tracking: make BedSim the single Bedrock movement physics oracle

[HashimTheArab]

Goal

Make BedSim the single deterministic Bedrock player-movement physics oracle used by Oomph and Baritone.

This issue tracks BedSim-owned physics and contract work. It does not move packet authority, correction policy, or path planning into BedSim.

Easiest-to-hardest order

This is an implementation-difficulty ranking, not a priority ranking. Later items depend on contracts established by earlier ones.

1. Observability and focused regression coverage

   • Add deterministic traces, stage markers, confidence labels, and golden fixtures.
   • Add property/fuzz tests for collision and state transitions.
   • Fix small, isolated parity issues such as step grounding and already-known block constants.

2. Existing block semantics

   • Complete and validate current ice, soul, slime, bed, web, berry-bush, powder-snow, and climbable paths.
   • Resolve honey and scaffolding behavior.
   • Add mud, snow-layer, door, gate, trapdoor, and variant-shape semantics.

3. Effects, equipment, and item-use modifiers

   • Add speed/slowness and movement-affecting attribute modifiers.
   • Track effect duration, stacking, expiry, and amplifier semantics.
   • Replace the generic item-use clamp with per-item-category rules.
   • Synchronize equipment/enchantment state with the initiating tick.

4. Pose, geometry, and input contract

   • Separate authoritative, client-observed, and policy-only state.
   • Add eye position, pose transitions, riding dimensions, support shape, and interaction rotation.
   • Expand input beyond the normalized move vector: raw/analogue vectors, camera orientation, tick, delta, input mode, play mode, interaction model, item actions, block actions, and vehicle data.

5. Fluid completeness

   • Validate water/lava immersion, surface, exit, gravity, drag, flow, and side-closure rules.
   • Validate bubble-column source, overlap iteration, surface, sneak, and vehicle behavior.
   • Complete Depth Strider, Dolphin's Grace, waterlogging, and fluid/effect stacking.

6. Special travel modes

   • Implement creative and spectator flight equations and vertical input.
   • Validate full Elytra start/stop, collision, landing, equipment, firework boost, and damage edge cases.
   • Complete Riptide eligibility, duration, collision, mounted behavior, and external-motion interaction.

7. Revisioned world and collision model

   • Replace ad-hoc lookups with a revisioned snapshot contract.
   • Support loaded/unknown results, entity shapes, moving shapes, and world bounds.
   • Validate float32 rounding, collision epsilon, axis order, tie-breaking, substeps, penetration, high velocity, and pathological geometry.
   • Add ordered moving-piston shapes and entity collision behavior.

8. External motion and vehicle state

   • Add an ordered, one-shot event queue for knockback, explosions, projectiles, hooks, SetActorMotion, entity pushes, vehicles, and teleports.
   • Represent replace-vs-add semantics and event acknowledgement.
   • Add mount/dismount state and prevent simultaneous player/vehicle integration.
   • Preserve fall state and damage-relevant transitions.

9. Cross-repository migration

   • Replace duplicate physics formulas in Oomph with a BedSim adapter.
   • Route every Baritone rollout through BedSim.
   • Keep rewind/replay and authority policy in Oomph, and planning/execution policy in Baritone.

Ownership

• BedSim: deterministic movement state transitions, travel physics, collision, poses, fluids, block effects, external-motion application, and physics traces.
• Oomph: PlayerAuthInput decoding, tick/latency handling, acknowledgements, authority modes, corrections, history/replay, and server-event ingestion. See oomph#154.
• Baritone: planning, goals, costs, parkour decisions, terrain actions, and executor policy. See baritone#22.

State and provider contract

• Separate authoritative, client-observed, and policy-only state.
• Add complete pose/geometry state: eye position, pose transitions, riding state, dimensions, scale, support shape, and interaction rotation.
• Add complete attributes, effects, equipment, item-use, and timer state with source/expiry information.
• Expand per-tick input beyond the normalized move vector: raw/analogue vectors, camera orientation, tick, delta, input mode, play mode, interaction model, item actions, block actions, and vehicle data.
• Replace ad-hoc world lookups with a revisioned snapshot contract.
• Support loaded/unknown results, liquid layers, entity shapes, moving shapes, and world bounds.
• Add deterministic trace output for intermediate values and stage ordering.

Ground, air, poses, and collision

• Validate exact modifier and tick ordering for ground/air acceleration, sprint, sneak, item use, effects, and friction.
• Validate exact float32 rounding, collision epsilon, axis ordering, tie-breaking, and substep behavior.
• Complete standing, sneaking, swimming, crawling, gliding, and riding dimensions and headroom transitions.
• Fix or validate grounded state after step-up transitions; see #5.
• Complete partial-shape support and moving/entity collision ordering.
• Add penetration, high-velocity, pathological-geometry, and unloaded-world fixtures.

Block and inside-effect matrix

• Resolve the honey movement stratum; see #3.
• Resolve scaffolding climb, descend, stand-on-top, and fall-through behavior; see #4.
• Validate soul blocks, ice variants, slime, beds, webs, honey, powder snow, berry bushes, mud, and all climbable variants.
• Add stateful support for snow layers, doors, gates, trapdoors, stairs, slabs, panes, fences, walls, and waterlogged shapes.
• Add moving piston shapes and ordered piston/entity pushes.
• Keep contact damage, fall damage, oxygen, and hazard effects separate from velocity physics but expose the required state/events.

Fluids and special travel

• Validate water and lava immersion, surface, exit, gravity, drag, flow, and side-closure rules.
• Validate bubble-column source, overlap iteration, surface behavior, sneak behavior, and vehicle behavior.
• Complete Depth Strider, Dolphin's Grace, waterlogging, and fluid/effect stacking.
• Implement creative and spectator flight equations and vertical input.
• Validate full Elytra start/stop, collision, landing, equipment, firework boost, and damage edge cases.
• Complete Riptide eligibility, duration, collision, mounted behavior, and external-motion interaction. The mounted launch guard is tracked in PR #12.

Effects, equipment, and item use

• Add speed/slowness and other movement-affecting attribute modifiers.
• Track effect duration, stacking, expiry, and amplifier semantics.
• Model item-use categories separately instead of relying on one generic clamp.
• Synchronize equipment/enchantment state to the same tick as the initiating input.
• Keep Soul Speed, Swift Sneak, Depth Strider, Riptide, Elytra, boots, and powder-snow behavior in the movement contract.

External motion and authority-neutral events

• Add an ordered, one-shot motion-event queue for knockback, explosions, projectiles, hooks, SetActorMotion, entity pushes, vehicles, and teleports.
• Represent replace-vs-add semantics and event acknowledgement explicitly.
• Add mount/dismount state and prevent simultaneous player/vehicle integration.
• Preserve fall state, bounce, damage-relevant transitions, and correction-safe external events.
• Keep rewind/replay policy in Oomph while making BedSim deterministic for a supplied event sequence.

Validation

• Add golden trajectories for ground, collision, poses, fluids, blocks, effects, Elytra, and Riptide.
• Add differential fixtures for tick-order candidates and edge cases.
• Add property/fuzz tests for collision and state transitions.
• Require every promoted constant to have a fixture and confidence classification.
• Replace duplicate physics formulas in Oomph and Baritone with BedSim adapter calls.

Definition of done

BedSim can deterministically reproduce every supported player travel mode from a complete tick input, revisioned world snapshot, equipment/effect state, and ordered external-event list. Oomph and Baritone consume that result instead of maintaining competing movement formulas.

Parity audit follow-up — 2026-08-20

The latest full movement pass produced the following concrete status.

Corrected in PR #14

• Apply bubble-column impulses once per overlapping contact, preserve exact surface classification, and clear fall distance.
• Use uncapped 0.75 bed restitution.
• Reject shallow liquid cells whose surface does not reach the movement contact box.
• Apply grounded Riptide vertical compensation using water/head state.
• Preserve scaffolding descent at -0.15, skip ordinary gravity, and clear fall distance.
• Clear fall distance on climbable contact and qualifying honey side slides.
• Add honey 0.8 friction and frosted-ice 0.98 friction to built-in semantics.
• Honour solid faces for same-liquid flow through waterlogged non-stair blocks.
• Reject mounted movement instead of integrating it as ordinary on-foot movement.
• Check the swept movement area rather than only the current chunk.

Still needs a narrower contract or dedicated implementation

• Define exact swimming-contact retention separately from optional anticheat hardening. The current grace window is intentionally not a strict movement-oracle rule.
• Replace generic consuming/sneaking input clamps with exact per-item and Swift Sneak movement stages, including tick ordering.
• Complete liquid material permeability for non-liquid neighbours; face closure is now exact for same-liquid waterlogged contacts, but the world contract does not expose every material rule.
• Implement vehicle-specific travel and mount/dismount state instead of stopping at the current mounted outcome.
• Implement creative/spectator flight and supported no-clip transitions.
• Narrow the complete pose/riding dimensions and vehicle-controlled input contract.
• Add externally captured differential trajectory fixtures for ground, collision, fluids, blocks, Elytra, Riptide, and vehicles.