the `arr_validate` function, which were part of `boon`'s original design. Since our new validation flow is different but correct, these assertions were removed.