diff --git a/src/app/(dashboard)/dashboard/combos/page.tsx b/src/app/(dashboard)/dashboard/combos/page.tsx
index e2af3ab665..27af619bd1 100644
--- a/src/app/(dashboard)/dashboard/combos/page.tsx
+++ b/src/app/(dashboard)/dashboard/combos/page.tsx
@@ -2512,7 +2512,19 @@ function ComboFormModal({ isOpen, combo, onClose, onSave, activeProviders, combo
   };
 
   const handleAddModel = (model) => {
-    const nextEntry = { model: model.value, weight: 0 };
+    const qualifiedModel = typeof model?.value === "string" ? model.value : "";
+    const parsedModel = parseQualifiedModel(qualifiedModel);
+    const resolvedProviderId =
+      resolveComboBuilderProviderId(model?.providerId, builderProviders) ||
+      resolveComboBuilderProviderId(parsedModel?.providerId, builderProviders) ||
+      (typeof model?.providerId === "string" && model.providerId.trim()) ||
+      parsedModel?.providerId ||
+      null;
+    const nextEntry = {
+      model: qualifiedModel,
+      ...(resolvedProviderId ? { providerId: resolvedProviderId } : {}),
+      weight: 0,
+    };
     if (hasExactModelStepDuplicate(models, nextEntry)) {
       setBuilderError(
         getI18nOrFallback(
diff --git a/src/sse/services/auth.ts b/src/sse/services/auth.ts
index 65a69f194f..fd645bc84c 100644
--- a/src/sse/services/auth.ts
+++ b/src/sse/services/auth.ts
@@ -1,6 +1,7 @@
 import { randomUUID, createHash } from "crypto";
 import {
   getProviderConnections,
+  getProviderNodes,
   validateApiKey,
   updateProviderConnection,
   getSettings,
@@ -44,6 +45,7 @@ import {
 import { looksLikeQuotaExhausted } from "@/shared/utils/classify429";
 import { getCodexModelScope } from "@omniroute/open-sse/executors/codex.ts";
 import {
+  getProviderById,
   getProviderAlias,
   resolveProviderId,
   NOAUTH_PROVIDERS,
@@ -791,7 +793,7 @@ export { fisherYatesShuffle, getNextFromDeckSync as getNextFromDeck };
 /**
  * Resolve provider aliases (e.g., nvidia -> nvidia_nim) for DB lookup
  */
-function getProviderSearchPool(provider: string): string[] {
+async function getProviderSearchPool(provider: string): Promise<string[]> {
   const canonicalProvider = resolveProviderId(provider);
   const canonicalAlias = getProviderAlias(canonicalProvider);
 
@@ -802,7 +804,34 @@ function getProviderSearchPool(provider: string): string[] {
     return ["nvidia_nim", "nvidia"];
   }
 
-  return Array.from(new Set([provider, canonicalProvider, canonicalAlias].filter(Boolean)));
+  const searchPool = new Set([provider, canonicalProvider, canonicalAlias].filter(Boolean));
+
+  // Built-in providers already resolve through static ids/aliases. Only
+  // compatible/custom providers need provider_nodes expansion back to the
+  // generated internal connection ids.
+  if (getProviderById(canonicalProvider)) {
+    return Array.from(searchPool);
+  }
+
+  // Custom provider nodes are referenced by user-facing prefixes in combos
+  // (for example "78code/gpt-5.4"), but live credentials are stored under
+  // internal provider ids like openai-compatible-responses-<uuid>.
+  try {
+    const providerNodes = await getProviderNodes();
+    for (const node of Array.isArray(providerNodes) ? providerNodes : []) {
+      const nodeRecord = asRecord(node);
+      const nodePrefix = typeof nodeRecord.prefix === "string" ? nodeRecord.prefix.trim() : "";
+      const nodeId = typeof nodeRecord.id === "string" ? nodeRecord.id.trim() : "";
+      if (!nodePrefix || !nodeId) continue;
+      if (nodePrefix === provider || nodePrefix === canonicalProvider || nodePrefix === canonicalAlias) {
+        searchPool.add(nodeId);
+      }
+    }
+  } catch {
+    // Best-effort alias expansion only.
+  }
+
+  return Array.from(searchPool);
 }
 
 /**
@@ -864,7 +893,7 @@ export async function getProviderCredentials(
     );
 
     // Fix #922: Check for aliases (nvidia/nvidia_nim) to ensure credentials are found
-    const providersToSearch = getProviderSearchPool(provider);
+    const providersToSearch = await getProviderSearchPool(provider);
     const connectionResults = await Promise.all(
       providersToSearch.map((p) => getProviderConnections({ provider: p, isActive: true }))
     );
diff --git a/tests/unit/combo-custom-provider-resolution.test.ts b/tests/unit/combo-custom-provider-resolution.test.ts
index fcd5933c9f..ae8a30bad0 100644
--- a/tests/unit/combo-custom-provider-resolution.test.ts
+++ b/tests/unit/combo-custom-provider-resolution.test.ts
@@ -149,3 +149,28 @@ test("#2778 matching logic: node with prefix=flymux and id=UUID-id still matches
   assert.ok(matchByPrefixOrId !== undefined, "Alias-based match must still work after the fix");
   assert.strictEqual(matchByPrefixOrId?.id, FAKE_UUID_NODE_ID);
 });
+
+test("custom provider auth lookup search pool maps alias prefixes to internal provider ids", async () => {
+  const authSrc = fs.readFileSync(path.resolve(__dirname, "../../src/sse/services/auth.ts"), "utf8");
+
+  assert.match(
+    authSrc,
+    /async function getProviderSearchPool\(provider: string\): Promise<string\[]>/,
+    "getProviderSearchPool should be async so it can expand custom provider aliases via provider_nodes"
+  );
+  assert.match(
+    authSrc,
+    /getProviderNodes\(/,
+    "auth lookup should read provider_nodes to map custom prefixes like 78code/micu back to internal provider ids"
+  );
+  assert.match(
+    authSrc,
+    /nodePrefix === provider \|\| nodePrefix === canonicalProvider \|\| nodePrefix === canonicalAlias/,
+    "auth lookup should match provider node prefixes against the requested alias/canonical provider values"
+  );
+  assert.match(
+    authSrc,
+    /searchPool\.add\(nodeId\)/,
+    "auth lookup should add the matched custom provider node id into the credential search pool"
+  );
+});