enrol_rekey shared the enrol: bucket and metered before auth, so junk
calls could lock out incident-response rekey. Use a separate rekey:
bucket and charge it only after a bad bootstrap secret, so a valid seed
always proceeds.
In-flight verify/issue_code could insert a session or code after revoke
or rekey. sessions.resolve now refuses if the agent is revoked, has no
live key, or (agent sessions) the fingerprint no longer matches.
View codes store the issuing fingerprint and redeem refuses after
rekey/wipe; issue_code re-checks agent state. DESIGN matches the choke
point. Regression tests plant race-surviving sessions and stale codes.
claim_code now requires redeem_expires_at > now in the CAS UPDATE.
enrol_rekey shares the enrol: rate-limit bucket. spend_bootstrap and
sibling clear delete rows instead of retaining spent hashes, matching
the schema comment.
