Merge remote-tracking branch 'origin/master' into worktree/default-model-persistence

Carries two edits beyond conflict resolution, both forced by what master
brought in:

- `CustomProviderCard`: master added front-end key validation and a
  component-level `keyValue` (already trimmed) while still writing
  `apiKeyEnv` unconditionally. Kept this branch's blank-key rule and its
  committed-profile retry gate, and adopted master's single `keyValue` so
  the component has one spelling of the key rather than two.
- `docs/user/guide/providers`: master merged #1810, whose default-model
  section still taught overriding the `api-gateway` row in
  `$DSH_HOME/config.yaml` — the behavior this branch replaced. Rewritten
  for the settings section the picker now writes, plus the review fix from
  #1810 replacing the colloquial 挂着 in the opener.

docs/config-catalog.md

@@ -680,8 +680,11 @@ Requires: `llm`
  */
 export interface Config {
   /**
-   * Trimmed literal API key; whitespace-only is absent. Prefer
-   * {@link apiKeyEnv} to keep secrets out of configuration files.
+   * Trimmed literal API key; whitespace-only is absent, so it resolves through
+   * {@link apiKeyEnv} like an omitted one. Prefer {@link apiKeyEnv} to keep
+   * secrets out of configuration files. {@link resolveAdapterOptions} also
+   * format-checks what remains: a value no HTTP header can carry fails there
+   * rather than inside `fetch`.
    */
   apiKey?: string
   /** Credential reference (environment-variable name) resolved per request; defaults to `DEEPSEEK_API_KEY`. */
@@ -740,7 +743,11 @@ export interface Config {
 
 /** Configuration for one pi-ai provider route; the `providers` dict key IS the route. */
 export interface PiAiProviderProfile {
-  /** Literal provider credential; prefer {@link apiKeyEnv}. With both absent pi-ai uses its provider-native ambient discovery. */
+  /**
+   * Literal provider credential; prefer {@link apiKeyEnv}. With both absent pi-ai uses its
+   * provider-native ambient discovery. Trimmed and format-checked by {@link resolveProfiles}; a
+   * value no HTTP header can carry fails there rather than inside `fetch`.
+   */
   apiKey?: string
   /** Credential reference (environment-variable name) resolved per request through `ctx.credentials`. */
   apiKeyEnv?: string
@@ -812,7 +819,7 @@ export interface PiAiModelProfile {
 
 Depends on: `CacheRetention` (`@earendil-works/pi-ai`) · `ModelThinkingLevel` (`@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:122`](../packages/llm/llm-pi-ai/src/config.ts)
+Source: [`packages/llm/llm-pi-ai/src/config.ts:126`](../packages/llm/llm-pi-ai/src/config.ts)
 
 ## `@deepseek-ai/dsh-llm-replay`