The canary tag regex capped the major at 3 digits while the stable
shape had no cap. The repo's current stable line is CalVer (v2026.9.14),
so canary_tag_for_date cuts v2026.9.15-canary.<ts> — which
handoff.validate_identity then rejected as 'Invalid release handoff
identity', killing every tag-mode stage leg (Windows and Darwin) while
the same-minor stable staged fine.
Lift the cap in the canonical _CANARY_TAG_RE and the Termux mirror
regex; add the stable-vs-canary shape-parity invariant, proven red on
the base regexes.