fix(openrouter): route reasoning_effort to verbosity for adaptive Anthropic models (#43436)

* fix(openrouter): route reasoning_effort to verbosity for adaptive Anthropic models

Reasoning-mandatory Anthropic models (Claude 4.6+/fable/mythos-class) over
OpenRouter ignore reasoning.effort and use adaptive thinking. #42991 correctly
stopped Hermes from sending a reasoning field to them (it 400s), but put nothing
in its place — leaving agent.reasoning_effort a silent no-op on the OpenRouter
path: the model always ran at its adaptive default (high) regardless of config.

OpenRouter honors the requested effort on the top-level verbosity field instead
(maps to Anthropic output_config.effort). Route the existing
reasoning_config[effort] there for these models while still never emitting a
reasoning field, preserving the #42991 fix. No new config arg — the value the
user already sets via agent.reasoning_effort now flows to verbosity.

- low/medium/high/xhigh/max pass through verbatim (OpenRouter accepts the
  extended scale for Claude; verified live HTTP 200 + monotonic token spend).
- effort unset/none/disabled omits verbosity so the model keeps its default.
- native Anthropic transport already correct; unchanged.

Fixes #43432

* test(openrouter): cover real effort range (add minimal, frame max as passthrough)

Adversarial review noted the verbosity tests looped over 'max' — a value
parse_reasoning_effort can never produce — while omitting 'minimal', which it
can. Align the routing test with the real config range
(VALID_REASONING_EFFORTS = minimal/low/medium/high/xhigh) and keep a separate
value-agnostic passthrough test that documents why xhigh/max must survive
verbatim (TypedDict, no runtime literal validation; OpenRouter accepts the
extended scale for Claude).

* docs: explain reasoning_effort -> verbosity routing for adaptive Anthropic models

Document that reasoning_effort transparently maps to OpenRouter's verbosity
field for adaptive-thinking Anthropic models (Claude 4.6+/Fable/Mythos), where
reasoning.effort is ignored. Note xhigh is the configurable ceiling (max is wire-
only). Add verbosity as a top-level-kwarg example in the provider-plugin guide.

website/docs/developer-guide/model-provider-plugin.md

@@ -131,8 +131,9 @@ class AcmeProfile(ProviderProfile):
 
     def build_api_kwargs_extras(self, *, reasoning_config=None, **context):
         """Returns (extra_body_additions, top_level_kwargs). Needed when some
-        fields go top-level (Kimi's reasoning_effort) and some go in extra_body
-        (OpenRouter's reasoning dict). Default: ({}, {})."""
+        fields go top-level (Kimi's reasoning_effort, OpenRouter's verbosity for
+        adaptive Anthropic models) and some go in extra_body (OpenRouter's
+        reasoning dict). Default: ({}, {})."""
         return {}, {}
 
     def fetch_models(self, *, api_key=None, timeout=8.0) -> list[str] | None: