fix(motion): jump direction, AutoPos cadence, backward/strafe wire & anim

Closes a multi-bug knot in player motion outbound + remote inbound,
discovered via cdb live trace of retail (2026-05-01) and follow-up
visual verification.

Outbound (acdream → ACE):
- JumpAction velocity is BODY-LOCAL, not world (per retail
  CPhysicsObj::get_local_physics_velocity at 0x00512140 + ACE
  Player.HandleActionJump's set_local_velocity call). Was sending
  world; observers saw jump rotated by player yaw.
- Capture get_jump_v_z BEFORE LeaveGround() — the latter resets
  JumpExtent to 0, after which get_jump_v_z returned 0. Was sending
  Z=0 in every JumpAction.
- Backward/strafe-left jumps lost their horizontal velocity because
  LeaveGround → get_state_velocity returns zero for non-canonical
  motion (faithful to retail's FUN_00528960; retail papers over via
  adjust_motion translation, not yet ported). Compute the correct
  body-local launch velocity from input directly and push it back
  into the body so local prediction matches what we send.
- IsRunning HoldKey was gated on `input.Run && input.Forward`, so
  strafe-run and backward-run incorrectly broadcast as walk to
  observers — ACE then animated walk + dead-reckoned at walk speed
  while server position moved at run speed (visible as observer
  lag). Fixed: gate on any active directional axis.
- AutonomousPosition heartbeat 0.2s → 1.0s to match holtburger's
  AUTONOMOUS_POSITION_HEARTBEAT_INTERVAL and the ~1Hz observed in
  retail trace.
- Heartbeat now fires while in-world regardless of motion state
  (matches holtburger + retail's transient_state-based gate, not
  motion-based). Pre-fix the at-rest heartbeat was suppressed.

Inbound (ACE → acdream, remote retail player):
- Remote backward walk arrives as cmd=WalkForward + speed=-1.91
  (retail's adjust_motion'd form). Two bugs were stacking:
  1. AnimationSequencer fast-path returned without updating when
     sign(speedMod) flipped while motion stayed equal — kept playing
     forward at old positive framerate. Fixed: bypass fast-path on
     sign change so the full re-setup runs.
  2. GameWindow clamped negative speedMod to 1.0 when stuffing
     InterpretedState.ForwardSpeed, making get_state_velocity
     produce forward velocity. Fixed: pass speedMod through verbatim
     so the dead-reckoning body translates backward.

Issue #38 filed: 30Hz physics tick produces a chase-camera smoothness
regression at 60+ FPS render. Standard render-time interpolation is
the recommended fix (separate phase).

Findings + comparison vs retail/holtburger:
  docs/research/2026-05-01-retail-motion-trace/findings.md
  docs/research/2026-05-01-retail-motion-trace/fixes.md

TODO: port retail's adjust_motion (FUN_00528010) properly so
get_state_velocity works for all directions natively — would let us
drop the workaround in PlayerMovementController jump path and the
clamp in GameWindow.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

docs/ISSUES.md

@@ -46,6 +46,74 @@ Copy this block when adding a new issue:
 
 # Active issues
 
+## #38 — Chase camera + player feel "30 fps" since L.5 physics-tick gate
+
+**Status:** OPEN
+**Severity:** MEDIUM (gameplay-feel regression; not a correctness bug)
+**Filed:** 2026-05-01
+**Component:** rendering / physics / camera
+
+**Description:** User reports that running around in third-person /
+chase camera feels less smooth than it did before the L.5 physics-tick
+work. FPS counter still reads 60+, but the *motion* of the player
+character + camera looks like it's updating at ~30 fps.
+
+**Root cause / status:**
+
+Almost certainly the L.5 `_physicsAccum` gate in
+`PlayerMovementController.cs` (lines ~448-456). Retail integrates
+physics at 30 Hz (`MinQuantum = 1/30 s`); we ported that faithfully so
+collision behavior matches. Side effect: `_body.Position` only updates
+on physics ticks, i.e. every 33 ms. Render runs at 60+ Hz but the
+chase camera follows `_body.Position` directly — so the *visible*
+position changes in 33 ms steps, even though we render at 60+ FPS.
+First-person is less affected because the world rotates with Yaw (which
+*does* update every render frame); third-person is hit hardest because
+the character itself is the moving thing.
+
+Retail in 2013 didn't see this because render was also ~30 fps —
+render rate ≈ physics rate. Our 60+ Hz render exposes the gap.
+
+Discussion + fix options at the end of `docs/research/2026-05-01-retail-motion-trace/findings.md`
+("Other things still don't have…" → camera smoothness discussion in
+chat, not yet captured in the doc — TODO migrate the discussion in).
+
+Recommended fix: **render-time interpolation between physics ticks**
+(standard fixed-timestep + interpolated rendering pattern from Quake /
+Source / Unreal). Snapshot `_prevPhysicsPos` and `_currPhysicsPos` at
+each tick; render player + camera target at
+`Lerp(_prev, _curr, _physicsAccum / PhysicsTick)`. Cost: ~33 ms visual
+latency between input and what you see (matches retail's perceived
+latency anyway). Network outbound stays on the discrete tick value —
+no wire change.
+
+Quick confirmation test before any code change: temporarily set
+`PhysicsTick` to `1.0/60.0` and see if chase camera feels smooth again.
+If yes, gate is confirmed cause. (Don't ship that — it'd undo the L.5
+collision fixes.)
+
+**Files:**
+
+- `src/AcDream.App/Input/PlayerMovementController.cs:172` — `PhysicsTick` constant
+- `src/AcDream.App/Input/PlayerMovementController.cs:448-456` — `_physicsAccum` gate
+- `src/AcDream.App/Rendering/GameWindow.cs` — wherever player render position + chase camera read `_body.Position`
+
+**Research:**
+
+- L.5 background: `memory/project_retail_debugger.md` (the 30 Hz
+  MinQuantum gate, the cdb trace evidence)
+- Discussed during 2026-05-01 motion-trace work
+
+**Acceptance:**
+
+- Chase-camera run-around at 60+ FPS feels as smooth as render rate
+  suggests (no perceptual stepping)
+- Network outbound (MoveToState / AutonomousPosition cadence + values)
+  unchanged from current behavior
+- Collision behavior unchanged (the L.5 wedge / steep-roof scenarios
+  still resolve correctly)
+- Observer view from a parallel retail client unchanged
+
 ## #37 — Humanoid coat doesn't extend up to neck (visible "skin stub" between hair and coat)
 
 **Status:** OPEN