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Xuanru Li
e710a1686f
## What it catches A gauge needle / clock hand / dial pointer / radar sweep that rotates about the **wrong pivot** — the recovered center-of-rotation sits far from the dial hub (e.g. `transform-origin` at the needle base or SVG element edge instead of the dial center). Visually the needle "wobbles" or orbits off-axis instead of sweeping cleanly about the hub. This is a genuine gap in the current checks: `rotation_pivot_drift` (#2741) provably **cannot** catch it — a correct sweeping needle's bbox-center orbits identically to a broken one, so only a **dial-hub reference** distinguishes them. This is the separate hub-referenced check that analysis called for. ## How it works - Sampler maps 2 material endpoints per frame via `getScreenCTM` (honors the actual rendered transform, independent of `svgOrigin`). - Resolves the dial hub = shared center of the modal set of static concentric circles, or the arc-center of the largest static near-circular path (Kasa circle fit). - Fits a circle to the endpoint trajectory to recover the true center-of-rotation; flags drift `> 0.35 * pointer_length`. One warning per hub. - Never fires without a resolvable hub. Walks the rotation reference to the composition root (not the `<svg>`) so a pointer rotated by a `div` ancestor is measured correctly. - Multi-body guard: `>= 2` bodies at distinct angular positions on one hub = orbit/atom system, not a dial → suppressed. ## Corpus evidence (autonomous geometry-fuzz run, 81 fuzzed diagrams) - **7 / 7 true positives, 0 false positives across all 81 samples.** - Assigned TPs: fuzz005, fuzz017, fuzz032. Bonus TPs: fuzz044, fuzz056, fuzz068, fuzz080. - **The Gemini-3.6 video-judge itself MISSED all 4 bonus TPs** (`vlm_has_defects: false`) — the deterministic hub-reference check beats the VLM on this defect class. - FPs driven to 0 by the two principled guards above: fuzz016 (planet arc rotated by a `div` ancestor) cleared by root-walk; fuzz055 (atom) cleared by the multi-body guard. - fuzz080 reads as a false positive to the connector check but is a true positive here — confirms the architectural boundary between the two checks is drawn correctly. ## Validation - Autonomous Gemini-3.6 **video**-judge fuzz run to surface candidate defects, then a **deterministic FP sweep** across all 81 rendered compositions (not VLM-gated — code inspection is the arbiter, since the VLM both over- and under-calls this class). - 9 unit tests (`checkPipeline.offPivotRotation.test.ts`) + full check suite pass; `bun run build` green. 🤖 Generated with [Claude Code](https://claude.com/claude-code)