diff --git a/src/lib/accounts/account-service.ts b/src/lib/accounts/account-service.ts
index 175a22b..591ad3c 100644
--- a/src/lib/accounts/account-service.ts
+++ b/src/lib/accounts/account-service.ts
@@ -121,7 +121,8 @@ export class AccountService {
       initialAuthState &&
       !initialAuthState.isSymbolicLink &&
       !externalSyncForced &&
-      (await this.getSessionAuthFingerprint()) === initialAuthState.fingerprint
+      (await this.getSessionAuthFingerprint()) === initialAuthState.fingerprint &&
+      (await this.sessionSnapshotExists())
     ) {
       return {
         synchronized: false,
@@ -429,14 +430,15 @@ export class AccountService {
 
   public async useAccount(rawName: string): Promise<string> {
     const name = this.normalizeAccountName(rawName);
-    await this.activateSnapshot(name);
+    const resolvedName = await this.resolveUsableAccountName(name);
+    await this.activateSnapshot(resolvedName);
 
     const registry = await loadRegistry();
-    await this.hydrateSnapshotMetadataIfMissing(registry, name);
-    registry.activeAccountName = name;
+    await this.hydrateSnapshotMetadataIfMissing(registry, resolvedName);
+    registry.activeAccountName = resolvedName;
     await saveRegistry(registry);
 
-    return name;
+    return resolvedName;
   }
 
   public async removeAccounts(accountNames: string[]): Promise<RemoveResult> {
@@ -1182,6 +1184,59 @@ export class AccountService {
     });
   }
 
+  private async resolveUsableAccountName(accountName: string): Promise<string> {
+    if (await this.pathExists(this.accountFilePath(accountName))) {
+      return accountName;
+    }
+
+    await this.syncExternalAuthSnapshotIfNeeded();
+
+    if (await this.pathExists(this.accountFilePath(accountName))) {
+      return accountName;
+    }
+
+    const emailMatches = await this.findSnapshotNamesByExactEmail(accountName);
+    if (emailMatches.length === 1) {
+      return emailMatches[0];
+    }
+    if (emailMatches.length > 1) {
+      throw new AmbiguousAccountQueryError(accountName);
+    }
+
+    throw new AccountNotFoundError(accountName);
+  }
+
+  private async findSnapshotNamesByExactEmail(rawEmail: string): Promise<string[]> {
+    const normalizedEmail = rawEmail.trim().toLowerCase();
+    if (!normalizedEmail.includes("@")) {
+      return [];
+    }
+
+    const accountNames = await this.listAccountNames();
+    const matches: string[] = [];
+    for (const name of accountNames) {
+      const snapshotPath = this.accountFilePath(name);
+      try {
+        const snapshot = await parseAuthSnapshotFile(snapshotPath);
+        if (snapshot.email?.trim().toLowerCase() === normalizedEmail) {
+          matches.push(name);
+        }
+      } catch {
+        // Ignore unreadable snapshots here so the existing not-found path
+        // remains actionable for the requested email.
+      }
+    }
+    return matches.sort((a, b) => a.localeCompare(b, undefined, { sensitivity: "base" }));
+  }
+
+  private async sessionSnapshotExists(): Promise<boolean> {
+    const sessionAccountName = await this.getSessionAccountName();
+    if (!sessionAccountName) {
+      return true;
+    }
+    return this.pathExists(this.accountFilePath(sessionAccountName));
+  }
+
   private async clearActivePointers(): Promise<void> {
     const currentPath = resolveCurrentNamePath();
     const authPath = resolveAuthPath();
diff --git a/src/tests/save-account-safety.test.ts b/src/tests/save-account-safety.test.ts
index cd8ac3e..47a852b 100644
--- a/src/tests/save-account-safety.test.ts
+++ b/src/tests/save-account-safety.test.ts
@@ -63,6 +63,7 @@ async function withIsolatedCodexDir(
     CODEX_AUTH_ACCOUNTS_DIR: process.env.CODEX_AUTH_ACCOUNTS_DIR,
     CODEX_AUTH_JSON_PATH: process.env.CODEX_AUTH_JSON_PATH,
     CODEX_AUTH_CURRENT_PATH: process.env.CODEX_AUTH_CURRENT_PATH,
+    CODEX_AUTH_SESSION_KEY: process.env.CODEX_AUTH_SESSION_KEY,
     CODEX_AUTH_SESSION_ACTIVE_OVERRIDE: process.env.CODEX_AUTH_SESSION_ACTIVE_OVERRIDE,
   };
 
@@ -72,11 +73,13 @@ async function withIsolatedCodexDir(
   delete process.env.CODEX_AUTH_CURRENT_PATH;
 
   t.after(async () => {
-    process.env.CODEX_AUTH_CODEX_DIR = previousEnv.CODEX_AUTH_CODEX_DIR;
-    process.env.CODEX_AUTH_ACCOUNTS_DIR = previousEnv.CODEX_AUTH_ACCOUNTS_DIR;
-    process.env.CODEX_AUTH_JSON_PATH = previousEnv.CODEX_AUTH_JSON_PATH;
-    process.env.CODEX_AUTH_CURRENT_PATH = previousEnv.CODEX_AUTH_CURRENT_PATH;
-    process.env.CODEX_AUTH_SESSION_ACTIVE_OVERRIDE = previousEnv.CODEX_AUTH_SESSION_ACTIVE_OVERRIDE;
+    for (const [key, value] of Object.entries(previousEnv)) {
+      if (typeof value === "string") {
+        process.env[key] = value;
+      } else {
+        delete process.env[key];
+      }
+    }
     await fsp.rm(codexDir, { recursive: true, force: true });
   });
 
@@ -805,6 +808,70 @@ test("syncExternalAuthSnapshotIfNeeded refreshes active same-identity snapshot a
   });
 });
 
+test("syncExternalAuthSnapshotIfNeeded recreates a missing snapshot even when auth fingerprint is unchanged", async (t) => {
+  await withIsolatedCodexDir(t, async ({ accountsDir, authPath }) => {
+    const service = new AccountService();
+    const email = "moncsi@gitguardex.com";
+    process.env.CODEX_AUTH_SESSION_KEY = "terminal-moncsi";
+    process.env.CODEX_AUTH_SESSION_ACTIVE_OVERRIDE = "1";
+
+    await fsp.writeFile(
+      authPath,
+      buildAuthPayload(email, {
+        accountId: "acct-moncsi",
+        userId: "user-moncsi",
+      }),
+      "utf8",
+    );
+
+    const firstSync = await service.syncExternalAuthSnapshotIfNeeded();
+    assert.equal(firstSync.savedName, email);
+
+    const snapshotPath = path.join(accountsDir, `${email}.json`);
+    await fsp.rm(snapshotPath, { force: true });
+
+    const secondSync = await service.syncExternalAuthSnapshotIfNeeded();
+    assert.deepEqual(secondSync, {
+      synchronized: true,
+      savedName: email,
+      autoSwitchDisabled: false,
+    });
+
+    const restored = await parseAuthSnapshotFile(snapshotPath);
+    assert.equal(restored.email, email);
+  });
+});
+
+test("useAccount resolves an exact email to its saved duplicate snapshot", async (t) => {
+  await withIsolatedCodexDir(t, async ({ codexDir, accountsDir, authPath }) => {
+    const service = new AccountService();
+    const email = "moncsi@gitguardex.com";
+    const duplicateName = `${email}--dup-2`;
+
+    await fsp.writeFile(
+      path.join(accountsDir, `${duplicateName}.json`),
+      buildAuthPayload(email, {
+        accountId: "acct-moncsi",
+        userId: "user-moncsi",
+      }),
+      "utf8",
+    );
+    await fsp.writeFile(
+      authPath,
+      buildAuthPayload(email, {
+        accountId: "acct-moncsi",
+        userId: "user-moncsi",
+      }),
+      "utf8",
+    );
+
+    const activated = await service.useAccount(email);
+
+    assert.equal(activated, duplicateName);
+    assert.equal((await fsp.readFile(path.join(codexDir, "current"), "utf8")).trim(), duplicateName);
+  });
+});
+
 test("syncExternalAuthSnapshotIfNeeded reuses a saved alias that matches relogin identity", async (t) => {
   await withIsolatedCodexDir(t, async ({ codexDir, accountsDir, authPath }) => {
     const service = new AccountService();