refactor(providers): one record per provider, one place for the key-and-URL decision (#988)

Every fact about a provider lives in one record in lib/providers.ts (SDK kind,
credential kind, env var prefix, default URL, picker group, four-language
notes, and a short model list for the six providers that cannot list models).
The thirteen tables keyed by provider name are gone. resolveEndpoint decides
whose key a call uses and where it goes; usesServerCredentials reads its
answer instead of mirroring getAIModel's branches; serverCredentialError holds
the server credential check once. The UI, the connection test and the routes
read the record's credential and sdk fields instead of comparing provider
names (44 such checks before, 6 after, in the admin panel's fixed-variable
branches).

Intended behavior changes: providers that can list their models have no
hand-written list; the settings dialog fetches the live list in the background
once credentials are entered for a provider without models and offers it
behind "Browse models". Azure has no placeholder default URL (old entries that
hold it still count as unset); the base URL field of Azure and of the new
"custom" OpenAI-compatible preset (CUSTOM_API_KEY, CUSTOM_BASE_URL) is
labelled required. The connection test answers 400 for an unknown provider
name; prototype names are refused everywhere. Provider lists in error messages
and the admin "add provider" dropdown follow the picker's order.

Also fixed, from before the refactor: the redirect guard drops x-access-code
on cross-origin redirects, and edgeOneEndpoint accepts the Origin header only
when it matches Host or X-Forwarded-Host.

Verification: a behavior snapshot of getAIModel's SDK factory calls and the
quota functions over 25 providers, 22 client override shapes and 9 server
environments (5843 rows), recorded on the old code and unchanged apart from
the intended changes; 752 unit tests, 65 provider e2e tests, tsc, biome,
next build. Reviewed by five models from one brief; their findings and the
resulting fixes are recorded in docs/plans/2026-10-provider-refactor.md.

lib/admin/providers.ts

@@ -1,14 +1,10 @@
 import { z } from "zod"
+import { PROVIDER_NAMES, PROVIDERS, type ProviderName } from "@/lib/providers"
 import {
     ProviderNameSchema,
     type ServerModelsConfig,
     slugify,
 } from "@/lib/server-model-config"
-import {
-    FIXED_CRED_PROVIDERS,
-    PROVIDER_INFO,
-    type ProviderName,
-} from "@/lib/types/model-config"
 import { type MaskedSecret, maskSecret } from "./auth"
 import { loadSettings } from "./settings"
 
@@ -80,20 +76,19 @@ const SECRET_FIELDS = [
     "vertexApiKey",
 ] as const
 
-// ADMIN_-prefixed env var names for instance `index` (0-based) of a provider
-function credEnvNames(
+// ADMIN_-prefixed env var names for instance `index` (0-based) of a
+// provider. None for providers whose credentials live in fixed variables
+// (Bedrock, Vertex AI, Ollama) or that have none (EdgeOne).
+export function credEnvNames(
     provider: ProviderName,
     index: number,
 ): { key?: string; url?: string } {
-    if (FIXED_CRED_PROVIDERS.includes(provider) || provider === "edgeone") {
-        return {}
-    }
-    const prefix =
-        provider === "gateway" ? "AI_GATEWAY" : provider.toUpperCase()
+    const { fixedCredentials, envPrefix } = PROVIDERS[provider]
+    if (fixedCredentials || envPrefix === null) return {}
     const suffix = index === 0 ? "" : `_${index + 1}`
     return {
-        key: `ADMIN_${prefix}_API_KEY${suffix}`,
-        url: `ADMIN_${prefix}_BASE_URL${suffix}`,
+        key: `ADMIN_${envPrefix}_API_KEY${suffix}`,
+        url: `ADMIN_${envPrefix}_BASE_URL${suffix}`,
     }
 }
 
@@ -162,7 +157,7 @@ export function mergeSecrets(
 }
 
 function displayName(p: StoredAdminProvider): string {
-    return p.name?.trim() || PROVIDER_INFO[p.provider].label
+    return p.name?.trim() || PROVIDERS[p.provider].label
 }
 
 export function validateAdminProviders(
@@ -170,9 +165,11 @@ export function validateAdminProviders(
     envConfig: ServerModelsConfig | null = null,
 ): string | null {
     const envProviders = envConfig?.providers ?? []
-    for (const single of FIXED_CRED_PROVIDERS) {
+    // Providers whose credentials live in fixed variables can have one entry
+    const fixed = PROVIDER_NAMES.filter((p) => PROVIDERS[p].fixedCredentials)
+    for (const single of fixed) {
         if (list.filter((p) => p.provider === single).length > 1) {
-            return `Only one ${PROVIDER_INFO[single].label} provider is supported (its credentials use fixed environment variables).`
+            return `Only one ${PROVIDERS[single].label} provider is supported (its credentials use fixed environment variables).`
         }
         // Its credentials are global; a panel instance would silently
         // override the credentials env-configured models rely on
@@ -180,7 +177,7 @@ export function validateAdminProviders(
             list.some((p) => p.provider === single) &&
             envProviders.some((p) => p.provider === single)
         ) {
-            return `${PROVIDER_INFO[single].label} is already configured in AI_MODELS_CONFIG / ai-models.json and shares global credentials. Manage it via the environment configuration instead.`
+            return `${PROVIDERS[single].label} is already configured in AI_MODELS_CONFIG / ai-models.json and shares global credentials. Manage it via the environment configuration instead.`
         }
     }
     // Server model ids are built from the slugified name, so names must