fix(sse): register Arcee AI in the executor provider registry (#12784) (#13277)

Merged as part of the 39-PR owner batch of 2026-09-11, validated as a unit.

Boarded into one consolidated worktree cut from `release/v3.8.51` with the other 38 — zero conflicts between them.

- ESLint over every changed file: no errors (the only finding was one suppression entry the batch emptied, pruned on #13243)
- `typecheck:core` clean; `check:dashboard-typecheck` OK (206 pre-existing, within baseline); `check:changelog-integrity` OK
- complexity 2821 / baseline 3218 and cognitive-complexity 1272 / baseline 1437 — both under baseline
- 256 assertions green: 246 under node:test and 10 under vitest, which is where `tests/unit/**/*.test.tsx` actually runs
- `check-file-size`: `chatCore.ts` rebaselined 6144 → 6146 for #13278 and #13276, annotated and landed on #13243

⚠️ base-red inherited: #12732 — the provider count (356 in the docs vs the 358 the modules define) and `open-sse/utils/stream.ts` at 3115 > frozen 3098 both reproduce on the pure tip with zero contribution from this batch.

changelog.d/fixes/12784-arcee-ai-provider-registry.md

@@ -0,0 +1 @@
+- fix(sse): register Arcee AI in the executor provider registry so requests reach api.arcee.ai instead of silently falling back to OpenAI (#12784)

open-sse/config/providers/index.ts

@@ -136,6 +136,7 @@ import { freemodel_devProvider } from "./registry/freemodel-dev/index.ts";
 import { gitlawb_gmiProvider } from "./registry/gitlawb/gmi/index.ts";
 import { gitlawbProvider } from "./registry/gitlawb/index.ts";
 import { liquidProvider } from "./registry/liquid/index.ts";
+import { arceeAiProvider } from "./registry/arcee-ai/index.ts";
 import { deepinfraProvider } from "./registry/deepinfra/index.ts";
 import { agyProvider } from "./registry/agy/index.ts";
 import { agnesProvider } from "./registry/agnes/index.ts";
@@ -409,6 +410,7 @@ export const REGISTRY: Record<string, RegistryEntry> = {
   "gitlawb-gmi": gitlawb_gmiProvider,
   gitlawb: gitlawbProvider,
   liquid: liquidProvider,
+  "arcee-ai": arceeAiProvider,
   deepinfra: deepinfraProvider,
   agy: agyProvider,
   agnes: agnesProvider,

open-sse/config/providers/registry/arcee-ai/index.ts

@@ -0,0 +1,10 @@
+import type { RegistryEntry } from "../../shared.ts";
+import { buildOpenAiCompatibleRegistryEntry } from "../../shared.ts";
+
+export const arceeAiProvider: RegistryEntry = buildOpenAiCompatibleRegistryEntry({
+  id: "arcee-ai",
+  alias: "arcee",
+  baseUrl: "https://api.arcee.ai/api/v1/chat/completions",
+  models: [],
+  passthroughModels: true,
+});

tests/unit/arcee-ai-provider.test.ts

@@ -0,0 +1,44 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+
+const TEST_DATA_DIR = fs.mkdtempSync(path.join(os.tmpdir(), "omniroute-arcee-provider-"));
+process.env.DATA_DIR = TEST_DATA_DIR;
+
+const { PROVIDERS } = await import("../../open-sse/config/constants.ts");
+const { REGISTRY: providerRegistry } = await import("../../open-sse/config/providerRegistry.ts");
+const { APIKEY_PROVIDERS } = await import("../../src/shared/constants/providers.ts");
+const { DefaultExecutor } = await import("../../open-sse/executors/default.ts");
+const dbCore = await import("../../src/lib/db/core.ts");
+
+test.after(() => {
+  dbCore.closeDbInstance();
+  fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true, maxRetries: 5, retryDelay: 100 });
+});
+
+const ARCEE_CHAT_URL = "https://api.arcee.ai/api/v1/chat/completions";
+
+test("arcee-ai is offered in the onboarding catalog", () => {
+  assert.ok(APIKEY_PROVIDERS["arcee-ai"]);
+});
+
+test("arcee-ai has a routing entry in the executor REGISTRY", () => {
+  const entry = providerRegistry["arcee-ai"];
+  assert.ok(entry, "providerRegistry['arcee-ai'] must be defined");
+  assert.equal(entry.id, "arcee-ai");
+  assert.equal(entry.alias, "arcee");
+  assert.equal(entry.format, "openai");
+  assert.equal(entry.executor, "default");
+  assert.equal(entry.baseUrl, ARCEE_CHAT_URL);
+  assert.equal(entry.authType, "apikey");
+  assert.equal(entry.authHeader, "bearer");
+  assert.equal(entry.passthroughModels, true);
+});
+
+test("DefaultExecutor routes arcee-ai to Arcee's own base URL, not OpenAI's", () => {
+  const executor = new DefaultExecutor("arcee-ai");
+  assert.equal(executor.config.baseUrl, ARCEE_CHAT_URL);
+  assert.notEqual(executor.config.baseUrl, PROVIDERS.openai.baseUrl);
+});