docs(protocol): P_StandardUpdate detail page (per-tick movement broadcast)

[CoreyRDean]

Summary

Second per-packet detail page after #285 (P_InventoryUpdate). Documents the highest-network-volume packet in the protocol — every connected player sends one to the server per movement-tick, and the server broadcasts every visible actor's position to every nearby player.

Non-technical

P_StandardUpdate is the per-frame heartbeat of the game's network surface. Understanding it is required for ANY perf or anti-cheat work. The doc captures the full anti-cheat rationale (speed-hack delta clamp, backward-running prevention, mount-rider sync) which has accreted across many PRs and was previously only readable from the source.

What's documented

• Field layouts with per-byte offset/width/type tables for both C→S (22 bytes, 7 fields) and S→C (variable length with 3 conditional tails).
• The non-obvious offset-23 dual-purpose field: Energy stat when receiver is the actor, Y-float when the actor is in Environment_Fly. The conditional predicates that select between them.
• Six validation requirements tied to specific source lines:
  • ClampWorldCoord# on all 5 floats
  • Speed-hack delta clamp (per-packet MoveDist vs Speed*Elapsed)
  • WalkingBackward forces IsRunning = False (anti-cheat)
  • Rider-mount synchronisation
  • AI\Rider = Null precondition
  • AI\IgnoreUpdate = 0 precondition
• Server broadcast scheduler with the three distance bands (UpdateDistance / UpdateFarDistance) and the AlsoUpdateMiddleRange alternation that halves mid-range bandwidth.
• Historical PR references (Sanitise BVM_MOVEACTOR / BVM_ROTATEACTOR float params #237-Sanitise BVM_ANIMATEACTOR speed and BVM_CREATEEMITTER offsets #239 float clamp, perf(serverwater): O(actors*global_waters) → O(actors*per_area_waters) in per-tick underwater check #270/perf(serverareas): finish ServerWater chain sweep — SaveArea + ServerUnloadArea #272 per-Area chain, fix(gameserver): Null-guard the stale ServerWater handle on per-tick underwater damage branch #277 Null-guard, refactor(actors): O(1) ActorByRNID sender-resolution index (Phase 1) #282 O(1) sender, refactor(actors): FirstOnlinePlayer chain — convert 7 broadcast loops to O(online) walks (Phase 3) #283 broadcast-loop chain).

Acceptance criteria

• C→S 22-byte layout documented (DestX/Z, NewY, NewX, NewZ, IsRunning, WalkingBackward)
• S→C variable-length layout with conditional tails documented
• Every validation requirement linked to specific source line
• Server broadcast scheduler explained
• Catalog index regenerated; Detail column links to new page
• No .bb source changes
• compile.bat -t clean
• test.bat — 25/25 pass

Test plan

• ./scripts/gen_packet_index.sh --check idempotent (verified before commit)
• Spot-check 4 sub-fields against the actual Mid$ calls in ServerNet.bb:1773-1780 and ClientNet.bb:1491-1538 — offsets and widths match
• Local compile.bat -t + test.bat — pass

Trade-offs / deferred

• 53 packet detail pages remain. Next recommended:
  • P_AttackActor — combat math + damage + faction gating
  • P_SpellUpdate — multi-sub-code spell lifecycle
  • P_ChatMessage — multi-prefix dispatch (Chr$(252/253/254) channels)
  • P_VerifyAccount — the auth state machine (PRs P_VerifyAccount: close username/ban/presence enumeration oracle #264-Extend LoginAttemptOk throttle to 4 sibling auth handlers #268 history)
• Other deferred items unchanged.

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