fix(subagent): state when to query child routes and when to omit them

The discovery tool presented itself as the place to inspect options before
selecting a child route, and rejected every provider or model outside the
Session's authorized routes, including providers that do not exist. A model
that skipped the no-argument call therefore had no way to learn the correct
ids or that omission was legal, and repeated identical denials.

Say that queries exist to override the child route, that omitting both route
fields inherits the parent route, that a field is omitted rather than sent
empty, and, in each optional route field, that omitting it inherits the
parent value.

docs/tool-catalog.i18n.yaml

@@ -246,7 +246,7 @@
   en: 841abe0dd5913ea7
   zh: 841abe0dd5913ea7
 /tool-schema-catalog/deepseek-ai-dsh-tool-subagent/list-subagent-models:
-  en: 207228068bc61885
+  en: 2f6d3f253af50d47
   zh: 36e9344ee1af8869
 /tool-schema-catalog/deepseek-ai-dsh-tool-subagent/subagent:
   en: 430672da3c1a6ca6

docs/tool-catalog.md

@@ -2039,7 +2039,7 @@ The subagent_oar tool selects among configured aliases for external providers. T
 
 ### `list_subagent_models`
 
-Inspect subagent models without changing the current Agent. No arguments: providers; `provider`: allowed models; `provider` + `model`: that model and its reasoning efforts. Inspect options here before selecting a child provider and model; use returned ids for delegation.
+Inspect the subagent routes this Session authorizes. No arguments: authorized providers. `provider`: that provider's authorized models. `provider` + `model`: that model and its reasoning efforts. Query only to override the child route; delegation without `provider` and `model` inherits the parent route. Omit a field rather than sending an empty string.
 
 ```json
 {