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npub1cc3ha7z055mu0rwwu7806t2wt8mj3pvu0uv5mfp2c50dahaqhczshdalg6andTyler Longwell b0005dfc49 test(desktop): media-corpus classifier — media reflow is absorbed-class under w4a-gate-1

Answers Eva's leg question (thread 0a496379): are the felt −240-class media
reflow snaps on scroll-up momentum-class (killed by w4a-gate-1), walk-blind
(RO-path, a separate leg), or SHRINK-class (needs Max's pre-realization band)?

Adds a committed media corpus + classifier so the answer is reproducible from
the tip on a fresh build, mirroring the jitter/fast-classify arm.

Corpus (e2eBridge `mediaCorpusBody`, channel `media-corpus`, 400 rows, 8 kinds).
Row-height error is MEDIA reserve-vs-true mismatch, not text mis-estimation,
from three in-source-verified divergence sources:
- Link-preview cards reserved flat at PREVIEW_CARD=70 but rendered taller (GROW).
- Width-clamp images: CORRECT dims, but the estimator hardcodes MEDIA_MAX_WIDTH=384
  while render clamps to max-w-[min(24rem,100%)]; in a column < 384px the render is
  width-limited shorter than reserved (SHRINK, no lying dim, no decode timing).
- Dim-mismatch images in BOTH directions: overstate height (SHRINK) and understate
  (GROW), so the corpus CAN produce SHRINK — the GROW-dominant prediction is
  falsifiable, not baked in.
No dim-less band: that path is pinned to a fixed 256px box (reserve==mount) and
provably cannot reflow. Images use a tiny inline PNG data-URL so they realize
without network. (Eva verified the mechanism chain independently in mainbase
2cc0eb53.)

Fixture (upscroll-media.perf.ts) clones the fast classifier verbatim — probeLen
append-count join, SKIP/GROW/SHRINK/UNATTRIBUTED discriminator, dev, ±2-frame
firedNear admission — and only:
- navigates to channel-media-corpus, then narrows the viewport to 450px so the
  timeline column lands below 384px; asserts the measured media-container width
  is < 384 so the width-clamp SHRINK source provably bites (else it fails loudly);
- adds a MEDIA-REFLOW CENSUS: for every above-anchor reflow (|signedShift|>3px),
  whether it landed on a tracked in-band row and the worst (most-backward) rowMove
  across it, collapsing a persistent gate-held reflow's per-rAF re-measure into one
  run so a stuck 198px GROW isn't inflated into hundreds;
- asserts MEDIA LIVENESS (>=1 in-band reflow) so a zero-reversal result cannot be
  a dead corpus; drops the fast arm's decomposition self-test (that re-proves the
  gate mechanism the jitter arm already ratifies — off-charter here).

Result, fresh w4a-gate-1 build, BOTH engines, reproducible from this tip:
- Chromium: 0 reversals. 9 reflow runs (5 in-band), 7 GROW / 2 SHRINK. Every
  in-band reflow worstRowMove >= 0 — incl. a persistent +198 GROW held 170 frames
  at rowMove 0.0.
- WebKit:   0 reversals. 8 reflow runs (4 in-band), 6 GROW / 2 SHRINK. GROW runs
  gate-SKIPed to rowMove 0.0; SHRINK runs (−14.5) fired-and-corrected to +0.5
  (forward).

CLASSIFICATION: the media reserve-vs-true reflows are momentum/absorbed-class —
the landed w4a-gate-1 fix + correction eat them; not one renders a felt backward
snap on either engine. NOT walk-blind, NOT needing Max's pre-realization band.
Neither Dawn's GROW-likely nor Eva's SHRINK-likely prediction "wins" in the felt
sense: both classes fire, both are absorbed.

HONESTY BOUND: this is a deterministic proxy for media reflow, not a claim to
reproduce Tyler's exact frames. His live trackpad still owns acceptance; #1662
stays draft.

Co-authored-by: Tyler Longwell <tlongwell@block.xyz>
Signed-off-by: Tyler Longwell <tlongwell@block.xyz>

2026-07-09 02:09:16 -04:00