diag(motion): instrumentation for remote walk↔run leg-cycle bug (Commit A)

Adds five diagnostics, no behavior changes. All gated on existing
ACDREAM_REMOTE_VEL_DIAG=1 env var. Plan at
~/.claude/plans/yes-make-a-plan-parsed-axolotl.md.

Five hypotheses surviving from the four-agent investigation
(docs/research/2026-05-03-remote-anim-cycle/investigation-prompt.md):

  H1  SEQSTATE silently swallowed by OMEGA_DIAG sharing throttle clock
  H2  ApplyServerControlledVelocityCycle races UM-driven SetCycle per UP
  H3  SetCycle fast-path returns without updating _currNode
  H4  GetLink/GetCycle null → defensive fallback lands on stale head
  H5  PartTemplate.Count diverges from anim PartFrames.Count → silent
       identity-quat freeze

Diagnostics added (all log lines are grep-prefixed):

  D1  Split LastSeqStateLogTime field for SEQSTATE — own throttle.
      Foundational: every other diag depends on SEQSTATE telling truth.
  D2  [UPCYCLE] inside ApplyServerControlledVelocityCycle, +
      [UPCYCLE_SRC] at the call site (wire vs synth velocity).
  D3  [SCFAST] in fast-path return, [SCFULL] at full-rebuild end.
  D4  [SCNULLFALLBACK] in the null-data defensive fallback.
  D5  [PARTSDIAG] with pt.Count / seqFrames.Count / setup.Parts.Count /
       anim.PartFrames[0].Frames.Count + sum-of-components hash.

Repro recipe:

  $env:ACDREAM_INTERP_MANAGER  = "1"
  $env:ACDREAM_REMOTE_VEL_DIAG = "1"
  dotnet run … 2>&1 | Tee-Object tools/diag-logs/walkrun-<ts>.log

Then watch a retail-driven character through acdream and exercise:
idle → W run → release → shift+W walk → release → demote → promote →
run+turn (this last one is the H1 trap).

Decision matrix in the plan file maps each [TAG] signature to a
specific Commit B fix.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tools/diag-logs/.gitignore

@@ -0,0 +1 @@
+*.log