7b5a18817 migrated the sibling slug sites to custom_provider_slug, which
keeps a keyed providers: entry's config key as its durable identity. It
covered find_custom_provider_identity_by_model; canonical_custom_identity's
third recovery source - the configured-provider fallback - still built
f"custom:{normalized}" out of whatever string the caller happened to hold.
_get_named_custom_provider matches on either spelling, so a display name
that differs from its config key matches the entry and then heals to
custom:<display-name>. That is a second identity for one endpoint: the
endpoint- and model-based sources of the same function return
custom:<config-key>, and so does everything that persists or restores a
session's provider override. canonical_custom_identity exists precisely to
make a bare "custom" routable again, and tui_gateway calls it on the
session-persist, resume and recovery paths - so the divergence lands in
stored session identity.
Re-resolve through the endpoint the matched entry owns, reusing the
function's own URL-based canonicaliser rather than duplicating the match
logic. Legacy unkeyed custom_providers: entries keep their name identity,
and an unconfigured candidate still returns None.
Drexuxux