docs(protocol): give INVALID_FIELD one published meaning (#15883)

`error-handling.mdx` published «Field value has wrong type» with the example
message `Field 'age' must be a number`, while `error-catalog.mdx` publishes the
name/resolution meaning. A repo-wide producer sweep finds 22 assignment sites in
5 files, all name/resolution-shaped, and none of the 14 type-shaped refusal
texts carries `INVALID_FIELD` — so the type meaning had no emitter and the
example message quoted no producer.

Rewrite only the `#### INVALID_FIELD` block: the Meaning now matches the
catalog, and the example message is the real producer text from
`packages/rest/src/error-response.ts:1655` (`Unknown field '<field>' on object
'<object>'`) with the `field`/`object` details that producer actually sets.
Status stays 400, as every producer sets and `error-response.ts` maps.


Claude-Session: https://claude.ai/code/session_012zGPuVVX3deAx9LdjK8jCk

Co-authored-by: Claude <noreply@anthropic.com>

Author: claude[bot]

content/docs/protocol/kernel/error-handling.mdx

@@ -301,25 +301,30 @@ deriving it from this page.
 
 #### `INVALID_FIELD`
 **HTTP Status:** 400  
-**Meaning:** Field value has wrong type
+**Meaning:** A field name in the request does not exist on the target object — a name that
+resolves to nothing, not a value of the wrong type. On a list read it also covers an
+unreserved query parameter, which `GET /data/:object` reads as a field filter.
 
 **Example:**
 ```json
 {
   "success": false,
   "error": {
     "code": "INVALID_FIELD",
-    "message": "Field 'age' must be a number",
+    "message": "Unknown field 'age' on object 'contact'",
     "details": {
       "field": "age",
-      "expected_type": "number",
-      "actual_type": "string",
-      "value": "twenty-five"
+      "object": "contact"
     }
   }
 }
 ```
 
+The [error catalog's `INVALID_FIELD` entry](/docs/api/error-catalog#invalid_field) carries
+the authoritative cause text — it enumerates every read axis this one code answers on
+(`select`, `expand`, `searchFields`, `groupBy`, `aggregations[].field`) and the
+off-request `backfillSummaryNulls` case.
+
 ### Resource Errors
 
 #### `RESOURCE_NOT_FOUND`