diff --git a/CHANGELOG.md b/CHANGELOG.md
index acbf704144..bcfe877de4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -38,6 +38,8 @@
 
 - **fix(github):** drop a trailing assistant prefill before dispatching to GitHub Copilot chat to avoid 400 errors. (thanks @baslr)
 
+- **fix(oauth):** prevent cross-IdP account overwrites by disambiguating OAuth connections on `username` when present, not email alone. (thanks @KunN-21)
+
 - **providers (Kiro — Claude Sonnet 5):** the Kiro provider's model catalog was missing `claude-sonnet-5`, so the model could not be selected or routed even on accounts that already had access to it ("claude-sonnet-5 is not supported"). Added the model to the Kiro registry (`open-sse/config/providers/registry/kiro/index.ts`) as a 1M-context / 128K-output Claude model, mirroring the existing Claude entries; the registry `models[]` feeds both the model selector and the live CodeWhisperer `ListAvailableModels` fallback, so the model is now selectable and routable. Regression guard: `tests/unit/kiro-claude-sonnet-5-2267.test.ts`. (thanks [@openbioinfo](https://github.com/openbioinfo))
 
 - **settings (model aliases — self-heal after restart):** the Settings → Routing page showed "No exact-match aliases configured" after a server restart even though the aliases were persisted in the DB. Aliases are held in a module-local `_customAliases` map in `modelDeprecation.ts` that the boot path hydrates, but Next.js compiles the app-route module graph separately from the startup graph (the same webpack chunk-splitting class as #5312), so the `GET /api/settings/model-aliases` handler read a different, un-hydrated copy. The handler now self-heals: when its in-memory alias map is empty it reads `settings.modelAliases` from the DB (via the existing `getSettings()` db module — no raw SQL in the route) and repopulates the map, so the UI reflects the persisted aliases on the first GET after a restart. Follow-up: the root cause is now also fixed — the `_customAliases` store in `modelDeprecation.ts` is backed by `globalThis` (key `__omniroute_customAliases__`), so the startup and app-route module graphs share **one** store and the route reads the boot-hydrated aliases directly (the DB self-heal remains as a harmless fallback), mirroring the same `globalThis` singleton pattern already applied to `thinkingBudget.ts`/`backgroundTaskDetector.ts` (#5312). Regression guards: `tests/unit/model-aliases-settings-route-selfheal.test.ts` + `tests/unit/model-aliases-globalthis-5777.test.ts`. ([#5777](https://github.com/diegosouzapw/OmniRoute/pull/5777) — thanks [@jleonar2](https://github.com/jleonar2))
diff --git a/src/lib/db/providers.ts b/src/lib/db/providers.ts
index 029e78d333..9323dbc10e 100644
--- a/src/lib/db/providers.ts
+++ b/src/lib/db/providers.ts
@@ -170,13 +170,31 @@ export async function createProviderConnection(data: JsonRecord) {
       // For Codex with workspaceId, don't fall back to email-only check
       // This allows creating new connections for different workspaces
     } else {
-      // For other providers (or Codex without workspaceId), use email check
+      // For other providers (or Codex without workspaceId), match on email —
+      // disambiguated by providerSpecificData.username when present on both
+      // sides. Two different IdPs can share the same email address (e.g. a
+      // Google account and a HuggingFace account); matching on email alone
+      // would silently overwrite the other account's connection on the
+      // second login. Only fall back to the bare email-only match when
+      // neither side carries a username (legacy rows created before this
+      // disambiguation existed).
+      const incomingUsername = toStringOrNull(providerSpecificData.username);
+      const emailMatches = db
+        .prepare(
+          "SELECT * FROM provider_connections WHERE provider = ? AND auth_type = 'oauth' AND email = ?"
+        )
+        .all(data.provider, data.email) as JsonRecord[];
       existing =
-        (db
-          .prepare(
-            "SELECT * FROM provider_connections WHERE provider = ? AND auth_type = 'oauth' AND email = ?"
-          )
-          .get(data.provider, data.email) as JsonRecord | undefined) || null;
+        emailMatches.find((row) => {
+          const existingUsername = toStringOrNull(
+            parseProviderSpecificData(row.provider_specific_data)?.username
+          );
+          if (incomingUsername && existingUsername) {
+            return incomingUsername === existingUsername;
+          }
+          if (incomingUsername || existingUsername) return false;
+          return true;
+        }) || null;
     }
   } else if (data.authType === "apikey") {
     // Name-based upsert (existing behavior): same provider + same name → update.
diff --git a/tests/unit/db-providers-cross-idp-dedup-2244.test.ts b/tests/unit/db-providers-cross-idp-dedup-2244.test.ts
new file mode 100644
index 0000000000..fd74044cc4
--- /dev/null
+++ b/tests/unit/db-providers-cross-idp-dedup-2244.test.ts
@@ -0,0 +1,156 @@
+// Cross-IdP OAuth account dedup — createProviderConnection matched OAuth
+// connections by email only, so two different IdPs that happen to share an
+// email address (e.g. a Google account and a HuggingFace account) would
+// silently overwrite each other on the second login. Disambiguate on
+// providerSpecificData.username when BOTH the incoming and an existing
+// connection carry one; fall back to the legacy email-only match when
+// neither side has a username (backward compat for rows created before
+// this fix). This test fails before the fix (case b overwrites instead of
+// inserting a new row).
+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-cross-idp-dedup-"));
+process.env.DATA_DIR = TEST_DATA_DIR;
+
+const core = await import("../../src/lib/db/core.ts");
+const providersDb = await import("../../src/lib/db/providers.ts");
+
+async function resetStorage() {
+  core.resetDbInstance();
+  for (let attempt = 0; attempt < 10; attempt++) {
+    try {
+      if (fs.existsSync(TEST_DATA_DIR)) {
+        fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+      }
+      break;
+    } catch (error: unknown) {
+      const code = (error as { code?: string } | null)?.code;
+      if ((code === "EBUSY" || code === "EPERM") && attempt < 9) {
+        await new Promise((resolve) => setTimeout(resolve, 50 * (attempt + 1)));
+      } else {
+        throw error;
+      }
+    }
+  }
+  fs.mkdirSync(TEST_DATA_DIR, { recursive: true });
+}
+
+test.beforeEach(async () => {
+  await resetStorage();
+});
+
+test.after(async () => {
+  core.resetDbInstance();
+  fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+});
+
+test("#2244 cross-IdP dedup: same email + same username updates the existing connection", async () => {
+  const first = await providersDb.createProviderConnection({
+    provider: "glm",
+    authType: "oauth",
+    email: "shared@example.com",
+    providerSpecificData: { username: "alice-google" },
+    isActive: true,
+  });
+  const second = await providersDb.createProviderConnection({
+    provider: "glm",
+    authType: "oauth",
+    email: "shared@example.com",
+    providerSpecificData: { username: "alice-google" },
+    isActive: true,
+  });
+
+  const conns = await providersDb.getProviderConnections({ provider: "glm" });
+  assert.equal(conns.length, 1, "same email + same username must dedupe to a single connection");
+  assert.equal((first as { id: string }).id, (second as { id: string }).id);
+});
+
+test("#2244 cross-IdP dedup: same email + DIFFERENT username creates a separate connection", async () => {
+  await providersDb.createProviderConnection({
+    provider: "glm",
+    authType: "oauth",
+    email: "shared@example.com",
+    providerSpecificData: { username: "alice-google" },
+    isActive: true,
+  });
+  await providersDb.createProviderConnection({
+    provider: "glm",
+    authType: "oauth",
+    email: "shared@example.com",
+    providerSpecificData: { username: "alice-huggingface" },
+    isActive: true,
+  });
+
+  const conns = await providersDb.getProviderConnections({ provider: "glm" });
+  assert.equal(
+    conns.length,
+    2,
+    "two different IdP identities sharing an email must NOT be collapsed into one connection"
+  );
+  const usernames = conns
+    .map((c) => (c as { providerSpecificData?: { username?: string } }).providerSpecificData?.username)
+    .sort();
+  assert.deepEqual(usernames, ["alice-google", "alice-huggingface"]);
+});
+
+test("#2244 cross-IdP dedup: legacy rows without username still dedupe against incoming without username", async () => {
+  const first = await providersDb.createProviderConnection({
+    provider: "glm",
+    authType: "oauth",
+    email: "legacy@example.com",
+    providerSpecificData: {},
+    isActive: true,
+  });
+  const second = await providersDb.createProviderConnection({
+    provider: "glm",
+    authType: "oauth",
+    email: "legacy@example.com",
+    providerSpecificData: {},
+    isActive: true,
+  });
+
+  const conns = await providersDb.getProviderConnections({ provider: "glm" });
+  assert.equal(
+    conns.length,
+    1,
+    "legacy email-only rows without a username must keep deduping on email alone"
+  );
+  assert.equal((first as { id: string }).id, (second as { id: string }).id);
+});
+
+test("#2244 cross-IdP dedup: Codex workspaceId matching path is unaffected", async () => {
+  const first = await providersDb.createProviderConnection({
+    provider: "codex",
+    authType: "oauth",
+    email: "team@example.com",
+    providerSpecificData: { workspaceId: "ws-1", username: "team-user" },
+    isActive: true,
+  });
+  const second = await providersDb.createProviderConnection({
+    provider: "codex",
+    authType: "oauth",
+    email: "team@example.com",
+    providerSpecificData: { workspaceId: "ws-1", username: "team-user-renamed" },
+    isActive: true,
+  });
+  const third = await providersDb.createProviderConnection({
+    provider: "codex",
+    authType: "oauth",
+    email: "team@example.com",
+    providerSpecificData: { workspaceId: "ws-2", username: "team-user" },
+    isActive: true,
+  });
+
+  const conns = await providersDb.getProviderConnections({ provider: "codex" });
+  assert.equal(
+    conns.length,
+    2,
+    "Codex must keep matching on workspaceId + email regardless of username, and a different workspace must stay a separate connection"
+  );
+  assert.equal((first as { id: string }).id, (second as { id: string }).id);
+  assert.notEqual((first as { id: string }).id, (third as { id: string }).id);
+});