M4: NVS-backed /config with partial updates + validation

nvs_config.{h,c} — persist the runtime config (viewport, scrypted,
idle_timeout_ms, orientation, brightness) under a single NVS namespace.
nvs_config_load() applies persisted values over the in-RAM defaults on
boot and flips state from UNCONFIGURED to ASLEEP once both name and
Scrypted URL are present. nvs_config_save() commits the whole record
atomically.

http_api.c — add GET /config and POST /config:
  - GET serializes viewport_state to the spec's JSON shape, with null
    for unset string fields and defaults filled in for the rest.
  - POST is partial: each field is optional; only present fields are
    validated and applied. Validation runs on a staged copy and errors
    short-circuit with 400 + reason before any state mutation, so a
    rejected request leaves the device untouched.
  - Validation rules: viewport non-empty <64 chars; scrypted starts with
    http:// and <256 chars; idle_timeout_ms 0 or >=5000; orientation in
    {portrait,landscape}; brightness 0..100.
  - Side-effects fire after the lock + save: brightness change pushes
    PWM to the panel MCU; viewport/orientation change reapplies mDNS
    hostname + TXT.
  - 204 on success; 400 with a single-line reason on validation error.

app_main calls nvs_config_load() right after viewport_state_init(), so
mdns_service_start() and display_init() see the persisted hostname,
orientation, and brightness from the first packet/PWM.

Build clean against ESP-IDF 5.4 (binary ~620 KB).

TESTING.md M3 now documents the Hosyond jumper wiring (5V/GND/SDA=GPIO7/
SCL=GPIO8 from board to panel header; DSI FPC carries only the high-
speed lanes). M4 entry expands the validation matrix and side-effects
to verify.

1 files changed, 119 insertions, 0 deletions

diff --git a/main/nvs_config.c b/main/nvs_config.c
new file mode 100644
index 0000000..164db53
--- /dev/null
+++ b/main/nvs_config.c
@@ -0,0 +1,119 @@
+#include "nvs_config.h"
+
+#include <string.h>
+
+#include "esp_log.h"
+#include "nvs.h"
+#include "nvs_flash.h"
+
+#include "viewport_state.h"
+
+static const char *TAG = "nvs_config";
+static const char *NS  = "viewport";
+
+static const char *K_VIEWPORT = "viewport";
+static const char *K_SCRYPTED = "scrypted";
+static const char *K_IDLE_MS  = "idle_ms";
+static const char *K_ORIENT   = "orient";    // 0 = portrait, 1 = landscape
+static const char *K_BRIGHT   = "bright";
+
+esp_err_t nvs_config_load(void)
+{
+    nvs_handle_t h;
+    esp_err_t err = nvs_open(NS, NVS_READONLY, &h);
+    if (err == ESP_ERR_NVS_NOT_FOUND) {
+        ESP_LOGI(TAG, "no saved config — first boot");
+        return ESP_OK;
+    }
+    if (err != ESP_OK) return err;
+
+    viewport_state_lock();
+    viewport_state_t *st = viewport_state_get();
+
+    size_t len = sizeof(st->viewport_name);
+    err = nvs_get_str(h, K_VIEWPORT, st->viewport_name, &len);
+    if (err != ESP_OK && err != ESP_ERR_NVS_NOT_FOUND) goto done;
+
+    len = sizeof(st->scrypted_url);
+    err = nvs_get_str(h, K_SCRYPTED, st->scrypted_url, &len);
+    if (err != ESP_OK && err != ESP_ERR_NVS_NOT_FOUND) goto done;
+
+    uint32_t u32 = 0;
+    err = nvs_get_u32(h, K_IDLE_MS, &u32);
+    if (err == ESP_OK) st->idle_timeout_ms = u32;
+    else if (err != ESP_ERR_NVS_NOT_FOUND) goto done;
+
+    uint8_t u8 = 0;
+    err = nvs_get_u8(h, K_ORIENT, &u8);
+    if (err == ESP_OK) {
+        st->orientation = (u8 == 1) ? VIEWPORT_ORIENTATION_LANDSCAPE
+                                    : VIEWPORT_ORIENTATION_PORTRAIT;
+    } else if (err != ESP_ERR_NVS_NOT_FOUND) {
+        goto done;
+    }
+
+    err = nvs_get_u8(h, K_BRIGHT, &u8);
+    if (err == ESP_OK) st->brightness = u8;
+    else if (err != ESP_ERR_NVS_NOT_FOUND) goto done;
+
+    err = ESP_OK;
+
+    // A device is "configured" only once both name and Scrypted URL are set.
+    if (st->viewport_name[0] && st->scrypted_url[0]) {
+        st->configured = true;
+        st->state      = VIEWPORT_STATE_ASLEEP;  // configured devices boot asleep
+        ESP_LOGI(TAG, "loaded config: viewport=%s scrypted=%s "
+                      "idle_ms=%u orient=%s bright=%u",
+                 st->viewport_name, st->scrypted_url,
+                 (unsigned)st->idle_timeout_ms,
+                 st->orientation == VIEWPORT_ORIENTATION_LANDSCAPE
+                     ? "landscape" : "portrait",
+                 st->brightness);
+    } else {
+        ESP_LOGI(TAG, "partial config in NVS — staying unconfigured");
+    }
+
+done:
+    viewport_state_unlock();
+    nvs_close(h);
+    return err;
+}
+
+esp_err_t nvs_config_save(void)
+{
+    nvs_handle_t h;
+    esp_err_t err = nvs_open(NS, NVS_READWRITE, &h);
+    if (err != ESP_OK) return err;
+
+    viewport_state_lock();
+    viewport_state_t *st = viewport_state_get();
+
+    if ((err = nvs_set_str(h, K_VIEWPORT, st->viewport_name)) != ESP_OK) goto done;
+    if ((err = nvs_set_str(h, K_SCRYPTED, st->scrypted_url))  != ESP_OK) goto done;
+    if ((err = nvs_set_u32(h, K_IDLE_MS,  st->idle_timeout_ms)) != ESP_OK) goto done;
+    if ((err = nvs_set_u8 (h, K_ORIENT,
+                          (st->orientation == VIEWPORT_ORIENTATION_LANDSCAPE)
+                              ? 1 : 0)) != ESP_OK) goto done;
+    if ((err = nvs_set_u8 (h, K_BRIGHT,   st->brightness))     != ESP_OK) goto done;
+
+    err = nvs_commit(h);
+
+done:
+    viewport_state_unlock();
+    nvs_close(h);
+    return err;
+}
+
+esp_err_t nvs_config_reset(void)
+{
+    nvs_handle_t h;
+    esp_err_t err = nvs_open(NS, NVS_READWRITE, &h);
+    if (err == ESP_ERR_NVS_NOT_FOUND) return ESP_OK;
+    if (err != ESP_OK) return err;
+
+    nvs_erase_all(h);
+    err = nvs_commit(h);
+    nvs_close(h);
+    ESP_LOGI(TAG, "NVS config cleared");
+    return err;
+}