diff --git a/openapi.yaml b/openapi.yaml
index 6e203b1cd..82ff5b003 100644
--- a/openapi.yaml
+++ b/openapi.yaml
@@ -896,11 +896,6 @@ components:
                     additionalProperties: true
                     description: The workflow graph to execute
                     type: object
-                prompt_id:
-                    description: Optional client-supplied job id. Must be a UUID in canonical lowercase hyphenated form; it is echoed back in the response. Omitted or null means the server generates one.
-                    format: uuid
-                    nullable: true
-                    type: string
                 workflow_id:
                     description: UUID identifying the cloud workflow entity to associate with this job
                     type: string
@@ -1800,7 +1795,9 @@ paths:
                         application/json:
                             schema:
                                 $ref: '#/components/schemas/ErrorResponse'
-                    description: Invalid request (no fields provided)
+                    description: |
+                        Invalid request — no fields provided, or `preview_id` is the zero UUID
+                        (`INVALID_PREVIEW_ID`).
                 "401":
                     content:
                         application/json:
@@ -1812,7 +1809,10 @@ paths:
                         application/json:
                             schema:
                                 $ref: '#/components/schemas/ErrorResponse'
-                    description: Asset not found
+                    description: |
+                        Asset not found — returned both when the asset being updated does
+                        not exist and when `preview_id` does not reference an asset
+                        accessible to the caller.
                 "500":
                     content:
                         application/json:
@@ -3050,6 +3050,12 @@ paths:
                             schema:
                                 $ref: '#/components/schemas/PromptErrorResponse'
                     description: Payment required - Insufficient credits
+                "413":
+                    content:
+                        application/json:
+                            schema:
+                                $ref: '#/components/schemas/PromptErrorResponse'
+                    description: Workflow JSON too large
                 "429":
                     content:
                         application/json: