fix(llm-pi-ai): withhold OAuth-only providers from the configurable directory

pi-ai resolves an OAuth provider from a stored OAuth credential alone, and
this adapter builds its Models collection with no credential store and runs
no login flow. `openai-codex` — the one installed provider declaring
`auth.oauth` with no `auth.apiKey` — was therefore offered on the Models page
with the keyless placeholder every pi-ai route carries, and every request on
it failed `Provider is not configured` before going out.

`catalogProviderTakesApiKey()` answers whether pi-ai's installed provider for
a route declares the one method this adapter can supply, and the directory
skips the catalog routes that fail it. Catalog membership is unchanged, so
`declared` still answers what pi-ai ships; the profile half of the union stays
unconditional, so a route a settings document already names keeps its entry
and can be edited or deleted.

Resolution is untouched: a profile naming `apiKeyEnv` on such a route still
builds a working provider.

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

@@ -189,6 +189,8 @@ Recorded response content appends to the next request and does not invalidate it
 
 ## Known Limitations and Deferred Work
 
+- **A provider that authenticates through OAuth alone is not offered** — pi-ai resolves OAuth from a *stored* OAuth credential, and this adapter builds its `Models` collection with no credential store and runs no login flow, so every request on such a route fails `Provider is not configured` before it goes out. The configurable-provider directory withholds them; `openai-codex` is the only one the installed catalog ships. A route a settings document already names keeps its entry so a configuration surface can edit or delete it, and `apiKeyEnv` still authenticates it with that key — which for Codex is a token that expires with nothing here to refresh it.
+- **Provider-native discovery reads the process environment only** — a route naming no credential defers to the catalog provider's own resolution, which interrogates environment variables (`AZURE_OPENAI_API_KEY`, `AWS_PROFILE`, `AWS_ACCESS_KEY_ID`, and each provider's own set). It reads no local credential directory, so `~/.aws/credentials` without an exported `AWS_PROFILE` resolves as unconfigured, and a value held by the harness credential seam is invisible to it unless the process environment carries it too.
 - **Settings can add or override routes, not remove composition routes** — the user layer merges over the composition `base`, so deleting a `cordis.yml`-provided provider is a composition change; `replace` on the namespace only resets the user layer.
 - **The layered merge has no delete for dict keys** — the settings seam merges the composition `base` and the user layer per key, recursively, so a `reasoningEfforts` level, `modelOverrides` entry, or `compat` field the base declares cannot be removed by the user layer, only overridden — and for `reasoningEfforts` absence *is* the meaning ("not offered"), so a base-declared level stays offered. This only triggers when a `cordis.yml` entry config declares per-model reasoning fields for the same model the user layer edits; the supported posture is to leave those to the settings document (the shipped composition mounts the adapter dormant), and a `models` list is an array replacing wholesale, which is the in-band escape.
 - **`headers` can carry a credential the redactor never sees** — the profile's `headers` dict is plain strings, so `Authorization` or `api-key` set there is returned verbatim by a redacted `describe()` and rendered by any configuration UI. Store credentials as `apiKeyEnv` references; making the dict write-only is deferred with the rest of the [wire-boundary work](../llm/README.md#known-limitations-and-deferred-work).