feat(tsconnect): add outgoing file transfer progress notifications

- Export UpdateOutgoingFiles on taildrop.Extension so it can be called
  from outside the package (wasm bridge, package main).
- Wrap sendFile's PUT body with progresstracking.NewReader so bytes-sent
  is sampled roughly once per second during transfer.
- Create an OutgoingFile entry (with UUID, peer ID, name, declared size)
  before the PUT and call UpdateOutgoingFiles on each progress tick and
  on completion (setting Finished/Succeeded). This flows into the IPN
  notify stream as OutgoingFiles notifications.
- Add jsOutgoingFile struct and wire n.OutgoingFiles into a new
  notifyOutgoingFiles callback in run(), mirroring notifyIncomingFiles.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cmd/tsconnect/wasm/taildrop.go

@@ -23,8 +23,11 @@ import (
 
 	"tailscale.com/client/tailscale/apitype"
 	"tailscale.com/feature/taildrop"
+	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnlocal"
 	"tailscale.com/tailcfg"
+	"tailscale.com/util/progresstracking"
+	"tailscale.com/util/rands"
 )
 
 // Compile-time check that jsFileOps implements taildrop.FileOps.
@@ -78,7 +81,8 @@ func (i *jsIPN) listFileTargets() js.Value {
 	})
 }
 
-// sendFile sends data as filename to the peer identified by stableNodeID.
+// sendFile sends data as filename to the peer identified by stableNodeID,
+// reporting progress via notifyOutgoingFiles callbacks roughly once per second.
 func (i *jsIPN) sendFile(stableNodeID, filename string, data js.Value) js.Value {
 	return makePromise(func() (any, error) {
 		ext, err := i.taildropExt()
@@ -105,20 +109,46 @@ func (i *jsIPN) sendFile(stableNodeID, filename string, data js.Value) js.Value
 		}
 		b := make([]byte, data.Get("byteLength").Int())
 		js.CopyBytesToGo(b, data)
-		req, err := http.NewRequest("PUT", dstURL.String()+"/v0/put/"+url.PathEscape(filename), bytes.NewReader(b))
+
+		outgoing := &ipn.OutgoingFile{
+			ID:           rands.HexString(30),
+			PeerID:       tailcfg.StableNodeID(stableNodeID),
+			Name:         filename,
+			DeclaredSize: int64(len(b)),
+			Started:      time.Now(),
+		}
+		updates := map[string]*ipn.OutgoingFile{outgoing.ID: outgoing}
+
+		// Report final state (success or failure) when the function returns.
+		var sendErr error
+		defer func() {
+			outgoing.Finished = true
+			outgoing.Succeeded = sendErr == nil
+			ext.UpdateOutgoingFiles(updates)
+		}()
+
+		body := progresstracking.NewReader(bytes.NewReader(b), time.Second, func(n int, _ error) {
+			outgoing.Sent = int64(n)
+			ext.UpdateOutgoingFiles(updates)
+		})
+
+		req, err := http.NewRequest("PUT", dstURL.String()+"/v0/put/"+url.PathEscape(filename), body)
 		if err != nil {
+			sendErr = err
 			return nil, err
 		}
 		req.ContentLength = int64(len(b))
 		client := &http.Client{Transport: i.lb.Dialer().PeerAPITransport()}
 		resp, err := client.Do(req)
 		if err != nil {
+			sendErr = err
 			return nil, err
 		}
 		defer resp.Body.Close()
 		if resp.StatusCode != http.StatusOK && resp.StatusCode != http.StatusCreated {
-			body, _ := io.ReadAll(resp.Body)
-			return nil, fmt.Errorf("send file: %s: %s", resp.Status, bytes.TrimSpace(body))
+			respBody, _ := io.ReadAll(resp.Body)
+			sendErr = fmt.Errorf("send file: %s: %s", resp.Status, bytes.TrimSpace(respBody))
+			return nil, sendErr
 		}
 		return nil, nil
 	})

cmd/tsconnect/wasm/wasm_js.go

@@ -413,6 +413,26 @@ func (i *jsIPN) run(jsCallbacks js.Value) {
 				log.Printf("could not marshal IncomingFiles: %v", err)
 			}
 		}
+		if n.OutgoingFiles != nil {
+			files := make([]jsOutgoingFile, len(n.OutgoingFiles))
+			for i, f := range n.OutgoingFiles {
+				files[i] = jsOutgoingFile{
+					ID:           f.ID,
+					PeerID:       string(f.PeerID),
+					Name:         f.Name,
+					Started:      f.Started.UnixMilli(),
+					DeclaredSize: f.DeclaredSize,
+					Sent:         f.Sent,
+					Finished:     f.Finished,
+					Succeeded:    f.Succeeded,
+				}
+			}
+			if b, err := json.Marshal(files); err == nil {
+				jsCallbacks.Call("notifyOutgoingFiles", string(b))
+			} else {
+				log.Printf("could not marshal OutgoingFiles: %v", err)
+			}
+		}
 	})
 
 	go func() {
@@ -949,6 +969,19 @@ type jsIncomingFile struct {
 	Received     int64  `json:"received"`     // bytes received so far
 }
 
+// jsOutgoingFile is the JSON representation of an outgoing file transfer
+// sent to the notifyOutgoingFiles callback.
+type jsOutgoingFile struct {
+	ID           string `json:"id"`
+	PeerID       string `json:"peerID"`
+	Name         string `json:"name"`
+	Started      int64  `json:"started"`      // Unix milliseconds
+	DeclaredSize int64  `json:"declaredSize"` // -1 if unknown
+	Sent         int64  `json:"sent"`         // bytes sent so far
+	Finished     bool   `json:"finished"`
+	Succeeded    bool   `json:"succeeded"` // only meaningful when finished
+}
+
 type jsNetMap struct {
 	Self      jsNetMapSelfNode   `json:"self"`
 	Peers     []jsNetMapPeerNode `json:"peers"`