# Mutable Metadata & Per-Client Custom Schemas - Combined Design Plan (v2)

## Status: DRAFT - Combined Claude + Codex + Jay's recommendations (2026-03-24, rev 2026-03-31 post-review, rev 2026-04-10: schema administration restricted to `super_admin` role only)

**Lineage**: This plan was informed by two original detailed specs done adversarily. One by claude Opus 4.6 and one by Codex 5.4 (xhigh) based on human written requirements. Each was human reviewed for common items and conflicting items. Where there were conflicts the human was the final decision maker. This resulting hybrid document represents an improved design over each of the source documents.

**v2 change summary (2026-04-10)**: In v1 all mutable-metadata administrative endpoints lived under `/admin/*`. Because the Permit.io middleware maps resources from the first path segment and both `user_admin` and `super_admin` hold full permissions on the `admin` resource, v1 exposed schema CRUD and schema assignment to the lesser (client-scoped) `user_admin` role. v2 moves every schema administration endpoint onto a new `/super-admin/*` path prefix backed by a new Permit.io resource named `super-admin` that only the `super_admin` role can access. User-facing custom metadata read/write endpoints (`/custom-metadata/*`) are unchanged. The underlying service layer, database schema, triggers, and validation strategy are unchanged -- this is strictly an authorization and routing change.

---

## 1. Problem Statement

Today, all field extraction data is stored in a rigid 3-table schema with ~130 statically-defined columns (19 single-value fields + 112 array fields). Every client shares the same field definitions. This means:

- Clients cannot define domain-specific fields (e.g., "aircraft engineering" vs. "auto engineering" document classes)
- Adding new fields requires database migrations and code changes across the full stack
- The system cannot accommodate varying data shapes per document class within a single client

**Goal**: Allow each client to curate their own collections of document schemas, where each schema defines the custom fields (with types and constraints) that a document's metadata must conform to. Administration of these schemas (create, update, retire, list, assign to documents/folders) is a platform-level responsibility and must be restricted to the `super_admin` role, not delegated to the lower-privileged `user_admin` role.

---

## 2. Current Architecture Summary

### 2.1 Existing Tables

```
documentFieldExtractions          -- 19 single-value fields (1:1 per document)
documentFieldExtractionVersions   -- Version tracking with row-level locking
documentFieldExtractionArrayFields -- 112 array fields (1:N per extraction)
```

### 2.2 Existing API Endpoints

| Method | Path | Description |
|--------|------|-------------|
| POST | `/field-extractions` | Create versioned extraction (singleFields + arrayFields) |
| GET | `/field-extractions` | Get current (latest version) extraction for a document |
| GET | `/field-extractions/version` | Get extraction by specific version |
| GET | `/field-extractions/history` | List all versions for a document |

### 2.3 Key Relationships

- `documents.id` -> `documentFieldExtractions.documentId` (1:N via versions)
- `documentFieldExtractions.id` -> `documentFieldExtractionArrayFields.fieldExtractionId` (1:N)
- `documentFieldExtractions.id` -> `documentFieldExtractionVersions.fieldExtractionId` (1:N)
- Documents belong to clients via `documents.clientId`
- No per-client customization of field definitions exists today

### 2.4 Current Role Model (Relevant to This Plan)

Two admin-class roles exist today, both configured in `cmd/auth_related/permit.setup/permit_policies.yaml`:

- **`super_admin`**: Platform administrator. Holds full permissions across every resource (`admin`, `client`, `clients`, `document`, `documents`, `folders`, etc.). Intended for AArete-internal operators.
- **`user_admin`**: Client-scoped administrator. Primarily used for creating new client users via the admin user tool. Holds full permissions on the `admin` resource but intentionally does **not** hold permissions on `client`, `clients`, or `document` at the resource level.

Because the middleware extracts the resource from the first path segment (`/admin/foo` -> resource `admin`), any endpoint placed under `/admin/*` is accessible to both `super_admin` and `user_admin`. v1 of this plan placed schema administration under `/admin/*` and therefore exposed schema CRUD and assignment to `user_admin`. v2 corrects this.

---

## 3. Design Principles

1. **Additive, not destructive** - The existing static field extraction system continues to work unchanged for documents that do not opt into custom schemas. Custom schemas are an additive capability.
2. **Mutual exclusivity** - A document uses EITHER the legacy static field extraction system OR the custom schema system, never both. This prevents ambiguity about which system is authoritative for a document's metadata. Once a document is assigned a custom schema, the legacy field extraction endpoints reject writes for that document, and vice versa.
3. **Schema-as-data** - Schemas are stored as JSON Schema documents in the database, not as DDL. No migrations needed when clients add/modify schemas.
4. **Immutable schema versions** - When a schema is updated, a new version (with new ID) is created. Old versions remain for historical reference. No backward compatibility checking is required between versions since each version gets a distinct ID.
5. **Schema binding is permanent** - Once custom metadata is written to a document with a schema ID, that schema ID cannot be changed on the document. This guarantees data integrity.
6. **JSON blob storage** - Custom metadata is stored as JSONB in PostgreSQL, validated against the schema at write time. This avoids dynamic column creation.
7. **Client isolation** - Schemas are scoped to clients. A client cannot reference another client's schema.
8. **Size limits** - Schema definitions are capped at 64KB (`MaxSchemaDefinitionBytes = 65536`). Metadata payloads are capped at 1MB (`MaxMetadataPayloadBytes = 1048576`). Bulk folder assignments are capped at 10,000 documents (`MaxBulkAssignDocuments = 10000`). All are tunable constants.
9. **No JSONB search/filter** - The system does NOT support querying or filtering documents by custom metadata values. Custom metadata is opaque storage validated on write. If search is needed in the future, it would require GIN indexes on the JSONB columns and a dedicated query API (separate phase).
10. **`super_admin`-scoped schema management** - Schema CRUD operations, single-document schema assignment, and bulk folder-level schema assignment live under `/super-admin/*` and require the `super_admin` role. The lesser `user_admin` role does NOT have access to schema administration. Custom metadata read/write on documents (`/custom-metadata/*`) is available to regular `client_user` users and to both admin roles.
11. **Defense-in-depth** - Critical invariants (schema lock after first extraction, client/schema ownership match, schema_id consistency across metadata versions) are enforced at BOTH the application layer AND the database layer via triggers. The app-layer checks provide better error messages; the DB triggers are safety nets against bypass.
12. **No migration from static fields** - There is no migration path from the existing static field extraction data into the custom schema system. They are mutually exclusive per document. Out of scope.

---

## 4. Database Schema Design

### 4.1 New Type: `schema_status_type`

A three-state enum that distinguishes between different reasons a schema is no longer assignable:

```sql
CREATE TYPE schema_status_type AS ENUM ('active', 'superseded', 'retired');
```

- **`active`**: The schema version is current and can be assigned to new documents.
- **`superseded`**: A newer version of this schema (same `name`) was created. The schema is still valid for documents already using it, but should not be assigned to new documents. Set automatically when a new version is created via `PUT`.
- **`retired`**: An admin explicitly disabled this schema version. Functionally similar to `superseded` but indicates a deliberate administrative action rather than an automatic version succession.

### 4.2 New Table: `client_metadata_schemas`

Stores client-defined JSON Schema documents. Each row is an immutable version of a schema definition.

```sql
CREATE TABLE client_metadata_schemas (
    id              uuid PRIMARY KEY DEFAULT uuid_generate_v7(),
    client_id       varchar(255) NOT NULL REFERENCES clients(clientId),
    name            varchar(255) NOT NULL,
    description     text,
    schema_def      jsonb NOT NULL,          -- The JSON Schema document (max 64KB enforced at app layer)
    version         int NOT NULL DEFAULT 1,   -- Auto-incremented per (client_id, name)
    status          schema_status_type NOT NULL DEFAULT 'active',
    created_at      timestamptz NOT NULL DEFAULT NOW(),
    created_by      varchar(255) NOT NULL,

    CONSTRAINT uq_client_schema_name_version UNIQUE (client_id, name, version),
    CONSTRAINT chk_schema_def_size CHECK (pg_column_size(schema_def) <= 70000)  -- ~68KB to account for JSONB overhead; app layer enforces 64KB on raw JSON
);

CREATE INDEX idx_cms_client_id ON client_metadata_schemas(client_id);
CREATE INDEX idx_cms_client_name ON client_metadata_schemas(client_id, name);
CREATE INDEX idx_cms_client_status ON client_metadata_schemas(client_id, status);
```

> **Note**: The 64KB limit is enforced at the application layer (Go constant `MaxSchemaDefinitionBytes = 65536`) by checking `len(rawJSON)`. The database CHECK constraint uses `pg_column_size()` which measures on-disk JSONB storage (includes header overhead), so it is set slightly higher (~68KB) as a safety net. The app-layer check provides the user-facing 64KB limit and a better error message.

**Design decisions:**

- **`name` + `version`** scoped to client: Allows human-friendly naming ("aircraft-engineering-v3") with automatic versioning. When a schema is "updated," a new row is inserted with `version = max(version) + 1` for that `(client_id, name)`.
- **`schema_def` is JSONB**: Stores the full JSON Schema document. PostgreSQL can index into it if needed later.
- **`status` enum**: Three-state lifecycle. `superseded` is set automatically when a newer version is created. `retired` is set explicitly by admin action (soft-delete). Both states prevent assignment to new documents but allow existing documents to continue using the schema for validation. This is richer than a boolean `is_active` because it distinguishes "replaced by v2" from "admin decided this is bad."
- **`id` is the schema version ID**: This is what documents reference. Each update creates a new `id`. The `(client_id, name, version)` tuple provides the human-readable lineage.

### 4.3 New Table: `document_custom_metadata`

Stores the actual custom metadata for documents, validated against the referenced schema.

```sql
CREATE TABLE document_custom_metadata (
    id              uuid PRIMARY KEY DEFAULT uuid_generate_v7(),
    document_id     uuid NOT NULL REFERENCES documents(id),
    schema_id       uuid NOT NULL REFERENCES client_metadata_schemas(id),
    metadata        jsonb NOT NULL,           -- The actual custom field values
    version         int NOT NULL DEFAULT 1,   -- Versioned like field extractions
    created_at      timestamptz NOT NULL DEFAULT NOW(),
    created_by      varchar(255) NOT NULL,

    CONSTRAINT uq_doc_custom_metadata_version UNIQUE (document_id, version)
);

CREATE INDEX idx_dcm_document_id ON document_custom_metadata(document_id);
CREATE INDEX idx_dcm_schema_id ON document_custom_metadata(schema_id);
CREATE INDEX idx_dcm_doc_version_desc ON document_custom_metadata(document_id, version DESC);  -- Enables efficient DISTINCT ON in current_document_custom_metadata view
```

**Design decisions:**

- **Single table with version column**: We use one table (rather than separate extraction + version tables like the legacy pattern) because the simpler design is sufficient. The legacy two-table pattern exists to support row-level locking on the version counter independently of the data row. For custom metadata, the `UNIQUE (document_id, version)` constraint plus `SELECT ... FOR UPDATE` on the max-version row provides the same concurrency safety with less complexity. If this proves insufficient under load, splitting into two tables is a backward-compatible change.
- **`schema_id` is immutable per document**: Enforced at both the application layer and the database trigger (see Section 4.7). All versions of custom metadata for a document must reference the same schema ID.
- **`metadata` is JSONB**: Validated against `client_metadata_schemas.schema_def` at write time. Stored as a single blob for simplicity and query flexibility.

### 4.4 Alteration: `documents` Table

Add an optional schema binding column:

```sql
ALTER TABLE documents
    ADD COLUMN custom_schema_id uuid NULL REFERENCES client_metadata_schemas(id);

CREATE INDEX idx_documents_custom_schema_id ON documents(custom_schema_id);
```

**Behavior:**

- `NULL` = document uses the legacy static field extraction system (default, backward-compatible)
- `NOT NULL` = document is opted into the custom schema system; legacy field extraction endpoints will reject writes for this document
- Once set AND custom metadata has been written, this field becomes immutable (enforced at app layer AND DB trigger)
- Can be set before metadata is written (pre-binding) and changed freely until first metadata write
- Must reference a schema owned by the same client as the document (cross-client reference check enforced at app layer AND DB trigger)
- Cannot be set on a document that already has legacy field extractions (returns 409 Conflict)

### 4.5 New View: `current_document_custom_metadata`

```sql
CREATE VIEW current_document_custom_metadata AS
SELECT DISTINCT ON (document_id)
    id,
    document_id,
    schema_id,
    metadata,
    version,
    created_at,
    created_by
FROM document_custom_metadata
ORDER BY document_id, version DESC;
```

### 4.6 Entity Relationship Diagram

```
clients
  |
  |-- 1:N --> client_metadata_schemas (per-client schema definitions)
  |              |
  |              |-- referenced by --> documents.custom_schema_id
  |              |-- referenced by --> document_custom_metadata.schema_id
  |
  |-- 1:N --> documents
                 |
                 |-- 1:N --> document_custom_metadata (versioned JSONB blobs)
                 |           [MUTUALLY EXCLUSIVE with legacy extractions]
                 |-- 1:N --> documentFieldExtractions (existing static fields)
                             [MUTUALLY EXCLUSIVE with custom metadata]
```

### 4.7 Database Triggers (Defense-in-Depth)

Three triggers enforce critical invariants at the database level, providing a safety net regardless of which code path modifies the data.

#### Trigger 1: Prevent schema reassignment after first extraction

Fires on `documents` BEFORE UPDATE of `custom_schema_id`. Prevents changes if the document has any extraction data (legacy or custom).

```sql
CREATE OR REPLACE FUNCTION trg_prevent_schema_reassignment()
RETURNS TRIGGER AS $$
BEGIN
    -- Only fire if custom_schema_id is actually changing
    IF OLD.custom_schema_id IS DISTINCT FROM NEW.custom_schema_id THEN
        -- Check for existing custom metadata
        IF EXISTS (
            SELECT 1 FROM document_custom_metadata
            WHERE document_id = NEW.id
            LIMIT 1
        ) THEN
            RAISE EXCEPTION 'Cannot change custom_schema_id on document % because custom metadata already exists', NEW.id;
        END IF;

        -- Check for existing legacy field extractions
        IF EXISTS (
            SELECT 1 FROM "documentFieldExtractionVersions"
            WHERE "documentId" = NEW.id
            LIMIT 1
        ) THEN
            RAISE EXCEPTION 'Cannot change custom_schema_id on document % because legacy field extractions already exist', NEW.id;
        END IF;
    END IF;

    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER trg_documents_prevent_schema_reassignment
    BEFORE UPDATE OF custom_schema_id ON documents
    FOR EACH ROW
    EXECUTE FUNCTION trg_prevent_schema_reassignment();
```

#### Trigger 2: Validate client/schema ownership match

Fires on `documents` BEFORE INSERT OR UPDATE of `custom_schema_id`. Ensures the referenced schema belongs to the same client as the document.

```sql
CREATE OR REPLACE FUNCTION trg_validate_schema_client_match()
RETURNS TRIGGER AS $$
DECLARE
    schema_client_id varchar(255);
BEGIN
    -- Only check when custom_schema_id is non-null
    IF NEW.custom_schema_id IS NOT NULL THEN
        SELECT client_id INTO schema_client_id
        FROM client_metadata_schemas
        WHERE id = NEW.custom_schema_id;

        IF schema_client_id IS NULL THEN
            RAISE EXCEPTION 'Schema % does not exist', NEW.custom_schema_id;
        END IF;

        IF schema_client_id != NEW."clientId" THEN
            RAISE EXCEPTION 'Schema % belongs to client %, but document % belongs to client %',
                NEW.custom_schema_id, schema_client_id, NEW.id, NEW."clientId";
        END IF;
    END IF;

    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER trg_documents_validate_schema_client
    BEFORE INSERT OR UPDATE OF custom_schema_id ON documents
    FOR EACH ROW
    EXECUTE FUNCTION trg_validate_schema_client_match();
```

#### Trigger 3: Enforce consistent schema_id across metadata versions

Fires on `document_custom_metadata` BEFORE INSERT. Ensures all metadata versions for a document reference the same schema ID. This is the database-level safety net for Invariant 7.

```sql
CREATE OR REPLACE FUNCTION trg_enforce_consistent_schema_id()
RETURNS TRIGGER AS $$
DECLARE
    existing_schema_id uuid;
BEGIN
    SELECT schema_id INTO existing_schema_id
    FROM document_custom_metadata
    WHERE document_id = NEW.document_id
    LIMIT 1;

    IF existing_schema_id IS NOT NULL AND existing_schema_id != NEW.schema_id THEN
        RAISE EXCEPTION 'All custom metadata for document % must use schema %, but got %',
            NEW.document_id, existing_schema_id, NEW.schema_id;
    END IF;

    RETURN NEW;
END;
$$ LANGUAGE plpgsql;

CREATE TRIGGER trg_dcm_enforce_consistent_schema
    BEFORE INSERT ON document_custom_metadata
    FOR EACH ROW
    EXECUTE FUNCTION trg_enforce_consistent_schema_id();
```

> **Note**: These triggers duplicate checks that also exist in the application service layer. This is intentional. The app-layer checks return structured HTTP error responses (400/409). The triggers are a last-resort safety net that fires even if a future code path, migration script, or admin query bypasses the service layer.

---

## 5. API Design

### 5.1 Schema Management Endpoints (`super_admin` only)

All schema CRUD endpoints live under the `/super-admin/custom-schemas` path prefix. The first path segment `super-admin` maps (via the existing first-segment resource extraction rule in the Permit.io middleware) to a new Permit.io resource named `super-admin`. Only the `super_admin` role holds permissions on this resource. The `user_admin` role does NOT have access.

These endpoints are grouped under a new OpenAPI tag `SuperAdminSchemaService` (distinct from the existing `AdminService`) to make the authorization boundary visible in the generated client and in Swagger.

#### `POST /super-admin/custom-schemas`

Create a new schema for a client.

**Request:**
```json
{
    "clientId": "acme-corp",
    "name": "aircraft-engineering",
    "description": "Custom fields for aircraft engineering documents",
    "schema": {
        "$schema": "https://json-schema.org/draft/2020-12/schema",
        "type": "object",
        "properties": {
            "aircraft_model": {
                "type": "string",
                "maxLength": 100
            },
            "certification_date": {
                "type": "string",
                "format": "date"
            },
            "max_altitude_ft": {
                "type": "number",
                "minimum": 0,
                "maximum": 100000
            },
            "engine_count": {
                "type": "integer",
                "minimum": 1,
                "maximum": 12
            }
        },
        "required": ["aircraft_model"],
        "additionalProperties": false
    },
    "createdBy": "admin@acme.com"
}
```

**Response (201):**
```json
{
    "id": "019577a3-...",
    "clientId": "acme-corp",
    "name": "aircraft-engineering",
    "description": "Custom fields for aircraft engineering documents",
    "schema": { ... },
    "version": 1,
    "status": "active",
    "createdAt": "2026-03-23T12:00:00Z",
    "createdBy": "admin@acme.com"
}
```

**Validation:**
- The `schema` field MUST be a valid JSON Schema document (validated server-side using a JSON Schema meta-validator)
- The `schema` field must be <= 64KB in size (returns 400 with message referencing the limit)
- Root `type` must be `"object"`
- Root `additionalProperties` MUST be explicitly present (either `true` or `false`). If omitted, the server returns 400 with a message explaining that `additionalProperties` must be explicitly declared. This prevents the common mistake of omitting it and inadvertently accepting arbitrary extra fields.
- `name` must be unique within the client (for active schemas at the same version)

#### `PUT /super-admin/custom-schemas/{schemaId}`

Update an existing schema. Creates a new version with a new ID. The old version remains intact and its status is set to `superseded`. No backward compatibility check is performed -- the new version is treated as an independent schema that happens to share a name lineage.

**Request:**
```json
{
    "description": "Updated aircraft engineering fields (added wingspan)",
    "schema": {
        "$schema": "https://json-schema.org/draft/2020-12/schema",
        "type": "object",
        "properties": {
            "aircraft_model": { "type": "string", "maxLength": 100 },
            "certification_date": { "type": "string", "format": "date" },
            "max_altitude_ft": { "type": "number", "minimum": 0, "maximum": 100000 },
            "engine_count": { "type": "integer", "minimum": 1, "maximum": 12 },
            "wingspan_meters": { "type": "number", "minimum": 0 }
        },
        "required": ["aircraft_model"],
        "additionalProperties": false
    },
    "createdBy": "admin@acme.com"
}
```

**Response (201):**
```json
{
    "id": "019577b4-...",
    "clientId": "acme-corp",
    "name": "aircraft-engineering",
    "version": 2,
    "status": "active",
    "previousVersionId": "019577a3-...",
    ...
}
```

**Behavior:**
- The `schemaId` in the path identifies the schema to "update" (really: create a new version of)
- The new version inherits the `name` from the previous version
- The old version's status is set to `superseded` (it remains valid for existing documents but should not be assigned to new ones)
- Returns the newly created schema version
- The `schema` field in the request body follows the same validation rules as `POST` (including the `additionalProperties` requirement)
- **Concurrency**: Uses `SELECT ... FOR UPDATE` on `client_metadata_schemas WHERE client_id = $1 AND name = $2` to lock existing versions before reading `max(version)`. This prevents two concurrent PUTs from computing the same next version number. The unique constraint `uq_client_schema_name_version` is the final safety net.

#### `GET /super-admin/custom-schemas`

List all schemas for a client.

**Query Parameters:**
- `clientId` (required): The client whose schemas to list
- `name` (optional): Filter by schema name
- `status` (optional): Filter by status (`active`, `superseded`, `retired`). Default: return only `active`.
- `includeAllVersions` (optional, default: false): Return all versions or just latest per name
- `limit` (optional, default: 50, max: 200): Maximum number of results to return
- `offset` (optional, default: 0): Number of results to skip for pagination

**Response (200):**
```json
{
    "schemas": [
        {
            "id": "019577b4-...",
            "clientId": "acme-corp",
            "name": "aircraft-engineering",
            "description": "...",
            "version": 2,
            "status": "active",
            "documentCount": 45,
            "canDelete": false,
            "createdAt": "...",
            "createdBy": "..."
        },
        {
            "id": "019577c1-...",
            "clientId": "acme-corp",
            "name": "auto-engineering",
            "description": "...",
            "version": 1,
            "status": "active",
            "documentCount": 0,
            "canDelete": true,
            "createdAt": "...",
            "createdBy": "..."
        }
    ]
}
```

**Notes:**
- `documentCount` shows how many documents reference each schema version. Computed via a subquery or join.
- `canDelete` is `true` when `documentCount == 0` AND no `document_custom_metadata` rows reference the schema. This saves the client a round-trip to check before attempting delete.

#### `GET /super-admin/custom-schemas/{schemaId}`

Get a specific schema by ID (returns full schema definition).

**Response (200):**
```json
{
    "id": "019577a3-...",
    "clientId": "acme-corp",
    "name": "aircraft-engineering",
    "description": "...",
    "schema": { ... },
    "version": 1,
    "status": "superseded",
    "documentCount": 45,
    "canDelete": false,
    "createdAt": "...",
    "createdBy": "..."
}
```

#### `DELETE /super-admin/custom-schemas/{schemaId}`

Retire a schema. Only succeeds if no documents reference it.

**Response (204):** No content on success.

**Response (409 Conflict):**
```json
{
    "error": "Schema is in use by 45 documents and cannot be deleted"
}
```

**Behavior:**
- Sets `status = 'retired'`
- Fails with 409 if any documents reference this schema ID (via `documents.custom_schema_id` or `document_custom_metadata.schema_id`)
- Retired schemas still serve validation for existing documents but cannot be assigned to new documents

---

### 5.2 Document Schema Assignment Endpoints (`super_admin` only)

Schema assignment endpoints also live under `/super-admin/*` so that the same first-segment resource extraction rule confines them to the `super-admin` Permit.io resource. Placing them under `/admin/*` (v1) or under `/document/*` would expose them to `user_admin` or `client_user` respectively, which we explicitly do not want.

#### `PATCH /super-admin/documents/{id}/schema`

Assign or change a custom schema on a single document.

> **Path note**: The sub-segment uses plural `documents/{id}` (not `document/{id}` as in v1) to avoid any possible collision with the existing top-level `/document/{id}` resource path during code review or manual URL inspection. This has no authorization impact because the first segment (`super-admin`) is what the middleware uses to resolve the resource, but it makes the namespacing visually unambiguous.

**Request:**
```json
{
    "customSchemaId": "019577a3-..."
}
```

**Response (200):**
```json
{
    "documentId": "...",
    "customSchemaId": "019577a3-...",
    "schemaName": "aircraft-engineering",
    "schemaVersion": 1
}
```

**Validation rules:**
- Schema must belong to the same client as the document (enforced at app layer + DB trigger)
- Schema must have status `active`
- If the document already has custom metadata written, the schema cannot be changed (returns 409, also enforced by DB trigger)
- If the document already has legacy field extractions, the schema cannot be assigned (returns 409 -- mutual exclusivity)
- Setting `customSchemaId` to `null` removes the binding (only if no custom metadata exists)

#### `POST /super-admin/folders/{folderId}/assign-schema` (Bulk Folder Assignment)

Assign a custom schema to ALL documents in a folder and all its subfolders (recursive).

**Request:**
```json
{
    "customSchemaId": "019577a3-...",
    "createdBy": "admin@acme.com"
}
```

**Response (200):**
```json
{
    "folderId": "...",
    "customSchemaId": "019577a3-...",
    "schemaName": "aircraft-engineering",
    "documentsUpdated": 87,
    "documentsSkipped": 5,
    "skippedReasons": [
        {"documentId": "...", "reason": "Document already has custom metadata with a different schema"},
        {"documentId": "...", "reason": "Document already has custom metadata with a different schema"},
        {"documentId": "...", "reason": "Document already assigned to same schema (no-op)"},
        {"documentId": "...", "reason": "Document has legacy field extractions"},
        {"documentId": "...", "reason": "Document has legacy field extractions"}
    ]
}
```

**Behavior:**
- Uses `WITH RECURSIVE` CTE to walk the entire folder subtree (same pattern as folder deletion)
- For each document in the tree:
  - If the document has no schema, no custom metadata, and no legacy extractions -> assign the schema
  - If the document already has the same schema -> skip (no-op, counted in `documentsSkipped`)
  - If the document has a different schema but no custom metadata yet -> reassign to new schema
  - If the document has a different schema AND has custom metadata -> skip with reason (cannot change)
  - If the document has legacy field extractions -> skip with reason (mutual exclusivity)
- Runs in a single transaction
- **Document count limit**: If the folder subtree contains more than `MaxBulkAssignDocuments` (10,000) documents, returns `422 Unprocessable Entity` with a message explaining the limit. This prevents unbounded transaction duration, excessive lock contention, and replication lag.
- Returns summary of what was updated and what was skipped (with reasons)
- Requires `super_admin` role (the `super-admin` resource grants neither `user_admin` nor `client_user` access)

#### `GET /document/{id}` (Modified)

Add `customSchemaId` and `customMetadata` fields to `DocumentEnriched`:

```json
{
    "id": "...",
    "clientId": "acme-corp",
    "hash": "...",
    "customSchemaId": "019577a3-...",
    "customSchemaName": "aircraft-engineering",
    "hasCustomMetadata": true,
    "customMetadata": { ... },
    ...existing fields...
}
```

**Query parameter:** `customMetadata` (boolean, default: false) - when true, includes the full custom metadata in the response (like the existing `textRecord` parameter).

> **Authorization note**: The `GET /document/{id}` endpoint stays on the existing `document` resource. Both admin roles, `client_user`, and `auditor` can read it today. Returning `customSchemaId` / `customSchemaName` / `customMetadata` on this endpoint is read-only and does not grant any administrative capability. The `super-admin` gating applies only to the write/assign/manage paths.

---

### 5.3 Authorization & Permit.io Changes

v2 splits admin-class authorization for mutable metadata into two tiers:

| Role | Schema CRUD (`/super-admin/custom-schemas/*`) | Schema Assignment (`/super-admin/documents/{id}/schema`, `/super-admin/folders/{folderId}/assign-schema`) | Metadata Read (`GET /custom-metadata/*`, `GET /document/{id}` enrichment) | Metadata Write (`POST /custom-metadata`) |
|------|-----------------------------------------------|-----------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------|-------------------------------------------|
| `super_admin` | Yes | Yes | Yes | Yes |
| `user_admin`  | **No** | **No** | Yes | Yes |
| `auditor`     | Read-only (`GET` only) | No | Read-only | No |
| `client_user` | No | No | Yes | Yes |

Key change from v1: `user_admin` has NO schema CRUD and NO schema assignment rights. The role continues to function exactly as it does today for everything else (user creation, labels, folders, etc.).

#### New Permit.io resource: `super-admin`

Add a new resource to `cmd/auth_related/permit.setup/permit_policies.yaml`:

```yaml
resources:
  # ...existing resources unchanged...

  - name: super-admin
    description: Platform-level administrative functions restricted to super_admin role (custom metadata schema management, schema assignment)
    actions:
      - get
      - post
      - patch
      - delete
```

#### Role permission updates

```yaml
roles:
  - name: super_admin
    description: Full system access for platform administrators
    permissions:
      # ...existing permissions unchanged...
      super-admin:
        - get
        - post
        - patch
        - delete
      custom-metadata:
        - get
        - post

  - name: user_admin
    description: User management - primarily for creating new client users
    permissions:
      # ...existing permissions unchanged (admin, documents, field-extractions, folders)...
      # NOTE: user_admin is intentionally NOT granted super-admin:* permissions.
      custom-metadata:
        - get
        - post

  - name: auditor
    description: Full read-only access across the entire system for auditing and compliance
    permissions:
      # ...existing permissions unchanged...
      super-admin:
        - get
      custom-metadata:
        - get

  - name: client_user
    description: Client-specific access for external users (requires tenant filtering)
    permissions:
      # ...existing permissions unchanged...
      custom-metadata:
        - get
        - post
```

#### New custom-metadata resource

The user-facing custom metadata endpoints (`/custom-metadata/*`) use a separate `custom-metadata` resource (first path segment). This is unchanged from v1 except that it now also needs to be granted to `super_admin` explicitly (v1 relied on `admin:*` coverage which no longer covers the metadata path).

```yaml
resources:
  - name: custom-metadata
    description: Per-document custom metadata read/write (validated against client schemas)
    actions:
      - get
      - post
```

#### Policy mapping documentation additions

Add to the documentation-only `policy_mappings` section at the bottom of `permit_policies.yaml`:

```yaml
super_admin_endpoints:
  - path: /super-admin/custom-schemas
    methods:
      GET: super-admin:get
      POST: super-admin:post
  - path: /super-admin/custom-schemas/{schemaId}
    methods:
      GET: super-admin:get
      PUT: super-admin:patch      # PUT maps to patch action (create-new-version semantics)
      DELETE: super-admin:delete
  - path: /super-admin/documents/{id}/schema
    methods:
      PATCH: super-admin:patch
  - path: /super-admin/folders/{folderId}/assign-schema
    methods:
      POST: super-admin:post

custom_metadata_endpoints:
  - path: /custom-metadata
    methods:
      GET: custom-metadata:get
      POST: custom-metadata:post
  - path: /custom-metadata/version
    methods:
      GET: custom-metadata:get
  - path: /custom-metadata/history
    methods:
      GET: custom-metadata:get
```

> **PUT-to-patch action note**: The Permit.io middleware lowercases the HTTP method. Permit.io's default action vocabulary does not include `put`; the existing middleware either maps `PUT` to `patch` or requires the action to exist. Confirm during implementation whether the middleware needs a `put` action added to each resource or whether mapping `PUT` -> `patch` is acceptable. If a new action is needed, add `put` to both `super-admin.actions` and the `super_admin` role permissions. The same consideration applies to any other resources that currently have no `put` action.

#### Middleware impact

The Permit.io resource-extraction middleware uses the first path segment. Introducing `super-admin` as a resource requires no middleware code changes -- it is purely a configuration addition via the permit setup tool. The setup tool (`cmd/auth_related/permit.setup/`) must be re-run in each environment (dev, uat, prod) to provision the new resource and role permissions before these endpoints can pass authorization.

#### Deployment ordering

Because the authorization changes must land in Permit.io before the API routes are live, the deployment sequence is:

1. Update `permit_policies.yaml` with the new resources and role grants.
2. Run the permit setup tool against dev/uat/prod to provision the new resource and permissions.
3. Deploy the API code containing the new endpoints.

Step 2 must complete before step 3 in each environment, otherwise the new endpoints would either be rejected by Permit.io (if fail-closed) or accidentally allowed (if fail-open) during the window between code deploy and permit sync.

---

### 5.4 Custom Metadata CRUD Endpoints (User-Facing)

All under a new `CustomMetadataService` tag. These endpoints are NOT moved under `/super-admin/*` because they are intended for regular users (including `client_user`) to read and write the custom metadata values on documents. Schema administration and schema assignment are separated from value read/write precisely so the day-to-day data entry workload does not require super_admin.

#### `POST /custom-metadata`

Create or update custom metadata for a document. Creates a new version.

**Request:**
```json
{
    "documentId": "...",
    "metadata": {
        "aircraft_model": "Boeing 737-800",
        "certification_date": "2024-06-15",
        "max_altitude_ft": 41000,
        "engine_count": 2
    },
    "createdBy": "analyst@acme.com"
}
```

**Response (201):**
```json
{
    "id": "...",
    "documentId": "...",
    "schemaId": "019577a3-...",
    "metadata": { ... },
    "version": 1,
    "createdAt": "...",
    "createdBy": "analyst@acme.com"
}
```

**Validation:**
- Document must have a `custom_schema_id` assigned (400 if not -- a super_admin must have assigned the schema first)
- Document must NOT have any legacy field extractions (409 if it does -- mutual exclusivity, also enforced by DB trigger on schema assignment)
- The `metadata` payload must be <= 1MB in size (`MaxMetadataPayloadBytes = 1048576`). Returns 400 if exceeded.
- The `metadata` payload is validated against the JSON Schema stored in `client_metadata_schemas.schema_def`
- The request body does NOT include `schemaId` -- the server derives it from the document's `custom_schema_id`. This prevents client/server drift.
- If validation fails, returns 400 with detailed validation errors:
  ```json
  {
      "error": "Metadata does not conform to schema",
      "validationErrors": [
          {"field": "engine_count", "message": "must be >= 1, got 0"},
          {"field": "aircraft_model", "message": "required field missing"}
      ]
  }
  ```
- On first write, locks the document's `custom_schema_id` (makes it immutable via app-layer flag + DB trigger)
- Subsequent writes create new versions but must use the same schema

#### `GET /custom-metadata`

Get current (latest version) custom metadata for a document.

**Query Parameters:**
- `documentId` (required)

**Response (200):**
```json
{
    "id": "...",
    "documentId": "...",
    "schemaId": "019577a3-...",
    "schemaName": "aircraft-engineering",
    "metadata": { ... },
    "version": 3,
    "createdAt": "...",
    "createdBy": "..."
}
```

#### `GET /custom-metadata/version`

Get a specific version of custom metadata.

**Query Parameters:**
- `documentId` (required)
- `version` (required, >= 1)

#### `GET /custom-metadata/history`

Get version history for a document's custom metadata.

**Query Parameters:**
- `documentId` (required)
- `limit` (optional, default: 50, max: 200): Maximum number of versions to return
- `offset` (optional, default: 0): Number of versions to skip for pagination

**Response (200):**
```json
{
    "versions": [
        {"id": "...", "documentId": "...", "version": 3, "createdAt": "...", "createdBy": "..."},
        {"id": "...", "documentId": "...", "version": 2, "createdAt": "...", "createdBy": "..."},
        {"id": "...", "documentId": "...", "version": 1, "createdAt": "...", "createdBy": "..."}
    ]
}
```

---

## 6. Validation Strategy

### 6.1 JSON Schema Validation

Use a Go JSON Schema validation library for both:

1. **Schema validation** (meta-validation): When a super_admin submits a new schema, validate it against the JSON Schema meta-schema to ensure it is a well-formed JSON Schema document.
2. **Metadata validation**: When custom metadata is submitted, validate the payload against the document's assigned schema.

**Recommended library**: `github.com/santhosh-tekuri/jsonschema/v6`

Reasons:
- Supports JSON Schema draft 2020-12
- Active maintenance
- Good error reporting
- Supports custom formats

### 6.2 Schema Definition Requirements

When a schema definition is submitted (via `POST` or `PUT`), the server validates:

1. It is a valid JSON object
2. It compiles successfully as a JSON Schema document (meta-validation)
3. Root `type` is `"object"`
4. Root `additionalProperties` is explicitly present (either `true` or `false`). This is required because JSON Schema defaults `additionalProperties` to `true` when omitted, which silently accepts any extra fields. Requiring explicit declaration forces a conscious choice.
5. Size is <= 64KB

### 6.3 Supported JSON Schema Features

The system will support the following JSON Schema keywords for custom field definitions:

| Feature | JSON Schema Keyword | Example |
|---------|-------------------|---------|
| Data type | `type` | `"string"`, `"number"`, `"integer"`, `"boolean"`, `"array"`, `"object"` |
| Required fields | `required` | `["field1", "field2"]` |
| String length | `minLength`, `maxLength` | `"maxLength": 100` |
| Numeric range | `minimum`, `maximum` | `"minimum": 0` |
| Pattern matching | `pattern` | `"pattern": "^[A-Z]{2}$"` |
| Enum values | `enum` | `"enum": ["active", "inactive"]` |
| Date/time format | `format` | `"format": "date"` |
| Array items | `items`, `minItems`, `maxItems` | Nested array support |
| Nested objects | `properties` | Hierarchical field groups |
| No extra fields | `additionalProperties` | `false` to enforce strict schemas |

### 6.4 Validation Error Reporting

Validation errors will be returned as structured JSON with:
- The JSON pointer to the failing field (`/aircraft_model`)
- The constraint that was violated (`maxLength`)
- A human-readable message

---

## 7. Service Layer Design

### 7.1 New Service: `internal/customschema/`

```
internal/customschema/
    service.go       -- CustomSchemaService (CRUD + validation)
    models.go        -- Input/output types
    validator.go     -- JSON Schema meta-validation + payload validation
    constants.go     -- MaxSchemaDefinitionBytes and other limits
    service_test.go  -- Integration tests
```

**Constants (`constants.go`):**

```go
const (
    // MaxSchemaDefinitionBytes is the maximum size of a JSON Schema definition.
    // This limit can be increased if clients need larger schemas.
    MaxSchemaDefinitionBytes = 65536 // 64KB

    // MaxMetadataPayloadBytes is the maximum size of a custom metadata JSON payload.
    // Prevents unbounded JSONB blobs when schemas use additionalProperties: true.
    MaxMetadataPayloadBytes = 1048576 // 1MB

    // MaxBulkAssignDocuments is the maximum number of documents that can be updated
    // in a single bulk folder schema assignment. Prevents unbounded transactions.
    MaxBulkAssignDocuments = 10000
)
```

**Key methods:**

```go
type Service struct {
    cfg       serviceconfig.ConfigProvider
    validator *SchemaValidator
}

// Schema management (super_admin operations)
func (s *Service) CreateSchema(ctx, input CreateSchemaInput) (*Schema, error)
func (s *Service) UpdateSchema(ctx, schemaID uuid.UUID, input UpdateSchemaInput) (*Schema, error)
func (s *Service) GetSchema(ctx, schemaID uuid.UUID) (*Schema, error)
func (s *Service) ListSchemas(ctx, clientID string, filters ListFilters) ([]SchemaSummary, error)
func (s *Service) DeleteSchema(ctx, schemaID uuid.UUID) error

// Metadata operations (client_user / admin operations)
func (s *Service) SetDocumentMetadata(ctx, input SetMetadataInput) (*CustomMetadata, error)
func (s *Service) GetCurrentMetadata(ctx, documentID uuid.UUID) (*CustomMetadata, error)
func (s *Service) GetMetadataByVersion(ctx, documentID uuid.UUID, version int) (*CustomMetadata, error)
func (s *Service) GetMetadataHistory(ctx, documentID uuid.UUID) ([]MetadataVersion, error)

// Document schema binding (super_admin operations)
func (s *Service) AssignSchema(ctx, documentID uuid.UUID, schemaID uuid.UUID) error
func (s *Service) AssignSchemaToFolder(ctx, folderID uuid.UUID, schemaID uuid.UUID, createdBy string) (*BulkAssignResult, error)
```

**BulkAssignResult:**

```go
type BulkAssignResult struct {
    FolderID         uuid.UUID
    SchemaID         uuid.UUID
    DocumentsUpdated int
    DocumentsSkipped int
    SkippedReasons   []SkippedDocument
}

type SkippedDocument struct {
    DocumentID uuid.UUID
    Reason     string
}
```

> **Authorization is enforced at the HTTP middleware layer via Permit.io**, not inside these service methods. The service methods are agnostic to the caller's role. The routing layer for `/super-admin/*` endpoints is what ensures only `super_admin` can invoke `CreateSchema`, `UpdateSchema`, `DeleteSchema`, `AssignSchema`, and `AssignSchemaToFolder`. Keeping the service layer role-unaware preserves testability and makes integration tests simpler.

### 7.2 Validator Component

```go
type SchemaValidator struct{}

// ValidateSchemaDefinition checks that a schema_def is valid JSON Schema.
// Returns error if: not a valid JSON object, fails meta-validation,
// root type is not "object", or additionalProperties is not explicitly present.
func (v *SchemaValidator) ValidateSchemaDefinition(schemaDef json.RawMessage) error

// ValidateMetadata checks that metadata conforms to a compiled schema
func (v *SchemaValidator) ValidateMetadata(schemaDef json.RawMessage, metadata json.RawMessage) ([]ValidationError, error)
```

### 7.3 Mutual Exclusivity Guard

The service layer enforces mutual exclusivity at two points:

1. **Schema assignment** (`AssignSchema`): Before setting `custom_schema_id` on a document, check that no rows exist in `documentFieldExtractionVersions` for that document. If they do, return `409 Conflict`.
2. **Legacy field extraction write** (modification to existing `FieldExtractionService`): Before creating a new field extraction, check that `documents.custom_schema_id IS NULL` for the target document. If it is not null, return `409 Conflict` with a message explaining that the document uses the custom schema system.

> **Note**: The DB trigger on `documents.custom_schema_id` (Section 4.7, Trigger 1) also prevents schema assignment if legacy extractions exist. This is the defense-in-depth pattern: the service layer returns a clean 409; the trigger catches anything that slips through.

### 7.4 API Controller: `api/queryAPI/customschemas.go`

Follows the same pattern as `fieldextractions.go`:
- Parse and validate request
- Call service layer
- Convert between API and service types
- Return appropriate HTTP status codes

The controller file holds all `/super-admin/custom-schemas/*`, `/super-admin/documents/{id}/schema`, and `/super-admin/folders/{folderId}/assign-schema` handlers. A separate controller file `api/queryAPI/custommetadata.go` holds the user-facing `/custom-metadata/*` handlers. Separating them by file mirrors the separation of authorization tiers and makes it obvious at code-review time which handlers are super_admin-gated.

---

## 8. Migration Plan

### 8.1 Migration Files

Four new migrations:

**Migration 120: Create `schema_status_type` enum + `client_metadata_schemas` table**
```
00000000000120_create_client_metadata_schemas.up.sql
00000000000120_create_client_metadata_schemas.down.sql
```

**Migration 121: Create `document_custom_metadata` table + view**
```
00000000000121_create_document_custom_metadata.up.sql
00000000000121_create_document_custom_metadata.down.sql
```

**Migration 122: Add `custom_schema_id` to `documents` table**
```
00000000000122_add_custom_schema_id_to_documents.up.sql
00000000000122_add_custom_schema_id_to_documents.down.sql
```

**Migration 123: Add database triggers for invariant enforcement**
```
00000000000123_add_schema_invariant_triggers.up.sql
00000000000123_add_schema_invariant_triggers.down.sql
```

Contents:
- `trg_prevent_schema_reassignment` function + trigger (Section 4.7, Trigger 1)
- `trg_validate_schema_client_match` function + trigger (Section 4.7, Trigger 2)
- `trg_enforce_consistent_schema_id` function + trigger (Section 4.7, Trigger 3)
- Down migration drops triggers and functions

### 8.2 SQLC Queries

New query file: `internal/database/queries/customschemas.sql`

**Schema operations:**
- `CreateClientMetadataSchema` - Insert new schema
- `GetClientMetadataSchema` - Get by ID
- `ListClientMetadataSchemas` - List by client with filters (status filter)
- `GetLatestSchemaByName` - Get latest version of a named schema
- `GetSchemaDocumentCount` - Count documents using a schema
- `GetSchemaMetadataRecordCount` - Count metadata records referencing a schema (for `canDelete`)
- `SetSchemaStatus` - Update status (for supersede/retire)
- `GetMaxSchemaVersion` - For auto-incrementing version
- `LockSchemaVersionsForName` - `SELECT ... FOR UPDATE` on all versions of a (client_id, name) pair to prevent concurrent version creation race

**Metadata operations:**
- `CreateDocumentCustomMetadata` - Insert new metadata version
- `GetCurrentDocumentCustomMetadata` - Latest version (via view)
- `GetDocumentCustomMetadataByVersion` - Specific version
- `GetDocumentCustomMetadataHistory` - All versions
- `LockDocumentCustomMetadataForVersion` - Row-level locking (SELECT FOR UPDATE on max version)

**Document modifications:**
- `SetDocumentCustomSchemaId` - Update documents.custom_schema_id
- `GetDocumentCustomSchemaId` - Read documents.custom_schema_id
- `BulkSetDocumentCustomSchemaIdInFolderTree` - Set schema for all docs in folder subtree (WITH RECURSIVE)
- `GetDocumentsWithMetadataInFolderTree` - Find docs that already have metadata (for skip reporting)
- `GetDocumentsWithLegacyExtractionsInFolderTree` - Find docs that have legacy extractions (for skip reporting)
- `DocumentHasLegacyExtractions` - Check if a single document has any legacy field extraction versions
- `CountDocumentsInFolderTree` - Count total documents in a folder subtree (for `MaxBulkAssignDocuments` limit check)

**Delete cascade operations (additions to `document.sql` and `client.sql`):**
- `DeleteDocumentCustomMetadata` - Delete all custom metadata versions for a document
- `NullifyDocumentCustomSchemaId` - Set `custom_schema_id = NULL` on a document (before hard delete)
- `DeleteClientMetadataSchemas` - Delete all schemas for a client (after all documents deleted)

### 8.3 OpenAPI Spec Changes

Add to `serviceAPIs/queryAPI.yaml`:

**New `SuperAdminSchemaService` tag** for super_admin-only endpoints:
- `POST /super-admin/custom-schemas`
- `GET /super-admin/custom-schemas`
- `GET /super-admin/custom-schemas/{schemaId}`
- `PUT /super-admin/custom-schemas/{schemaId}`
- `DELETE /super-admin/custom-schemas/{schemaId}`
- `PATCH /super-admin/documents/{id}/schema`
- `POST /super-admin/folders/{folderId}/assign-schema`

**New `CustomMetadataService` tag** for end-user endpoints:
- `GET /custom-metadata`
- `POST /custom-metadata`
- `GET /custom-metadata/version`
- `GET /custom-metadata/history`

**New schemas**: `CustomSchemaRequest`, `CustomSchemaResponse`, `CustomSchemaListResponse`, `CustomMetadataRequest`, `CustomMetadataResponse`, `CustomMetadataHistoryResponse`, `ValidationErrorResponse`, `BulkSchemaAssignRequest`, `BulkSchemaAssignResponse`, `DocumentSchemaAssignRequest`, `DocumentSchemaAssignResponse`

**New enum**: `SchemaStatus` with values `active`, `superseded`, `retired`

**Modified schemas**: `DocumentEnriched` (add `customSchemaId`, `customSchemaName`, `hasCustomMetadata`, `customMetadata` fields)

**Tag descriptions should explicitly call out the authorization boundary:**
- `SuperAdminSchemaService` description: "Custom metadata schema management and assignment. Restricted to the `super_admin` role. Not accessible to `user_admin`."
- `CustomMetadataService` description: "Per-document custom metadata read/write. Accessible to `client_user`, `user_admin`, and `super_admin`."

### 8.4 Legacy Field Extraction Guard

Add a check to the existing field extraction service (`internal/fieldextraction/service.go`):

Before creating a new field extraction, verify that `documents.custom_schema_id IS NULL` for the target document. If the document has a custom schema assigned, return a `409 Conflict` error explaining that the document uses the custom schema system and legacy field extractions are not allowed.

This is a small modification to the existing code path, not a new endpoint.

### 8.5 Delete Path Updates (Cascade Cleanup)

The new tables and FKs require updates to existing delete paths. Without these changes, hard-deleting a document or client will fail with FK violations.

#### Document Delete Cascade

The existing `DeleteDocumentCascade` function (in `internal/document/`) and the SQLC queries in `internal/database/queries/document.sql` must be updated to delete custom metadata before deleting the document:

**New SQLC queries to add to `document.sql`:**
- `DeleteDocumentCustomMetadata` - `DELETE FROM document_custom_metadata WHERE document_id = @document_id`
- `NullifyDocumentCustomSchemaId` - `UPDATE documents SET custom_schema_id = NULL WHERE id = @document_id`

**Updated delete order in `DeleteDocumentCascade`:**
1. Delete `documentFieldExtractionArrayFields` (existing)
2. Delete `documentFieldExtractionVersions` (existing)
3. Delete `documentFieldExtractions` (existing)
4. **Delete `document_custom_metadata`** (new -- must come before document row delete)
5. **Nullify `documents.custom_schema_id`** (new -- removes FK to `client_metadata_schemas` before document delete)
6. Delete `documentCleanEntries` / `documentCleans` / `documentEntries` (existing)
7. Delete `documents` row (existing)

> **Note**: Step 5 (nullify `custom_schema_id`) must happen before step 7 because the FK from `documents.custom_schema_id` to `client_metadata_schemas` would block deletion otherwise. The nullify is safe because step 4 already removed all custom metadata, and Trigger 1 only fires on changes when metadata exists.

#### Client Delete Cascade

The existing `client.HardDelete` and `deleteClientDependencies` functions must be updated to clean up schema data after all documents are deleted:

**New SQLC queries:**
- `DeleteClientMetadataSchemas` - `DELETE FROM client_metadata_schemas WHERE client_id = @client_id`

**Updated delete order in `client.HardDelete`:**
1. Delete all documents with full cascade (existing, now includes custom metadata cleanup per above)
2. Delete `documentUploads` (existing)
3. Delete all folders (existing)
4. **Delete `client_metadata_schemas`** (new -- safe after all documents are gone since no FKs reference these rows)
5. Delete collector data, batch uploads, sync records (existing)
6. Delete client row (existing)

### 8.6 Permit.io Setup Tool Run

After updating `permit_policies.yaml` per Section 5.3, run the permit setup tool in each environment:

```
cmd/auth_related/permit.setup/run.tool.dev.sh
cmd/auth_related/permit.setup/run.tool.uat.sh
cmd/auth_related/permit.setup/run.tool.prod.sh
```

The tool is idempotent and will provision the new `super-admin` and `custom-metadata` resources and update role grants without disturbing existing resources. Run this **before** deploying the API code so the new endpoints are authorized the moment they go live.

---

## 9. Invariants & Business Rules

| # | Rule | Enforcement |
|---|------|-------------|
| 1 | Schema must be valid JSON Schema with explicit `additionalProperties` | Application: meta-validation on create/update |
| 2 | Schema `name` + `version` unique per client | Database: unique constraint |
| 3 | Updated schema gets new ID and version; old version becomes `superseded` | Application: INSERT new row, UPDATE old status |
| 4 | Schema deletion blocked if documents reference it | Application: count check before retirement |
| 5 | Document's `custom_schema_id` is immutable once any extraction exists | Application: check in AssignSchema + DB trigger: `trg_prevent_schema_reassignment` |
| 6 | Custom metadata must conform to assigned schema | Application: JSON Schema validation on write |
| 7 | All custom metadata versions for a document use same schema ID | Application: consistency check on write + DB trigger: `trg_enforce_consistent_schema_id` |
| 8 | Schema must belong to same client as document | Application: cross-reference check + DB trigger: `trg_validate_schema_client_match` |
| 9 | Only `active` schemas can be assigned to new documents | Application: status check |
| 10 | Custom metadata is versioned (no in-place updates) | Database: version column + unique constraint |
| 11 | Schema definition must be <= 64KB | Application: size check + Database: CHECK constraint |
| 12 | Schema management requires `super_admin` role (NOT `user_admin`) | Permit.io: role-based access on new `super-admin` resource; `user_admin` is explicitly NOT granted this resource |
| 13 | No query/filter on custom metadata values | By design: not implemented (see Principle 9) |
| 14 | A document uses EITHER legacy extractions OR custom metadata, never both | Application: mutual exclusivity checks in both services + DB trigger: `trg_prevent_schema_reassignment` |
| 15 | Legacy field extraction writes rejected if document has `custom_schema_id` set | Application: guard in `FieldExtractionService` |
| 16 | Custom schema assignment rejected if document has legacy extractions | Application: guard in `AssignSchema` + DB trigger |
| 17 | Metadata payload must be <= 1MB | Application: size check (`MaxMetadataPayloadBytes`) |
| 18 | Bulk folder assignment capped at 10,000 documents | Application: count check (`MaxBulkAssignDocuments`), returns 422 if exceeded |
| 19 | Schema assignment (single doc + bulk folder) requires `super_admin` role | Permit.io: endpoints under `/super-admin/` prefix map to `super-admin` resource; `user_admin` is NOT granted |
| 20 | Delete cascade must clean up custom metadata and schema bindings | Application: updated `DeleteDocumentCascade` + `deleteClientDependencies` (Section 8.5) |
| 21 | Metadata read/write is available to `client_user`, `user_admin`, `super_admin` (not `auditor` for writes) | Permit.io: `custom-metadata` resource grants on each role per Section 5.3 |

---

## 10. Relationship to Existing Field Extraction System

The existing static field extraction system (`/field-extractions`) and the new custom schema system (`/super-admin/custom-schemas` + `/custom-metadata`) are **mutually exclusive per document**:

- A document uses EITHER the legacy static field extraction system OR the custom schema system
- A document CANNOT have both legacy field extractions AND custom metadata
- Assigning a custom schema to a document that already has legacy extractions returns `409 Conflict`
- Writing a legacy field extraction to a document that has a custom schema assigned returns `409 Conflict`
- Documents without a custom schema (the default) continue to use the legacy system unchanged
- There is no migration path from legacy to custom for individual documents. If a document needs custom metadata, it should not have legacy extractions written to it first.

**Rationale**: This prevents ambiguity about which system is "authoritative" for a document's metadata. With mutual exclusivity, there is exactly one source of truth per document. This is simpler to reason about, simpler to query, and avoids the data governance problem of conflicting data in two stores.

**No breaking changes** to the existing API or database schema for documents that do not opt into custom schemas. The existing `/field-extractions` endpoints remain on the `field-extractions` resource and are unaffected by the new `super-admin` resource.

---

## 11. Implementation Order

| Phase | Work | Dependencies |
|-------|------|--------------|
| 1 | Database migrations (enum, tables, view, document column, triggers) | None |
| 2 | SQLC queries + `task generate` | Phase 1 |
| 3 | Schema validator component (`internal/customschema/validator.go`) | JSON Schema library added to go.mod |
| 4 | Service layer (`internal/customschema/service.go`) incl. bulk folder assignment + mutual exclusivity guards | Phase 2, 3 |
| 5a | Legacy field extraction guard (add check to existing `FieldExtractionService`) | Phase 2 |
| 5b | Delete cascade updates (`DeleteDocumentCascade`, `deleteClientDependencies`, new SQLC queries) | Phase 2 |
| 6 | OpenAPI spec updates (`SuperAdminSchemaService` + `CustomMetadataService` tags) | None (can parallel with 1-3) |
| 7a | Permit.io policy file updates (`permit_policies.yaml`: new `super-admin` + `custom-metadata` resources, role grants) | None (can parallel with 1-6) |
| 7b | Run permit setup tool against dev/uat/prod to provision new resources and role permissions | Phase 7a |
| 8 | API controllers + code generation (super_admin schema CRUD in `customschemas.go`, metadata CRUD in `custommetadata.go`) | Phase 4, 6 |
| 9 | Document endpoint modifications (`PATCH /super-admin/documents/{id}/schema`, `GET /document/{id}` enrichment) | Phase 4, 8 |
| 10 | Bulk folder schema assignment endpoint (`POST /super-admin/folders/{folderId}/assign-schema`) | Phase 4, 8 |
| 11 | Integration tests (including explicit role-based authorization tests per Section 12) | Phase 10, 7b |
| 12 | Documentation updates (`docs/ai.generated/`) incl. sample schemas, authorization matrix | Phase 11 |

> **Ordering constraint**: Phase 7b (permit setup run) must complete in each environment before Phase 8 code is deployed to that environment. Otherwise the new endpoints will be rejected by Permit.io (fail-closed) until the setup runs.

---

## 12. Testing Strategy

- **Schema validation tests**: Valid and invalid JSON Schema documents, edge cases (empty schema, deeply nested, self-referential, oversized >64KB, missing `additionalProperties`)
- **Metadata validation tests**: Conforming and non-conforming payloads, all supported JSON Schema keywords
- **Service integration tests**: Full CRUD lifecycle using testcontainers (real PostgreSQL)
- **API integration tests**: HTTP-level tests for all new endpoints under both `/super-admin/*` and `/custom-metadata/*`
- **Invariant tests**: Schema immutability, cross-client isolation, deletion guards, size limits
- **DB trigger tests**: Verify triggers fire correctly when bypassing the service layer (direct SQL inserts/updates via testcontainers)
- **Schema status lifecycle tests**: `active` -> `superseded` on version create, `active` -> `retired` on delete, assignment rejected for non-`active` schemas
- **Mutual exclusivity tests**: Legacy extraction blocked when schema assigned, schema assignment blocked when legacy extractions exist, bulk folder assignment skips documents with legacy extractions
- **Bulk folder assignment tests**: Recursive assignment, skip behavior for locked docs and legacy docs, empty folders, deeply nested folder trees
- **Authorization tests (expanded for v2)**:
  - `super_admin` CAN create, list, get, update, delete schemas, assign schemas to documents, assign schemas to folders
  - `user_admin` CANNOT access any `/super-admin/*` endpoint (expect 403 on every method + path combination)
  - `user_admin` CAN read and write custom metadata via `/custom-metadata` (no regression)
  - `client_user` CANNOT access any `/super-admin/*` endpoint (expect 403)
  - `client_user` CAN read and write custom metadata via `/custom-metadata`
  - `auditor` CAN read (`GET`) `/super-admin/custom-schemas` and `/super-admin/custom-schemas/{schemaId}` but CANNOT POST/PUT/PATCH/DELETE
  - `auditor` CAN read but CANNOT write `/custom-metadata`
  - Each test should assert both the HTTP status code AND that the database state is unchanged on denial
- **Backward compatibility tests**: Existing field extraction endpoints continue to work unchanged for documents without custom schemas; existing `/admin/*` endpoints are unaffected by the new `super-admin` resource
- **Delete cascade tests**: Document hard-delete succeeds when document has custom metadata, client hard-delete succeeds when client has schemas and metadata, verify no orphaned rows remain
- **Metadata size limit tests**: Payloads at/above 1MB boundary, verify 400 response with clear message
- **Bulk assignment limit tests**: Folder trees exceeding `MaxBulkAssignDocuments`, verify 422 response
- **Schema version concurrency tests**: Concurrent PUT requests for same schema name produce distinct version numbers
- **Permit.io setup tool tests**: After running the setup tool against a disposable dev tenant, verify that the `super-admin` and `custom-metadata` resources exist with the expected actions and that each role has exactly the grants defined in Section 5.3

---

## 13. Resolved Design Decisions

| # | Question | Decision |
|---|----------|----------|
| 1 | Schema size limits | 64KB cap via `MaxSchemaDefinitionBytes` constant (tunable) |
| 2 | Schema backward compatibility | Not required. New version = new ID. Old docs keep old schema. |
| 3 | Bulk operations | Yes. `POST /super-admin/folders/{folderId}/assign-schema` assigns recursively through folder tree. |
| 4 | Custom metadata search/filter | **Not supported.** No GIN indexes, no query API. Metadata is opaque storage. |
| 5 | Schema templates | No system templates. Documentation will include sample schemas covering all supported types. |
| 6 | Existing field migration path | **Out of scope.** Static fields and custom schemas are mutually exclusive per document. |
| 7 | Endpoint naming/placement | Schema CRUD under `/super-admin/custom-schemas` (requires the `super_admin` role on the new `super-admin` Permit.io resource). Metadata CRUD under `/custom-metadata` (regular `client_user` access; also granted to `user_admin` and `super_admin`). |
| 8 | Legacy/custom coexistence | **Mutually exclusive.** A document uses EITHER legacy OR custom, never both. Simplifies data governance and prevents source-of-truth ambiguity. |
| 9 | Schema status model | Three-state enum (`active`/`superseded`/`retired`) instead of boolean. Distinguishes automatic version succession from explicit admin retirement. |
| 10 | DB-level invariant enforcement | Yes. Three database triggers enforce schema lock, client ownership match, and consistent schema_id as defense-in-depth alongside application-layer checks. |
| 11 | `additionalProperties` in schemas | Required to be explicitly present (not necessarily `false`). Prevents the common mistake of omitting it and silently accepting arbitrary extra fields. |
| 12 | Metadata table design | Single table with version column (simpler than the legacy two-table pattern). Sufficient for our concurrency needs. Can split later if needed. |
| 13 | Schema assignment endpoint path | Under `/super-admin/documents/{id}/schema` (NOT `/admin/document/{id}/schema` as in v1 and NOT `/document/{id}/schema`). The `/super-admin` first segment maps to the new `super-admin` Permit.io resource which only `super_admin` holds. Placing it under `/admin` would also grant `user_admin`; placing it under `/document` would also grant `client_user`. |
| 14 | Metadata payload size limit | 1MB cap via `MaxMetadataPayloadBytes` constant. Prevents unbounded JSONB blobs when schemas allow `additionalProperties: true`. |
| 15 | Bulk assignment document limit | 10,000 documents via `MaxBulkAssignDocuments` constant. Prevents unbounded transactions and lock contention. |
| 16 | Schema_id consistency trigger | DB trigger `trg_enforce_consistent_schema_id` on `document_custom_metadata` INSERT enforces same schema across all metadata versions for a document (defense-in-depth for Invariant 7). |
| 17 | **v2**: Who can administer schemas? | **Only `super_admin`.** v1 unintentionally granted `user_admin` access by placing endpoints under `/admin/*`. v2 moves them to `/super-admin/*` and introduces a new `super-admin` Permit.io resource that only `super_admin` holds. `user_admin` retains its existing capabilities (user creation, field extractions, documents/folders, admin endpoints) but has no schema administration rights. |
| 18 | **v2**: Why a new resource instead of path-specific rules? | The Permit.io middleware resolves resources from the first path segment. Adding path-specific overrides would require middleware code changes. Adding a new first-segment resource (`super-admin`) is a pure configuration change and keeps the middleware simple. |
| 19 | **v2**: Does the service layer enforce role checks? | No. Authorization lives in the HTTP/Permit.io layer. The service layer (`internal/customschema/`) is role-agnostic and remains easy to test without fake identity contexts. |

---

## 14. v1 -> v2 Change Log

For reviewers comparing to `plans/mutable.metadata.plan.combo.md`:

| Area | v1 | v2 |
|------|----|----|
| Schema CRUD path | `/admin/custom-schemas` | `/super-admin/custom-schemas` |
| Single-doc schema assignment path | `/admin/document/{id}/schema` | `/super-admin/documents/{id}/schema` |
| Bulk folder assignment path | `/admin/folders/{folderId}/assign-schema` | `/super-admin/folders/{folderId}/assign-schema` |
| Permit.io resource for schema admin | `admin` (shared by `user_admin` and `super_admin`) | NEW `super-admin` (held only by `super_admin`) |
| `user_admin` schema CRUD | Allowed (unintentional) | Denied |
| `user_admin` schema assignment | Allowed (unintentional) | Denied |
| `user_admin` custom metadata read/write | Allowed | Allowed (unchanged) |
| `client_user` custom metadata read/write | Allowed | Allowed (unchanged) |
| `auditor` read schemas / metadata | Allowed (read-only) | Allowed (read-only, now via `super-admin:get` grant) |
| OpenAPI tag for schema admin | `AdminService` | NEW `SuperAdminSchemaService` |
| Service layer | Role-agnostic | Role-agnostic (unchanged) |
| Database schema, triggers, migrations | Unchanged | Unchanged |
| Validation strategy, size limits, constants | Unchanged | Unchanged |

No database migration or data change is required to move from v1 to v2 -- this is strictly a routing and authorization change. If v1 were already deployed, the migration would be: (1) add the new Permit.io resource and grants, (2) add the new endpoints alongside the old ones, (3) point clients at the new paths, (4) remove the old paths once all clients have migrated. Since v1 is not deployed, v2 simply supersedes it.

---

## Appendix A: Sample JSON Schemas

These examples demonstrate all supported JSON Schema features and data types. They should be included in the API documentation.

### A.1 Comprehensive Schema (All Supported Types)

```json
{
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
        "document_title": {
            "type": "string",
            "minLength": 1,
            "maxLength": 500,
            "description": "Title of the document"
        },
        "document_code": {
            "type": "string",
            "pattern": "^[A-Z]{3}-[0-9]{4}$",
            "description": "Document code in format XXX-0000"
        },
        "status": {
            "type": "string",
            "enum": ["draft", "review", "approved", "rejected", "archived"],
            "description": "Current document status"
        },
        "review_date": {
            "type": "string",
            "format": "date",
            "description": "Date of last review (YYYY-MM-DD)"
        },
        "created_timestamp": {
            "type": "string",
            "format": "date-time",
            "description": "Creation timestamp (ISO 8601)"
        },
        "page_count": {
            "type": "integer",
            "minimum": 1,
            "maximum": 10000,
            "description": "Total number of pages"
        },
        "confidence_score": {
            "type": "number",
            "minimum": 0.0,
            "maximum": 1.0,
            "description": "Extraction confidence (0.0 to 1.0)"
        },
        "is_verified": {
            "type": "boolean",
            "description": "Whether the extraction has been human-verified"
        },
        "tags": {
            "type": "array",
            "items": { "type": "string", "maxLength": 50 },
            "minItems": 0,
            "maxItems": 20,
            "description": "Classification tags"
        },
        "numeric_values": {
            "type": "array",
            "items": { "type": "number" },
            "maxItems": 100,
            "description": "Extracted numeric values"
        },
        "contact_info": {
            "type": "object",
            "properties": {
                "name": { "type": "string", "maxLength": 200 },
                "email": { "type": "string", "format": "email" },
                "phone": { "type": "string", "pattern": "^\\+?[0-9\\-\\s()]+$" }
            },
            "required": ["name"],
            "additionalProperties": false,
            "description": "Primary contact information"
        }
    },
    "required": ["document_title", "status"],
    "additionalProperties": false
}
```

### A.2 Aircraft Engineering Schema (Domain Example)

```json
{
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
        "aircraft_model": {
            "type": "string",
            "maxLength": 100
        },
        "manufacturer": {
            "type": "string",
            "enum": ["Boeing", "Airbus", "Embraer", "Bombardier", "Other"]
        },
        "certification_date": {
            "type": "string",
            "format": "date"
        },
        "max_altitude_ft": {
            "type": "integer",
            "minimum": 0,
            "maximum": 100000
        },
        "max_range_nm": {
            "type": "number",
            "minimum": 0
        },
        "engine_count": {
            "type": "integer",
            "minimum": 1,
            "maximum": 12
        },
        "engine_type": {
            "type": "string",
            "enum": ["turbofan", "turboprop", "turbojet", "piston", "electric"]
        },
        "wingspan_meters": {
            "type": "number",
            "minimum": 0,
            "maximum": 100
        },
        "is_pressurized": {
            "type": "boolean"
        },
        "applicable_regulations": {
            "type": "array",
            "items": {
                "type": "string",
                "pattern": "^(FAR|EASA|CAAC)-[0-9A-Z\\.]+$"
            },
            "maxItems": 50
        }
    },
    "required": ["aircraft_model", "manufacturer"],
    "additionalProperties": false
}
```

### A.3 Auto Engineering Schema (Domain Example)

```json
{
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
        "vehicle_make": {
            "type": "string",
            "maxLength": 100
        },
        "vehicle_model": {
            "type": "string",
            "maxLength": 100
        },
        "model_year": {
            "type": "integer",
            "minimum": 1900,
            "maximum": 2100
        },
        "vin": {
            "type": "string",
            "pattern": "^[A-HJ-NPR-Z0-9]{17}$",
            "description": "17-character Vehicle Identification Number"
        },
        "engine_displacement_liters": {
            "type": "number",
            "minimum": 0,
            "maximum": 20
        },
        "horsepower": {
            "type": "integer",
            "minimum": 0
        },
        "transmission_type": {
            "type": "string",
            "enum": ["manual", "automatic", "cvt", "dct", "ev"]
        },
        "is_electric": {
            "type": "boolean"
        },
        "safety_ratings": {
            "type": "object",
            "properties": {
                "nhtsa_overall": { "type": "integer", "minimum": 1, "maximum": 5 },
                "iihs_rating": { "type": "string", "enum": ["Poor", "Marginal", "Acceptable", "Good", "Good+"] }
            },
            "additionalProperties": false
        },
        "recall_ids": {
            "type": "array",
            "items": { "type": "string", "maxLength": 20 },
            "maxItems": 100
        }
    },
    "required": ["vehicle_make", "vehicle_model", "model_year"],
    "additionalProperties": false
}
```

### Supported JSON Schema Data Types Summary

| JSON Schema Type | Go Equivalent | Example Constraint Keywords |
|-----------------|---------------|---------------------------|
| `string` | `string` | `minLength`, `maxLength`, `pattern`, `format`, `enum` |
| `integer` | `int64` | `minimum`, `maximum` |
| `number` | `float64` | `minimum`, `maximum` |
| `boolean` | `bool` | (none) |
| `array` | `[]T` | `items`, `minItems`, `maxItems` |
| `object` | `map/struct` | `properties`, `required`, `additionalProperties` |

**Supported `format` values**: `date`, `date-time`, `email`, `uri`, `uuid`


## Implemnentation journal
In order to be able to have another agent pick up the work in progress, all completed work and milestones must be journaled to the ./journals/implement_mutableMetadata.md 

Each time a milestone or signficant part of a milestone is completed there needs to be a date/time stamped journal entry showing the item is done.  So that a new agent taking over will know exactly where we are in the process and can resume the work. 

At any give time I should be able to clear your context and have you resume your work based on this document, the code (git diffs) and the journal of what is completed. 

If we run into any issues where Q has to be consulted about an issue that needs a decision , then Qs answer should also be written to the journal along with the question.