A clean review window only proves an interface was silent for that window.
For a heavily used interface that is weak evidence -- an infrequent caller
can fall outside the window entirely, so the interface reads as retirable
while still having consumers.
_retirement_state now also requires silence since last_seen_at, scaled by
all-time volume (RETIREMENT_QUIET_LADDER): 7d under 100 calls, 30d under
10k, 60d above. Existing guards (retired / manual hold / replacement ref /
replacement verified / in-window traffic) still take precedence.
On the 2026-08-20 capture this makes 15 of 19 legacy interfaces retirable
and holds 4: the three six-figure /workstreams/ read paths, and
GET /tasks/?workstream_id which still has live traffic.
Unblocks the bulk of Wave E2 in the cutover slice plan. 7 new tests.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
tegwick
93e95f93e7