diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3ea247d..579bab3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,24 @@ skip versions are the composition of each intervening adjacent
 release's steps in order — no A-to-B path is pre-computed beyond
 that.
 
+## 0.54.1 — 2026-06-09
+
+**Patch — the Gitea-OAuth sign-in no longer 500s when an account was first
+created via OTC; no operator action required.**
+
+`auth.provision_user` (the Gitea-OAuth callback path) matched an existing
+`users` row only by `gitea_id`. A human who signed in first via the OTC
+email path owns an email-only row (`gitea_id` NULL); when they later signed
+in via Gitea OAuth with the same email, the lookup missed and the code
+INSERTed a new row — colliding on the `idx_users_email` case-insensitive
+unique index and raising `IntegrityError`, which 500-ed the callback. Now,
+when no `gitea_id` row exists, `provision_user` reconciles by email and links
+the OAuth identity (`gitea_id` / `gitea_login` / profile) onto the existing
+row — the mirror of the OTC linker, which already links an OAuth-era email row
+on first OTC sign-in. The §6.1 owner-zero bootstrap is applied on link
+(matching the fresh-insert path); the row's `permission_state` is preserved so
+linking never changes a human's admission status as a side effect.
+
 ## 0.54.0 — 2026-06-09
 
 **Minor — the AI "Ask" affordance now works from an entry's canonical view
diff --git a/VERSION b/VERSION
index 524456c..1942d77 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-0.54.0
+0.54.1
diff --git a/backend/app/auth.py b/backend/app/auth.py
index c7ab37f..dc37912 100644
--- a/backend/app/auth.py
+++ b/backend/app/auth.py
@@ -145,6 +145,19 @@ def provision_user(config: Config, profile: dict[str, Any]) -> SessionUser:
 
     c = db.conn()
     existing = c.execute("SELECT * FROM users WHERE gitea_id = ?", (gitea_id,)).fetchone()
+    # No row for this gitea_id yet. A prior OTC sign-in (`provision_or_link_user`)
+    # may have created an email-only row with this same email and `gitea_id`
+    # NULL; `idx_users_email` is a unique index, so a blind INSERT below would
+    # raise IntegrityError and 500 the OAuth callback. Reconcile by email: link
+    # the OAuth identity onto that existing row instead. Mirror of the OTC
+    # linker, which links an OAuth-era email row on first OTC sign-in.
+    linked = False
+    if existing is None and email:
+        existing = c.execute(
+            "SELECT * FROM users WHERE email = ? COLLATE NOCASE AND gitea_id IS NULL LIMIT 1",
+            (email,),
+        ).fetchone()
+        linked = existing is not None
     if existing is None:
         role = "owner" if config.owner_gitea_login and login == config.owner_gitea_login else "contributor"
         # v0.8.0: a fresh OAuth-provisioned user is also subject to
@@ -166,15 +179,26 @@ def provision_user(config: Config, profile: dict[str, Any]) -> SessionUser:
         permission_state = "granted"
     else:
         user_id = existing["id"]
-        role = existing["role"]
+        # On a fresh link this OAuth sign-in is the row's first, so apply the
+        # §6.1 owner-zero bootstrap (matching the INSERT path). For a row already
+        # matched by gitea_id the role is settled — preserve it. `permission_state`
+        # is preserved either way: linking an OAuth identity onto an existing
+        # email row must not silently change the human's admission status.
+        if linked and config.owner_gitea_login and login == config.owner_gitea_login:
+            role = "owner"
+        else:
+            role = existing["role"]
         permission_state = existing["permission_state"] or "granted"
+        # Setting `gitea_id` matters only on the link path (it was NULL); on the
+        # gitea_id-matched path it re-writes the same value. `role` is likewise a
+        # no-op there. Always refresh the mutable profile fields + last_seen.
         c.execute(
             """
             UPDATE users
-               SET gitea_login = ?, email = ?, display_name = ?, avatar_url = ?, last_seen_at = datetime('now')
+               SET gitea_id = ?, gitea_login = ?, email = ?, display_name = ?, avatar_url = ?, role = ?, last_seen_at = datetime('now')
              WHERE id = ?
             """,
-            (login, email, display, avatar, user_id),
+            (gitea_id, login, email, display, avatar, role, user_id),
         )
 
     return SessionUser(
diff --git a/backend/tests/test_provision_user_email_link.py b/backend/tests/test_provision_user_email_link.py
new file mode 100644
index 0000000..eca0c8c
--- /dev/null
+++ b/backend/tests/test_provision_user_email_link.py
@@ -0,0 +1,107 @@
+"""§6 hardening — the Gitea-OAuth `auth.provision_user` reconciles by email.
+
+Regression cover for a §9-surfaced fragility: a human who signed in first via
+OTC owns an email-only `users` row (`gitea_id` NULL). When they later sign in
+via Gitea OAuth with the SAME email, `provision_user` used to match only by
+`gitea_id`, miss the OTC row, and INSERT a new row — colliding on the
+`idx_users_email` unique index and 500-ing the callback. The fix links the OAuth
+identity onto the existing email row (the mirror of the OTC linker).
+"""
+from __future__ import annotations
+
+from test_propose_vertical import (  # noqa: F401
+    FakeGitea,
+    app_with_fake_gitea,
+    provision_user_row,
+    tmp_env,
+)
+
+
+def _cfg():
+    from app.config import load_config
+    return load_config()
+
+
+def test_oauth_links_onto_existing_otc_email_row(app_with_fake_gitea):
+    from fastapi.testclient import TestClient
+    from app import auth, db
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app):
+        # An OTC-first user: email-only row, gitea_id NULL, still 'pending'.
+        db.conn().execute(
+            """
+            INSERT INTO users (gitea_id, gitea_login, email, display_name, avatar_url, role, permission_state)
+            VALUES (NULL, NULL, ?, ?, '', 'contributor', 'pending')
+            """,
+            ("dual@example.com", "dual"),
+        )
+        otc_id = db.conn().execute(
+            "SELECT id FROM users WHERE email = ? COLLATE NOCASE", ("dual@example.com",)
+        ).fetchone()["id"]
+
+        # Now the same human signs in via Gitea OAuth (new gitea_id, same email).
+        # Case-different email proves the NOCASE match.
+        user = auth.provision_user(
+            _cfg(),
+            {"id": 9001, "login": "dualgitea", "email": "Dual@Example.com",
+             "full_name": "Dual User", "avatar_url": "http://x/a.png"},
+        )
+
+        # Linked onto the SAME row — no second row, no 500.
+        assert user.user_id == otc_id
+        rows = db.conn().execute(
+            "SELECT id, gitea_id, gitea_login, permission_state, role FROM users WHERE email = ? COLLATE NOCASE",
+            ("dual@example.com",),
+        ).fetchall()
+        assert len(rows) == 1
+        assert rows[0]["id"] == otc_id
+        assert rows[0]["gitea_id"] == 9001           # OAuth identity attached
+        assert rows[0]["gitea_login"] == "dualgitea"
+        assert rows[0]["permission_state"] == "pending"  # admission state preserved
+        assert rows[0]["role"] == "contributor"
+
+
+def test_oauth_provisions_fresh_user_when_email_matches_no_one(app_with_fake_gitea):
+    from fastapi.testclient import TestClient
+    from app import auth, db
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app):
+        user = auth.provision_user(
+            _cfg(),
+            {"id": 9100, "login": "freshoauth", "email": "fresh@example.com",
+             "full_name": "Fresh", "avatar_url": ""},
+        )
+        row = db.conn().execute(
+            "SELECT gitea_id, gitea_login, role, permission_state FROM users WHERE id = ?",
+            (user.user_id,),
+        ).fetchone()
+        assert row["gitea_id"] == 9100
+        assert row["gitea_login"] == "freshoauth"
+        # Reaching provision_user means admission passed → granted (unchanged).
+        assert row["permission_state"] == "granted"
+
+
+def test_returning_oauth_user_matched_by_gitea_id_not_duplicated(app_with_fake_gitea):
+    from fastapi.testclient import TestClient
+    from app import auth, db
+
+    app, _fake = app_with_fake_gitea
+    with TestClient(app):
+        provision_user_row(user_id=55, login="returning", role="contributor")
+        before = db.conn().execute("SELECT COUNT(*) AS n FROM users").fetchone()["n"]
+
+        user = auth.provision_user(
+            _cfg(),
+            {"id": 55, "login": "returning-renamed", "email": "returning@test",
+             "full_name": "Returning", "avatar_url": ""},
+        )
+        after = db.conn().execute("SELECT COUNT(*) AS n FROM users").fetchone()["n"]
+
+        assert user.user_id == 55
+        assert after == before  # matched by gitea_id; no new row
+        row = db.conn().execute(
+            "SELECT gitea_login FROM users WHERE id = ?", (55,)
+        ).fetchone()
+        assert row["gitea_login"] == "returning-renamed"  # profile refreshed
diff --git a/frontend/package.json b/frontend/package.json
index 5f2cc41..4790ae4 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -1,7 +1,7 @@
 {
   "name": "rfc-app-frontend",
   "private": true,
-  "version": "0.54.0",
+  "version": "0.54.1",
   "type": "module",
   "scripts": {
     "dev": "vite",