improve model provider selection algorithm

server/lib/aiProviderSelection.ts

@@ -0,0 +1,97 @@
+import {
+    aiModelCatalog,
+    getCatalogProviderForType,
+    type CatalogProvider
+} from "@server/lib/aiModelCatalog";
+import type { AiProviderType } from "@server/lib/aiProviderDefaults";
+
+function stripVendorPrefix(modelId: string): string | null {
+    const idx = modelId.indexOf("/");
+    if (idx === -1 || idx === modelId.length - 1) {
+        return null;
+    }
+    return modelId.slice(idx + 1);
+}
+
+function modelKeysToTry(modelId: string): string[] {
+    const keys = [modelId];
+    const stripped = stripVendorPrefix(modelId);
+    if (stripped) {
+        keys.push(stripped);
+    }
+    return keys;
+}
+
+function catalogOwnsModel(
+    catalogProvider: CatalogProvider,
+    modelId: string
+): boolean {
+    for (const key of modelKeysToTry(modelId)) {
+        if (aiModelCatalog.get(catalogProvider, key)) {
+            return true;
+        }
+    }
+    return false;
+}
+
+function modelKnownInAnyCatalog(modelId: string): boolean {
+    for (const key of modelKeysToTry(modelId)) {
+        if (aiModelCatalog.listByKey(key).length > 0) {
+            return true;
+        }
+    }
+    return false;
+}
+
+/**
+ * How strongly a provider "owns" a requested model id via the known catalog.
+ *
+ * 2 - Typed provider whose catalog contains the model
+ * 1 - Aggregator/custom that can proxy a catalog-known model
+ * 0 - No ownership signal (typed miss, or unknown model on aggregator/custom)
+ */
+export function catalogOwnershipScore(
+    type: AiProviderType,
+    modelId: string
+): number {
+    const catalogProvider = getCatalogProviderForType(type);
+    if (catalogProvider != null) {
+        return catalogOwnsModel(catalogProvider, modelId) ? 2 : 0;
+    }
+    return modelKnownInAnyCatalog(modelId) ? 1 : 0;
+}
+
+/**
+ * Prefer native vendor providers over aggregators over custom when catalog
+ * ownership is tied.
+ *
+ * 2 - Native typed provider (openai, anthropic, gemini, ...)
+ * 1 - Aggregator gateway (openRouter, vercelAiGateway)
+ * 0 - Custom
+ */
+export function providerClassRank(type: AiProviderType): number {
+    if (type === "custom") {
+        return 0;
+    }
+    if (type === "openRouter" || type === "vercelAiGateway") {
+        return 1;
+    }
+    return 2;
+}
+
+export function keepBestScored<T>(
+    items: T[],
+    scoreFn: (item: T) => number
+): T[] {
+    if (items.length <= 1) {
+        return items;
+    }
+    let best = Number.NEGATIVE_INFINITY;
+    for (const item of items) {
+        const score = scoreFn(item);
+        if (score > best) {
+            best = score;
+        }
+    }
+    return items.filter((item) => scoreFn(item) === best);
+}