motion

Motion

Pulp's agent-first motion observability — sample view geometry / scalar values / scroll state over time, emit epsilon-bounded events with monotonic timestamps and burst framing, and route them to log lines + inspector events + JSONL fixtures. You are reading this skill because an agent needs to debug, validate, or reproduce a motion behavior.

When to rope this skill in

Trigger this skill the moment a user (or your own reasoning) describes any of these symptoms — don't reach for grep or git log, attach a trace:

• "this fade / slide / scale is too fast / too slow / starts late / ends early"
• "the knob value isn't reaching its target" / "what value at frame N?"
• "two elements drift apart during the transition"
• "scroll position jumps when I restore state"
• "imported design's motion doesn't match the source intent"
• "is this animation monotonic / does it overshoot / how long to settle?"
• "which animation is expensive and why?" → Path F (cost attribution)
• "reduced-motion path is broken" → Path B + assert under MotionPolicy
• "I want to scrub through a recorded fixture" → Path E (scrubber)

If the user says any of those, this skill applies. Don't suggest reading source; attach a trace and read the numbers.

Quick decision

Eight paths — pick by what you have, all eight terminate at the same motion::Coordinator so fixtures, scrubber, cost, reduced-motion, and provenance work identically across surfaces.

You have	Path	Tool
C++ fixture code + a node id + a scalar / geometry of interest	A — In-process trace	motion::Coordinator / MotionInspector fixture APIs; an admitted exact T1 host may inject ControlMotionExecutor
A ScrollView whose offset / visible rect / content size you need to observe	A — Runtime trace (scroll)	Trace.scroll_geometry(name, scroll_view, props) — emits contentOffsetX/Y, visibleRect*, contentSize*, scrollableMax*, inset*
A captured frame sequence (no app instrumentation available)	B — Visual analysis	tools/motion/visual/analyze_sequence.py
A previously recorded .motion.jsonl fixture	C — Replay + assert	motion::replay_fixture + motion::assert_matches
An interaction that drives the suspect motion	D — Input record + replay	motion::make_input_recorder + motion::replay_inputs
A fixture available to C++ host/test code (design review / CI triage)	E — Timeline scrubber	Direct MotionScrubber fixture load; canonical T1 scrub/play/pause is capped at 4,096 emitted events
"Which animation is expensive and why?"	F — Cost attribution	CostAttributor + make_render_cost_probe; canonical T1 returns at most 64 redacted finite samples
SwiftUI / UIKit / AppKit / iOS / macOS / AUv3 host code path	G — Swift native	View.pulpMotionTrace { Trace.* } / PulpMotionGeometryProbe
Jetpack Compose or Android View code path	H — Android native	Modifier.pulpMotionGeometry { +Trace.* } / View.pulpMotionTrace
Imported design + intent doc (e.g. "fade in 350 ms ease-out")	Both A + C	Record a fixture from the import, assert timing / monotonicity