fix(llm-pi-ai): describing a model must not fail on a bad profile level

`resolveModel` validated the profile's reasoning level against the exact
model and threw when it did not fit. That call builds the model catalog,
and the catalog build catches per PROVIDER — so one mis-set field took the
whole provider out of every picker behind a single error row, hiding even
the models that do support the level. Measured: `anthropic` set to `max`
threw for six of its eight models.

Describing what a model can do now reports an unusable profile level as no
default rather than throwing; the request path still refuses it, which is
where a bad configuration belongs. The existing spec asserted the old
throw and now asserts both halves of that split.

Known gap, left deliberately: a model that cannot take the route's level
still fails its first request while the picker shows 「Default」 for it,
because the request path keeps using the profile level as the fallback.
Reaching that needs a hand-written `settings.yaml` — the Models page no
longer writes the field — and the error names the model and the level, so
selecting a supported level is a way out. Closing it properly means giving
`AgentOptions` a `reasoningEffort` so compositions without a model picker
keep an entry point, then dropping the provider-scoped field altogether;
that is its own change.

packages/llm/llm-pi-ai/README.md

@@ -73,7 +73,7 @@ The adapter exposes each configured route's models through `ctx.llm.listModels(p
 
 A model that carries reasoning metadata exposes pi-ai's ordered `getSupportedThinkingLevels(model)` result without filtering or normalization, including `off` and the model-specific availability of `xhigh` or `max`. The Harness exposes each canonical pi-ai level as an opaque ID; provider/model wire spellings remain inside pi-ai's `thinkingLevelMap`.
 
-A model **without** that metadata — every hand-declared one, and a catalog model pi-ai marks as non-reasoning — exposes no `reasoning` at all. pi-ai reports such a model as supporting the single level `off`, but `off` is translated to *omitting* the reasoning option, which is byte-for-byte the request that naming no effort already produces: selecting it could not disable anything, so a provider whose own default is to think would keep thinking with `off` shown as selected. Reporting the capability as unavailable leaves a surface offering the provider's default and nothing that misrepresents it. The profile `reasoning` value, including `off`, is the deployment default when configured; omitting it preserves the provider default. Per-request `GenerateOptions.reasoningEffort` takes precedence, and any explicit value absent from the exact model capability fails with `UNSUPPORTED_REASONING_EFFORT` before network I/O instead of being clamped. pi-ai's common stream options represent `off` by omitting `reasoning`.
+A model **without** that metadata — every hand-declared one, and a catalog model pi-ai marks as non-reasoning — exposes no `reasoning` at all. pi-ai reports such a model as supporting the single level `off`, but `off` is translated to *omitting* the reasoning option, which is byte-for-byte the request that naming no effort already produces: selecting it could not disable anything, so a provider whose own default is to think would keep thinking with `off` shown as selected. Reporting the capability as unavailable leaves a surface offering the provider's default and nothing that misrepresents it. The profile `reasoning` value, including `off`, is the deployment default when configured; omitting it preserves the provider default. Per-request `GenerateOptions.reasoningEffort` takes precedence, and a level absent from the exact model capability fails the REQUEST with `UNSUPPORTED_REASONING_EFFORT` before network I/O instead of being clamped. Describing a model never fails that way: the models under one provider disagree about which levels they accept, so `resolveModel` reports a profile level the exact model cannot take as no default at all rather than throwing. A throw there would take the whole provider out of every model catalog built over it — one mis-set profile field hiding even the models that do support the level — so a bad configuration surfaces where it is acted on, not where it is described. pi-ai's common stream options represent `off` by omitting `reasoning`.
 
 Supported profile fields are `apiKey`, `apiKeyEnv`, `displayName`, `api`, `baseURL`, `models`, `defaultContextWindow`, `defaultMaxTokens`, `headers`, `reasoning`, `thinkingBudgets`, `cacheRetention`, `transport`, `timeoutMs`, `websocketConnectTimeoutMs`, `streamIdleTimeoutMs`, and `retryPolicy`. Each profile's optional retry policy is captured with that provider route; omission uses bounded normal defaults. The stream-idle interval is a positive finite Node timer delay, defaults to five minutes, and covers only an outstanding provider read, not consumer think time. Harness app attribution wins a conflicting configured header name.