audit building checkpoints and preserve production gate

docs/reviews/2026-08-09-ai-assisted-checkpoint-review.md

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+# AI-assisted building checkpoint review — 2026-08-09
+
+## Outcome
+
+GeoIntel still runs the proven active building checkpoint. A new 12-epoch GPU
+fine-tune was rejected because it reduced mAP and introduced three detections
+on pure-background validation tiles. A wider checkpoint comparison identified
+the older `reviewedexp6` checkpoint as the strongest non-protected validation
+challenger, but it was not promoted.
+
+The production runtime was verified healthy after the review with:
+
+- image `geointel-all-in-one:0209167cfd37-wip25e7de62cde9-ai`;
+- active weights SHA-256
+  `a9088b8491dfae36694b53e9e9406cb4e3511d334a5712fa34f75078a47759c1`;
+- NVIDIA RTX 4080 SUPER inference; and
+- the existing Kempen validation-scope enforcement.
+
+## Metric review
+
+The checkpoint matrix used only the 36-image non-protected validation split:
+18 positive images and 18 declared pure-background images. The active model
+measured mAP50 `0.345426` and mAP50-95 `0.140719`. The `reviewedexp6`
+challenger measured `0.368177` and `0.155438` respectively.
+
+At confidence `0.25` and match IoU `0.25`, the active model measured F1
+`0.633058`; the challenger measured `0.642599`. Both produced zero detections
+on the 18 pure-background validation tiles at this threshold. At confidence
+`0.15`, however, the challenger still reproduces the two background detections
+that blocked its July promotion.
+
+## Visual review
+
+The error sheets were inspected at original resolution. Green denotes a
+matched prediction, red a false positive, magenta a false negative and yellow
+the reference footprint. The challenger reduces missed-building pressure,
+particularly in Westerlo, but dense Turnhout tiles still show extensive
+low-IoU disagreement.
+
+A major part of that disagreement is not safely resolved by additional epochs:
+the aerial image shows a roof while GRB GBG represents the building footprint
+at ground level. Perspective, roof overhang and acquisition-date differences
+can therefore shift visible roofs relative to the authoritative footprint.
+These cases remain review candidates; they were not relabelled automatically.
+
+This is explicitly an AI-assisted inspection, not a signed human review. No
+human-review gate or label-acceptance record was fabricated.
+
+## Fail-closed production decision
+
+The existing seven-zone API benchmark was started with the challenger at
+confidence `0.25`, but the current provenance gate stopped it before model
+loading. The historical checkpoint predates the required neighbouring
+`.geointel-model.json` runtime manifest and its governed database snapshot.
+That control was not bypassed and no production inference from the unbound
+checkpoint was accepted.
+
+The challenger may only be reconsidered after its original training evidence
+is migrated without invented lineage, followed by the same seven positive
+zones and three pure-background controls. Until then, the active checkpoint is
+the only safe production choice.
+
+Machine-readable hashes, metrics, paths and the exact decision are in
+`artifacts/evidence/accuracy/model-training/20260809-v68-checkpoint-and-threshold-review.json`.