feat(ar-024): enforce the invariant statically, and delete the fallback it caught

AR-024's register row gives its verification tier as "Static check -- no
bare cosine outside a tagged EXCEPTION". No such check existed, so the
invariant was enforced by reading, and reading had missed a live
violation.

scripts/ci/check_raw_cosine.py is that check, wired into the
traceability workflow as a blocking step. It is honest about its reach:
it catches direct cosine_similarity() uses not routed through a
calibration, and it cannot follow a cosine through a variable across
statements. That limit is documented in the script rather than left for
someone to discover after trusting a pass.

What it caught, and what this commit removes with it:

The identity matcher's no-calibration fallback thresholded raw cosine
distance (match_threshold) plus a ratio test (match_ratio,
match_ratio_ceil). Worse than the invariant breach: it fed
max(0, cosine) into TrackRegistry::observe, whose contract reads
"posterior is a calibrated probability, never a raw cosine (AR-024) ...
so the accumulation cannot be fed an uncalibrated number by a careless
caller". It could, and did. And it disagreed with the rest of the
pipeline about what "the fit failed" means -- same_person_probability
answers that with the untuned default sigmoid and a loud warning, so
association stayed in probability space while matching alone left it.
One run, two policies, no announcement.

Now one rule: cal_.probability() always, with a warning when the fit is
not real. A worse answer than a fitted calibration, a better one than a
number whose units nothing else shares.

TrackGallery::set_calibration is mandatory for the same reason. Its
default was max(0, cosine), which made expand_band_lo = 0.90 mean
"cosine > 0.9" in a test and "P(same person) > 0.9" in production.
FaceTrackerFunc already threw without one; the expansion store now
matches.

One exception is recorded, in the calibration's own dedup. It is not a
close call: at 1 - 1e-7 it asks whether two vectors are the same vector,
and it runs on the fit's input, so a calibrated comparison there would
have to be calibrated by the fit it is feeding.

Also drops seven dead keys from the optimizer's CFG_KEYS. Config keys
are read with a contains() check, so each one had been silently inert
since the field behind it was deleted -- a sweep varying one of them
measured nothing and reported an ordinary-looking F1.

TRACES: AR-024, AR-023 | SR-002

scripts/optimizer/replay.py

@@ -243,9 +243,25 @@ def build_minimal(annotations, movie, fps, cfg) -> dict:
             "anneal_sec": anneal, "actors": actors}
 
 
-CFG_KEYS = ["detector_conf", "prob_threshold", "match_prior", "match_threshold", "match_ratio",
-            "match_ratio_ceil", "track_alpha", "track_min_iou", "track_max_embed_dist",
-            "track_max_frames_missing", "cut_revive_sim", "cut_inactive_max_frames",
+# TRACES: AR-024 | SR-002
+# Keys the C++ Config actually still has. Seven names were removed here, all of
+# them accepted silently for months after the fields behind them were deleted:
+#
+#   match_threshold, match_ratio, match_ratio_ceil  — the raw-cosine accept
+#     fallback, retired with AR-024's enforcement.
+#   track_max_embed_dist, cut_revive_sim            — raw cosines, retired
+#     earlier by AR-024 when association moved into probability space.
+#   track_max_frames_missing, cut_inactive_max_frames — frame counts whose
+#     meaning changed with sample_fps, retired by AR-008/AR-013 in favour of
+#     track_extinction_sec.
+#
+# A sweep that varied one of these was measuring nothing, and reported a
+# perfectly ordinary-looking F1 for its trouble. kpn_bindings.cpp reads config
+# keys with a contains() check, so an unknown key is not an error — which makes
+# a stale entry here silently inert rather than loudly wrong.
+CFG_KEYS = ["detector_conf", "prob_threshold", "match_prior",
+            "track_alpha", "track_min_iou", "track_assoc_min_prob",
+            "track_extinction_sec",
             "extinction_sec", "anneal_sec"]