test: two tests still describe the registry as it was before 1477c53

Both failed the first time CI was able to run this suite, and neither is
a new break. They assert semantics that two deliberate changes replaced,
and nothing noticed because nothing had ever executed them.

1477c53 (2026-08-09) made a dormant track associable only if it had been
identified: an unowned dormant track has no actor to re-attach to, so it
only enlarges the matcher's comparison set and invites a new face landing
on an anonymous stub. Its message records the trade -- "a small recall
cost (~1-3pp on some films, e.g. Lord of War -2.5) for a cleaner, bounded
pool. Kept deliberately." Both tests build tracks that are never
identified, so since that commit they are dropped from the pool one line
before the extinction horizon they were written to exercise. The tests
date from 2026-07-31 and 2026-08-08 -- they are older than the gate.
Fixed by owning the track while it is still on screen, which is what a
real run does and what makes the horizon reachable at all.

The second test needed more than that, and the rename says why. It was
built on association and reaping answering on DIFFERENT clocks -- the
tracker's for "may this associate?", the watermark for "is this
finished?" -- which is exactly the arrangement track_registry.hpp:184-203
now rules out: one clock, one threshold, "nothing is offered past its
reap horizon, nothing is reaped while still offerable". So there is no
longer an interval in which a track is retired from association but still
alive, and a test named for that interval cannot pass. Rewritten to
assert what the unified clock actually promises: a tracker racing 50 s
past the horizon retires nothing while the matcher lags, the votes in
flight still land, and the watermark passing the horizon retires, reaps
and emits in one step.

Kept: the AR-008 tag, the late-vote check and dropped_votes() == 0, which
were the point of the test and still hold.

Full suite now 151/151 in sae-builder-cpu.

TRACES: AR-008, AR-013 | SR-002

tests/test_face_tracker.cpp

@@ -192,6 +192,13 @@ TEST_CASE("a track within the extinction window is still a candidate",
 
     Embedding person = at_sim(0, 1, 0.99f);
     int id_pre = r.track_of(frame(0.0, 10, 10, person));
+
+    // Identify it while it is still on screen. Since 1477c53 a DORMANT track is
+    // only associable if it was owned -- an anonymous one has no actor to
+    // re-attach to, so it is dropped from the pool a line before the horizon is
+    // ever consulted. Without this the test cannot reach what it is about.
+    r.reg->observe(id_pre, /*actor=*/0, /*posterior=*/0.99f, person);
+
     r.track_of(frame(1.0, 300, 300, axis(7), /*is_cut=*/true));
 
     // Back inside the window: the same person continues the same track, so the