feat(uploads): direct-to-B2 presigned image upload from iOS + Android

iOS (Swift) — primary path, since iOS is the live platform:
  - ImageDownsampler.swift: ImageIO/CGImageSourceCreateThumbnailAtIndex
    based resize. Pays only the cost of the resized bitmap rather than
    decoding the full source — a 12 MP iPhone photo previously
    materialized ~50 MB regardless of JPEG size. Profiles: completion
    (2048 px / quality 0.85), document_image (2560 px / 0.90).
  - PresignedUploader.swift: three-step orchestration (POST /uploads/presign
    → multipart POST direct to B2 with the signed policy fields → return
    upload_id). Maps HTTP errors to user-facing copy. Concurrent uploads
    via TaskGroup.
  - CompleteTaskView.swift: replaces the multipart-with-images path with
    downsample → upload-to-B2 → create-completion-with-upload_ids[]. The
    no-image branch unchanged.

Android (Kotlin) — parity:
  - composeApp/.../media/ImageDownsampler.kt: BitmapFactory inSampleSize
    + proportional scale + JPEG compress. Same profiles as iOS.
  - composeApp/.../network/UploadApi.kt: Ktor-based presign + direct-to-B2
    POST. Preserves form-field order so the S3 policy signature validates.
  - APILayer.uploadImage(category, contentType, bytes, fileName) → upload_id.
    UI integration to follow.

Shared (Kotlin):
  - models/TaskCompletion.kt: added uploadIds: List<Int>? to
    TaskCompletionCreateRequest and a new PresignUploadRequest /
    PresignUploadResponse pair matching the Go API DTOs.
  - Existing call sites (WidgetActionProcessor, PushNotificationManager)
    explicitly pass uploadIds: nil for backwards compatibility — Swift's
    bridge to Kotlin doesn't honor Kotlin defaults for required-positional
    parameters.

The legacy multipart path remains functional alongside the new one for
soak-test purposes; per-platform feature flags can flip between them at
any time. After zero multipart traffic in production for 7 consecutive
days, the legacy paths can be dropped.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

iosApp/iosApp/Helpers/ImageDownsampler.swift

@@ -0,0 +1,100 @@
+import Foundation
+import ImageIO
+import UIKit
+import UniformTypeIdentifiers
+
+/// Memory-efficient image resizer for upload preprocessing.
+///
+/// Why not `UIImage.jpegData(compressionQuality:)` directly? UIImage decodes
+/// the entire source bitmap into RAM before re-encoding — a 12 MP iPhone
+/// photo decompresses to ~50 MB regardless of how big the JPEG is. With
+/// multiple selected images this can blow up memory on older devices.
+///
+/// `CGImageSourceCreateThumbnailAtIndex` reads the source incrementally and
+/// only allocates the *resized* bitmap, paying memory proportional to the
+/// output size (a 2048×1536 thumbnail is ~12 MB, but the source is never
+/// fully decoded).
+///
+/// Reference: https://nshipster.com/image-resizing/ — section "Image I/O".
+enum ImageDownsampler {
+
+    /// Settings tuned per upload category. Edit here, not at call sites.
+    struct Profile {
+        /// Largest dimension (in points-after-scale, i.e. pixels) of the
+        /// downsampled image. The shorter edge is set proportionally.
+        let maxPixelEdge: CGFloat
+
+        /// JPEG quality, 0...1. 0.85 is the WhatsApp / Slack default —
+        /// visually indistinguishable from quality 1.0 at typical viewing
+        /// sizes; cuts file size by ~3x.
+        let jpegQuality: CGFloat
+
+        static let completion = Profile(maxPixelEdge: 2048, jpegQuality: 0.85)
+        static let documentImage = Profile(maxPixelEdge: 2560, jpegQuality: 0.90)
+    }
+
+    /// Downsample raw image bytes (e.g. from a `PHPickerResult`'s
+    /// `loadDataRepresentation`) into a JPEG `Data` ready for upload.
+    ///
+    /// - Returns: encoded JPEG bytes, or nil if decoding failed.
+    static func downsample(data: Data, profile: Profile) -> Data? {
+        let options: [CFString: Any] = [
+            kCGImageSourceShouldCache: false, // don't keep the full image around
+            kCGImageSourceTypeIdentifierHint: UTType.jpeg.identifier as CFString, // best-effort hint
+        ]
+        guard let source = CGImageSourceCreateWithData(data as CFData, options as CFDictionary) else {
+            return nil
+        }
+        return downsample(source: source, profile: profile)
+    }
+
+    /// Downsample from a file URL (e.g. PhotosPicker's
+    /// `loadFileRepresentation`). Avoids materializing the full image in
+    /// memory before resize.
+    static func downsample(url: URL, profile: Profile) -> Data? {
+        let options: [CFString: Any] = [
+            kCGImageSourceShouldCache: false,
+        ]
+        guard let source = CGImageSourceCreateWithURL(url as CFURL, options as CFDictionary) else {
+            return nil
+        }
+        return downsample(source: source, profile: profile)
+    }
+
+    /// Convenience for callers that already have a `UIImage` (e.g. from
+    /// `UIImagePickerController`). We round-trip through PNG to get raw
+    /// data, then use the data path. Slightly less efficient than starting
+    /// from URL/Data, but still avoids the JPEG re-encode penalty for the
+    /// resize step itself.
+    static func downsample(uiImage: UIImage, profile: Profile) -> Data? {
+        // Use PNG for the intermediate to avoid double-JPEG quality loss.
+        // Even though PNG is larger, this stays in memory only briefly.
+        guard let intermediate = uiImage.pngData() else { return nil }
+        return downsample(data: intermediate, profile: profile)
+    }
+
+    // MARK: - Internal
+
+    private static func downsample(source: CGImageSource, profile: Profile) -> Data? {
+        // Compute the max pixel size in screen-resolution-aware units. We
+        // use a fixed pixel cap because uploads are about bytes, not display.
+        let scale: CGFloat = 1.0
+        let maxDimensionInPixels = profile.maxPixelEdge * scale
+
+        let downsampleOptions: [CFString: Any] = [
+            kCGImageSourceCreateThumbnailFromImageAlways: true,
+            kCGImageSourceShouldCacheImmediately: true, // decode on the calling thread
+            kCGImageSourceCreateThumbnailWithTransform: true, // honor EXIF orientation
+            kCGImageSourceThumbnailMaxPixelSize: maxDimensionInPixels,
+        ]
+
+        guard let cgImage = CGImageSourceCreateThumbnailAtIndex(
+            source, 0, downsampleOptions as CFDictionary
+        ) else {
+            return nil
+        }
+
+        let uiImage = UIImage(cgImage: cgImage)
+        return uiImage.jpegData(compressionQuality: profile.jpegQuality)
+    }
+}

iosApp/iosApp/Helpers/PresignedUploader.swift

@@ -0,0 +1,274 @@
+import Foundation
+import ComposeApp
+
+/// Three-step direct-to-B2 image upload.
+///
+/// Flow:
+///   1. POST /api/uploads/presign → server returns a B2 POST policy + form
+///      fields scoped to a single object key with a content-length-range
+///      condition that B2 enforces at the protocol level.
+///   2. Multipart POST the bytes directly to B2, no API server in the data
+///      path. B2 rejects the upload if the bytes don't match the policy.
+///   3. Caller passes the returned `uploadId` to /api/task-completions/ or
+///      /api/documents/ via `upload_ids[]`. The server HEADs the object,
+///      confirms the size, and creates the linked entity rows.
+///
+/// All errors map to `PresignedUploaderError` — the Swift call site can
+/// translate to user-facing copy without parsing nested HTTP details.
+enum PresignedUploaderError: Error, LocalizedError {
+    case notAuthenticated
+    case presignFailed(status: Int, body: String)
+    case uploadFailed(status: Int, body: String)
+    case sessionError(Error)
+
+    var errorDescription: String? {
+        switch self {
+        case .notAuthenticated:
+            return "You're not signed in."
+        case .presignFailed(let status, _):
+            switch status {
+            case 413: return "That photo is too large after resizing. Try a different one."
+            case 422: return "That image format isn't supported."
+            case 429: return "You're uploading too many photos. Try again in a few minutes."
+            default:  return "Couldn't start upload (server returned \(status))."
+            }
+        case .uploadFailed(let status, _):
+            return "Upload failed (B2 returned \(status))."
+        case .sessionError(let err):
+            return err.localizedDescription
+        }
+    }
+}
+
+/// Category passed to the presign endpoint. Matches the Go server's
+/// `UploadCategory` constants in `internal/models/pending_upload.go`.
+enum UploadCategory: String {
+    case completion = "completion"
+    case documentImage = "document_image"
+    case documentFile = "document_file"
+}
+
+/// Presigned-URL upload helper. Stateless — instantiate freely.
+///
+/// Concurrency: each `upload(...)` call runs to completion sequentially.
+/// For multiple images the caller can run several uploads in parallel via
+/// `withTaskGroup`; the server's per-user concurrency cap (10 in-flight
+/// presigns) is enforced server-side.
+final class PresignedUploader {
+
+    /// API base URL — read from KMP's ApiConfig so iOS and Android stay
+    /// in sync (LOCAL vs DEV vs PROD without divergent constants).
+    private let apiBaseURL: String
+
+    /// Bearer token. Read once at init; if the user re-auths mid-session,
+    /// the caller should construct a fresh PresignedUploader.
+    private let authToken: String
+
+    private let session: URLSession
+
+    init?(session: URLSession = .shared) {
+        // ApiConfig.shared.getBaseUrl() resolves Environment (LOCAL/DEV/PROD).
+        // DataManager.shared.authToken is a StateFlow<String?> — read the
+        // current value via .value (SKIE-exposed property).
+        let baseUrl = ApiConfig.shared.getBaseUrl()
+        guard let token = DataManager.shared.authToken.value as String? else {
+            return nil
+        }
+        self.apiBaseURL = baseUrl
+        self.authToken = token
+        self.session = session
+    }
+
+    /// Upload `data` to B2 in the named category. Returns the
+    /// pending_uploads.id the caller passes via `upload_ids[]` to attach
+    /// the object to a real entity.
+    func upload(
+        data: Data,
+        category: UploadCategory,
+        contentType: String = "image/jpeg",
+        fileName: String = "image.jpg"
+    ) async throws -> Int32 {
+        // Step 1: presign
+        let presigned = try await requestPresign(
+            category: category,
+            contentType: contentType,
+            contentLength: Int64(data.count)
+        )
+
+        // Step 2: direct POST to B2
+        try await postToStorage(
+            uploadURL: presigned.uploadUrl,
+            fields: presigned.fields,
+            data: data,
+            contentType: contentType,
+            fileName: fileName
+        )
+
+        return Int32(presigned.id)
+    }
+
+    /// Upload several images in parallel, returning their upload_ids in
+    /// input order. Stops at the first failure and surfaces it.
+    func uploadAll(
+        items: [(Data, String)],
+        category: UploadCategory,
+        contentType: String = "image/jpeg"
+    ) async throws -> [Int32] {
+        try await withThrowingTaskGroup(of: (Int, Int32).self) { group in
+            for (idx, item) in items.enumerated() {
+                let (data, name) = item
+                group.addTask { [self] in
+                    let id = try await upload(
+                        data: data,
+                        category: category,
+                        contentType: contentType,
+                        fileName: name
+                    )
+                    return (idx, id)
+                }
+            }
+            var pairs: [(Int, Int32)] = []
+            for try await pair in group {
+                pairs.append(pair)
+            }
+            return pairs.sorted { $0.0 < $1.0 }.map { $0.1 }
+        }
+    }
+
+    // MARK: - Step 1: presign
+
+    private struct PresignBody: Encodable {
+        let category: String
+        let content_type: String
+        let content_length: Int64
+    }
+
+    private struct PresignResponse: Decodable {
+        let id: Int
+        let upload_url: String
+        let fields: [String: String]
+        let key: String
+        let expires_at: String
+
+        // Map snake_case to nicer Swift names at the call site.
+        var uploadUrl: String { upload_url }
+    }
+
+    private func requestPresign(
+        category: UploadCategory,
+        contentType: String,
+        contentLength: Int64
+    ) async throws -> PresignResponse {
+        guard var url = URL(string: apiBaseURL) else {
+            throw PresignedUploaderError.presignFailed(status: 0, body: "invalid base url")
+        }
+        url.appendPathComponent("uploads/presign/")
+
+        var req = URLRequest(url: url)
+        req.httpMethod = "POST"
+        req.setValue("application/json", forHTTPHeaderField: "Content-Type")
+        req.setValue("Token \(authToken)", forHTTPHeaderField: "Authorization")
+        req.httpBody = try JSONEncoder().encode(PresignBody(
+            category: category.rawValue,
+            content_type: contentType,
+            content_length: contentLength
+        ))
+
+        let (body, response): (Data, URLResponse)
+        do {
+            (body, response) = try await session.data(for: req)
+        } catch {
+            throw PresignedUploaderError.sessionError(error)
+        }
+        guard let http = response as? HTTPURLResponse else {
+            throw PresignedUploaderError.presignFailed(status: 0, body: "no response")
+        }
+        guard (200..<300).contains(http.statusCode) else {
+            throw PresignedUploaderError.presignFailed(
+                status: http.statusCode,
+                body: String(data: body, encoding: .utf8) ?? ""
+            )
+        }
+        do {
+            return try JSONDecoder().decode(PresignResponse.self, from: body)
+        } catch {
+            throw PresignedUploaderError.presignFailed(status: http.statusCode, body: "decode failed: \(error)")
+        }
+    }
+
+    // MARK: - Step 2: POST to B2
+
+    private func postToStorage(
+        uploadURL: String,
+        fields: [String: String],
+        data: Data,
+        contentType: String,
+        fileName: String
+    ) async throws {
+        guard let url = URL(string: uploadURL) else {
+            throw PresignedUploaderError.uploadFailed(status: 0, body: "invalid upload url")
+        }
+
+        // Build a multipart/form-data body with all policy fields followed
+        // by a single "file" part (S3 POST policy mandates the file part
+        // come last).
+        let boundary = "Boundary-\(UUID().uuidString)"
+        var body = Data()
+        let crlf = "\r\n"
+        let appendString: (String) -> Void = { s in
+            body.append(s.data(using: .utf8) ?? Data())
+        }
+
+        // Stable order: ensure "key" and "Content-Type" appear before the
+        // file part so the policy signature validates. Unspecified order
+        // for the rest — S3 accepts any.
+        let orderedKeys = ["key", "Content-Type", "policy", "x-amz-algorithm",
+                           "x-amz-credential", "x-amz-date", "x-amz-signature",
+                           "x-amz-meta-uid"]
+        var emitted = Set<String>()
+        for k in orderedKeys {
+            if let v = fields[k] {
+                appendString("--\(boundary)\(crlf)")
+                appendString("Content-Disposition: form-data; name=\"\(k)\"\(crlf)\(crlf)")
+                appendString(v)
+                appendString(crlf)
+                emitted.insert(k)
+            }
+        }
+        for (k, v) in fields where !emitted.contains(k) {
+            appendString("--\(boundary)\(crlf)")
+            appendString("Content-Disposition: form-data; name=\"\(k)\"\(crlf)\(crlf)")
+            appendString(v)
+            appendString(crlf)
+        }
+
+        // file part — must be last
+        appendString("--\(boundary)\(crlf)")
+        appendString("Content-Disposition: form-data; name=\"file\"; filename=\"\(fileName)\"\(crlf)")
+        appendString("Content-Type: \(contentType)\(crlf)\(crlf)")
+        body.append(data)
+        appendString(crlf)
+        appendString("--\(boundary)--\(crlf)")
+
+        var req = URLRequest(url: url)
+        req.httpMethod = "POST"
+        req.setValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")
+        req.httpBody = body
+
+        let (respBody, response): (Data, URLResponse)
+        do {
+            (respBody, response) = try await session.data(for: req)
+        } catch {
+            throw PresignedUploaderError.sessionError(error)
+        }
+        guard let http = response as? HTTPURLResponse else {
+            throw PresignedUploaderError.uploadFailed(status: 0, body: "no response")
+        }
+        guard (200..<300).contains(http.statusCode) else {
+            throw PresignedUploaderError.uploadFailed(
+                status: http.statusCode,
+                body: String(data: respBody, encoding: .utf8) ?? ""
+            )
+        }
+    }
+}

iosApp/iosApp/Helpers/WidgetActionProcessor.swift

@@ -64,7 +64,8 @@ final class WidgetActionProcessor {
                 notes: "Completed from widget",
                 actualCost: nil,
                 rating: nil,
-                imageUrls: nil
+                imageUrls: nil,
+                uploadIds: nil
             )
 
             let result = try await APILayer.shared.createTaskCompletion(request: request)

iosApp/iosApp/PushNotifications/PushNotificationManager.swift

@@ -388,7 +388,8 @@ class PushNotificationManager: NSObject, ObservableObject {
                     notes: nil,
                     actualCost: nil,
                     rating: nil,
-                    imageUrls: nil
+                    imageUrls: nil,
+                    uploadIds: nil
                 )
                 let result = try await APILayer.shared.createTaskCompletion(request: request)
 

iosApp/iosApp/Task/CompleteTaskView.swift

@@ -337,51 +337,121 @@ struct CompleteTaskView: View {
 
         isSubmitting = true
 
-        // Create request with simplified Go API format
-        // Note: completedAt defaults to now on server if not provided
-        let request = TaskCompletionCreateRequest(
-            taskId: task.id,
-            completedAt: nil,
-            notes: notes.isEmpty ? nil : notes,
-            actualCost: actualCost.isEmpty ? nil : KotlinDouble(double: Double(actualCost) ?? 0.0),
-            rating: KotlinInt(int: Int32(rating)),
-            imageUrls: nil  // Images uploaded separately and URLs added by handler
-        )
-
-        // Use TaskCompletionViewModel to create completion
+        // New direct-to-B2 upload path: downsample on-device, presign, POST
+        // straight to B2, pass the resulting upload_ids to the completion
+        // create call. Bytes never traverse our API server. See
+        // /api/uploads/presign in honeyDueAPI-go.
         if !selectedImages.isEmpty {
-            // Convert images to ImageData for Kotlin
-            let imageDataList = selectedImages.compactMap { uiImage -> ComposeApp.ImageData? in
-                guard let jpegData = uiImage.jpegData(compressionQuality: 0.8) else { return nil }
-                let byteArray = KotlinByteArray(data: jpegData)
-                return ComposeApp.ImageData(bytes: byteArray, fileName: "completion_image.jpg")
-            }
-            completionViewModel.createTaskCompletionWithImages(request: request, images: imageDataList)
+            uploadAndCreate()
         } else {
+            // No images — go straight to the completion create.
+            let request = TaskCompletionCreateRequest(
+                taskId: task.id,
+                completedAt: nil,
+                notes: notes.isEmpty ? nil : notes,
+                actualCost: actualCost.isEmpty ? nil : KotlinDouble(double: Double(actualCost) ?? 0.0),
+                rating: KotlinInt(int: Int32(rating)),
+                imageUrls: nil,
+                uploadIds: nil
+            )
             completionViewModel.createTaskCompletion(request: request)
+            observeCompletionState()
         }
+    }
 
-        // Observe the result — store the Task so it can be cancelled on dismiss
+    /// Async pipeline: downsample → presign+upload to B2 → create completion
+    /// with the returned upload_ids. Errors at any stage become a single
+    /// alert; partial uploads (1 of 3 succeeded) currently fail the whole
+    /// flow — server-side cleanup reaps the orphans within the hour.
+    private func uploadAndCreate() {
         observationTask?.cancel()
         observationTask = Task {
-            for await state in completionViewModel.createCompletionState {
-                if Task.isCancelled { break }
+            // Step 1: downsample each image. Runs on the calling task; the
+            // ImageDownsampler is memory-bounded so this is safe for the
+            // expected batch sizes (≤5 images).
+            let payloads: [(Data, String)] = selectedImages.compactMap { uiImage -> (Data, String)? in
+                guard let data = ImageDownsampler.downsample(uiImage: uiImage, profile: .completion) else {
+                    return nil
+                }
+                return (data, "completion_\(UUID().uuidString).jpg")
+            }
+            guard payloads.count == selectedImages.count else {
                 await MainActor.run {
-                    if let success = state as? ApiResultSuccess<TaskCompletionResponse> {
-                        self.isSubmitting = false
-                        self.onComplete(success.data?.updatedTask)  // Pass back updated task
-                        self.dismiss()
-                    } else if let error = ApiResultBridge.error(from: state) {
-                        self.errorMessage = error.message
-                        self.showError = true
-                        self.isSubmitting = false
-                    }
+                    errorMessage = "One or more photos couldn't be processed."
+                    showError = true
+                    isSubmitting = false
                 }
+                return
+            }
 
-                // Break out of loop on terminal states
-                if state is ApiResultSuccess<TaskCompletionResponse> || ApiResultBridge.isError(state) {
-                    break
+            // Step 2: presign + upload each to B2. PresignedUploader runs
+            // them in parallel under a server-enforced concurrency cap of 10.
+            guard let uploader = PresignedUploader() else {
+                await MainActor.run {
+                    errorMessage = "Not authenticated"
+                    showError = true
+                    isSubmitting = false
                 }
+                return
+            }
+            let uploadIds: [Int32]
+            do {
+                uploadIds = try await uploader.uploadAll(items: payloads, category: .completion)
+            } catch {
+                await MainActor.run {
+                    errorMessage = (error as? PresignedUploaderError)?.errorDescription
+                        ?? error.localizedDescription
+                    showError = true
+                    isSubmitting = false
+                }
+                return
+            }
+
+            // Step 3: create completion via the existing endpoint, passing
+            // upload_ids so the server claims the pending_uploads rows and
+            // turns them into TaskCompletionImage rows.
+            let request = TaskCompletionCreateRequest(
+                taskId: task.id,
+                completedAt: nil,
+                notes: notes.isEmpty ? nil : notes,
+                actualCost: actualCost.isEmpty ? nil : KotlinDouble(double: Double(actualCost) ?? 0.0),
+                rating: KotlinInt(int: Int32(rating)),
+                imageUrls: nil,
+                uploadIds: uploadIds.map { KotlinInt(int: $0) }
+            )
+            await MainActor.run {
+                completionViewModel.createTaskCompletion(request: request)
+            }
+            await observeCompletionStateAsync()
+        }
+    }
+
+    /// Observe the createCompletionState StateFlow until a terminal value
+    /// arrives, then dismiss or surface an error. Called from the
+    /// no-images path.
+    private func observeCompletionState() {
+        observationTask?.cancel()
+        observationTask = Task {
+            await observeCompletionStateAsync()
+        }
+    }
+
+    private func observeCompletionStateAsync() async {
+        for await state in completionViewModel.createCompletionState {
+            if Task.isCancelled { break }
+            await MainActor.run {
+                if let success = state as? ApiResultSuccess<TaskCompletionResponse> {
+                    self.isSubmitting = false
+                    self.onComplete(success.data?.updatedTask)
+                    self.dismiss()
+                } else if let error = ApiResultBridge.error(from: state) {
+                    self.errorMessage = error.message
+                    self.showError = true
+                    self.isSubmitting = false
+                }
+            }
+            if state is ApiResultSuccess<TaskCompletionResponse> || ApiResultBridge.isError(state) {
+                break
             }
         }
     }