docs(overhaul): bound ramp building-bridge diagnostic

docs/research/2026-09-01-overhaul/c1a-building-bridge-diagnostic-contract.md

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+# C1a — explain the ramp's fourth cell without changing production
+
+Lead bounded diagnostic2026-09-05. C1a stopped before golden: full publication
+gives [F4180112,F4180113,F4180009,F4180114], seven ordered clip-required parts
+in each cell (28 entries). Omitting only CacheBuildings restores the old
+partial-engine comparator's three cells/21 entries. Both test-only diagnostic
+edits were restored to SHA256
+7B5A14F61ED22614DF34F35EEBA87CE3A95150796FDE1683B4DF041B75FD6400.
+No golden or production change is accepted by this contract.
+
+## Lead-confirmed distinction
+
+Root read actual BuildShadowCellSetFromParts: its outdoor arm calls the
+sphere-only CheckBuildingTransit. The real part-array retail call is NOT that
+sphere overload0052C5D0: CBuildingObj006B52A0 calls0052C680. That overload
+uses the reciprocal portal's sphere-side test, transformed part box versus
+portal plane, then destination box containment. This is ALREADY REGISTERED
+AP-159 remainder1, not a new unregistered regression. Root read all of
+2026-08-07-ap159-pseudocode.md and all507 lines of C4 closeout handoff.
+Do not fix AP-159 or its separate one-ULP tie under this test-only diagnostic.
+
+Root independently section-mapped paired C:/Turbine/Asheron's Call/acclient.exe,
+whole SHA256006FFEADC5D679C871497112A5BD1F87714D0E273E2166BAE5052DDE369297B1.
+The actual call006B52E5 (E8 96 73 E7 FF) targets0052C680. Its box calls and
+`83 F8 03 / 74 04 / 3B C5 / 75 32` at0052C799 confirm crossing OR SAME side;
+the indoor exiting-cell helper's opposite-side predicate must not be reused.
+Window hashes:00510FC0/101=20964C49EEA3AA24479F5BCF827FE5AA676558744B6C5FF4740D5CF62F73F55E;
+00533840/46=2C12F01D6173CCC8A8DE6A5A36AFBDD4E720B89107CFD02CB1F48C06C8F48D96;
+00534080/18=E133D325DD480F77CBF6F80817313077046FFD42BD23555EDDCFF3762FECF310;
+006B52A0/92=DD9E243A61B394F88B94896509E220BC6614FD46FEE59069A5431080A45665B2;
+0052C680/393-byte window=B10CC0B0206C68A8B469B1564FA8AF7A04A4EC5AFB21588B5C6F738DD50EBA85.
+
+## Bounded question and output
+
+In the existing frozen s5-c1a-geometry scratch, extend ONLY the new test class
+with one explicitly Purpose=Diagnostic fact, reusing the complete publication
+setup. Keep the original semantic assertion and placeholder golden unchanged.
+Before publication-derived assertions, inspect the actual ramp owner's retained
+whole part array and existing BuildFloodPartBoxes/BuildBspPartSpheres producers;
+test-local reflection is allowed, copied registration dispatch is not. Read the
+actual cache.GetBuilding(F4180009) and each real reciprocal portal/destination.
+
+For each ramp part and the0114 bridge, report source ID, actual sphere/box,
+destination transform, reciprocal portal index/side/plane, signed sphere-plane
+distance and padded radius, transformed box min/max, exact eight-corner side
+result, box containment and current sphere containment. Evaluate0052C680's
+finite-input predicates from the paired bytes independently; preserve inclusive
+cheap-reject ties and the strict which_side epsilon semantics. Use existing
+flat containment/box transform primitives; disclose any shared primitive and
+check that no sample sits on its registered epsilon tie. No new production
+traversal, synthetic cell membership or asserted retail result from a label.
+
+Return the exact data answering whether ANY real part admits0114 by the retail
+box bridge, versus the current sphere bridge; also whether0114 can enter by
+another already-present cell's normal box traversal. Do not claim an entire
+retail-world CELLARRAY solely from one bridge predicate. No automatic contract
+amendment to four cells/28 entries. The lead decides whether the earlier fact
+was only an incomplete fixture assumption or this sample exercises AP-159.
+
+Run one bounded diagnostic after Release green, both clients absent; preserve
+TRX/output, exact source hashes and the original failing C1a record. Stop and
+return if another prerequisite is missing. No other tests, commits, clients,
+agents, perf work, register edits or renderer fixes. Pause immediately for
+#476/#478/#479/#480 graphical work; owner FPS deferral remains binding.