diff --git a/git/install.sh b/git/install.sh
index b3925fb..a242461 100755
--- a/git/install.sh
+++ b/git/install.sh
@@ -30,4 +30,25 @@ say "fetch.prune = true (stale remote-tracking refs cleaned on every fetch)"
 git config --global credential.helper store
 say "credential.helper = store (~/.git-credentials, created on first auth)"
 
-say "Done. On the next HTTPS push/pull to a new host, git prompts once and caches the credential in ~/.git-credentials."
+# Our own Gitea authenticates from $GITEA_KEY (exported by secrets/ from the
+# vault), not from ~/.git-credentials.
+#
+# WHY: git never reads GITEA_KEY by itself. With only `store`, the token was
+# whatever got typed at the first prompt, copied into ~/.git-credentials, and
+# it silently went stale when the vault's key was rotated — or, on a box that
+# never pushed, there was no credential at all and the push just failed. Now
+# `opc GITEA_KEY` is the only step when the token changes.
+#
+# The empty helper first clears the inherited `store` for this host, so a
+# rejected token is never cached and a stale cached one can never win. Gitea
+# accepts the token as the password; the username is informational (GITEA_USER
+# overrides it). With GITEA_KEY unset the helper prints nothing and git falls
+# back to prompting, as before.
+GITEA_URL="https://git.nic-oconnor.com"
+git config --global --unset-all "credential.$GITEA_URL.helper" 2>/dev/null || true
+git config --global --add "credential.$GITEA_URL.helper" ''
+git config --global --add "credential.$GITEA_URL.helper" \
+  '!f() { test "$1" = get && test -n "${GITEA_KEY:-}" && printf "username=%s\npassword=%s\n" "${GITEA_USER:-$(id -un)}" "$GITEA_KEY"; }; f'
+say "credential helper for $GITEA_URL = \$GITEA_KEY (from secrets.env)"
+
+say "Done. $GITEA_URL uses \$GITEA_KEY; other HTTPS hosts prompt once and cache in ~/.git-credentials."