An embedding model's query_prefix, put before questions and never before documents

Qwen3-Embedding and models like it are trained with an instruction on the
query side only. The prefix goes before the question a knowledge-base
search embeds, at answer time and in the admin API's search; documents
reach /v1/embeddings from llmgw-kb as they are.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/reference.md

@@ -145,6 +145,7 @@ rather than repeated.
 | `context_length` | `int` | [Model](#model) |
 | `max_output` | `int` | [Model](#model) |
 | `capabilities` | `Capabilities` | [Model](#model) |
+| `query_prefix` | `string` | [Model](#model) |
 | `role` | `string` | [Model](#model) |
 | `guard` | `*GuardModel` | [Model](#model) |
 | `origin` | `*Origin` | [Model](#model) |
@@ -1389,6 +1390,16 @@ Capabilities is what this model can do beyond plain completion.
 
 Takes a [Capabilities](#capabilities) block.
 
+### `query_prefix`
+
+`string`
+
+QueryPrefix is put before a question an embedding model embeds for a
+knowledge-base search; documents are embedded without it. Models
+trained with an instruction on the query side want it, Qwen3-Embedding
+"Instruct: Given a web search query, retrieve relevant passages that
+answer the query\nQuery: " for one.
+
 ### `role`
 
 `string`