docs: record real 'wrong password after logout' fix (verify resolves username OR email)

docs/engineering-log/2026-08-07-login-email-fix.md

@@ -0,0 +1,37 @@
+# 2026-08-07 — BUG FOUND & FIXED: "wrong password" right after logout → login (no redeploy)
+
+## Updated diagnosis (user correction)
+The failure happens **immediately** after logout → login again (NOT after a redeploy),
+so data persistence was NOT the cause. The password change is on disk.
+
+## Real root cause
+`verify()` in `backend/app/auth/users.py` looked up the user **by USERNAME only**
+(`get_user_or_none(ident)`). After first-run setup sets an admin EMAIL, users naturally
+type that **email** in the login field on the next login. `verify("admin@corp.com", …)`
+found no user whose USERNAME is `admin@corp.com` → `AuthError("invalid credentials")`,
+rendered in the UI as "รหัสผ่านผิด" even though the password was correct.
+
+The login route's `_login_body` claimed to "accept email as a fallback", but the fallback
+was cosmetic — it never resolved email → the stored user record.
+
+## Fix (commit `…`, pushed as part of `3bc2399`)
+```python
+def verify(self, ident: str, password: str):
+    user = self.get_user_or_none(ident) or self.by_email(ident)
+    ...
+```
+`verify` now resolves by **username OR email** (checks stored `email` field too).
+
+## Evidence
+Live-server test (fresh user, not admin):
+- create → setup (set email `emtest@corp.com`, new password)
+- login by **username** + new pw → **200**
+- login by **email** + new pw → **200** (was 401 before the fix)
+=> this is exactly the user's scenario, now working.
+
+Also refreshed the committed `frontend/dist` (was stale — old build without the username
+login/setup flow) so EasyPanel serves the correct SPA on deploy.
+
+## Tests
+m0 / setup / e2e all pass. Backend logic confirmed on real on-disk data (scrypt hash
+changes on setup; new password accepted).