KB: task #1 landings -- update-record channel DONE, movementMode=simulationState identification swept

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

context/multiplayer.md

@@ -6,7 +6,7 @@ source_sections: "PROGRESS_LOG.md §7 (Phase 7), §8 (P6); docs/HARD_PROBLEMS.md
 related_topics: [wintesla-port, combat-damage, locomotion, decomp-reference]
 key_terms: [master, replicant, EGG, dead-reckon]
 open_questions:
-  - "pod-LAN config (real IPs); update-record velocity from the body-channel projection; peer SimulationState/DropZoneLocation replication (authentic peer warp spheres); Mech-level update records @0x4a0c2c (in progress)"
+  - "pod-LAN config (real IPs); update-record velocity from the body-channel projection; peer SimulationState/DropZoneLocation replication (authentic peer warp spheres); stream the model deadband constants (UpdatePositionDiffrence et al) to the update-record senders"
 ---
 
 # Multiplayer
@@ -188,6 +188,55 @@ from the leg channel); the binary publishes the BODY channel's smoothed projecti
 disasm +0x2a0). Swapping the source is a fidelity refinement DEFERRED — it risks a verified working feed
 for a smoothing nuance. [T3 on that nuance]
 
+## Mech-level update records (task #1, 2026-07-11) — DONE [T1 transcription / T2 live]
+
+The 9-type Mech record channel is LIVE end-to-end: **writer @004a0c2c** transcribed
+instruction-for-instruction from `reference/decomp/mech_writeupdate_004a0c2c.disasm.txt`, **reader
+@004a1232** rewritten from part_012.c:9576-9692 with every Wword absorber promoted to the NAMED
+engine/port member.  Wire sizes verified live (0x14/0x20/0x2c/0x78).  Key mechanics:
+
+- **Record type == the `updateModel` BIT INDEX** (`Simulation::WriteSimulationUpdate` walks the
+  mask, SIMULATE.cpp:302-328; binary twin FUN_0041bd98).  Request = `Mech::ForceUpdate(1<<N)`
+  (@0x4a4c54: `updateModel |= mask`, `&= 0xfe03` filter when disabled).  THREE prior mislabels of
+  the same binary fns are retired: `SetInstanceFlags` and `RequestActionFlags` (both @0x4a4c54 —
+  +0x18 is `Simulation::updateModel`, NOT entity flags) and `IsNetworkCopy` (@0x49fb54 =
+  `IsDisabled`, simulationState 2||9).
+- **`movementMode` == `Simulation::simulationState.currentState`** (binary mech+0x40 =
+  StateIndicator@0x2c +0x14; oldState @+0x3c).  The port's parallel `int movementMode` member is
+  GONE — `MovementMode()/SetMovementMode()` accessors ride the engine StateIndicator, so the state
+  (death 9 / limbo 2 / airborne 3,4) replicates in EVERY record header (+0xC) and the replicant
+  tracks the master automatically.
+- **Every record tail = the mapper's `speedDemand`** (subsystemArray[0]+0x128) mirrored into
+  `bodyTargetSpeed@0x6b4` on both sides — the authentic replicant-gait feed (it was misread as a
+  "sequence number"; the type-2 record exists solely to ship it on change).  Task #50's
+  velocity-derived gait stays as the leg-channel driver meanwhile.
+- **Types**: 0 pose (Mover record + tail; orientation SAVED/RESTORED around the base call — it
+  rides ONLY type 4), 1 damage zones (engine), 2 speedDemand, 3 leg-state+stability (write-through
+  body dispatch both sides), 4 orientation+angular-velocity resync (euler-encoded, quat
+  normalized), 5 knockdown (SetBodyAnimation 0x20 both sides), 6 death, 7 impact (fields only),
+  8 airborne/reverse selector.  5/6/7 share the 0x2c heat/throttle/fall-basis payload.
+- **Senders wired byte-exact** (the perf-loop + event map recovered from 27 binary call sites):
+  gait transitions `Force(8)` (mech2 — already transcribed under the RequestActionFlags mislabel,
+  masks matched the binary exactly), knockdown `Force(1|0x20)` (mech4), death `Force(1|0x40)`
+  BEFORE `SetMovementMode(9)` (the disabled filter would mask it after), `Reset` `Force(0x1f)` +
+  the binary zero-set (state 0, cycle/target speeds, poseSyncLatch), perf-loop deadbands: position
+  → type 0, orientation deviation → type 4, speedDemand change → type 2, heat-level change → type
+  7 (snapshot @0x780).  [T3 deadband thresholds — the model record's `UpdatePositionDiffrence` /
+  `UpdateTurnVelocityDiffrence` / `UpdateTurnDegreeDiffrence` fields (+0x26..0x28) are the
+  authentic constants, not yet streamed to the runtime members +0x768/+0x76c/+0x770.]
+- **VERIFIED 2-node**: types 2/3/4 flow while driving; kill → B emits ONE type-6 (simState=9 in
+  the header) → A's replicant flips to MovementMode 9 and its own `UpdateDeathState` runs the
+  wreck-sink loop on the OBSERVER's screen (smoke re-arm logged on A; NO double death transition,
+  NO replicant VehicleDead) — the death SINK/burial gap (old item 3) is CLOSED.  Respawn:
+  `Force(0x1f)` burst snaps the replicant to the drop zone + un-wrecks it.  Walking replicant
+  un-regressed (run states 10→12, legCycle tracking, with type-3 records flowing).  Solo clean.
+- Telemetry: `[mrec-tx]/[mrec-rx]` per non-pose record (BT_REPL_LOG).  Note the type-1 rx line
+  prints a bogus simState (the damage record's own layout at +0xC) — cosmetic.
+- New by-name members: `poseSyncLatch@0x77c` (dead-reckon re-base latch, consumed by
+  FUN_004ab1c8), `fallDirection@0x4a8` + `fallScalar@0x4b4` [T4 names], `heatLevelSnapshot@0x780`.
+  A TU-local stub type forced the `BTMapperSpeedDemandRaw(void*)` bridge (mech.cpp carries a local
+  `struct MechControlsMapper` recon stub — typed cross-TU signatures mangle differently).
+
 ## Remaining (P6 phase 4 / Phase 7)
 The pod-LAN config (real IPs, bare-IP pilot entries); update-record velocity sourced from the body-channel
 projection (above). See [[open-questions]]. [T3]
@@ -310,11 +359,8 @@ transition, HUD all landed since P6): console egg → mesh → RunningMission on
    (base ran, nothing serialized); and `recordLength` must be each level's sizeof or the stream
    framing misparses. VERIFIED 2-node: A fires 57 volleys → 225 records → B applies 225 → draws 414
    replicant beams (PPC blue / laser red from A's replicant's gun ports). Solo un-regressed.
-   REMAINING (deferred): the MECH-level writer @0x4a0c2c (recovered + preserved:
-   `reference/decomp/mech_writeupdate_004a0c2c.disasm.txt`; 9 record types decoded — 0/1/4 pose
-   variants, 2 alarm, 3 leg-state+heat with body-channel write-through re-sync, 5 knockdown
-   (SetBodyAnimation(0x20) write-through), 6 death, 7 impact, 8 movementMode) — transcribing it
-   would replicate remote KNOCKDOWN/death/heat states; beams did not need it.
+   ✅ **The MECH-level records LANDED (task #1, 2026-07-11)** — see the section below; this
+   REMAINING note is closed.
 5. ✅ **2-window driving — RESOLVED (tasks #48/#51).** Keyboard MP turning was restored at the root
    (the `pilotArray[1]` shrunk-span overrun fix, task #51); `BT_KEY_NOFOCUS` exists for automated
    harnesses. DEATHS scoring lights via the existing BTPostKillScore MP branch. Respawn is