food_chain/docs/reported-view-bugfix/IMPLEMENTATION.md

Reported deep-view artifact investigation and fix

Date: 2026-09-29

Purpose

Investigate the reported URL state that displayed large yellow/black geometric regions and sometimes an almost entirely black frame. The production source before this pass is preserved as index.before.html. The fix is intentionally narrow: do not restore previously removed expensive work unless evidence points to it.

Reported state:

• bits: 273
• re: -15958919693715511752069626580195447581643016686947107473855747766272418724092005269
• im: 3884297345146583343999140717464554120497735725078805729405733239132420430333375719
• span: 35679807704506851074208413824041445358585910697267232113437882789120793
• palette: 0
• cycle: 0.008
• shift: 0.18
• base iteration: 350, adaptive enabled, quality high

At 1108×1582, the adaptive initial target for this region is approximately 1536 iterations and the renderer takes the fast-extended path.

Root cause 1: unsafe series jump

The integrated fourth-order series approximation was enabled for the reported view. The fast-reference worker selected:

• reference pixel ≈ (69.5, 922.5)
• reference length: 1285
• series jump: 773
• fourth-order coefficient components up to approximately 2.35e38, close to the maximum finite f32 magnitude

The series validity test checked truncation terms in unscaled orbit space, but did not bound the intermediate scaled f32 polynomial products used by WGSL. At screen-domain deltas away from the selected reference, a4 * d^4 can overflow before the later ldexp rescales the term.

The reproducible probe in experiments/reported-view/analyze.mjs evaluates the exact worker output from the preserved pre-fix source. On a 32×32 viewport sample grid:

• pre-fix: 290 / 1024 series starts produce a non-finite fourth-order intermediate
• fixed: 0 / 1024, because series acceleration is disabled

This is sufficient to generate RANGE failures and black unknown pixels. Separate CPU surrogate comparison also showed large escape-iteration deviations in this state, so merely adding an overflow clamp would not make the current jump trustworthy enough for publication.

Fix

SERIES_APPROXIMATION_ENABLED=false now disables production series construction. The code remains present for future work, but the fast-reference worker emits jump=0 and zero coefficients.

Re-enabling series should require at minimum:

1. viewport/reference-relative bounds on all scaled polynomial intermediates,
2. a propagated truncation/rounding error bound carried into the perturbation path,
3. a corpus test that checks false escapes, not only absolute approximation error,
4. strict handling when the selected reference is off-center.

Root cause 2: publishing numerical failures before repair

The FAST primary frame was colored and presented immediately after the primary perturbation pass, before recoverNumericalCostOrdered() repaired REFERENCE_END, RANGE, and other numerical failures.

COLOR_WGSL writes alpha zero for FIELD_UNKNOWN. Therefore an early provisional frame can appear:

• black when there is no usable history,
• mixed with reprojected old colors when stable history exists,
• as large geometric regions reflecting reference validity / numerical-failure domains rather than Mandelbrot geometry.

Fix

For fast-extended:

• primary colorization is deferred (deferPrimaryColor = deferColor || fastExtended),
• unresolved statistics are read,
• numerical failures are repaired,
• only then is the first provisional recolor/presentation allowed.

Direct rendering keeps its existing provisional behavior.

What was not reverted

The previous FAST coverage-repair dispatch was not restored. The existing full-frame unknown reduction and final invariant still detect untouched reason-0 pixels, and prior A/B coverage tests found no holes. The reported state produced a concrete series failure mechanism, so restoring an O(pixels) repair pass would treat the symptom without addressing the cause.

Other removal-pass optimizations are unchanged.

Verification

Regression

node tests/regression.mjs

Result: PASS, 19 WGSL kernels.

Additional regression pins were added for:

• SERIES_APPROXIMATION_ENABLED=false
• FAST primary-color deferral via deferPrimaryColor=deferColor||fastExtended

Reported-view worker probe

node experiments/reported-view/analyze.mjs

See results.json.

Key result:

Metric	Before	After
reference length	1285	1285
series jump	773	0
non-finite series-start samples	290 / 1024	0 / 1024

Existing integrated CPU benchmark

node experiments/integrated_bench.mjs

Completed successfully. The series section now reports jump 0 at all tested spans, while periodicity, sparse active state, multi-reference, and CPU fallback tests continue to run.

Browser/WebGPU smoke

tests/browser_smoke.mjs could not run because its expected external Chromium remote-debug endpoint at 127.0.0.1:9333 was not available in this environment. This is an environment limitation, not a test assertion failure. Actual WebGPU visual confirmation of the supplied URL remains the most important local-device check.

Build summary

See build-summary.json.

• before SHA-256: e69b91ead027927d977a065d27d9e27629110122df20aa470eab877e23f77ac7
• fixed SHA-256: c53c0dc4cb9fa2d2046aaa12ef03cc79c61a710b0c8db36dea1a87be2d9aedd8
• HTML size delta: +396 bytes (comments/guard and publication-order logic)

The WGSL kernels themselves were not changed in this pass, so kernel hashes remain pinned to the prior 19-kernel set.