fix(sse): skip disabled providers in combo fallback (404 instead of 400)

CHANGELOG.md

@@ -45,6 +45,7 @@ _In development — bullets added per PR; finalized at release._
 
 ### 🐛 Fixed
 
+- **fix(sse): combo routing now skips a provider whose credentials are all disabled instead of failing the whole request** — when a combo like `antigravity/opus → github/opus` hit a leg whose only configured connections were disabled (or where no connections existed at all), `handleNoCredentials` returned `400 BAD_REQUEST`, which the combo target loop treats as a hard stop (combo's 400-break guard from PR #4316 / issue #4279 prevents infinite fallback loops on body-specific 4xx errors). The combo therefore died on the first leg even when later targets were perfectly healthy. The no-active-credentials branch now returns `404 NOT_FOUND` with `"No active credentials for provider: <p>"` instead — `404` flows through `checkFallbackError` as `shouldFallback: true` (generic-error catch-all path in `open-sse/services/accountFallback.ts`), so the next combo target is tried. The log level for this branch also drops from `error` to `warn` because zero active credentials is an expected operator-driven state, not a server fault. Inspired-by upstream decolua/9router PR #336. (thanks @East-rayyy)
 - **fix(embeddings):** forward output dimensions to Gemini for consistent embedding dims. (thanks @nguyenha935)
 - **fix(translator):** sanitize Read tool args from non-Anthropic models to prevent retry loops. (thanks @GodrezJr2)
 - **fix(usage):** reuse Gemini CLI project ID for quota checks (avoid re-discovery). (thanks @Delcado19)

src/sse/handlers/chatHelpers.ts

@@ -585,8 +585,21 @@ export function handleNoCredentials(
     return errorResponse(lastStatus, lastError);
   }
   if (!excludeConnectionId) {
-    log.error("AUTH", `No credentials for provider: ${provider}`);
-    return errorResponse(HTTP_STATUS.BAD_REQUEST, `No credentials for provider: ${provider}`);
+    // Ported from upstream decolua/9router#336 (Ibrahim Ryan): surface as 404
+    // NOT_FOUND instead of 400 BAD_REQUEST so combo routing can fall through to
+    // the next target. The combo target loop (open-sse/services/combo.ts) treats
+    // 400 as a hard stop to break body-specific infinite fallback loops
+    // (PR #4316 / issue #4279). 404 flows through checkFallbackError as
+    // `shouldFallback: true` (generic-error catch-all path in
+    // open-sse/services/accountFallback.ts), letting a combo like
+    // `antigravity/opus → github/opus` skip a provider whose credentials are
+    // all disabled. log level is `warn` rather than `error` because zero active
+    // credentials is an expected operator-driven state, not a server fault.
+    log.warn("AUTH", `No active credentials for provider: ${provider}`);
+    return errorResponse(
+      HTTP_STATUS.NOT_FOUND,
+      `No active credentials for provider: ${provider}`
+    );
   }
   log.warn("CHAT", "No more accounts available", { provider });
   return errorResponse(

tests/integration/chat-pipeline.test.ts

@@ -1184,8 +1184,9 @@ test("chat pipeline allows unauthenticated requests through to provider resoluti
 
   // handleChat does not enforce REQUIRE_API_KEY — that's the authz pipeline's job.
   // Without provider credentials seeded, the request falls through to the "no credentials" path.
-  assert.equal(response.status, 400);
-  assert.match(json.error.message, /No credentials for provider/i);
+  // Upstream port decolua/9router#336: 400 → 404 so combo routing can fall through.
+  assert.equal(response.status, 404);
+  assert.match(json.error.message, /No active credentials for provider/i);
 });
 
 test("chat pipeline returns 400 when the model field is omitted", async () => {
@@ -1298,8 +1299,9 @@ test("chat pipeline returns current no-credentials contract when no provider con
   );
 
   const json = (await response.json()) as any;
-  assert.equal(response.status, 400);
-  assert.match(json.error.message, /No credentials for provider: openai/);
+  // Upstream port decolua/9router#336: 400 → 404 so combo routing can fall through.
+  assert.equal(response.status, 404);
+  assert.match(json.error.message, /No active credentials for provider: openai/);
 });
 
 test("chat pipeline surfaces upstream 500 responses as structured errors", async () => {

tests/integration/combo-routing-e2e.test.ts

@@ -364,8 +364,10 @@ test("unmapped custom model requests fail after combo resolution falls through",
   );
   const json = (await response.json()) as any;
 
-  assert.equal(response.status, 400);
-  assert.match(json.error.message, /No credentials for provider: tenant/);
+  // Upstream port decolua/9router#336: 400 → 404 so combo routing can fall through
+  // to the next target when a provider has zero usable credentials.
+  assert.equal(response.status, 404);
+  assert.match(json.error.message, /No active credentials for provider: tenant/);
 });
 
 test("strategy updates take effect for later requests on the same combo name", async () => {

tests/integration/llama-cpp-provider.test.ts

@@ -171,7 +171,8 @@ test("llama-cpp provider: alias matching works via model catalog prefix", async
   assert.equal(json.choices[0].message.content, "42");
 });
 
-test("llama-cpp provider: returns 400 when no connection exists", async () => {
+test("llama-cpp provider: returns 404 when no connection exists", async () => {
+  // Upstream port decolua/9router#336: 400 → 404 so combo routing can fall through.
   const response = await handleChat(
     buildRequest({
       body: {
@@ -182,7 +183,7 @@ test("llama-cpp provider: returns 400 when no connection exists", async () => {
     })
   );
 
-  assert.equal(response.status, 400);
+  assert.equal(response.status, 404);
   const json = (await response.json()) as any;
-  assert.match(json.error.message, /No credentials for provider/);
+  assert.match(json.error.message, /No active credentials for provider/);
 });

tests/unit/chat-helpers.test.ts

@@ -247,6 +247,19 @@ test("checkPipelineGates reapplies runtime breaker settings to existing breakers
 });
 
 test("handleNoCredentials reports missing provider credentials and exhausted accounts", async () => {
+  // Ported from upstream decolua/9router#336 (Ibrahim Ryan): when a provider has
+  // zero usable connections (all disabled, or none configured at all), the
+  // historical 400 BAD_REQUEST classified the failure as non-fallbackable, so a
+  // combo like `antigravity/opus → github/opus` died on the first leg with a
+  // hard 400 even though the next combo target was perfectly healthy.
+  //
+  // The combo target loop (open-sse/services/combo.ts) deliberately breaks on
+  // 400 to prevent infinite fallback loops with body-specific 4xx errors
+  // (#4279/PR#4316). 404 NOT_FOUND, by contrast, flows through checkFallbackError
+  // as `shouldFallback: true` (generic-error catch-all path,
+  // open-sse/services/accountFallback.ts:1593-1599) so the next combo target is
+  // tried. We surface "no active credentials" as 404 so combo can skip past a
+  // disabled-credentials provider instead of failing the whole request.
   const missing = handleNoCredentials(null, null, "openai", "gpt-4o-mini", null, null);
   const exhausted = handleNoCredentials(
     null,
@@ -260,8 +273,8 @@ test("handleNoCredentials reports missing provider credentials and exhausted acc
   const missingJson = (await missing.json()) as any;
   const exhaustedJson = (await exhausted.json()) as any;
 
-  assert.equal(missing.status, 400);
-  assert.match(missingJson.error.message, /No credentials for provider: openai/);
+  assert.equal(missing.status, 404);
+  assert.match(missingJson.error.message, /No active credentials for provider: openai/);
   assert.equal(exhausted.status, 500);
   assert.match(exhaustedJson.error.message, /Primary account failed/);
 });

tests/unit/chat-route-coverage.test.ts

@@ -300,7 +300,11 @@ test("handleChat keeps the combo error when the global fallback throws", async (
   assert.match(json.error.message, /primary combo failed/i);
 });
 
-test("handleChat returns 400 when no provider credentials exist", async () => {
+test("handleChat returns 404 when no provider credentials exist", async () => {
+  // Upstream port decolua/9router#336 (Ibrahim Ryan): the no-credentials branch
+  // of handleNoCredentials now surfaces 404 NOT_FOUND so combo routing can fall
+  // through to the next target instead of being killed by the combo 400-hard-stop
+  // guard (open-sse/services/combo.ts, PR #4316 / issue #4279).
   const response = await handleChat(
     buildRequest({
       body: {
@@ -312,8 +316,8 @@ test("handleChat returns 400 when no provider credentials exist", async () => {
   );
   const json = (await response.json()) as any;
 
-  assert.equal(response.status, 400);
-  assert.match(json.error.message, /No credentials for provider: openai/);
+  assert.equal(response.status, 404);
+  assert.match(json.error.message, /No active credentials for provider: openai/);
 });
 
 test("handleChat returns 503 for cooled-down connections and 503 for open circuit breakers", async () => {

tests/unit/vscode-token-routes.test.ts

@@ -1115,9 +1115,12 @@ test("vscode tokenized /chat/completions route applies the path token and codex
   );
   const body = (await response.json()) as any;
 
-  assert.equal(response.status, 400);
-  assert.equal(body.error?.code, "bad_request");
-  assert.equal(body.error?.message, "No credentials for provider: codex");
+  // Upstream port decolua/9router#336: zero-active-credentials now surfaces as
+  // 404 (combo-fallbackable) instead of 400 (combo hard-stop). The 404 OpenAI
+  // error code mapping is "model_not_found" (open-sse/config/errorConfig.ts:29).
+  assert.equal(response.status, 404);
+  assert.equal(body.error?.code, "model_not_found");
+  assert.equal(body.error?.message, "No active credentials for provider: codex");
 });
 
 test("vscode tokenized /responses route applies the path token and codex tier rewrite", async () => {
@@ -1142,9 +1145,10 @@ test("vscode tokenized /responses route applies the path token and codex tier re
   );
   const body = (await response.json()) as any;
 
-  assert.equal(response.status, 400);
-  assert.equal(body.error?.code, "bad_request");
-  assert.equal(body.error?.message, "No credentials for provider: codex");
+  // Upstream port decolua/9router#336: see chat/completions sibling test above.
+  assert.equal(response.status, 404);
+  assert.equal(body.error?.code, "model_not_found");
+  assert.equal(body.error?.message, "No active credentials for provider: codex");
 });
 
 test("vscode tokenized api/show route preserves the selected reasoning effort for codex variants", async () => {