[nicolas-maman]

All the remaining animation work in one pull request, in this order: the README, docs and images (#902), a character component (#903), then natural motion (#858, #859, #861), with the other milestones alongside. #891 landed the pipeline's first layers and closed its milestones before their lists were met; they are reopened, each with its remaining work written out. A box is ticked only when its issue's own list is met on this branch.

Issues

• Closes README, docs and images that show what ae3d is for #902: README, docs and images that show what ae3d is for
• Closes A character component: a moving, aiming, reacting person in a few lines #903: a character component, a person in a few lines
• Closes M0 ground truth: a real human in CI (Quaternius mannequins, UAL clips), motion metrics, a viewer #854: M0 ground truth: a metrics module, the viewer, the cycle test (motion: the animation and physics cycle tested end to end on a real person (idle, walk, run, struck, down, up, walk), held to how a person moves #850)
• Closes M1 skeleton, pose, clips, retargeting and root motion (L0, L1) #855: M1: up to 256 bones (skinning's 96 cap)
• Closes M3 IK and constraints: two-bone with limits, FABRIK, full-body IK, foot placement, aim, hand IK (L3) #857: M3: one foot system, a reach across the trunk (motion: a hand reaching across the body stops short; the two-bone reach doesn't route the forearm around the trunk #700), footsteps onto treads (Feet land across stair edges: place footsteps onto treads #897), what still reads wrong (Legs and shoulders that read wrong in the showcase: the female's idle, the sprint's shoulders #898), the walker's drift (The captured walker drifts off its line: 4 cm, then 58 cm over 15 out-and-backs #900)
• Closes M4 physics asset and physical animation with per-body weights (L4) #858: M4 physics asset and physical animation (engine: physics steps before motion in each fixed step, so every followed body chases last step's rig #845, physics: fitted ragdolls are 25 to 100% thicker than the figure: capsule radii scale the reference's, not the mesh's flesh #779, physics: the box man stands with all its weight on its right foot (844 N against 0) #777, physics/motion: adopt aephysics ankles (#152 landed in 8c7f397): feet as bones, soles flat in a crouch #709, motion.hold: the drawn hands are on the grips but the forearm bodies are 13 to 50 cm off them (held off by the thighs) #843, Muscles: a 0.8 m/s push from the side fells a standing POWERED figure that the servo holds by stepping #821, motion: hold, eat and drink standing and walking, not only seated (a camp drinks at a barrel) #842)
• Closes M5 ragdoll and get-up from a pose snapshot into a matched clip (L5) #859: M5 ragdoll and get-up (get-up: the drawn feet go up to 8.8 cm into the ground; test_get_up holds only the bodies #841, get-up: two knocked figures getting up side by side are drawn inside each other for up to 2 s #835, Siltreach's stand-up hand-off and seat)
• Closes M6 migration onto the animation pipeline; old writers retired #860: M6 migration onto the pipeline, Siltreach moved across
• Closes M7 behaviours on physical animation, optional (L6) #861: M7 behaviours (Motion: animation as the reference, physics as the body (compliant muscles with feedforward, balance through the legs, behaviours as layers) #790, motion: no weight shift; a standing figure can't carry its weight over one foot before lifting the other #705, motion: a POWERED figure doesn't follow its animation's footwork; a stance change drags the legs instead of stepping #767, motion: a POWERED figure's feet slide along the ground while no step is under way, 50 to 80 cm a shove #778, motion: shoved again and again, standing figures drift off their spots, 7 cm a cycle and 14 m in an hour of the showcase #847, motion: after a stagger a figure can stand leaning 0.2 to 0.37 rad for seconds, then stumble with nothing touching it #718, motion: a hard side stagger turns the figure 10 to 45 degrees off its heading; test_stagger's 10-degree check (#689) passes by chance #752, ae3d.motion: a figure on the ground cannot crawl -- a down figure keeps 4% of its arm muscle, and at full muscle its arms move it 0.07-0.18 m in 10 s (the pull never takes the chest's weight) #625, What a game's day asks of a figure: sit, lie down, eat, kneel, work, carry, fight, each with the number it is judged by #825)
• Closes M8 crowds and animation LOD #862: M8 crowds and animation LOD (A crowd's instances take a position and a yaw but no scale of their own: every person one height #766)
• Closes Epic: a AAA animation system any game can use (pose pipeline, clips, blending, IK, physical animation, ragdoll transitions) #853: the epic

In this push

Handing a figure between writers, which Siltreach needs to put its settlers on the pipeline while motion sits them down (part of #860):

• An animator freed while the engine runs leaves the engine's loop. It used to stay in it, and the pose phase called it on freed memory.
• A behaviour removed mid-frame no longer shifts the list under the loop walking it: its slot is emptied and the holes close at the next frame. With the old removal, an animator freed in the pose phase left the next figure unposed for that frame (its clock 20 frames on of 21; now 21 of 21).
• animator.pause / resume: paused, it writes none of the figure's joints (what another writer drew stands, 3·10⁻⁶° off). Resumed over 0.3 s, it eases out of that pose: the fastest joint turn is 9.7 rad/s against the clips' own 8.3 plus the easing's 6.7. Taken back at once, it snaps at 60.9 rad/s. ikrig.feet_reset lets go of locks held from before the pause.
• animator.share_take: one take retargeted once and shared by every figure on a rig. It plays alike on two figures, outlives their animators, and is refused to a rig of another size.

test_anim_pipeline: 85 checks, all passing.