mandelbrot/docs/black-regression-rollback/IMPLEMENTATION.md

Black regression rollback

Intent

A previous deep-zoom root-cause attempt introduced a broad f32 perturbation error propagation guard and progressive publication of partially resolved FAST fields. User testing showed this regressed rendering severely: most of the viewport could become black.

This pass is deliberately a rollback, not another numerical heuristic. It restores the pre-regression FAST perturbation and publication behavior while keeping the later removal of adaptive-primary hysteresis.

Removed from the failed attempt

1. FAST primary propagated errScaled acceptance/rejection logic.
2. Low-part delta rewrite that was bundled with that unvalidated FAST change.
3. Per-strip publishNumericProgress() during FAST primary.
4. Per-batch publishNumericProgress() during sparse correction.
5. Same-reference DS correction pre-pass added solely to service the broad FAST guard.
6. Publication of a FAST primary before numerical failure repair is complete.

Preserved

• No adaptive-primary hysteresis.
• Series approximation remains disabled.
• Sparse active state, dynamic references, CPU fallback and the prior supported removal pass remain.
• FAST frames are withheld until numerical failures are repaired, so UNKNOWN alpha=0 pixels are not intentionally exposed as a fresh-frame partial image.

Validation

• node tests/regression.mjs: PASS.
• 19 WGSL kernels pinned by SHA-256.
• JavaScript syntax is checked by the regression suite.
• Static invariants:
  • no ADAPTIVE_PRIMARY_HYSTERESIS
  • no stabilizeAdaptiveInitialChoice
  • no lastPrimaryPolicy
  • no nearbyAdaptiveViewSafe
  • no failed-attempt progressive FAST publication
  • no same-reference-ds-guided-precision
  • deferPrimaryColor=deferColor||fastExtended

Scope / remaining issue

This rollback fixes the newly introduced near-all-black regression. It does not claim that the earlier deep-view reference-dependence / coordinate-shift instability is solved. That issue must be addressed from numerical validity (perturbation/rebasing/reference-domain correctness), not from view-history hysteresis.