M6: state machine — POST /state, idle timer, /frame 409 guard

state_machine.{h,c} — central wake/sleep transitions:
- state_machine_init() creates the esp_timer one-shot for the idle timer.
- state_machine_set(target) is idempotent and atomic. On AWAKE: backlight
  on, idle timer (re)armed. On ASLEEP: idle timer cancelled, backlight off.
  Rejects with INVALID_STATE when the device is unconfigured.
- state_machine_frame_painted() restarts the idle timer if awake; called
  by /frame after each successful paint.
- Idle-timer callback transitions to ASLEEP. TODO M7 hook: outbound POST
  {viewport, state:sleep} to <scrypted>/state.

http_api.c:
- POST /state: parse {state}, accept "wake"/"sleep", reject others 400.
  Unconfigured device → 409 "device unconfigured". Already-in-state → 204
  (idempotent no-op). Successful transition → 204.
- POST /frame: 409 Conflict when state != AWAKE. After successful paint,
  call state_machine_frame_painted() so the idle clock keeps resetting
  while frames stream.

app_main:
- Initialize state_machine before http_api so the route handler can drive
  it from request 0.
- After display_init(), reconcile the panel with the boot state:
    UNCONFIGURED → test pattern (placeholder until M8 IP screen)
    ASLEEP       → display_sleep() so a configured device boots dark
    AWAKE        → leave on (not reached on fresh boot)

Disable path: idle_timeout_ms=0 in /config means the timer is never armed
and a wake state persists until /state {sleep} or a power cycle.

Build clean against ESP-IDF 5.4 (binary ~645 KB).

TESTING.md M6 expands with idempotency checks, 409-when-asleep, 409-when-
unconfigured, idle-timer firing within idle_timeout_ms+slack, /frame
restarting the idle timer, idle-timer disable via idle_timeout_ms=0, and
the M7 dependency note about the missing outbound sleep POST.

1 files changed, 96 insertions, 9 deletions

diff --git a/TESTING.md b/TESTING.md
index e5f156c..904a42a 100644
--- a/TESTING.md
+++ b/TESTING.md
@@ -274,25 +274,112 @@ After every error: `decode_errors` in `GET /state` should increment.
 
 **How to verify**
 
+First make sure the device is configured (M4 must be done):
+
+```bash
+curl -X POST -H "Content-Type: application/json" \
+  -d '{"viewport":"mudroom","scrypted":"http://host/cb","idle_timeout_ms":10000}' \
+  http://<device-ip>/config
+```
+
+Wake / sleep:
+
 ```bash
-curl -X POST -d '{"state":"sleep"}' http://<device-ip>/state   # backlight off
-curl -X POST -d '{"state":"wake"}'  http://<device-ip>/state   # backlight on, loading
+# Backlight off:
+curl -i -X POST -H "Content-Type: application/json" \
+  -d '{"state":"sleep"}' http://<device-ip>/state
+# expect: 204
+
+# Backlight on (loading-screen placeholder until M8):
+curl -i -X POST -H "Content-Type: application/json" \
+  -d '{"state":"wake"}' http://<device-ip>/state
+# expect: 204
+
+# Idempotency: repeating either is also 204 with no side effects:
+curl -X POST -H "Content-Type: application/json" \
+  -d '{"state":"wake"}' http://<device-ip>/state
+curl -X POST -H "Content-Type: application/json" \
+  -d '{"state":"wake"}' http://<device-ip>/state
+# Both: 204
+```
+
+`/frame` while asleep returns 409:
 
-# /frame while asleep:
-curl -X POST -d '{"state":"sleep"}' http://<device-ip>/state
+```bash
+curl -X POST -H "Content-Type: application/json" \
+  -d '{"state":"sleep"}' http://<device-ip>/state
 curl -i -X POST -H "Content-Type: image/jpeg" \
   --data-binary @test-480x800.jpg \
   http://<device-ip>/frame
-# expect: HTTP/1.1 409 Conflict
+# expect: HTTP/1.1 409 Conflict, body "device asleep — POST /state ..."
+```
 
-# Idle timer (assuming default 60000ms):
-curl -X POST -d '{"state":"wake"}' http://<device-ip>/state
-# wait 65s without sending /frame
+Idle timer:
+
+```bash
+curl -X POST -H "Content-Type: application/json" \
+  -d '{"state":"wake"}' http://<device-ip>/state
+sleep 12   # idle_timeout_ms was set to 10000 above
 curl http://<device-ip>/state | jq .state
 # expect: "asleep"
 ```
 
-**Status**: ⬜ pending.
+When the timer fires, the serial log should print:
+
+```
+I (xxx) state: idle timer expired — sleeping
+I (xxx) state: ASLEEP
+```
+
+Disabling the idle timer:
+
+```bash
+curl -X POST -H "Content-Type: application/json" \
+  -d '{"idle_timeout_ms":0}' http://<device-ip>/config
+curl -X POST -H "Content-Type: application/json" \
+  -d '{"state":"wake"}' http://<device-ip>/state
+sleep 70
+curl http://<device-ip>/state | jq .state
+# expect: still "awake"
+```
+
+Resetting on `/frame`: every successful paint restarts the idle timer.
+
+```bash
+# Set short idle, then keep painting to keep awake:
+curl -X POST -d '{"idle_timeout_ms":10000}' \
+  -H "Content-Type: application/json" http://<device-ip>/config
+curl -X POST -d '{"state":"wake"}' \
+  -H "Content-Type: application/json" http://<device-ip>/state
+for i in 1 2 3 4 5; do
+  sleep 8
+  curl -X POST -H "Content-Type: image/jpeg" \
+    --data-binary @test-480x800.jpg http://<device-ip>/frame
+done
+curl http://<device-ip>/state | jq .state   # expect "awake"
+```
+
+Unconfigured device rejects `POST /state` with 409:
+
+```bash
+# (After factory reset / fresh boot, no /config yet)
+curl -i -X POST -H "Content-Type: application/json" \
+  -d '{"state":"wake"}' http://<device-ip>/state
+# expect: 409 Conflict "device unconfigured"
+```
+
+Bad input:
+
+```bash
+curl -i -X POST -d '{"state":"middle"}' \
+  -H "Content-Type: application/json" http://<device-ip>/state    # 400
+curl -i -X POST -d 'not json' \
+  -H "Content-Type: application/json" http://<device-ip>/state    # 400
+```
+
+**Known gap (M7 closes this)**: when the idle timer fires the device transitions to ASLEEP locally but does NOT yet POST `{viewport,state:sleep}` to `<scrypted>/state`. That outbound POST lands with `state_client` in M7.
+
+**Status**: 🟡 builds clean against ESP-IDF 5.4. Awaiting hardware.
 
 ---