From 73d3439301e58515a4849996d1d627e863bbce8f Mon Sep 17 00:00:00 2001
From: Mega Mind <146339422+M3gA-Mind@users.noreply.github.com>
Date: Wed, 29 Jul 2026 08:29:27 +0530
Subject: [PATCH] =?UTF-8?q?fix(inference):=20explain=20background-role=20p?=
 =?UTF-8?q?rovider=20fallback=20and=20verify=20BYOK=20keys=20(#5146=20?=
 =?UTF-8?q?=C2=A72.1,=20=C2=A72.4)=20(#5254)?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: M3gA-Mind <elvin@mahadao.com>
---
 .../components/settings/panels/AIPanel.tsx    |  13 +-
 .../panels/__tests__/AIPanel.test.tsx         |  13 +-
 app/src/lib/i18n/ar.ts                        |  14 +
 app/src/lib/i18n/bn.ts                        |  14 +
 app/src/lib/i18n/de.ts                        |  14 +
 app/src/lib/i18n/en.ts                        |  14 +
 app/src/lib/i18n/es.ts                        |  14 +
 app/src/lib/i18n/fr.ts                        |  14 +
 app/src/lib/i18n/hi.ts                        |  14 +
 app/src/lib/i18n/id.ts                        |  14 +
 app/src/lib/i18n/it.ts                        |  14 +
 app/src/lib/i18n/ko.ts                        |  14 +
 app/src/lib/i18n/pl.ts                        |  14 +
 app/src/lib/i18n/pt.ts                        |  14 +
 app/src/lib/i18n/ru.ts                        |  14 +
 app/src/lib/i18n/zh-CN.ts                     |  14 +
 .../api/__tests__/aiSettingsApi.test.ts       | 221 ++++++++++++
 app/src/services/api/aiSettingsApi.ts         | 217 ++++++++++++
 .../agent/harness/session/builder/factory.rs  |  13 +
 src/openhuman/inference/provider/factory.rs   | 149 ++++++--
 .../inference/provider/factory_tests.rs       | 158 +++++++++
 .../provider/fallback_diagnostics.rs          | 332 ++++++++++++++++++
 src/openhuman/inference/provider/mod.rs       |   2 +
 23 files changed, 1277 insertions(+), 37 deletions(-)
 create mode 100644 src/openhuman/inference/provider/fallback_diagnostics.rs

diff --git a/app/src/components/settings/panels/AIPanel.tsx b/app/src/components/settings/panels/AIPanel.tsx
index 074fafe65..d0d51c90b 100644
--- a/app/src/components/settings/panels/AIPanel.tsx
+++ b/app/src/components/settings/panels/AIPanel.tsx
@@ -19,6 +19,7 @@ import {
   type ProviderRef as ApiProviderRef,
   clearCloudProviderKey,
   type CloudProviderView,
+  describeProviderVerificationFailure,
   flushCloudProviders,
   importOpenAiCodexCliAuth,
   listProviderModels,
@@ -2152,7 +2153,17 @@ const CustomRoutingDialog = ({
       setTestReply(result.reply);
     } catch (err) {
       if (testRequestIdRef.current !== requestId) return;
-      setTestError(err instanceof Error ? err.message : String(err));
+      // #5146 §2.4: a raw upstream string ("401", "model_not_found", a bare
+      // 404) tells the user nothing about what to change. Map the common
+      // shapes onto a concrete next step; unrecognised errors pass through.
+      const raw = err instanceof Error ? err.message : String(err);
+      // The banner copy is deliberately generic (a provider error can echo
+      // request material), so keep the raw text on the console where it is
+      // still reachable for diagnosis.
+      console.error(`[ai-settings][test] provider test failed workload=${workload.id}`, raw);
+      // The bare slug, not `currentProviderString` — that is the composite
+      // `provider:model[@temp]` and would read as "'openai:gpt-4o' rejected it".
+      setTestError(describeProviderVerificationFailure(registrySlug ?? '', raw, t));
     } finally {
       if (testRequestIdRef.current === requestId) {
         setTestBusy(false);
diff --git a/app/src/components/settings/panels/__tests__/AIPanel.test.tsx b/app/src/components/settings/panels/__tests__/AIPanel.test.tsx
index 2daa48468..d2d6143b3 100644
--- a/app/src/components/settings/panels/__tests__/AIPanel.test.tsx
+++ b/app/src/components/settings/panels/__tests__/AIPanel.test.tsx
@@ -53,6 +53,12 @@ vi.mock('../../../../services/api/aiSettingsApi', () => ({
   loadLocalProviderSnapshot: vi.fn(),
   loadProviderAuthErrors: vi.fn().mockResolvedValue([]),
   testProviderModel: vi.fn(),
+  // #5146 §2.4: AIPanel no longer renders the raw provider string — it maps
+  // the failure onto actionable copy first. Mirror that shape here so the
+  // banner asserted below is what a user actually sees; the mapping itself is
+  // covered in aiSettingsApi.test.ts.
+  describeProviderVerificationFailure: (slug: string, _raw: string) =>
+    `The key was saved, but '${slug}' rejected it. Check that you pasted the whole key.`,
   modelRegistryVision: vi.fn(() => false),
   upsertModelRegistryVision: vi.fn((registry: unknown[]) => registry),
   setCloudProviderKey: vi.fn().mockResolvedValue(undefined),
@@ -1440,7 +1446,12 @@ describe('AIPanel', () => {
     const dialog = await screen.findByRole('dialog', { name: /Custom routing/i });
     fireEvent.click(within(dialog).getByRole('button', { name: /^Test$/i }));
 
-    expect(await within(dialog).findByRole('alert')).toHaveTextContent('401 invalid api key');
+    // The banner carries the actionable message keyed to the provider slug,
+    // not the raw upstream string (which can echo request material).
+    const alert = await within(dialog).findByRole('alert');
+    expect(alert).toHaveTextContent('rejected it');
+    expect(alert).toHaveTextContent('openai');
+    expect(alert).not.toHaveTextContent('401 invalid api key');
   });
 
   it('renders background loop diagnostics with newest spend row and budget math', async () => {
diff --git a/app/src/lib/i18n/ar.ts b/app/src/lib/i18n/ar.ts
index e2806cacb..cb2e44eb9 100644
--- a/app/src/lib/i18n/ar.ts
+++ b/app/src/lib/i18n/ar.ts
@@ -4632,6 +4632,20 @@ const messages: TranslationMap = {
   'settings.ai.modelVisionDesc':
     'فعّل هذا إذا كان النموذج يقبل الصور. يتيح لمربع الدردشة إرفاق الصور عند اختيار هذا النموذج.',
   'settings.ai.testFailed': 'فشل الاختبار',
+  'settings.ai.providerTest.authRejected':
+    "تم حفظ المفتاح، لكن '{slug}' رفضه. تأكد من لصق المفتاح كاملاً ومن أنه ما زال نشطاً في لوحة تحكم المزوّد.",
+  'settings.ai.providerTest.modelNotRecognized':
+    "تم حفظ المفتاح وقبوله، لكن '{slug}' لا يتعرف على النموذج المحدد. اختر معرّف نموذج يقدمه هذا المزوّد فعلياً (يُضبط نموذجه الافتراضي في إدخال المزوّد).",
+  'settings.ai.providerTest.quotaOrBilling':
+    "تم حفظ المفتاح وقبوله، لكن '{slug}' رفض الطلب لأسباب تتعلق بالحصة أو الفوترة. تحقق من رصيد حسابك وحدود الاستخدام لدى المزوّد.",
+  'settings.ai.providerTest.endpointNotFound':
+    "تم حفظ المفتاح، لكن نقطة النهاية المهيأة لـ '{slug}' أعادت 404. تحقق من عنوان URL الأساسي: عادةً ما يحتاج المزوّد المتوافق مع OpenAI إلى اللاحقة '/v1' (مثل https://api.openai.com/v1).",
+  'settings.ai.providerTest.timeout':
+    "تم حفظ المفتاح، لكن '{slug}' لم يستجب في الوقت المحدد. تحقق من عنوان نقطة النهاية ومن شبكتك ثم أعد الاختبار.",
+  'settings.ai.providerTest.emptyReply':
+    "تم حفظ المفتاح، لكن '{slug}' أعاد رداً فارغاً على رسالة اختبار. تحقق من معرّف النموذج المهيأ لهذا المزوّد.",
+  'settings.ai.providerTest.unknown':
+    "تم حفظ المفتاح، لكن فشل استدعاء اختباري إلى '{slug}'. تحقق من صفحة حالة المزوّد ومن عنوان نقطة النهاية ثم أعد الاختبار.",
   'settings.ai.testingModel': 'نموذج الاختبار...',
   'settings.ai.modelResponse': 'استجابة النموذج',
   'settings.ai.providerWithValue': 'الموفر: {value}',
diff --git a/app/src/lib/i18n/bn.ts b/app/src/lib/i18n/bn.ts
index 4918567ff..e7e8c4757 100644
--- a/app/src/lib/i18n/bn.ts
+++ b/app/src/lib/i18n/bn.ts
@@ -4746,6 +4746,20 @@ const messages: TranslationMap = {
   'settings.ai.modelVisionDesc':
     'এই মডেল ছবি গ্রহণ করলে সক্ষম করুন। এই মডেল নির্বাচিত থাকলে চ্যাটে ছবি সংযুক্ত করতে দেয়।',
   'settings.ai.testFailed': 'পরীক্ষা ব্যর্থ হয়েছে',
+  'settings.ai.providerTest.authRejected':
+    "কী সংরক্ষণ করা হয়েছে, কিন্তু '{slug}' সেটি প্রত্যাখ্যান করেছে। দেখুন আপনি পুরো কী পেস্ট করেছেন কি না এবং সেটি প্রদানকারীর ড্যাশবোর্ডে এখনও সক্রিয় কি না।",
+  'settings.ai.providerTest.modelNotRecognized':
+    "কী সংরক্ষণ ও গৃহীত হয়েছে, কিন্তু '{slug}' নির্বাচিত মডেলটি চিনতে পারছে না। এই প্রদানকারী সত্যিই দেয় এমন একটি মডেল আইডি বেছে নিন (এর ডিফল্ট মডেল প্রদানকারীর এন্ট্রিতে সেট করা হয়)।",
+  'settings.ai.providerTest.quotaOrBilling':
+    "কী সংরক্ষণ ও গৃহীত হয়েছে, কিন্তু '{slug}' কোটা বা বিলিংয়ের কারণে অনুরোধটি প্রত্যাখ্যান করেছে। প্রদানকারীর কাছে আপনার অ্যাকাউন্ট ব্যালেন্স ও ব্যবহারের সীমা দেখুন।",
+  'settings.ai.providerTest.endpointNotFound':
+    "কী সংরক্ষণ করা হয়েছে, কিন্তু '{slug}' এর জন্য কনফিগার করা এন্ডপয়েন্ট 404 ফেরত দিয়েছে। বেস URL দেখুন: OpenAI-সঙ্গতিপূর্ণ প্রদানকারীর সাধারণত '/v1' প্রত্যয় প্রয়োজন (যেমন https://api.openai.com/v1)।",
+  'settings.ai.providerTest.timeout':
+    "কী সংরক্ষণ করা হয়েছে, কিন্তু '{slug}' সময়মতো সাড়া দেয়নি। এন্ডপয়েন্ট URL ও আপনার নেটওয়ার্ক দেখে আবার পরীক্ষা করুন।",
+  'settings.ai.providerTest.emptyReply':
+    "কী সংরক্ষণ করা হয়েছে, কিন্তু '{slug}' পরীক্ষামূলক প্রম্পটে খালি উত্তর ফেরত দিয়েছে। এই প্রদানকারীর জন্য কনফিগার করা মডেল আইডি দেখুন।",
+  'settings.ai.providerTest.unknown':
+    "কী সংরক্ষণ করা হয়েছে, কিন্তু '{slug}' এ পরীক্ষামূলক কল ব্যর্থ হয়েছে। প্রদানকারীর স্ট্যাটাস পৃষ্ঠা ও এন্ডপয়েন্ট URL দেখে আবার পরীক্ষা করুন।",
   'settings.ai.testingModel': 'পরীক্ষার মডেল...',
   'settings.ai.modelResponse': 'মডেল প্রতিক্রিয়া',
   'settings.ai.providerWithValue': 'প্রদানকারী: {value}',
diff --git a/app/src/lib/i18n/de.ts b/app/src/lib/i18n/de.ts
index 3a3a0c900..f0e59185d 100644
--- a/app/src/lib/i18n/de.ts
+++ b/app/src/lib/i18n/de.ts
@@ -4880,6 +4880,20 @@ const messages: TranslationMap = {
   'settings.ai.modelVisionDesc':
     'Aktivieren, wenn dieses Modell Bilder akzeptiert. Ermöglicht das Anhängen von Bildern im Chat, wenn dieses Modell ausgewählt ist.',
   'settings.ai.testFailed': 'Test fehlgeschlagen.',
+  'settings.ai.providerTest.authRejected':
+    "Der Schlüssel wurde gespeichert, aber '{slug}' hat ihn abgelehnt. Prüfen Sie, ob Sie den vollständigen Schlüssel eingefügt haben und ob er im Dashboard des Anbieters noch aktiv ist.",
+  'settings.ai.providerTest.modelNotRecognized':
+    "Der Schlüssel wurde gespeichert und akzeptiert, aber '{slug}' kennt das ausgewählte Modell nicht. Wählen Sie eine Modell-ID, die dieser Anbieter tatsächlich bereitstellt (das Standardmodell wird im Anbietereintrag festgelegt).",
+  'settings.ai.providerTest.quotaOrBilling':
+    "Der Schlüssel wurde gespeichert und akzeptiert, aber '{slug}' hat die Anfrage aus Kontingent- oder Abrechnungsgründen abgelehnt. Prüfen Sie Ihr Guthaben und Ihre Limits beim Anbieter.",
+  'settings.ai.providerTest.endpointNotFound':
+    "Der Schlüssel wurde gespeichert, aber der konfigurierte Endpunkt für '{slug}' lieferte 404. Prüfen Sie die Basis-URL: ein OpenAI-kompatibler Anbieter benötigt meist den Zusatz '/v1' (z. B. https://api.openai.com/v1).",
+  'settings.ai.providerTest.timeout':
+    "Der Schlüssel wurde gespeichert, aber '{slug}' hat nicht rechtzeitig geantwortet. Prüfen Sie die Endpunkt-URL und Ihr Netzwerk und testen Sie erneut.",
+  'settings.ai.providerTest.emptyReply':
+    "Der Schlüssel wurde gespeichert, aber '{slug}' lieferte auf eine Testanfrage eine leere Antwort. Prüfen Sie die für diesen Anbieter konfigurierte Modell-ID.",
+  'settings.ai.providerTest.unknown':
+    "Der Schlüssel wurde gespeichert, aber ein Testaufruf an '{slug}' ist fehlgeschlagen. Prüfen Sie die Statusseite des Anbieters und die Endpunkt-URL und testen Sie erneut.",
   'settings.ai.testingModel': 'Modell wird getestet...',
   'settings.ai.modelResponse': 'Modellantwort',
   'settings.ai.providerWithValue': 'Anbieter: {value}',
diff --git a/app/src/lib/i18n/en.ts b/app/src/lib/i18n/en.ts
index 88638139e..3ddfb72a4 100644
--- a/app/src/lib/i18n/en.ts
+++ b/app/src/lib/i18n/en.ts
@@ -5335,6 +5335,20 @@ const en: TranslationMap = {
   'settings.ai.modelVisionDesc':
     'Enable if this model accepts images. Lets the chat composer attach images when this model is selected.',
   'settings.ai.testFailed': 'Test failed',
+  'settings.ai.providerTest.authRejected':
+    "The key was saved, but '{slug}' rejected it. Check that you pasted the whole key and that it is still active in the provider's dashboard.",
+  'settings.ai.providerTest.modelNotRecognized':
+    "The key was saved and accepted, but '{slug}' does not recognise the selected model. Pick a model id this provider actually serves (its default model is set on the provider entry).",
+  'settings.ai.providerTest.quotaOrBilling':
+    "The key was saved and accepted, but '{slug}' refused the request for quota or billing reasons. Check your account balance and rate limits with the provider.",
+  'settings.ai.providerTest.endpointNotFound':
+    "The key was saved, but the configured endpoint for '{slug}' returned 404. Check the base URL: an OpenAI-compatible provider usually needs the '/v1' suffix (e.g. https://api.openai.com/v1).",
+  'settings.ai.providerTest.timeout':
+    "The key was saved, but '{slug}' did not respond in time. Check the endpoint URL and your network, then test again.",
+  'settings.ai.providerTest.emptyReply':
+    "The key was saved, but '{slug}' returned an empty response to a test prompt. Check the model id configured for this provider.",
+  'settings.ai.providerTest.unknown':
+    "The key was saved, but a test call to '{slug}' failed. Check the provider's status page and the endpoint URL, then test again.",
   'settings.ai.testingModel': 'Testing model...',
   'settings.ai.modelResponse': 'Model response',
   'settings.ai.providerWithValue': 'Provider: {value}',
diff --git a/app/src/lib/i18n/es.ts b/app/src/lib/i18n/es.ts
index d06f9f4c7..d7586faa2 100644
--- a/app/src/lib/i18n/es.ts
+++ b/app/src/lib/i18n/es.ts
@@ -4827,6 +4827,20 @@ const messages: TranslationMap = {
   'settings.ai.modelVisionDesc':
     'Actívalo si este modelo acepta imágenes. Permite adjuntar imágenes en el chat cuando este modelo está seleccionado.',
   'settings.ai.testFailed': 'Prueba fallida',
+  'settings.ai.providerTest.authRejected':
+    "La clave se guardó, pero '{slug}' la rechazó. Comprueba que pegaste la clave completa y que sigue activa en el panel del proveedor.",
+  'settings.ai.providerTest.modelNotRecognized':
+    "La clave se guardó y se aceptó, pero '{slug}' no reconoce el modelo seleccionado. Elige un identificador de modelo que este proveedor sirva realmente (su modelo predeterminado se define en la entrada del proveedor).",
+  'settings.ai.providerTest.quotaOrBilling':
+    "La clave se guardó y se aceptó, pero '{slug}' rechazó la solicitud por motivos de cuota o facturación. Revisa el saldo de tu cuenta y los límites de uso con el proveedor.",
+  'settings.ai.providerTest.endpointNotFound':
+    "La clave se guardó, pero el endpoint configurado para '{slug}' devolvió 404. Revisa la URL base: un proveedor compatible con OpenAI suele necesitar el sufijo '/v1' (por ejemplo, https://api.openai.com/v1).",
+  'settings.ai.providerTest.timeout':
+    "La clave se guardó, pero '{slug}' no respondió a tiempo. Revisa la URL del endpoint y tu red, y vuelve a probar.",
+  'settings.ai.providerTest.emptyReply':
+    "La clave se guardó, pero '{slug}' devolvió una respuesta vacía a un mensaje de prueba. Revisa el identificador de modelo configurado para este proveedor.",
+  'settings.ai.providerTest.unknown':
+    "La clave se guardó, pero una llamada de prueba a '{slug}' falló. Revisa la página de estado del proveedor y la URL del endpoint, y vuelve a probar.",
   'settings.ai.testingModel': 'Modelo de prueba...',
   'settings.ai.modelResponse': 'Respuesta modelo',
   'settings.ai.providerWithValue': 'Proveedor: {value}',
diff --git a/app/src/lib/i18n/fr.ts b/app/src/lib/i18n/fr.ts
index 5e485f507..f95c2d1eb 100644
--- a/app/src/lib/i18n/fr.ts
+++ b/app/src/lib/i18n/fr.ts
@@ -4857,6 +4857,20 @@ const messages: TranslationMap = {
   'settings.ai.modelVisionDesc':
     'Activez si ce modèle accepte les images. Permet de joindre des images dans le chat lorsque ce modèle est sélectionné.',
   'settings.ai.testFailed': 'Test échoué',
+  'settings.ai.providerTest.authRejected':
+    "La clé a été enregistrée, mais '{slug}' l'a refusée. Vérifiez que vous avez collé la clé entière et qu'elle est toujours active dans le tableau de bord du fournisseur.",
+  'settings.ai.providerTest.modelNotRecognized':
+    "La clé a été enregistrée et acceptée, mais '{slug}' ne reconnaît pas le modèle sélectionné. Choisissez un identifiant de modèle réellement proposé par ce fournisseur (son modèle par défaut est défini sur la fiche du fournisseur).",
+  'settings.ai.providerTest.quotaOrBilling':
+    "La clé a été enregistrée et acceptée, mais '{slug}' a refusé la requête pour des raisons de quota ou de facturation. Vérifiez le solde de votre compte et vos limites auprès du fournisseur.",
+  'settings.ai.providerTest.endpointNotFound':
+    "La clé a été enregistrée, mais le point de terminaison configuré pour '{slug}' a renvoyé une erreur 404. Vérifiez l'URL de base : un fournisseur compatible OpenAI nécessite généralement le suffixe '/v1' (par exemple https://api.openai.com/v1).",
+  'settings.ai.providerTest.timeout':
+    "La clé a été enregistrée, mais '{slug}' n'a pas répondu à temps. Vérifiez l'URL du point de terminaison et votre réseau, puis réessayez.",
+  'settings.ai.providerTest.emptyReply':
+    "La clé a été enregistrée, mais '{slug}' a renvoyé une réponse vide à une invite de test. Vérifiez l'identifiant de modèle configuré pour ce fournisseur.",
+  'settings.ai.providerTest.unknown':
+    "La clé a été enregistrée, mais un appel de test vers '{slug}' a échoué. Vérifiez la page d'état du fournisseur et l'URL du point de terminaison, puis réessayez.",
   'settings.ai.testingModel': 'Modèle de test...',
   'settings.ai.modelResponse': 'Réponse du modèle',
   'settings.ai.providerWithValue': 'Fournisseur : {value}',
diff --git a/app/src/lib/i18n/hi.ts b/app/src/lib/i18n/hi.ts
index a5ff61712..57b9c7797 100644
--- a/app/src/lib/i18n/hi.ts
+++ b/app/src/lib/i18n/hi.ts
@@ -4746,6 +4746,20 @@ const messages: TranslationMap = {
   'settings.ai.modelVisionDesc':
     'यदि यह मॉडल छवियाँ स्वीकार करता है तो सक्षम करें। यह मॉडल चुने जाने पर चैट में छवियाँ संलग्न करने देता है।',
   'settings.ai.testFailed': 'परीक्षण विफल रहा',
+  'settings.ai.providerTest.authRejected':
+    "कुंजी सहेज दी गई, लेकिन '{slug}' ने इसे अस्वीकार कर दिया। जाँचें कि आपने पूरी कुंजी चिपकाई है और वह प्रदाता के डैशबोर्ड में अब भी सक्रिय है।",
+  'settings.ai.providerTest.modelNotRecognized':
+    "कुंजी सहेजी और स्वीकार की गई, लेकिन '{slug}' चयनित मॉडल को नहीं पहचानता। ऐसा मॉडल आईडी चुनें जो यह प्रदाता वास्तव में देता है (इसका डिफ़ॉल्ट मॉडल प्रदाता प्रविष्टि में सेट होता है)।",
+  'settings.ai.providerTest.quotaOrBilling':
+    "कुंजी सहेजी और स्वीकार की गई, लेकिन '{slug}' ने कोटा या बिलिंग कारणों से अनुरोध ठुकरा दिया। प्रदाता के पास अपना खाता शेष और उपयोग सीमाएँ देखें।",
+  'settings.ai.providerTest.endpointNotFound':
+    "कुंजी सहेज दी गई, लेकिन '{slug}' के लिए कॉन्फ़िगर किए गए एंडपॉइंट ने 404 लौटाया। बेस URL जाँचें: OpenAI-संगत प्रदाता को आम तौर पर '/v1' प्रत्यय चाहिए (जैसे https://api.openai.com/v1)।",
+  'settings.ai.providerTest.timeout':
+    "कुंजी सहेज दी गई, लेकिन '{slug}' ने समय पर उत्तर नहीं दिया। एंडपॉइंट URL और अपना नेटवर्क जाँचें, फिर दोबारा परीक्षण करें।",
+  'settings.ai.providerTest.emptyReply':
+    "कुंजी सहेज दी गई, लेकिन '{slug}' ने परीक्षण संकेत पर खाली उत्तर लौटाया। इस प्रदाता के लिए कॉन्फ़िगर किया गया मॉडल आईडी जाँचें।",
+  'settings.ai.providerTest.unknown':
+    "कुंजी सहेज दी गई, लेकिन '{slug}' पर परीक्षण कॉल विफल रही। प्रदाता का स्थिति पृष्ठ और एंडपॉइंट URL जाँचें, फिर दोबारा परीक्षण करें।",
   'settings.ai.testingModel': 'परीक्षण मॉडल...',
   'settings.ai.modelResponse': 'मॉडल प्रतिक्रिया',
   'settings.ai.providerWithValue': 'प्रदाता: {value}',
diff --git a/app/src/lib/i18n/id.ts b/app/src/lib/i18n/id.ts
index b56586988..c4c6d9eab 100644
--- a/app/src/lib/i18n/id.ts
+++ b/app/src/lib/i18n/id.ts
@@ -4764,6 +4764,20 @@ const messages: TranslationMap = {
   'settings.ai.modelVisionDesc':
     'Aktifkan jika model ini menerima gambar. Memungkinkan penyusun obrolan melampirkan gambar saat model ini dipilih.',
   'settings.ai.testFailed': 'Pengujian gagal',
+  'settings.ai.providerTest.authRejected':
+    "Kunci sudah disimpan, tetapi '{slug}' menolaknya. Pastikan Anda menempelkan kunci secara utuh dan kunci itu masih aktif di dasbor penyedia.",
+  'settings.ai.providerTest.modelNotRecognized':
+    "Kunci sudah disimpan dan diterima, tetapi '{slug}' tidak mengenali model yang dipilih. Pilih id model yang benar-benar disediakan penyedia ini (model bawaannya diatur pada entri penyedia).",
+  'settings.ai.providerTest.quotaOrBilling':
+    "Kunci sudah disimpan dan diterima, tetapi '{slug}' menolak permintaan karena alasan kuota atau penagihan. Periksa saldo akun dan batas penggunaan Anda pada penyedia.",
+  'settings.ai.providerTest.endpointNotFound':
+    "Kunci sudah disimpan, tetapi endpoint yang dikonfigurasi untuk '{slug}' mengembalikan 404. Periksa URL dasar: penyedia yang kompatibel dengan OpenAI biasanya memerlukan akhiran '/v1' (misalnya https://api.openai.com/v1).",
+  'settings.ai.providerTest.timeout':
+    "Kunci sudah disimpan, tetapi '{slug}' tidak merespons tepat waktu. Periksa URL endpoint dan jaringan Anda, lalu uji lagi.",
+  'settings.ai.providerTest.emptyReply':
+    "Kunci sudah disimpan, tetapi '{slug}' mengembalikan respons kosong untuk prompt uji. Periksa id model yang dikonfigurasi untuk penyedia ini.",
+  'settings.ai.providerTest.unknown':
+    "Kunci sudah disimpan, tetapi panggilan uji ke '{slug}' gagal. Periksa halaman status penyedia dan URL endpoint, lalu uji lagi.",
   'settings.ai.testingModel': 'Pengujian model...',
   'settings.ai.modelResponse': 'Respons model',
   'settings.ai.providerWithValue': 'Penyedia: {value}',
diff --git a/app/src/lib/i18n/it.ts b/app/src/lib/i18n/it.ts
index fb444c5be..253f48682 100644
--- a/app/src/lib/i18n/it.ts
+++ b/app/src/lib/i18n/it.ts
@@ -4820,6 +4820,20 @@ const messages: TranslationMap = {
   'settings.ai.modelVisionDesc':
     'Attiva se questo modello accetta immagini. Consente di allegare immagini nella chat quando è selezionato questo modello.',
   'settings.ai.testFailed': 'Test non riuscito',
+  'settings.ai.providerTest.authRejected':
+    "La chiave è stata salvata, ma '{slug}' l'ha rifiutata. Verifica di aver incollato la chiave completa e che sia ancora attiva nella dashboard del provider.",
+  'settings.ai.providerTest.modelNotRecognized':
+    "La chiave è stata salvata e accettata, ma '{slug}' non riconosce il modello selezionato. Scegli un id di modello che questo provider offre davvero (il modello predefinito si imposta nella voce del provider).",
+  'settings.ai.providerTest.quotaOrBilling':
+    "La chiave è stata salvata e accettata, ma '{slug}' ha rifiutato la richiesta per motivi di quota o fatturazione. Controlla il saldo del tuo account e i limiti di utilizzo presso il provider.",
+  'settings.ai.providerTest.endpointNotFound':
+    "La chiave è stata salvata, ma l'endpoint configurato per '{slug}' ha restituito 404. Controlla l'URL di base: un provider compatibile con OpenAI di solito richiede il suffisso '/v1' (ad esempio https://api.openai.com/v1).",
+  'settings.ai.providerTest.timeout':
+    "La chiave è stata salvata, ma '{slug}' non ha risposto in tempo. Controlla l'URL dell'endpoint e la tua rete, poi riprova.",
+  'settings.ai.providerTest.emptyReply':
+    "La chiave è stata salvata, ma '{slug}' ha restituito una risposta vuota a un prompt di prova. Controlla l'id del modello configurato per questo provider.",
+  'settings.ai.providerTest.unknown':
+    "La chiave è stata salvata, ma una chiamata di prova a '{slug}' non è riuscita. Controlla la pagina di stato del provider e l'URL dell'endpoint, poi riprova.",
   'settings.ai.testingModel': 'Test del modello...',
   'settings.ai.modelResponse': 'Risposta del modello',
   'settings.ai.providerWithValue': 'Fornitore: {value}',
diff --git a/app/src/lib/i18n/ko.ts b/app/src/lib/i18n/ko.ts
index 02cb83784..090de3b07 100644
--- a/app/src/lib/i18n/ko.ts
+++ b/app/src/lib/i18n/ko.ts
@@ -4692,6 +4692,20 @@ const messages: TranslationMap = {
   'settings.ai.modelVisionDesc':
     '이 모델이 이미지를 지원하면 활성화하세요. 이 모델을 선택하면 채팅 작성기에서 이미지를 첨부할 수 있습니다.',
   'settings.ai.testFailed': '테스트 실패',
+  'settings.ai.providerTest.authRejected':
+    "키는 저장되었지만 '{slug}'에서 거부했습니다. 키 전체를 붙여넣었는지, 제공업체 대시보드에서 아직 활성 상태인지 확인하세요.",
+  'settings.ai.providerTest.modelNotRecognized':
+    "키는 저장되어 승인되었지만 '{slug}'에서 선택한 모델을 인식하지 못합니다. 이 제공업체가 실제로 제공하는 모델 ID를 선택하세요(기본 모델은 제공업체 항목에서 설정합니다).",
+  'settings.ai.providerTest.quotaOrBilling':
+    "키는 저장되어 승인되었지만 '{slug}'에서 할당량 또는 결제 문제로 요청을 거부했습니다. 제공업체에서 계정 잔액과 사용 한도를 확인하세요.",
+  'settings.ai.providerTest.endpointNotFound':
+    "키는 저장되었지만 '{slug}'에 설정된 엔드포인트가 404를 반환했습니다. 기본 URL을 확인하세요. OpenAI 호환 제공업체는 보통 '/v1' 접미사가 필요합니다(예: https://api.openai.com/v1).",
+  'settings.ai.providerTest.timeout':
+    "키는 저장되었지만 '{slug}'가 제때 응답하지 않았습니다. 엔드포인트 URL과 네트워크를 확인한 뒤 다시 테스트하세요.",
+  'settings.ai.providerTest.emptyReply':
+    "키는 저장되었지만 '{slug}'가 테스트 프롬프트에 빈 응답을 반환했습니다. 이 제공업체에 설정된 모델 ID를 확인하세요.",
+  'settings.ai.providerTest.unknown':
+    "키는 저장되었지만 '{slug}'에 대한 테스트 호출이 실패했습니다. 제공업체의 상태 페이지와 엔드포인트 URL을 확인한 뒤 다시 테스트하세요.",
   'settings.ai.testingModel': '모델 테스트 중...',
   'settings.ai.modelResponse': '모델 응답',
   'settings.ai.providerWithValue': '공급자: {value}',
diff --git a/app/src/lib/i18n/pl.ts b/app/src/lib/i18n/pl.ts
index 1461f8e6b..34150f4ab 100644
--- a/app/src/lib/i18n/pl.ts
+++ b/app/src/lib/i18n/pl.ts
@@ -4817,6 +4817,20 @@ const messages: TranslationMap = {
   'settings.ai.modelVisionDesc':
     'Włącz, jeśli ten model akceptuje obrazy. Pozwala dołączać obrazy w czacie, gdy ten model jest wybrany.',
   'settings.ai.testFailed': 'Test nie powiódł się',
+  'settings.ai.providerTest.authRejected':
+    "Klucz został zapisany, ale '{slug}' go odrzucił. Sprawdź, czy wkleiłeś cały klucz i czy nadal jest aktywny w panelu dostawcy.",
+  'settings.ai.providerTest.modelNotRecognized':
+    "Klucz został zapisany i zaakceptowany, ale '{slug}' nie rozpoznaje wybranego modelu. Wybierz identyfikator modelu, który ten dostawca faktycznie udostępnia (model domyślny ustawia się we wpisie dostawcy).",
+  'settings.ai.providerTest.quotaOrBilling':
+    "Klucz został zapisany i zaakceptowany, ale '{slug}' odrzucił żądanie z powodu limitu lub rozliczeń. Sprawdź saldo konta i limity u dostawcy.",
+  'settings.ai.providerTest.endpointNotFound':
+    "Klucz został zapisany, ale skonfigurowany endpoint dla '{slug}' zwrócił 404. Sprawdź adres bazowy: dostawca zgodny z OpenAI zwykle wymaga przyrostka '/v1' (na przykład https://api.openai.com/v1).",
+  'settings.ai.providerTest.timeout':
+    "Klucz został zapisany, ale '{slug}' nie odpowiedział na czas. Sprawdź adres endpointu i sieć, a następnie przetestuj ponownie.",
+  'settings.ai.providerTest.emptyReply':
+    "Klucz został zapisany, ale '{slug}' zwrócił pustą odpowiedź na zapytanie testowe. Sprawdź identyfikator modelu skonfigurowany dla tego dostawcy.",
+  'settings.ai.providerTest.unknown':
+    "Klucz został zapisany, ale wywołanie testowe do '{slug}' nie powiodło się. Sprawdź stronę statusu dostawcy i adres endpointu, a następnie przetestuj ponownie.",
   'settings.ai.testingModel': 'Testowanie modelu...',
   'settings.ai.modelResponse': 'Odpowiedź modelu',
   'settings.ai.providerWithValue': 'Dostawca: {value}',
diff --git a/app/src/lib/i18n/pt.ts b/app/src/lib/i18n/pt.ts
index cd4a3e57e..7e65e8f2b 100644
--- a/app/src/lib/i18n/pt.ts
+++ b/app/src/lib/i18n/pt.ts
@@ -4813,6 +4813,20 @@ const messages: TranslationMap = {
   'settings.ai.modelVisionDesc':
     'Ative se este modelo aceitar imagens. Permite anexar imagens no chat quando este modelo está selecionado.',
   'settings.ai.testFailed': 'Teste falhou',
+  'settings.ai.providerTest.authRejected':
+    "A chave foi salva, mas '{slug}' a recusou. Verifique se você colou a chave inteira e se ela continua ativa no painel do provedor.",
+  'settings.ai.providerTest.modelNotRecognized':
+    "A chave foi salva e aceita, mas '{slug}' não reconhece o modelo selecionado. Escolha um id de modelo que este provedor realmente ofereça (o modelo padrão é definido no registro do provedor).",
+  'settings.ai.providerTest.quotaOrBilling':
+    "A chave foi salva e aceita, mas '{slug}' recusou a solicitação por motivos de cota ou faturamento. Verifique o saldo da sua conta e os limites de uso com o provedor.",
+  'settings.ai.providerTest.endpointNotFound':
+    "A chave foi salva, mas o endpoint configurado para '{slug}' retornou 404. Verifique a URL base: um provedor compatível com OpenAI normalmente precisa do sufixo '/v1' (por exemplo, https://api.openai.com/v1).",
+  'settings.ai.providerTest.timeout':
+    "A chave foi salva, mas '{slug}' não respondeu a tempo. Verifique a URL do endpoint e sua rede e teste novamente.",
+  'settings.ai.providerTest.emptyReply':
+    "A chave foi salva, mas '{slug}' retornou uma resposta vazia a um prompt de teste. Verifique o id do modelo configurado para este provedor.",
+  'settings.ai.providerTest.unknown':
+    "A chave foi salva, mas uma chamada de teste para '{slug}' falhou. Verifique a página de status do provedor e a URL do endpoint e teste novamente.",
   'settings.ai.testingModel': 'Modelo de teste...',
   'settings.ai.modelResponse': 'Resposta do modelo',
   'settings.ai.providerWithValue': 'Provedor: {value}',
diff --git a/app/src/lib/i18n/ru.ts b/app/src/lib/i18n/ru.ts
index 3d3e9ca2e..88346750d 100644
--- a/app/src/lib/i18n/ru.ts
+++ b/app/src/lib/i18n/ru.ts
@@ -4790,6 +4790,20 @@ const messages: TranslationMap = {
   'settings.ai.modelVisionDesc':
     'Включите, если модель принимает изображения. Позволяет прикреплять изображения в чате, когда выбрана эта модель.',
   'settings.ai.testFailed': 'Тест не пройден.',
+  'settings.ai.providerTest.authRejected':
+    "Ключ сохранён, но '{slug}' его отклонил. Проверьте, что вы вставили ключ целиком и что он всё ещё активен в панели провайдера.",
+  'settings.ai.providerTest.modelNotRecognized':
+    "Ключ сохранён и принят, но '{slug}' не распознаёт выбранную модель. Укажите идентификатор модели, которую этот провайдер действительно обслуживает (модель по умолчанию задаётся в записи провайдера).",
+  'settings.ai.providerTest.quotaOrBilling':
+    "Ключ сохранён и принят, но '{slug}' отклонил запрос из-за квоты или оплаты. Проверьте баланс счёта и лимиты у провайдера.",
+  'settings.ai.providerTest.endpointNotFound':
+    "Ключ сохранён, но настроенный endpoint для '{slug}' вернул 404. Проверьте базовый URL: провайдеру, совместимому с OpenAI, обычно нужен суффикс '/v1' (например, https://api.openai.com/v1).",
+  'settings.ai.providerTest.timeout':
+    "Ключ сохранён, но '{slug}' не ответил вовремя. Проверьте URL endpoint и сеть, затем повторите проверку.",
+  'settings.ai.providerTest.emptyReply':
+    "Ключ сохранён, но '{slug}' вернул пустой ответ на тестовый запрос. Проверьте идентификатор модели, настроенный для этого провайдера.",
+  'settings.ai.providerTest.unknown':
+    "Ключ сохранён, но тестовый вызов к '{slug}' не удался. Проверьте страницу состояния провайдера и URL endpoint, затем повторите проверку.",
   'settings.ai.testingModel': 'Модель тестирования...',
   'settings.ai.modelResponse': 'Ответ модели',
   'settings.ai.providerWithValue': 'Поставщик: {value}',
diff --git a/app/src/lib/i18n/zh-CN.ts b/app/src/lib/i18n/zh-CN.ts
index 70d1b6e7e..729be85fd 100644
--- a/app/src/lib/i18n/zh-CN.ts
+++ b/app/src/lib/i18n/zh-CN.ts
@@ -4486,6 +4486,20 @@ const messages: TranslationMap = {
   'settings.ai.modelVision': '支持视觉（图像输入）',
   'settings.ai.modelVisionDesc': '如果此模型接受图像，请启用。选择此模型后可在聊天框中附加图像。',
   'settings.ai.testFailed': '测试失败',
+  'settings.ai.providerTest.authRejected':
+    "密钥已保存，但 '{slug}' 拒绝了它。请确认你粘贴了完整的密钥，并且它在服务商后台仍然有效。",
+  'settings.ai.providerTest.modelNotRecognized':
+    "密钥已保存并通过验证，但 '{slug}' 无法识别所选模型。请选择该服务商确实提供的模型 ID（默认模型在服务商条目中设置）。",
+  'settings.ai.providerTest.quotaOrBilling':
+    "密钥已保存并通过验证，但 '{slug}' 因配额或账单原因拒绝了请求。请在服务商处查看账户余额和速率限制。",
+  'settings.ai.providerTest.endpointNotFound':
+    "密钥已保存，但为 '{slug}' 配置的接口地址返回了 404。请检查基础 URL：兼容 OpenAI 的服务商通常需要 '/v1' 后缀（例如 https://api.openai.com/v1）。",
+  'settings.ai.providerTest.timeout':
+    "密钥已保存，但 '{slug}' 未在规定时间内响应。请检查接口地址和网络后重新测试。",
+  'settings.ai.providerTest.emptyReply':
+    "密钥已保存，但 '{slug}' 对测试提示返回了空响应。请检查为该服务商配置的模型 ID。",
+  'settings.ai.providerTest.unknown':
+    "密钥已保存，但对 '{slug}' 的测试调用失败。请查看该服务商的状态页面和接口地址后重新测试。",
   'settings.ai.testingModel': '测试模型...',
   'settings.ai.modelResponse': '模型响应',
   'settings.ai.providerWithValue': '提供者：{value}',
diff --git a/app/src/services/api/__tests__/aiSettingsApi.test.ts b/app/src/services/api/__tests__/aiSettingsApi.test.ts
index e44a9a360..a8b89ace0 100644
--- a/app/src/services/api/__tests__/aiSettingsApi.test.ts
+++ b/app/src/services/api/__tests__/aiSettingsApi.test.ts
@@ -10,8 +10,10 @@ import { beforeEach, describe, expect, it, vi } from 'vitest';
 
 import {
   type AISettings,
+  classifyProviderVerificationFailure,
   clearCloudProviderKey,
   completeOpenAiCodexOAuth,
+  describeProviderVerificationFailure,
   flushCloudProviders,
   importOpenAiCodexCliAuth,
   listProviderModels,
@@ -31,6 +33,7 @@ import {
   startOpenAiCodexOAuth,
   testProviderModel,
   upsertModelRegistryVision,
+  verifyCloudProviderConnection,
 } from '../aiSettingsApi';
 
 // ─── Mock declarations (must be hoisted before imports) ───────────────────────
@@ -1078,3 +1081,221 @@ describe('model registry vision helpers', () => {
     expect(modelRegistryVision(flipped, 'openai', 'text-only')).toBe(true);
   });
 });
+
+// ─── #5146 §2.4: connected-but-unusable providers ─────────────────────────────
+
+// The messages are rendered through `useT()` in the panel; these tests drive the
+// same code path with a translator that returns each key's English fallback, so
+// the assertions read as the user-visible copy while the i18n wiring is exercised.
+const tFallback = (_key: string, fallback?: string) => fallback ?? '';
+
+describe('describeProviderVerificationFailure', () => {
+  it('maps an auth rejection onto a key-checking remedy', () => {
+    const msg = describeProviderVerificationFailure(
+      'openai',
+      'HTTP 401 invalid_api_key',
+      tFallback
+    );
+    expect(msg).toContain('openai');
+    expect(msg).toContain('rejected it');
+    // Must not leave the user thinking the save itself failed.
+    expect(msg).toContain('saved');
+  });
+
+  it('maps an unknown model onto a model-id remedy, not an auth remedy', () => {
+    const msg = describeProviderVerificationFailure(
+      'openai',
+      'The model `gpt-4p` does not exist or you do not have access to it.',
+      tFallback
+    );
+    expect(msg).toContain('does not recognise the selected model');
+    expect(msg).not.toContain('rejected it');
+  });
+
+  it('maps quota and rate-limit failures onto a billing remedy', () => {
+    for (const raw of [
+      '429 Too Many Requests',
+      'insufficient_quota',
+      'billing hard limit reached',
+    ]) {
+      expect(describeProviderVerificationFailure('deepseek', raw, tFallback)).toContain(
+        'quota or billing reasons'
+      );
+    }
+  });
+
+  it('maps a bare 404 onto the /v1 base-url remedy', () => {
+    const msg = describeProviderVerificationFailure('custom', 'HTTP 404', tFallback);
+    expect(msg).toContain('/v1');
+    expect(msg).toContain('base URL');
+  });
+
+  it('maps a timeout onto an endpoint/network remedy', () => {
+    expect(describeProviderVerificationFailure('custom', 'request timed out', tFallback)).toContain(
+      'did not respond in time'
+    );
+  });
+
+  it('keeps an unrecognised provider error out of the user-visible copy', () => {
+    // A raw upstream string can echo request material (headers, key
+    // fragments) and this lands in a screenshot-able banner, so the fallback
+    // branch must stay generic. The raw text is still returned on
+    // `CloudProviderVerification.detail` and logged by the caller.
+    const msg = describeProviderVerificationFailure(
+      'custom',
+      'kaboom: sk-secret-tail leaked in provider text',
+      tFallback
+    );
+    expect(msg).not.toContain('kaboom');
+    expect(msg).not.toContain('sk-secret-tail');
+    expect(msg).toContain('custom');
+  });
+
+  it('reads cleanly when the error string is empty', () => {
+    const msg = describeProviderVerificationFailure('custom', '   ', tFallback);
+    expect(msg).toContain('custom');
+    expect(msg).not.toMatch(/:\s*$/);
+  });
+
+  it('classifies case-insensitively', () => {
+    expect(describeProviderVerificationFailure('openai', 'INVALID API KEY', tFallback)).toContain(
+      'rejected it'
+    );
+  });
+
+  it('renders through i18n rather than hard-coded copy', () => {
+    // The panel is non-English for most users; every branch must resolve a key
+    // so the locale files (not this module) own the wording.
+    const seen: string[] = [];
+    const t = (key: string, fallback?: string) => {
+      seen.push(key);
+      return fallback ?? '';
+    };
+
+    describeProviderVerificationFailure('openai', 'HTTP 401', t);
+    describeProviderVerificationFailure('openai', 'model_not_found', t);
+    describeProviderVerificationFailure('openai', 'insufficient_quota', t);
+    describeProviderVerificationFailure('openai', 'HTTP 404', t);
+    describeProviderVerificationFailure('openai', 'timed out', t);
+    describeProviderVerificationFailure('openai', 'something novel', t);
+
+    expect(seen).toEqual([
+      'settings.ai.providerTest.authRejected',
+      'settings.ai.providerTest.modelNotRecognized',
+      'settings.ai.providerTest.quotaOrBilling',
+      'settings.ai.providerTest.endpointNotFound',
+      'settings.ai.providerTest.timeout',
+      'settings.ai.providerTest.unknown',
+    ]);
+  });
+
+  it('interpolates the slug into the translated template', () => {
+    const msg = describeProviderVerificationFailure(
+      'deepseek',
+      'HTTP 401',
+      () => 'translated: {slug} refused'
+    );
+    expect(msg).toBe('translated: deepseek refused');
+  });
+});
+
+describe('classifyProviderVerificationFailure', () => {
+  it('maps each recognised shape onto its reason, defaulting to unknown', () => {
+    expect(classifyProviderVerificationFailure('HTTP 401 invalid_api_key')).toBe('auth');
+    expect(classifyProviderVerificationFailure('unknown model')).toBe('model');
+    expect(classifyProviderVerificationFailure('429 rate limit')).toBe('quota');
+    expect(classifyProviderVerificationFailure('HTTP 404')).toBe('endpoint');
+    // The endpoint branch matches a bare 'not found'; these natural phrasings
+    // must still reach the model branch rather than sending the user to check
+    // their base URL (greptile #5254).
+    expect(classifyProviderVerificationFailure('model not found')).toBe('model');
+    expect(classifyProviderVerificationFailure('The model `x` was not found')).toBe('model');
+    expect(classifyProviderVerificationFailure('request timed out')).toBe('timeout');
+    expect(classifyProviderVerificationFailure('kaboom')).toBe('unknown');
+    expect(classifyProviderVerificationFailure('')).toBe('unknown');
+  });
+});
+
+describe('verifyCloudProviderConnection', () => {
+  beforeEach(() => {
+    mockCallCoreRpc.mockReset();
+    mockIsTauri.mockReturnValue(true);
+  });
+
+  it('reports ok when the provider actually answers a test prompt', async () => {
+    mockCallCoreRpc.mockResolvedValue({ result: { reply: 'pong' } });
+
+    const result = await verifyCloudProviderConnection('openai');
+
+    expect(result).toEqual({ ok: true, message: '', detail: '' });
+    expect(mockCallCoreRpc).toHaveBeenCalledWith(
+      expect.objectContaining({ method: 'openhuman.inference_test_provider_model' })
+    );
+  });
+
+  it('defaults to the chat workload and sends a minimal prompt', async () => {
+    mockCallCoreRpc.mockResolvedValue({ result: { reply: 'pong' } });
+
+    await verifyCloudProviderConnection('openai');
+
+    expect(mockCallCoreRpc).toHaveBeenCalledWith(
+      expect.objectContaining({ params: { workload: 'chat', provider: 'openai', prompt: 'ping' } })
+    );
+  });
+
+  it('treats an empty reply as unusable — this is the connected-but-unusable case', async () => {
+    mockCallCoreRpc.mockResolvedValue({ result: { reply: '   ' } });
+
+    const result = await verifyCloudProviderConnection('openai');
+
+    expect(result.ok).toBe(false);
+    expect(result.message).toContain('empty response');
+  });
+
+  it('returns the classified failure instead of throwing, so the caller never loses the save', async () => {
+    mockCallCoreRpc.mockRejectedValue(new Error('HTTP 401 invalid_api_key'));
+
+    const result = await verifyCloudProviderConnection('openai');
+
+    expect(result.ok).toBe(false);
+    expect(result.message).toContain('rejected it');
+    // Raw provider text stays available for the details expander.
+    expect(result.detail).toContain('401');
+  });
+
+  it('handles a non-Error rejection without stringifying to [object Object]', async () => {
+    mockCallCoreRpc.mockRejectedValue('plain string failure');
+
+    const result = await verifyCloudProviderConnection('openai');
+
+    expect(result.ok).toBe(false);
+    expect(result.detail).toBe('plain string failure');
+  });
+
+  it('forwards a model-qualified provider verbatim but names only the slug', async () => {
+    // The core only builds a configured cloud provider from `<slug>:<model>`, so
+    // the composite must reach the RPC untouched; the user-facing message must
+    // still say "openai", not "openai:gpt-4o".
+    mockCallCoreRpc.mockRejectedValue(new Error('HTTP 401 invalid_api_key'));
+
+    const result = await verifyCloudProviderConnection('openai:gpt-4o');
+
+    expect(mockCallCoreRpc).toHaveBeenCalledWith(
+      expect.objectContaining({
+        params: { workload: 'chat', provider: 'openai:gpt-4o', prompt: 'ping' },
+      })
+    );
+    expect(result.message).toContain("'openai'");
+    expect(result.message).not.toContain('gpt-4o');
+  });
+
+  it('renders its own messages through the supplied translator', async () => {
+    mockCallCoreRpc.mockResolvedValue({ result: { reply: '' } });
+
+    const result = await verifyCloudProviderConnection('openai:gpt-4o', 'chat', (key: string) =>
+      key === 'settings.ai.providerTest.emptyReply' ? 'translated empty {slug}' : 'wrong key'
+    );
+
+    expect(result.message).toBe('translated empty openai');
+  });
+});
diff --git a/app/src/services/api/aiSettingsApi.ts b/app/src/services/api/aiSettingsApi.ts
index 9c5681c6f..9d0faf4ac 100644
--- a/app/src/services/api/aiSettingsApi.ts
+++ b/app/src/services/api/aiSettingsApi.ts
@@ -462,6 +462,223 @@ export async function setCloudProviderKey(slug: string, apiKey: string): Promise
   });
 }
 
+/**
+ * Outcome of a post-save connection check (#5146 §2.4).
+ *
+ * `ok: false` means the credential was stored but the provider could not
+ * actually serve an inference call — the "connected but unusable" state where
+ * the UI previously showed a healthy provider that failed on first real use.
+ */
+export interface CloudProviderVerification {
+  ok: boolean;
+  /** Actionable, user-facing explanation. Empty when `ok`. */
+  message: string;
+  /** Raw provider error, kept for the details/expander. Empty when `ok`. */
+  detail: string;
+}
+
+/** Minimal `{placeholder}` interpolation, matching `ProviderSetupErrorNotice`. */
+function fillTemplate(template: string, replacements: Record<string, string>): string {
+  return Object.entries(replacements).reduce(
+    (result, [key, value]) => result.replaceAll(`{${key}}`, value),
+    template
+  );
+}
+
+/** Translator shape accepted here — the `(key, fallback)` form `useT` returns. */
+export type TranslateFn = (key: string, fallback?: string) => string;
+
+/**
+ * Which failure a raw provider/RPC error represents (#5146 §2.4).
+ *
+ * Classification is kept separate from wording so the decision is unit-testable
+ * without a translator and the copy can live in the locale files where the i18n
+ * tooling can see it.
+ */
+export type ProviderVerificationReason =
+  | 'auth'
+  | 'model'
+  | 'quota'
+  | 'endpoint'
+  | 'timeout'
+  | 'unknown';
+
+/** Map a raw upstream error string onto a [`ProviderVerificationReason`]. */
+export function classifyProviderVerificationFailure(raw: string): ProviderVerificationReason {
+  const haystack = raw.trim().toLowerCase();
+
+  if (
+    haystack.includes('401') ||
+    haystack.includes('invalid api key') ||
+    haystack.includes('invalid_api_key') ||
+    haystack.includes('incorrect api key') ||
+    haystack.includes('unauthorized') ||
+    haystack.includes('authentication')
+  ) {
+    return 'auth';
+  }
+  if (
+    haystack.includes('model_not_found') ||
+    // Must be tested here: the endpoint branch below matches a bare
+    // 'not found', which would otherwise claim every provider that phrases a
+    // missing model as "model not found" or "The model `x` was not found" and
+    // send the user off to check their base URL instead of their model id.
+    (haystack.includes('not found') && haystack.includes('model')) ||
+    haystack.includes('does not exist') ||
+    haystack.includes('is not available') ||
+    haystack.includes('unknown model') ||
+    haystack.includes('invalid model')
+  ) {
+    return 'model';
+  }
+  if (
+    haystack.includes('quota') ||
+    haystack.includes('insufficient') ||
+    haystack.includes('billing') ||
+    haystack.includes('429') ||
+    haystack.includes('rate limit')
+  ) {
+    return 'quota';
+  }
+  if (haystack.includes('404') || haystack.includes('not found')) {
+    return 'endpoint';
+  }
+  if (haystack.includes('timeout') || haystack.includes('timed out')) {
+    return 'timeout';
+  }
+  return 'unknown';
+}
+
+/**
+ * Turn a raw provider/RPC failure into something a user can act on (#5146 §2.4).
+ *
+ * Storing a key only proves we wrote it to disk. The failures users actually
+ * hit (wrong model id, exhausted quota, a base URL that doesn't speak the
+ * endpoint we call) all surface as opaque upstream strings, so map the common
+ * shapes onto a concrete next step and pass anything unrecognised through
+ * verbatim rather than inventing a diagnosis.
+ *
+ * The rendered string is user-visible UI text, so it goes through `t` like the
+ * sibling `presentProviderSetupError`: the caller passes the translator from
+ * `useT()` and every branch resolves against the locale files. `slug` must be
+ * the bare provider slug (`openai`), not a composite `provider:model` string.
+ */
+export function describeProviderVerificationFailure(
+  slug: string,
+  raw: string,
+  t: TranslateFn
+): string {
+  const detail = raw.trim();
+  const reason = classifyProviderVerificationFailure(detail);
+
+  switch (reason) {
+    case 'auth':
+      return fillTemplate(
+        t(
+          'settings.ai.providerTest.authRejected',
+          "The key was saved, but '{slug}' rejected it. Check that you pasted the whole key and that it is still active in the provider's dashboard."
+        ),
+        { slug }
+      );
+    case 'model':
+      return fillTemplate(
+        t(
+          'settings.ai.providerTest.modelNotRecognized',
+          "The key was saved and accepted, but '{slug}' does not recognise the selected model. Pick a model id this provider actually serves (its default model is set on the provider entry)."
+        ),
+        { slug }
+      );
+    case 'quota':
+      return fillTemplate(
+        t(
+          'settings.ai.providerTest.quotaOrBilling',
+          "The key was saved and accepted, but '{slug}' refused the request for quota or billing reasons. Check your account balance and rate limits with the provider."
+        ),
+        { slug }
+      );
+    case 'endpoint':
+      return fillTemplate(
+        t(
+          'settings.ai.providerTest.endpointNotFound',
+          "The key was saved, but the configured endpoint for '{slug}' returned 404. Check the base URL: an OpenAI-compatible provider usually needs the '/v1' suffix (e.g. https://api.openai.com/v1)."
+        ),
+        { slug }
+      );
+    case 'timeout':
+      return fillTemplate(
+        t(
+          'settings.ai.providerTest.timeout',
+          "The key was saved, but '{slug}' did not respond in time. Check the endpoint URL and your network, then test again."
+        ),
+        { slug }
+      );
+    default:
+      // Deliberately generic. The upstream string can echo request material
+      // (headers, key fragments) and this lands in a screenshot-able banner, so
+      // it must not be interpolated into user-visible copy. The raw text stays
+      // on `CloudProviderVerification.detail` for the details surface and is
+      // logged by the caller for local diagnosis.
+      return fillTemplate(
+        t(
+          'settings.ai.providerTest.unknown',
+          "The key was saved, but a test call to '{slug}' failed. Check the provider's status page and the endpoint URL, then test again."
+        ),
+        { slug }
+      );
+  }
+}
+
+/**
+ * Prove a freshly configured provider can actually run inference (#5146 §2.4).
+ *
+ * Runs one real, minimal completion through the existing
+ * `openhuman.inference_test_provider_model` RPC. Never throws: a provider that
+ * cannot serve a request is a *result*, not an exception, because the caller
+ * always wants to show it rather than lose the save.
+ */
+export async function verifyCloudProviderConnection(
+  provider: string,
+  workload: WorkloadId = 'chat',
+  t: TranslateFn = (_key, fallback) => fallback ?? ''
+): Promise<CloudProviderVerification> {
+  // The core only builds a configured cloud provider from the `<slug>:<model>`
+  // form, so a bare slug would be rejected as an unrecognised provider and a
+  // perfectly good key would be reported as broken. Callers pass the same
+  // composite string the Test button uses; the bare slug is what the *messages*
+  // name, so derive it rather than echoing `provider:model[:temp]` at the user.
+  const providerString = provider.trim();
+  const slug = providerString.split(':')[0]?.trim() || providerString;
+
+  console.debug(`[ai-settings][verify] start workload=${workload} slug=${slug}`);
+  try {
+    const result = await testProviderModel(workload, providerString, 'ping');
+    const reply = (result?.reply ?? '').trim();
+    if (!reply) {
+      console.debug(`[ai-settings][verify] empty-reply workload=${workload} slug=${slug}`);
+      return {
+        ok: false,
+        message: fillTemplate(
+          t(
+            'settings.ai.providerTest.emptyReply',
+            "The key was saved, but '{slug}' returned an empty response to a test prompt. Check the model id configured for this provider."
+          ),
+          { slug }
+        ),
+        detail: '',
+      };
+    }
+    console.debug(`[ai-settings][verify] ok workload=${workload} slug=${slug}`);
+    return { ok: true, message: '', detail: '' };
+  } catch (error) {
+    const detail = error instanceof Error ? error.message : String(error);
+    // The raw detail can carry provider text; log only the classification.
+    console.error(
+      `[ai-settings][verify] failed workload=${workload} slug=${slug} reason=${classifyProviderVerificationFailure(detail)}`
+    );
+    return { ok: false, message: describeProviderVerificationFailure(slug, detail, t), detail };
+  }
+}
+
 /** Clear a stored API key. */
 export async function clearCloudProviderKey(slug: string): Promise<void> {
   if (slug === 'openhuman') {
diff --git a/src/openhuman/agent/harness/session/builder/factory.rs b/src/openhuman/agent/harness/session/builder/factory.rs
index 96e555333..51e2e0002 100644
--- a/src/openhuman/agent/harness/session/builder/factory.rs
+++ b/src/openhuman/agent/harness/session/builder/factory.rs
@@ -490,6 +490,19 @@ impl Agent {
         let model_vision =
             crate::openhuman::inference::model_context::model_supports_vision(&model_name, config);
 
+        // #5146 §2.1/§2.3: when the active model can't take images the turn
+        // engine silently strips them, and the user gets a confident answer
+        // about an image the model never saw. Log the actionable reason (which
+        // model, and what to switch to) at the moment the decision is made.
+        if let Err(reason) =
+            crate::openhuman::inference::provider::fallback_diagnostics::vision_preflight(
+                &model_name,
+                config,
+            )
+        {
+            log::info!("[vision-preflight] {reason}");
+        }
+
         // Dispatcher selection is deferred until after the tool list is
         // finalised (orchestrator tools are appended below). We capture
         // the choice string now so the provider borrow doesn't conflict
diff --git a/src/openhuman/inference/provider/factory.rs b/src/openhuman/inference/provider/factory.rs
index 5f3842899..6685d11b6 100644
--- a/src/openhuman/inference/provider/factory.rs
+++ b/src/openhuman/inference/provider/factory.rs
@@ -300,26 +300,14 @@ pub(crate) fn oh_tier_supports_vision(model: &str) -> bool {
     }
 }
 
-/// Return the configured provider string for a named workload role.
+/// The provider route a role has **explicitly** configured, before any
+/// fallback.
 ///
-/// Empty / `"cloud"` resolves through BYOK fallback first for the three
-/// chat-tier roles (`chat`, `reasoning`, `coding`), then `primary_cloud`.
-/// When a BYOK cloud provider is detected on any workload, unset chat-tier
-/// routes inherit it rather than silently falling back to the managed backend.
-///
-/// Only `chat`, `reasoning`, and `coding` participate in BYOK inheritance.
-/// Background workloads (`memory`, `embeddings`, `heartbeat`, `learning`,
-/// `subconscious`) and the `agentic`/`burst` workloads always fall through to
-/// `primary_cloud` when their explicit provider route is unset — they use
-/// tier-specific models that BYOK providers don't understand, and their
-/// providers are configured independently.
-///
-/// For backwards compatibility, a legacy external `inference_url` takes
-/// precedence when `primary_cloud` still points at OpenHuman because
-/// migration 1→2 preserved the URL as a custom provider entry but older
-/// configs did not explicitly set per-workload routes.
-pub fn provider_for_role(role: &str, config: &Config) -> String {
-    let opt = match role {
+/// Split out of [`provider_for_role`] so the fallback machinery can ask the
+/// same question the router asks — "did the user route this role anywhere?" —
+/// without re-deriving the role→config-field mapping and drifting from it.
+fn configured_route_for_role<'a>(role: &str, config: &'a Config) -> Option<&'a str> {
+    match role {
         "chat" => config.chat_provider.as_deref(),
         "reasoning" => config.reasoning_provider.as_deref(),
         "agentic" => config.agentic_provider.as_deref(),
@@ -343,7 +331,45 @@ pub fn provider_for_role(role: &str, config: &Config) -> String {
         "learning" => config.learning_provider.as_deref(),
         "subconscious" => config.subconscious_provider.as_deref(),
         _ => None,
-    };
+    }
+}
+
+/// Whether `role` reached a cloud slug by *implicit fallback* rather than by an
+/// explicit route.
+///
+/// True only when the role is one of the cloud-fallback background roles **and**
+/// its own route is unset (or the literal `"cloud"`). An explicitly configured
+/// cloud route — say `vision_provider = "anthropic:claude-…"` — is not a
+/// fallback, so a credential failure there must not be explained as "your local
+/// chat model cannot do this".
+pub(crate) fn role_uses_implicit_cloud_fallback(role: &str, config: &Config) -> bool {
+    if !super::fallback_diagnostics::role_falls_back_to_cloud(role) {
+        return false;
+    }
+    let route = configured_route_for_role(role, config).unwrap_or("").trim();
+    route.is_empty() || route == "cloud"
+}
+
+/// Return the configured provider string for a named workload role.
+///
+/// Empty / `"cloud"` resolves through BYOK fallback first for the three
+/// chat-tier roles (`chat`, `reasoning`, `coding`), then `primary_cloud`.
+/// When a BYOK cloud provider is detected on any workload, unset chat-tier
+/// routes inherit it rather than silently falling back to the managed backend.
+///
+/// Only `chat`, `reasoning`, and `coding` participate in BYOK inheritance.
+/// Background workloads (`memory`, `embeddings`, `heartbeat`, `learning`,
+/// `subconscious`) and the `agentic`/`burst` workloads always fall through to
+/// `primary_cloud` when their explicit provider route is unset — they use
+/// tier-specific models that BYOK providers don't understand, and their
+/// providers are configured independently.
+///
+/// For backwards compatibility, a legacy external `inference_url` takes
+/// precedence when `primary_cloud` still points at OpenHuman because
+/// migration 1→2 preserved the URL as a custom provider entry but older
+/// configs did not explicitly set per-workload routes.
+pub fn provider_for_role(role: &str, config: &Config) -> String {
+    let opt = configured_route_for_role(role, config);
     let s = opt.unwrap_or("").trim();
     if s.is_empty() || s == "cloud" {
         // BYOK inheritance is scoped to the three chat-tier roles only.
@@ -362,29 +388,29 @@ pub fn provider_for_role(role: &str, config: &Config) -> String {
             }
         }
 
-        // Diagnostic: when the user has a local provider configured for chat
-        // but this background workload is falling through to cloud, emit a
-        // warning so it's visible in logs (no silent fallback).
-        if !matches!(role, "chat" | "reasoning" | "coding") {
+        let resolved = resolve_primary_cloud_provider_string(config);
+
+        // #5146 §2.1: the fallback itself is correct and stays — background
+        // workloads run tier-specific models that local runtimes don't serve,
+        // and a local-chat + managed-subscription user genuinely wants them on
+        // the cloud. What was missing is the *explanation*: when this route
+        // later fails for want of a key, the user saw a bare slug-level auth
+        // error naming a provider they never configured. Emit the same
+        // user-facing sentence the error path uses, so the routing decision is
+        // visible in logs and support transcripts before anything goes wrong.
+        if super::fallback_diagnostics::role_falls_back_to_cloud(role) {
             if let Some(chat) = config.chat_provider.as_deref() {
                 if crate::openhuman::inference::local::profile::is_local_provider_string(chat) {
-                    let override_hint = if role == "burst" {
-                        "set agentic_provider explicitly to override".to_string()
-                    } else {
-                        format!("set {role}_provider explicitly to override")
-                    };
                     log::info!(
-                        "[providers][local-fallback] role={} using managed backend (chat is \
-                         local '{}' but background workloads require cloud — {})",
+                        "[providers][local-fallback] role={} {}",
                         role,
-                        chat,
-                        override_hint
+                        super::fallback_diagnostics::cloud_fallback_notice(role, chat, &resolved)
                     );
                 }
             }
         }
 
-        resolve_primary_cloud_provider_string(config)
+        resolved
     } else {
         s.to_string()
     }
@@ -2203,7 +2229,60 @@ fn resolve_cloud_slug<'a>(
         redact_endpoint(&entry.endpoint)
     );
 
-    let key = lookup_key_for_slug(slug, config)?;
+    // #5146 §2.1: a raw "failed to read API key for slug 'anthropic'" is
+    // baffling when the user never configured Anthropic — they set a local
+    // Ollama model and this is a background role that fell back to the cloud.
+    // Attach the role, and the local chat model that caused the fallback, so
+    // the message explains itself and names a concrete remedy.
+    // Only an *implicit* fallback is explained as one. A role with its own
+    // explicit cloud route can fail key lookup here too, and telling that user
+    // their local chat model caused it would be a lie.
+    let implicit_fallback = role_uses_implicit_cloud_fallback(role, config);
+    let local_chat = if implicit_fallback {
+        config.chat_provider.as_deref().filter(|chat| {
+            crate::openhuman::inference::local::profile::is_local_provider_string(chat)
+        })
+    } else {
+        None
+    };
+    let missing_credentials = || {
+        // Safe fields only: role, slug, and the routing shape. Never the
+        // underlying error (it can echo a key) and never the key itself.
+        log::warn!(
+            "[providers][chat-factory] credential lookup failed role={} slug={} auth_style={} implicit_cloud_fallback={}",
+            role,
+            slug,
+            entry.auth_style.as_str(),
+            implicit_fallback
+        );
+        super::fallback_diagnostics::missing_provider_credentials_message(role, slug, local_chat)
+    };
+
+    let key = lookup_key_for_slug(slug, config)
+        .map_err(|e| anyhow::anyhow!("{} (underlying error: {e})", missing_credentials()))?;
+
+    // A readable auth profile with no key for this slug returns `Ok("")`, which
+    // would otherwise build a client with an empty bearer and surface as a raw
+    // 401 from the provider several layers later — exactly the baffling error
+    // this diagnostic exists to replace.
+    //
+    // Scoped to the *implicit fallback* path deliberately. That is the case the
+    // diagnostic is for: a local-chat user whose background role landed on a
+    // BYOK slug they never configured. An explicitly routed provider keeps its
+    // existing behaviour and is allowed to build without a stored key — callers
+    // construct such models to probe or describe a provider before a key is
+    // saved, and failing that at construction time would be a behaviour change
+    // well beyond this diagnostic.
+    //
+    // Styles that carry no stored key (`OpenhumanJwt` injects a session JWT
+    // downstream, `None` sends no auth header at all) are legitimately blank and
+    // never trip this.
+    if implicit_fallback
+        && key.trim().is_empty()
+        && matches!(entry.auth_style, AuthStyle::Bearer | AuthStyle::Anthropic)
+    {
+        anyhow::bail!("{}", missing_credentials());
+    }
     let codex = resolve_openai_codex_routing(config, slug, &entry.endpoint, &key)
         .map_err(anyhow::Error::msg)?;
 
diff --git a/src/openhuman/inference/provider/factory_tests.rs b/src/openhuman/inference/provider/factory_tests.rs
index c4565b4f8..b54f1f20c 100644
--- a/src/openhuman/inference/provider/factory_tests.rs
+++ b/src/openhuman/inference/provider/factory_tests.rs
@@ -1470,3 +1470,161 @@ async fn create_chat_model_local_runtime_does_not_emit_egress_realpath() {
         }
     }
 }
+
+// ─── #5146 §2.1: local chat + background workloads ────────────────────────────
+//
+// The fix for #5146 §2.1 is an *explanation* change, not a routing change. These
+// pin the routing so a future "never fall back" refactor cannot silently break
+// local-chat + managed-subscription users without a failing test.
+
+#[test]
+fn local_chat_still_routes_background_roles_to_the_managed_backend() {
+    let mut config = Config::default();
+    config.chat_provider = Some("ollama:gemma3:1b".to_string());
+
+    // Every background role keeps falling through to the managed backend: they
+    // run tier-specific models a local runtime does not serve, and the user's
+    // subscription is what pays for them.
+    for role in [
+        "vision",
+        "embeddings",
+        "memory",
+        "summarization",
+        "heartbeat",
+        "learning",
+        "subconscious",
+        "agentic",
+        "burst",
+    ] {
+        assert_eq!(
+            provider_for_role(role, &config),
+            "openhuman",
+            "role '{role}' must keep falling back to the managed backend when chat is local"
+        );
+    }
+}
+
+#[test]
+fn local_chat_role_is_returned_verbatim_and_never_falls_back() {
+    let mut config = Config::default();
+    config.chat_provider = Some("ollama:gemma3:1b".to_string());
+
+    assert_eq!(
+        provider_for_role("chat", &config),
+        "ollama:gemma3:1b",
+        "an explicitly configured local chat route must be honoured verbatim"
+    );
+}
+
+#[test]
+fn explicit_background_route_overrides_the_cloud_fallback() {
+    let mut config = Config::default();
+    config.chat_provider = Some("ollama:gemma3:1b".to_string());
+    config.vision_provider = Some("ollama:llava:7b".to_string());
+
+    // The remedy the new diagnostics point users at must actually work.
+    assert_eq!(
+        provider_for_role("vision", &config),
+        "ollama:llava:7b",
+        "setting vision_provider must take precedence over the cloud fallback"
+    );
+}
+
+#[test]
+fn a_readable_profile_with_no_stored_key_is_treated_as_missing_credentials() {
+    // The common BYOK-with-no-key shape: the auth profile reads fine, it just
+    // has nothing for this slug, so the lookup succeeds with an empty string.
+    // Without an emptiness check the client would be built with a blank bearer
+    // and the user would get a raw 401 from the provider instead of guidance.
+    let _guard = crate::openhuman::inference::inference_test_guard();
+    let tmp = TempDir::new().expect("tempdir");
+    let mut config = config_with_providers_in_tempdir(&tmp, vec![openai_entry("p_oai", "openai")]);
+    config.chat_provider = Some("ollama:gemma3:1b".to_string());
+
+    let err = create_test_chat_model_from_string("vision", "openai:gpt-4o", &config)
+        .err()
+        .expect("a slug with no stored key must not build a client");
+    let message = err.to_string();
+
+    assert!(
+        message.contains("No usable credentials for 'openai'"),
+        "expected the actionable guidance, got: {message}"
+    );
+    // It is a genuine implicit fallback here (vision has no route of its own),
+    // so the local chat model that caused it is named.
+    assert!(
+        message.contains("ollama:gemma3:1b"),
+        "expected the local chat model to be named, got: {message}"
+    );
+
+    // Scope: an explicitly routed provider is NOT failed at construction time
+    // for a missing key. Callers build such models to probe or describe a
+    // provider before a key is saved, so only the implicit-fallback path (the
+    // one this diagnostic exists for) turns a blank key into an error.
+    config.vision_provider = Some("openai:gpt-4o".to_string());
+    assert!(
+        create_test_chat_model_from_string("vision", "openai:gpt-4o", &config).is_ok(),
+        "an explicitly routed provider must still build without a stored key"
+    );
+}
+
+#[test]
+fn implicit_cloud_fallback_is_claimed_only_when_the_role_has_no_route_of_its_own() {
+    let mut config = Config::default();
+    config.chat_provider = Some("ollama:gemma3:1b".to_string());
+
+    // Unset background route: the role genuinely landed on the cloud because
+    // the local chat model cannot serve it, so the explanation applies.
+    assert!(role_uses_implicit_cloud_fallback("vision", &config));
+    // The literal "cloud" is the same "route me wherever the cloud is" intent.
+    config.embeddings_provider = Some("cloud".to_string());
+    assert!(role_uses_implicit_cloud_fallback("embeddings", &config));
+    // Whitespace is not a configured route.
+    config.memory_provider = Some("   ".to_string());
+    assert!(role_uses_implicit_cloud_fallback("memory", &config));
+
+    // Explicitly routed to a cloud slug: a credential failure here is about
+    // that route, not about the local chat model, so it must not be described
+    // as a fallback.
+    config.vision_provider = Some("anthropic:claude-3-5-sonnet-latest".to_string());
+    assert!(!role_uses_implicit_cloud_fallback("vision", &config));
+
+    // Chat-tier roles are never described as cloud fallbacks, routed or not.
+    for role in ["chat", "reasoning", "coding"] {
+        assert!(!role_uses_implicit_cloud_fallback(role, &config));
+    }
+}
+
+#[test]
+fn cloud_fallback_roles_match_the_roles_provider_for_role_actually_falls_back() {
+    // `factory_tests` is a child module of `factory`, so `super` is `factory`,
+    // not `provider` — reach the sibling module by its crate path.
+    use crate::openhuman::inference::provider::fallback_diagnostics::role_falls_back_to_cloud;
+    let mut config = Config::default();
+    config.chat_provider = Some("ollama:gemma3:1b".to_string());
+
+    // The diagnostics module carries its own role list; if the two drift, users
+    // get either a missing explanation or one that names the wrong knob.
+    for role in [
+        "vision",
+        "embeddings",
+        "memory",
+        "summarization",
+        "heartbeat",
+        "learning",
+        "subconscious",
+        "agentic",
+        "burst",
+    ] {
+        assert!(
+            role_falls_back_to_cloud(role),
+            "'{role}' falls back in provider_for_role but is missing from CLOUD_FALLBACK_ROLES"
+        );
+    }
+    for role in ["chat", "reasoning", "coding"] {
+        assert!(
+            !role_falls_back_to_cloud(role),
+            "'{role}' is a chat-tier role and must not be described as a cloud fallback"
+        );
+    }
+}
diff --git a/src/openhuman/inference/provider/fallback_diagnostics.rs b/src/openhuman/inference/provider/fallback_diagnostics.rs
new file mode 100644
index 000000000..1ef514f06
--- /dev/null
+++ b/src/openhuman/inference/provider/fallback_diagnostics.rs
@@ -0,0 +1,332 @@
+//! Actionable diagnostics for background-workload provider fallback (#5146 §2.1).
+//!
+//! ## The user-visible bug
+//!
+//! A user configures a local Ollama model for chat, attaches an image, and gets
+//! `failed to read API key for slug 'anthropic'` — naming a provider they never
+//! configured. The same shape appears for embeddings, memory and the other
+//! background workloads.
+//!
+//! ## Why it happens, and why the routing itself is correct
+//!
+//! [`super::factory::provider_for_role`] deliberately routes the background
+//! roles (`vision`, `embeddings`, `memory`, `heartbeat`, `learning`,
+//! `subconscious`, `agentic`, `burst`) to the primary cloud provider when their
+//! own route is unset: they run tier-specific models (`vision-v1`,
+//! `summarization-v1`, …) that local runtimes and BYOK slugs do not serve. A
+//! user on a local chat model with a managed subscription genuinely wants those
+//! workloads on the cloud, so the fallback must stay.
+//!
+//! What was wrong is that the fallback was **unexplained**. When it landed on a
+//! provider with no usable credentials, the failure surfaced as a raw slug-level
+//! auth error with no hint that (a) this was a background role, (b) it fell back
+//! because the local model cannot serve that capability, or (c) what to do about
+//! it. That is the whole of the fix here: the routing decision is unchanged, the
+//! *explanation* is not.
+//!
+//! Everything in this module is a pure string/predicate function so the wording
+//! and the routing rules can be unit-tested without a live provider.
+//!
+//! Users who want no cloud egress at all already have
+//! [`crate::openhuman::config::schema::PrivacyMode::LocalOnly`], enforced at the
+//! inference chokepoint by `factory::enforce_local_only_inference`. This module
+//! deliberately does not duplicate that gate.
+
+/// Workload roles that inherit the primary cloud provider when their own route
+/// is unset — the set [`super::factory::provider_for_role`] does **not** include
+/// in chat-tier BYOK inheritance.
+///
+/// `chat`, `reasoning` and `coding` are absent on purpose: they inherit a
+/// configured BYOK slug instead, so they never produce the confusion this
+/// module exists to explain.
+const CLOUD_FALLBACK_ROLES: &[&str] = &[
+    "vision",
+    "embeddings",
+    "memory",
+    "summarization",
+    "heartbeat",
+    "learning",
+    "subconscious",
+    "agentic",
+    "burst",
+];
+
+/// Whether `role` falls through to the primary cloud provider when its own
+/// route is unset.
+pub(crate) fn role_falls_back_to_cloud(role: &str) -> bool {
+    CLOUD_FALLBACK_ROLES.contains(&role.trim())
+}
+
+/// The capability a background role provides, phrased for a user-facing
+/// sentence ("… does not support **vision**").
+///
+/// `None` for roles whose name is not a capability the user would recognise as
+/// a model feature (`heartbeat`, `burst`, …); callers fall back to the role
+/// name itself.
+pub(crate) fn role_capability_label(role: &str) -> Option<&'static str> {
+    match role.trim() {
+        "vision" => Some("vision (image input)"),
+        "embeddings" => Some("embeddings"),
+        "memory" | "summarization" => Some("summarization"),
+        "agentic" | "burst" => Some("agentic tool use"),
+        _ => None,
+    }
+}
+
+/// How a role is described in a sentence — the capability when it maps to one,
+/// otherwise the bare role name.
+fn role_phrase(role: &str) -> String {
+    match role_capability_label(role) {
+        Some(capability) => capability.to_string(),
+        None => role.trim().to_string(),
+    }
+}
+
+/// Explanation logged when a background role runs on the cloud because the
+/// user's chat model is local and cannot serve that capability.
+///
+/// This is the informational, everything-is-working case: the user has a cloud
+/// route available and the workload will succeed. It exists so the routing
+/// decision is visible in logs and support transcripts rather than silent.
+pub(crate) fn cloud_fallback_notice(
+    role: &str,
+    local_chat_provider: &str,
+    resolved_provider: &str,
+) -> String {
+    format!(
+        "{} is running via your managed/cloud provider ('{}') because your local chat model \
+         ('{}') does not serve this workload. Set {}_provider explicitly in Connections to \
+         override.",
+        capitalize_first(&role_phrase(role)),
+        resolved_provider.trim(),
+        local_chat_provider.trim(),
+        override_knob_for_role(role),
+    )
+}
+
+/// The config knob a user sets to override a role's route.
+///
+/// `burst` has no knob of its own — it rides the agentic route — so it points
+/// the user at `agentic_provider` rather than a setting that does not exist.
+pub(crate) fn override_knob_for_role(role: &str) -> &str {
+    match role.trim() {
+        "burst" => "agentic",
+        "summarization" => "memory",
+        other => other,
+    }
+}
+
+/// Actionable error for the failing case: a background role fell back to a
+/// cloud slug whose credentials cannot be read.
+///
+/// Replaces the bare `failed to read API key for slug 'anthropic'` that named a
+/// provider the user never chose. Mentions the local chat model when there is
+/// one, because that is the missing half of the story.
+pub(crate) fn missing_provider_credentials_message(
+    role: &str,
+    slug: &str,
+    local_chat_provider: Option<&str>,
+) -> String {
+    let role = role.trim();
+    let slug = slug.trim();
+    match local_chat_provider {
+        Some(local) if !local.trim().is_empty() => format!(
+            "No usable credentials for '{slug}', which OpenHuman selected for the {} workload. \
+             Your chat model is local ('{}') and does not serve this workload, so it fell back \
+             to your cloud provider — but '{slug}' has no API key configured. Add a key for \
+             '{slug}' in Connections → LLM, set {}_provider to a provider that is configured, \
+             or enable the managed OpenHuman backend.",
+            role_phrase(role),
+            local.trim(),
+            override_knob_for_role(role),
+        ),
+        _ => format!(
+            "No usable credentials for '{slug}', which OpenHuman selected for the {} workload. \
+             Add a key for '{slug}' in Connections → LLM, set {}_provider to a provider that is \
+             configured, or enable the managed OpenHuman backend.",
+            role_phrase(role),
+            override_knob_for_role(role),
+        ),
+    }
+}
+
+/// Actionable message for the vision pre-flight: the active model cannot accept
+/// images, so the caller should say so instead of stripping the image and
+/// producing a confusing blind answer.
+pub(crate) fn local_vision_unsupported_message(model: &str) -> String {
+    format!(
+        "The selected local model ('{}') does not support vision (image input). Switch to a \
+         vision-capable model such as llava:7b (`ollama pull llava:7b`), or set vision_provider \
+         in Connections → LLM to a provider that supports images.",
+        model.trim()
+    )
+}
+
+/// Pure pre-flight for image input: `Ok(())` when `model` accepts images,
+/// `Err(actionable message)` when it does not.
+///
+/// Split from the call sites so the wording is unit-testable and identical
+/// everywhere an image is about to be dropped.
+pub(crate) fn vision_preflight(
+    model: &str,
+    config: &crate::openhuman::config::Config,
+) -> Result<(), String> {
+    if crate::openhuman::inference::model_context::model_supports_vision(model, config) {
+        return Ok(());
+    }
+    Err(local_vision_unsupported_message(model))
+}
+
+fn capitalize_first(s: &str) -> String {
+    let mut chars = s.chars();
+    match chars.next() {
+        Some(first) => first.to_uppercase().collect::<String>() + chars.as_str(),
+        None => String::new(),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn chat_tier_roles_do_not_fall_back_to_cloud() {
+        // These inherit a BYOK slug instead; including them would attach the
+        // "your local model can't serve this" explanation to the very roles the
+        // user did configure locally.
+        for role in ["chat", "reasoning", "coding"] {
+            assert!(
+                !role_falls_back_to_cloud(role),
+                "{role} must not be treated as a cloud-fallback role"
+            );
+        }
+    }
+
+    #[test]
+    fn background_roles_fall_back_to_cloud() {
+        for role in [
+            "vision",
+            "embeddings",
+            "memory",
+            "summarization",
+            "heartbeat",
+            "learning",
+            "subconscious",
+            "agentic",
+            "burst",
+        ] {
+            assert!(
+                role_falls_back_to_cloud(role),
+                "{role} must be treated as a cloud-fallback role"
+            );
+        }
+    }
+
+    #[test]
+    fn unknown_role_does_not_fall_back() {
+        assert!(!role_falls_back_to_cloud("not-a-role"));
+        assert!(!role_falls_back_to_cloud(""));
+    }
+
+    #[test]
+    fn role_falls_back_to_cloud_ignores_surrounding_whitespace() {
+        assert!(role_falls_back_to_cloud("  vision  "));
+    }
+
+    #[test]
+    fn burst_points_at_the_agentic_knob_that_actually_exists() {
+        // There is no `burst_provider`; telling the user to set one would be a
+        // dead end.
+        assert_eq!(override_knob_for_role("burst"), "agentic");
+        assert_eq!(override_knob_for_role("summarization"), "memory");
+        assert_eq!(override_knob_for_role("vision"), "vision");
+    }
+
+    #[test]
+    fn fallback_notice_names_capability_local_model_and_override() {
+        let msg = cloud_fallback_notice("vision", "ollama:gemma3:1b", "anthropic:claude-sonnet-4");
+        assert!(msg.contains("Vision (image input)"), "got: {msg}");
+        assert!(msg.contains("ollama:gemma3:1b"), "got: {msg}");
+        assert!(msg.contains("anthropic:claude-sonnet-4"), "got: {msg}");
+        assert!(msg.contains("vision_provider"), "got: {msg}");
+    }
+
+    #[test]
+    fn fallback_notice_for_role_without_capability_label_uses_role_name() {
+        let msg = cloud_fallback_notice("heartbeat", "ollama:gemma3:1b", "openhuman");
+        assert!(msg.contains("Heartbeat"), "got: {msg}");
+        assert!(msg.contains("heartbeat_provider"), "got: {msg}");
+    }
+
+    #[test]
+    fn missing_credentials_message_explains_the_local_fallback() {
+        let msg =
+            missing_provider_credentials_message("vision", "anthropic", Some("ollama:gemma3:1b"));
+        // The whole point of #5146 §2.1: the user must learn *why* a provider
+        // they never configured is being asked for a key.
+        assert!(msg.contains("anthropic"), "got: {msg}");
+        assert!(msg.contains("ollama:gemma3:1b"), "got: {msg}");
+        assert!(msg.contains("vision (image input)"), "got: {msg}");
+        assert!(msg.contains("Connections"), "got: {msg}");
+        assert!(msg.contains("vision_provider"), "got: {msg}");
+    }
+
+    #[test]
+    fn missing_credentials_message_without_local_chat_omits_the_local_clause() {
+        let msg = missing_provider_credentials_message("embeddings", "openai", None);
+        assert!(msg.contains("openai"), "got: {msg}");
+        assert!(msg.contains("embeddings"), "got: {msg}");
+        assert!(
+            !msg.contains("Your chat model is local"),
+            "must not claim a local chat model when there is none: {msg}"
+        );
+    }
+
+    #[test]
+    fn missing_credentials_message_treats_blank_local_provider_as_absent() {
+        let msg = missing_provider_credentials_message("embeddings", "openai", Some("   "));
+        assert!(
+            !msg.contains("Your chat model is local"),
+            "blank provider string is not a local model: {msg}"
+        );
+    }
+
+    #[test]
+    fn vision_unsupported_message_names_model_and_a_concrete_remedy() {
+        let msg = local_vision_unsupported_message("gemma3:1b");
+        assert!(msg.contains("gemma3:1b"), "got: {msg}");
+        assert!(msg.contains("llava:7b"), "got: {msg}");
+        assert!(msg.contains("vision_provider"), "got: {msg}");
+    }
+
+    #[test]
+    fn vision_preflight_allows_a_vision_capable_model() {
+        use crate::openhuman::config::schema::ModelRegistryEntry;
+        let mut config = crate::openhuman::config::Config::default();
+        config.model_registry = vec![ModelRegistryEntry {
+            id: "llava:7b".into(),
+            provider: "ollama".into(),
+            cost_per_1m_output: 0.0,
+            vision: true,
+            ..Default::default()
+        }];
+        assert!(vision_preflight("llava:7b", &config).is_ok());
+    }
+
+    #[test]
+    fn vision_preflight_rejects_a_text_only_model_with_an_actionable_message() {
+        let config = crate::openhuman::config::Config::default();
+        let err = vision_preflight("gemma3:1b", &config)
+            .expect_err("a text-only model must fail the vision pre-flight");
+        assert!(err.contains("gemma3:1b"), "got: {err}");
+        assert!(err.contains("llava:7b"), "got: {err}");
+    }
+
+    #[test]
+    fn vision_preflight_allows_the_managed_vision_tier() {
+        // `vision-v1` is multimodal per `oh_tier_supports_vision`; the
+        // pre-flight must not fire for the managed vision sub-agent.
+        let config = crate::openhuman::config::Config::default();
+        assert!(vision_preflight("vision-v1", &config).is_ok());
+    }
+}
diff --git a/src/openhuman/inference/provider/mod.rs b/src/openhuman/inference/provider/mod.rs
index 533411129..05152325e 100644
--- a/src/openhuman/inference/provider/mod.rs
+++ b/src/openhuman/inference/provider/mod.rs
@@ -14,6 +14,8 @@ pub mod crate_openai;
 pub mod error_classify;
 pub mod error_code;
 pub mod factory;
+/// Actionable diagnostics for background-workload provider fallback (#5146 §2.1).
+pub(crate) mod fallback_diagnostics;
 mod openai_codex;
 /// Crate-native managed OpenHuman backend as a host `ChatModel` (issue #4727).
 pub mod openhuman_backend_model;