feat(ios): add markProcessed share-completion API (Phase 1D)

Add a native iOS markProcessed(shareId) method to the SharedImage plugin
that records an explicit completion signal in App Group UserDefaults
(sharedPhotoProcessedShareId) and logs "[ShareTarget] shareId=<id> marked
processed". The API is exposed to TypeScript via the plugin definitions and
a web no-op stub.

Deliberately does not delete files or clear share metadata (cleanup is
deferred to a later phase), is not yet called from application code, and
does not touch Android. Documents the share-target lifecycle and plugin API
in doc/share-target-ios-audit.md.

ios/App/App/SharedImagePlugin.swift

@@ -24,7 +24,8 @@ public class SharedImagePlugin: CAPPlugin, CAPBridgedPlugin {
     public var pluginMethods: [CAPPluginMethod] {
         return [
             CAPPluginMethod(#selector(getSharedImage(_:)), returnType: .promise),
-            CAPPluginMethod(#selector(hasSharedImage(_:)), returnType: .promise)
+            CAPPluginMethod(#selector(hasSharedImage(_:)), returnType: .promise),
+            CAPPluginMethod(#selector(markProcessed(_:)), returnType: .promise)
         ]
     }
     
@@ -62,5 +63,22 @@ public class SharedImagePlugin: CAPPlugin, CAPBridgedPlugin {
             "hasImage": hasImage
         ])
     }
+
+    /**
+     * Mark a share as processed by the application layer (Phase 1D)
+     * Records an explicit completion signal for the given shareId.
+     * Does NOT delete the stored image file - file cleanup is deferred to a later phase.
+     */
+    @objc public func markProcessed(_ call: CAPPluginCall) {
+        guard let shareId = call.getString("shareId"), !shareId.isEmpty else {
+            call.reject("markProcessed requires a non-empty 'shareId'")
+            return
+        }
+
+        let success = SharedImageUtility.markProcessed(shareId: shareId)
+        call.resolve([
+            "success": success
+        ])
+    }
 }
 

ios/App/App/SharedImageUtility.swift

@@ -15,6 +15,7 @@ public class SharedImageUtility {
     private static let sharedPhotoFilePathKey = "sharedPhotoFilePath"
     private static let sharedPhotoShareIdKey = "sharedPhotoShareId"
     private static let sharedPhotoReadyKey = "sharedPhotoReady"
+    private static let sharedPhotoProcessedShareIdKey = "sharedPhotoProcessedShareId"
     
     /// Get the App Group container URL for accessing shared files
     private static var appGroupContainerURL: URL? {
@@ -78,6 +79,32 @@ public class SharedImageUtility {
         return ["base64": base64String, "fileName": fileName]
     }
     
+    /**
+     * Mark a share as processed by the web/application layer (Phase 1D).
+     *
+     * Records the processed shareId in the App Group UserDefaults so that
+     * later phases can decide whether retrieval/cleanup should be skipped.
+     * This is an explicit completion signal: it does NOT delete the stored
+     * image file or clear the share metadata. File cleanup is deferred to a
+     * later phase.
+     *
+     * @param shareId The share identifier reported by getSharedImage()
+     * @returns true if the processed marker was recorded, false otherwise
+     */
+    @discardableResult
+    static func markProcessed(shareId: String) -> Bool {
+        guard let userDefaults = UserDefaults(suiteName: appGroupIdentifier) else {
+            print("[ShareTarget] shareId=\(shareId) markProcessed failed: UserDefaults unavailable for app group")
+            return false
+        }
+
+        userDefaults.set(shareId, forKey: sharedPhotoProcessedShareIdKey)
+        userDefaults.synchronize()
+
+        print("[ShareTarget] shareId=\(shareId) marked processed")
+        return true
+    }
+    
     /**
      * Check if shared image exists without reading it
      *