feat(game): implement authoritative movement and visibility core

PLANS.md

@@ -459,11 +459,11 @@ object placement and bounded memory use.
   `{"status":"serving","healthy":true,"version":"0.5.0","errorCode":0}`.
 - These deterministic, validator, resource, representative-map, build, and
   physical-board results provide concrete evidence for all six acceptance
-  criteria. Milestone 006 remains `NOT_STARTED`.
+  criteria and completed Milestone 005.
 
 ## Milestone 006 — Authoritative movement and visibility core
 
-**Status:** `NOT_STARTED`
+**Status:** `COMPLETE`
 
 ### Objective
 
@@ -497,9 +497,66 @@ server-enforced role-specific visibility.
 
 ### Evidence
 
-Completion evidence is not yet available because this milestone has not
-started. Required evidence includes host-test output, serialized payload
-inspection, and deterministic command-order tests.
+- On 2026-09-04,
+  `PLATFORMIO_SETTING_ENABLE_TELEMETRY=no /home/sasa/.platformio/penv/bin/pio
+  project config` exited successfully and resolved the production and isolated
+  `milestone-006-device-test` environments from `espressif32@7.0.1`, ESP-IDF,
+  the `esp32-c6-devkitm-1` profile, 4 MB Flash, and the root partition and
+  sdkconfig files.
+- `./scripts/run_host_tests.sh` passed every preceding suite and reported
+  `game movement, cooldown, and FIFO ordering: PASS (commands 1-7, states
+  0-3)`, `game bounded command queue: PASS (16 entries)`, `game shared-cell
+  meeting event: PASS (one event)`, and `game visibility and payload security:
+  PASS (r3=49/16, r6=64/49, observer=64)`. The same suite serialized a complete
+  default `128 x 64` observer snapshot as 345 chunks and reported a maximum
+  chunk size of 405 bytes against the 512-byte limit. A separate build with
+  `-fsanitize=address,undefined` repeated the game-core suite without an
+  address or undefined-behavior finding; leak detection was disabled because
+  the sandbox executes under `ptrace`.
+- The deterministic movement cases proved that queued commands are processed
+  in assigned FIFO order, each accepted direction changes exactly one
+  coordinate by one cell, and Player 1 and Player 2 may act at the same server
+  timestamp. Countdown, cooldown, out-of-order timestamp, closed-wall,
+  malformed-direction, observer, and full-queue rejections left player state,
+  accepted-move counters, cooldown clocks, and the authoritative state
+  sequence unchanged. Entering the other player's occupied cell left both
+  players there and emitted one meeting event.
+- Projection tests covered both player roles and reused a snapshot after an
+  opponent changed from visible to hidden. Radius-three squares contained 49
+  cells at an interior position and 16 at a corner; radius-six squares
+  contained 64 and 49 respectively on the `8 x 8` fixture. An internal wall
+  did not remove cells. Player structures and every serialized 512-byte-bounded
+  JSON chunk omitted hidden cell 63, its hidden key record, and stale opponent
+  state, while the observer contained all 64 cells, all ten fixture objects,
+  and both player positions. The serializer also emitted the versioned
+  envelope, authoritative sequence, phase, meeting sequence, and chunk
+  metadata.
+- `/home/sasa/.platformio/penv/bin/pio run -e esp32-c6-devkitm-1` completed
+  with `[SUCCESS]` and reported 47,508 of 327,680 RAM bytes and 1,005,274 of
+  2,097,152 application bytes in use. The production `firmware.bin` measured
+  1,005,904 bytes against the 2,097,152-byte factory partition.
+  `/home/sasa/.platformio/penv/bin/pio run -e esp32-c6-devkitm-1 --target
+  buildfs` completed with `[SUCCESS]`; the independent partition check reported
+  `littlefs.bin uses 2031616/2031616 bytes in partition littlefs`.
+- The isolated device image built with `[SUCCESS]`, using 124,468 of 327,680
+  RAM bytes and 1,016,242 of 2,097,152 application bytes. Its independent
+  partition check reported `firmware.bin uses 1016880/2097152 bytes in
+  partition factory`. Upload with `/home/sasa/.platformio/penv/bin/pio run -e
+  milestone-006-device-test --target upload --upload-port /dev/ttyACM0`
+  identified an ESP32-C6FH4 revision 0.2 with 4 MB embedded Flash and
+  hash-verified every written image.
+- The physical board logged an accepted command with command sequence one,
+  state sequence one, and the new position. It projected 28 player cells into
+  two bounded chunks and the complete 8,192-cell, 30-object observer state into
+  345 bounded chunks; the first serialized chunk was 372 bytes. It then logged
+  `fixed=34612/40960 bytes, runtime=5/50 ms, heap_delta=0` and
+  `M006 physical game test: PASS`.
+- The production image was restored and hash-verified after the isolated test.
+  A live `GET /health` returned
+  `{"status":"serving","healthy":true,"version":"0.6.0","errorCode":0}`.
+  These host, serialization, build, resource, and physical-board results
+  provide concrete evidence for all six acceptance criteria. Milestone 007
+  remains `NOT_STARTED`.
 
 ## Milestone 007 — Keys, artifacts, compasses, exits, and results