3f2b2dc3ed
The probe design: fires only on the stuck-tick predicate (zero XY yield against nonzero request), printing per-attempt phase outcomes, step-up/ step-down verdicts, every ValidateWalkable branch with its flag guards at the SetCollisionNormal site, and the AdjustOffset pair — the collN=(0,0,1) fingerprint's producer names itself. Trap inventory from the week's do-not-retry ledger attached so the eventual fix cannot stumble into a retail-faithful mechanism. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
60 lines
3.2 KiB
Markdown
60 lines
3.2 KiB
Markdown
# #345 mechanism-session contract — who eats angled input on the steep-slope approach?
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**Date:** 2026-08-08. **Order:** after #344 lands. **This is an
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instrumentation session, not a fix session** — the fix contract gets written
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from the capture, not before.
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## Evidence in hand (do not re-derive)
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- `uphill-45deg-capture.jsonl`: 838 uniform stuck ticks — request ~0.23 m/tick
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at 45° to the face, **result byte-identical to input position**,
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`collisionNormalValid=True` with **`collN=(0,0,1)`** (straight up),
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`slidingNormal=(0,0,0)`, carried contact = the ~6.8° approach terrain
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`(-0.083,0.083,0.993)`, `transient=0x3` (Contact|OnWalkable).
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- `uphill-slide-capture.log`: the steep face itself was reached only 18
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times; every reach took branch2 cliff-slide with a healthy applied
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constraint. The eater is UPSTREAM of the face.
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- `uphill-AB-precampaign.jsonl`: identical 0.0%-yield signature on the
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pre-campaign binary — **pre-existing**, Campaign S exonerated.
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- Ruled out by measurement: the #331 sliding absorb (no latch), cliff-slide
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degeneracy (#32 fixed, visibly healthy), all Campaign S landings.
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## The one probe this session builds
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A per-tick TRANSITION PHASE TRACE, `ACDREAM_DUMP_TRANSIT_FAIL=1`, firing ONLY
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when a resolve returns zero XY displacement against a nonzero XY request
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(the stuck-tick predicate — self-selecting, so a normal session prints
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nothing). For each such tick, one line each for:
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1. every `TransitionalInsert` attempt: attempt #, phase reached
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(env/building/objects), each phase's TransitionState, and on Collided the
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colliding polygon's plane normal + which BSP/terrain source produced it;
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2. every step-up entry and its step-down verdict (reuse/extend
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`ACDREAM_DUMP_STEPUP`'s existing lines — they already print the input
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normal and the landing verdict);
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3. every `ValidateWalkable` outcome on the tick: dist, waterDepth, which
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branch (resting / below-push / CheckWalkable-fail), and BOTH flag guards
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(`oi.Contact`, `sp.StepDown`) at its `SetCollisionNormal` site — the
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`collN=(0,0,1)` fingerprint most plausibly comes from a
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`SetCollisionNormal(groundNormal)` *somewhere*, and this names which.
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4. the final `AdjustOffset` input/output pair for the tick.
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House rules: lives in `PhysicsDiagnostics` (rule 5), self-selecting trigger,
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zero cost when off, mover id on every line
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(`feedback_probe_identity_attribution`).
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## The session
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Build with the probe → the user repeats the exact 45° protocol (~1 min) →
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read the trace → the failing phase + normal source IS the mechanism → write
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the fix contract from it, citing the retail counterpart
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(grep-named-first: `CTransition::transitional_insert` family, the step-down
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refusal path, `validate_walkable`'s collision-normal writes — all already
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mapped in this repo's pseudocode docs).
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## Known trap inventory for the eventual fix (from this week's do-not-retry ledger)
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The #331 absorb is retail-faithful — whatever the fix is, that
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characterization pin must stay green. The #32 setter split must not be
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re-latched. AD-65's snap arm is byte-anchored. The step-up chain's
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`stepDownHeight = oi.StepUpHeight` oddity is retail-verbatim (#338's
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research). Do not touch any of these on a theory.
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