feat(exif): write the Xiaomi watermark blob (0x889e) so HyperOS Gallery can frame our captures

HyperOS Gallery reads EXIF 0x889e (a JSON blob) to build its watermark
frame; without it a photo fails with "cannot recognize the parameters".
CameraX/HAL never supplies that vendor tag, so a capture from this app
lacked it while a stock-camera photo carried it.

Read back the same props the stock camera derives the blob from
(ro.product.device / ro.product.marketname / Build.MANUFACTURER) via the
native module, synthesize the blob in exifWrite, and write it only when
the source has none and the device is Xiaomi/Redmi/POCO - a source blob
is never overwritten.

modules/recipescam-export/android/src/main/java/com/locphamtran/recipescamera/export/RecipescamExportModule.kt

@@ -58,6 +58,17 @@ private class FramedResult(val bmp: Bitmap, val window: RectF?)
 // Font temp files are tiny and reused across exports — cache the Typefaces.
 private val typefaceCache = HashMap<String, Typeface>()
 
+// android.os.SystemProperties is hidden API: reflection keeps this compiling
+// without stubs and degrades to null if a future SDK moves it.
+private fun systemProp(key: String): String? = try {
+  val get = Class.forName("android.os.SystemProperties")
+    .getMethod("get", String::class.java, String::class.java)
+  (get.invoke(null, key, "") as String).ifEmpty { null }
+} catch (e: Throwable) {
+  Log.w(TAG, "systemProp($key) unavailable: ${e.message}")
+  null
+}
+
 class RecipescamExportModule : Module() {
   override fun definition() = ModuleDefinition {
     Name("RecipesCamExport")
@@ -104,6 +115,22 @@ class RecipescamExportModule : Module() {
       "pong"
     }
 
+    // Raw device identity the stock Xiaomi camera folds into EXIF 0x889e —
+    // the watermark blob HyperOS Gallery reads before it will open its
+    // watermark editor. CameraX/HAL never writes that tag, so Gallery reports
+    // it cannot recognize the parameters on our captures. JS formats the JSON
+    // (see exifWrite.watermarkBlob); native only reads the props.
+    Function("deviceInfo") { ->
+      mapOf(
+        "device" to (systemProp("ro.product.device") ?: ""),
+        "marketName" to (systemProp("ro.product.marketname")
+          ?: systemProp("ro.product.odm.marketname")
+          ?: systemProp("ro.product.vendor.marketname") ?: ""),
+        "manufacturer" to (android.os.Build.MANUFACTURER ?: ""),
+        "model" to (android.os.Build.MODEL ?: ""),
+      )
+    }
+
     // P0 spike harness: copy a bundled drawable asset (e.g. "wallframe", the
     // 3117x4000 artwork — representative 12MP decode) into cacheDir and hand the
     // real file path back to JS, which then runs decodeEncodeAsync on it. This

modules/recipescam-export/index.ts

@@ -91,6 +91,13 @@ export interface RecipescamExportModule {
   processPhotoAsync(srcPath: string, dstPath: string, matrix: number[], crop: CropRect | null, adjust?: PhotoAdjust): Promise<ColorTimings>;
   /** P1 alias: matrix + crop, no tone/cinema/enhance passes. */
   processColorAsync(srcPath: string, dstPath: string, matrix: number[], crop: CropRect | null, quality: number): Promise<ColorTimings>;
+  /**
+   * Raw device identity the stock Xiaomi camera folds into EXIF 0x889e (the
+   * watermark blob HyperOS Gallery reads) but CameraX/HAL never supplies:
+   * codename, marketing name, manufacturer, model. Empty strings when absent.
+   */
+  deviceInfo(): { device: string; marketName: string; manufacturer: string; model: string };
+
   /** P0 probe helpers — removed before ship. */
   ping(): Promise<string>;
   materializeBenchAsset(assetName: string): Promise<string>;