Two halves of one rule: the address someone typed is theirs to keep, and it must be
the one that gets them back in.
A plus-tagged or dotted Gmail is often a deliberate choice -- registering as
me+siftlode@gmail.com is how you find out later which site leaked your address. The
Google callback overwrote it with the account's primary, which can never contain a
'+', so the tag vanished on the first Google sign-in and, because sign-in matched the
stored address, took their chosen address with it. The rewrite line is older than
this epic, but S3 made it reachable here by matching adoption across spellings. It
now runs only when the mailbox GENUINELY changed, and lives in a named helper rather
than inline, so the rule has one home.
The three lookups that resolve a typed address -- password login, password reset,
verify resend -- go through find_user_by_email: exact spelling first, then the unique
canonical candidate, and None when several accounts share a mailbox rather than
guessing which one a password should open. Reset and resend previously answered a
different spelling with silence (they reply uniformly by design), which was a dead end
with no way out. Their mail now goes to the address on the account, never the one
typed into the form.
Gmail delivers x.y@, xy@ and xy+tag@ to one inbox; the invite gate only lowercased.
On 2026-09-03 that turned an approved user's Google sign-in into a silent SECOND
access request -- OAuth returns the account's stored primary, which need not be the
spelling they typed -- and left prod with two user rows for one mailbox (ids 13, 14).
The +tag case fails every time: a Google account cannot contain +, so OAuth can only
ever answer with the base address.
Mail still goes to the address AS TYPED; only identity matching uses the canonical
form. utils.canonical_email is the single definition, and a model validator derives
users.email_canonical / invites.email_canonical on every write, so no call site can
forget it. Scope is narrow on purpose: dots are significant on most providers and the
Gmail rule does not hold for Workspace custom domains.
Swept every sibling of the same principle, not just the reported one: is_allowed,
upsert_pending_invite, the Google-callback adoption, _register_account (so no new
duplicate pair can be created), _activate_user_by_email, admin _accounts_for (an
invite backing a live user under another spelling used to look deletable) and
add_invite, plus purge_user, which now erases every canonically-equal invite instead
of leaving one behind that still grants access.
Migration 0079 backfills both columns and indexes them NON-uniquely: prod already
carries canonical duplicates (approved invite pairs since 2026-06-16), and merging
accounts is a judgement call about people's data, not something a migration does on
its own. A test pins the backfill SQL against the Python helper.
peter