fix(llm-pi-ai): let a model declare the request modalities it accepts

A model the installed pi-ai catalog does not describe was reported as
text-only with no way to say otherwise, so a vision model added through
the custom-provider form was refused at every image admission point.
The justification in the source described the DeepSeek chat-completions
serializer, which does reject image blocks; the pi-ai request converter
and every wire protocol it speaks carry images.

Modalities now resolve entry `input` -> installed catalog entry -> route
`defaultInput`, the chain the two capacity fallbacks already use, so the
route value is a fallback and never narrows a catalog model. Its default
stays `[text]`: nothing can interrogate a gateway for its modalities, and
over-claiming admits an image the provider rejects mid-turn, after prompt
admission has already committed the message.

docs/config-catalog.md

@@ -858,6 +858,17 @@ export interface PiAiProviderProfile {
    * never becomes a per-request cap on its own.
    */
   defaultMaxTokens?: number
+  /**
+   * Request modalities for a model this route lists that neither its entry's
+   * {@link PiAiModelProfile.input} nor the installed catalog declares (default
+   * `[text]`). A fallback like the capacities above, not an override: a
+   * catalog model keeps the modalities the catalog records for it, and this
+   * value never narrows one. A gateway serving vision models the catalog does
+   * not describe declares `[text, image]` once here instead of on every entry.
+   * Unlike an entry's list, this one may not be empty — nothing sits below it
+   * to answer instead.
+   */
+  defaultInput?: PiAiModality[]
   /** Provider request headers; Harness attribution wins reserved names. */
   headers?: Record<string, string>
   /** Provider-neutral pi-ai reasoning level. */
@@ -893,6 +904,18 @@ export interface PiAiModelProfile {
    * default on its own.
    */
   maxTokens?: number
+  /**
+   * Request modalities this model accepts. Absent — or empty, which describes
+   * a model that accepts nothing and so states no answer either — keeps the
+   * installed catalog entry's modalities, then the route's `defaultInput`.
+   * Declaring images is what makes a hand-declared vision model usable, and
+   * declaring text alone corrects a catalog model whose gateway does not serve
+   * what the catalog records. This is a claim about the endpoint, not a check
+   * of it: nothing interrogates a gateway for what it accepts, so a model
+   * claiming images its endpoint refuses is refused by the provider instead,
+   * mid-turn.
+   */
+  input?: PiAiModality[]
   /**
    * Selectable reasoning efforts. Absent inherits the installed catalog
    * entry's capability (a hand-declared model has none and does not reason);
@@ -930,6 +953,9 @@ export interface PiAiCompatProfile {
   supportsReasoningEffort?: boolean
 }
 
+/** One request modality a pi-ai model may accept. */
+export type PiAiModality = Model<Api>['input'][number]
+
 /**
  * Selectable reasoning efforts for one model: each key is a level the model
  * offers (and selectors show), and its value is the wire spelling dispatch
@@ -953,9 +979,9 @@ type PiThinkingFormat = NonNullable<OpenAICompletionsCompat['thinkingFormat']>
 type WithheldThinkingFormat = 'chat-template' | 'qwen-chat-template'
 ```
 
-Depends on: `CacheRetention` (`@earendil-works/pi-ai`) · `ModelThinkingLevel` (`@earendil-works/pi-ai`) · `OpenAICompletionsCompat` (`@earendil-works/pi-ai`) · [`RetryPolicyConfig`](../packages/llm/llm/src/index.ts) · `ThinkingBudgets` (`@earendil-works/pi-ai`) · `Transport` (`@earendil-works/pi-ai`)
+Depends on: `Api` (`@earendil-works/pi-ai`) · `CacheRetention` (`@earendil-works/pi-ai`) · `Model` (`@earendil-works/pi-ai`) · `ModelThinkingLevel` (`@earendil-works/pi-ai`) · `OpenAICompletionsCompat` (`@earendil-works/pi-ai`) · [`RetryPolicyConfig`](../packages/llm/llm/src/index.ts) · `ThinkingBudgets` (`@earendil-works/pi-ai`) · `Transport` (`@earendil-works/pi-ai`)
 
-Source: [`packages/llm/llm-pi-ai/src/config.ts:142`](../packages/llm/llm-pi-ai/src/config.ts)
+Source: [`packages/llm/llm-pi-ai/src/config.ts:172`](../packages/llm/llm-pi-ai/src/config.ts)
 
 ## `@deepseek-ai/dsh-llm-replay`