feature: OneDrive folder as a second send transport

send(anchor:) now branches on TransportSettings.transport(). OneDrive mode
skips AirDrop entirely: it verifies the resolved OneDrive folder exists right
before composing (never trusts stale state), archives the session immediately
after the PDF lands, and sets "Saved to OneDrive — N page(s). Open it in Files
on your iPad." AirDrop's existing behaviour, including handleDidFailToShareItems,
is untouched and only reached from the .airDrop branch.

AppModel seeds outbox/watch from TransportSettings.effectiveFolders() instead
of FolderSettings.resolve() directly, tracks the live `transport`, and
bootstrap() creates the OneDrive folder and sets the watcher's
recordUncommented flag (true only for AirDrop) before the watcher starts.

Settings gets a "Send via" segmented picker above Folders. AirDrop shows the
existing watch/output rows; OneDrive shows a single read-only OneDrive folder
row (Choose... reuses the existing directory picker) plus one caption
explaining the same-folder round trip, or a "No OneDrive folder found" prompt
when nothing resolves (Choose... stays usable). Switching transport re-points
the watcher's folder and recordUncommended live; AirDrop's own folder
overrides are stored separately and are untouched by a OneDrive-and-back
round trip.

Menu's "Send..." row reads "Send to OneDrive" when that transport is active.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012ZiTXPbPCSjzPVsfoweAbp

Sources/Shotdeck/SendController.swift

@@ -16,6 +16,31 @@ extension AppModel: SendCapable {
         guard !session.isEmpty, !isSending else { return }
         setSending(true)
 
+        let transport = TransportSettings.transport()
+
+        // OneDrive mode: verify the real destination exists RIGHT NOW, before composing
+        // anything. `outboxURL` is kept in sync with the resolved OneDrive folder by
+        // bootstrap/chooseTransport/chooseOneDriveFolder, but this is re-resolved fresh
+        // here (never trusted stale) so a folder that vanished since then (OneDrive
+        // signed out, external volume unmounted, folder deleted) is caught instead of
+        // silently writing into whatever `outboxURL` happens to hold.
+        if transport == .oneDrive {
+            guard let folder = OneDriveLocator.resolveOneDriveFolder(),
+                  Self.directoryExists(at: folder)
+            else {
+                let path = OneDriveLocator.resolveOneDriveFolder()?.path
+                    ?? TransportSettings.storedOneDriveFolderPath()
+                    ?? "no OneDrive folder found"
+                setStatus(ShotdeckError.oneDriveFolderUnavailable(path: path).errorDescription)
+                setSending(false)
+                return
+            }
+            if outboxURL != folder || watchFolderURL != folder {
+                setFolderURLs(outbox: folder, watch: folder)
+                try? await watcher.updateWatchFolder(folder)
+            }
+        }
+
         let pending: ComposedSend
         do {
             pending = try await composePDFForSend()
@@ -27,32 +52,51 @@ extension AppModel: SendCapable {
             return
         }
 
-        guard let anchor else {
-            handleDidFailToShareItems(fileName: pending.fileName)
+        switch transport {
+        case .oneDrive:
+            // No AirDrop, no anchor needed — the PDF is already in the watched
+            // OneDrive folder. Archive immediately; the iPad marks it up in place.
+            await handleDidShareItems(fileName: pending.fileName, pageCount: pending.pageCount)
+            let pageWord = pending.pageCount == 1 ? "page" : "pages"
+            setStatus(
+                "Saved to OneDrive — \(pending.pageCount) \(pageWord). Open it in Files on your iPad."
+            )
             setSending(false)
-            return
-        }
 
-        do {
-            try Sharing.airDrop(fileURL: pending.fileURL, from: anchor) { [weak self] success in
-                guard let self else { return }
-                if success {
-                    await self.handleDidShareItems(
-                        fileName: pending.fileName,
-                        pageCount: pending.pageCount
-                    )
-                } else {
-                    self.handleDidFailToShareItems(fileName: pending.fileName)
+        case .airDrop:
+            guard let anchor else {
+                handleDidFailToShareItems(fileName: pending.fileName)
+                setSending(false)
+                return
+            }
+
+            do {
+                try Sharing.airDrop(fileURL: pending.fileURL, from: anchor) { [weak self] success in
+                    guard let self else { return }
+                    if success {
+                        await self.handleDidShareItems(
+                            fileName: pending.fileName,
+                            pageCount: pending.pageCount
+                        )
+                    } else {
+                        self.handleDidFailToShareItems(fileName: pending.fileName)
+                    }
+                    self.setSending(false)
                 }
-                self.setSending(false)
+            } catch {
+                // canPerform false, no service, or no visible window: same as cancel.
+                handleDidFailToShareItems(fileName: pending.fileName)
+                setSending(false)
             }
-        } catch {
-            // canPerform false, no service, or no visible window: same as cancel.
-            handleDidFailToShareItems(fileName: pending.fileName)
-            setSending(false)
         }
     }
 
+    private static func directoryExists(at url: URL) -> Bool {
+        var isDirectory: ObjCBool = false
+        let exists = FileManager.default.fileExists(atPath: url.path, isDirectory: &isDirectory)
+        return exists && isDirectory.boolValue
+    }
+
     /// Writes the PDF to the outbox and records its path. Does not archive the session
     /// and does not present AirDrop — that happens only after the share completes.
     func composePDFForSend() async throws -> ComposedSend {