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, 60 insertions, 1 deletions

diff --git a/main/http_api.c b/main/http_api.c
index 8bf5f81..b3378b5 100644
--- a/main/http_api.c
+++ b/main/http_api.c
@@ -16,6 +16,7 @@
 #include "mdns_service.h"
 #include "net_eth.h"
 #include "nvs_config.h"
+#include "state_machine.h"
 #include "viewport_state.h"
 
 static const char *TAG = "http_api";
@@ -274,6 +275,51 @@ static esp_err_t config_post_handler(httpd_req_t *req)
 }
 
 // ============================================================================
+// POST /state
+// ============================================================================
+static esp_err_t state_post_handler(httpd_req_t *req)
+{
+    char buf[64];
+    if (read_body(req, buf, sizeof(buf)) != ESP_OK)
+        return respond_400(req, "missing or oversized body");
+
+    cJSON *root = cJSON_Parse(buf);
+    if (!root) return respond_400(req, "invalid JSON");
+
+    cJSON *j = cJSON_GetObjectItemCaseSensitive(root, "state");
+    if (!cJSON_IsString(j)) {
+        cJSON_Delete(root);
+        return respond_400(req, "state must be 'wake' or 'sleep'");
+    }
+
+    viewport_run_state_t target;
+    if (strcmp(j->valuestring, "wake") == 0) {
+        target = VIEWPORT_STATE_AWAKE;
+    } else if (strcmp(j->valuestring, "sleep") == 0) {
+        target = VIEWPORT_STATE_ASLEEP;
+    } else {
+        cJSON_Delete(root);
+        return respond_400(req, "state must be 'wake' or 'sleep'");
+    }
+    cJSON_Delete(root);
+
+    esp_err_t err = state_machine_set(target);
+    if (err == ESP_ERR_INVALID_STATE) {
+        httpd_resp_set_status(req, "409 Conflict");
+        httpd_resp_set_type(req, "text/plain");
+        return httpd_resp_send(req, "device unconfigured", HTTPD_RESP_USE_STRLEN);
+    }
+    if (err != ESP_OK) {
+        httpd_resp_set_status(req, "500 Internal Server Error");
+        httpd_resp_set_type(req, "text/plain");
+        return httpd_resp_send(req, esp_err_to_name(err), HTTPD_RESP_USE_STRLEN);
+    }
+
+    httpd_resp_set_status(req, "204 No Content");
+    return httpd_resp_send(req, NULL, 0);
+}
+
+// ============================================================================
 // POST /frame
 // ============================================================================
 static esp_err_t respond_status(httpd_req_t *req, const char *status, const char *body)
@@ -312,6 +358,12 @@ static esp_err_t frame_post_handler(httpd_req_t *req)
         return respond_status(req, "500 Internal Server Error", "display not initialized");
     }
 
+    // /frame requires AWAKE. Asleep / unconfigured → 409.
+    if (state_machine_current() != VIEWPORT_STATE_AWAKE) {
+        return respond_status(req, "409 Conflict",
+            "device asleep — POST /state {\"state\":\"wake\"} first");
+    }
+
     // Single in-flight frame. Concurrent posts get 503 (spec).
     if (!jpeg_decoder_try_lock(0)) {
         return respond_status(req, "503 Service Unavailable", "frame in flight");
@@ -368,6 +420,8 @@ static esp_err_t frame_post_handler(httpd_req_t *req)
 
     jpeg_decoder_unlock();
 
+    state_machine_frame_painted();  // reset idle timer
+
     httpd_resp_set_status(req, "204 No Content");
     return httpd_resp_send(req, NULL, 0);
 }
@@ -384,6 +438,9 @@ static const httpd_uri_t s_config_get = {
 static const httpd_uri_t s_config_post = {
     .uri = "/config", .method = HTTP_POST, .handler = config_post_handler,
 };
+static const httpd_uri_t s_state_post = {
+    .uri = "/state",  .method = HTTP_POST, .handler = state_post_handler,
+};
 static const httpd_uri_t s_frame_post = {
     .uri = "/frame",  .method = HTTP_POST, .handler = frame_post_handler,
 };
@@ -403,10 +460,12 @@ esp_err_t http_api_start(void)
                        TAG, "register GET /config");
     ESP_RETURN_ON_ERROR(httpd_register_uri_handler(server, &s_config_post),
                        TAG, "register POST /config");
+    ESP_RETURN_ON_ERROR(httpd_register_uri_handler(server, &s_state_post),
+                       TAG, "register POST /state");
     ESP_RETURN_ON_ERROR(httpd_register_uri_handler(server, &s_frame_post),
                        TAG, "register POST /frame");
 
     ESP_LOGI(TAG, "http server listening on :80 "
-                  "(GET /state, GET/POST /config, POST /frame)");
+                  "(GET/POST /state, GET/POST /config, POST /frame)");
     return ESP_OK;
 }