Add guest.session.send and vm.workspace.export RPCs

guest.session.send — write to a pipe-mode session's stdin without
holding the exclusive attach. The daemon dials a fresh SSH connection,
uploads the payload to a temp file, and cats it into the session's
named FIFO. Linux atomicity for writes ≤ PIPE_BUF covers all pi RPC
JSONL lines. Attach exclusivity is unchanged.

vm.workspace.export — pull changes from guest back to host. Runs
`git add -A && git diff --cached HEAD --binary` inside the guest via a
new RunScriptOutput helper on guest.Client (stdout-only capture,
distinct from RunScript which merges stderr). Returns a binary-safe
patch and a list of changed files. CLI writes the patch to stdout for
`| git apply` or to a file via --output.

RunScriptOutput is implemented as a direct SSH session (same pattern as
runSession) rather than going through StartCommand/StreamSession to
avoid closing the underlying Client, which is required since
ExportVMWorkspace calls it twice on the same connection.

New files: internal/daemon/workspace_test.go

internal/daemon/guest_sessions.go

@@ -53,6 +53,7 @@ var guestSessionHostCommandOutputFunc = func(ctx context.Context, name string, a
 type guestSSHClient interface {
 	Close() error
 	RunScript(context.Context, string, io.Writer) error
+	RunScriptOutput(context.Context, string) ([]byte, error)
 	UploadFile(context.Context, string, os.FileMode, []byte, io.Writer) error
 	StreamTar(context.Context, string, string, io.Writer) error
 	StreamTarEntries(context.Context, string, []string, string, io.Writer) error
@@ -400,6 +401,50 @@ func (d *Daemon) GuestSessionLogs(ctx context.Context, params api.GuestSessionLo
 	return api.GuestSessionLogsResult{Session: session, Stream: streamName, Path: path, Content: content}, nil
 }
 
+func (d *Daemon) SendToGuestSession(ctx context.Context, params api.GuestSessionSendParams) (api.GuestSessionSendResult, error) {
+	vm, err := d.FindVM(ctx, params.VMIDOrName)
+	if err != nil {
+		return api.GuestSessionSendResult{}, err
+	}
+	session, err := d.findGuestSession(ctx, vm.ID, params.SessionIDOrName)
+	if err != nil {
+		return api.GuestSessionSendResult{}, err
+	}
+	if session.StdinMode != model.GuestSessionStdinPipe {
+		return api.GuestSessionSendResult{}, errors.New("session does not have a stdin pipe")
+	}
+	if session.Status != model.GuestSessionStatusRunning {
+		return api.GuestSessionSendResult{}, fmt.Errorf("session is not running (status=%s)", session.Status)
+	}
+	if vm.State != model.VMStateRunning || !system.ProcessRunning(vm.Runtime.PID, vm.Runtime.APISockPath) {
+		return api.GuestSessionSendResult{}, fmt.Errorf("vm %q is not running", vm.Name)
+	}
+	if len(params.Payload) == 0 {
+		return api.GuestSessionSendResult{Session: session}, nil
+	}
+	client, err := d.dialGuest(ctx, net.JoinHostPort(vm.Runtime.GuestIP, "22"))
+	if err != nil {
+		return api.GuestSessionSendResult{}, fmt.Errorf("dial guest: %w", err)
+	}
+	defer client.Close()
+	tmpPath := fmt.Sprintf("/tmp/banger-send-%s.bin", session.ID[:8])
+	var uploadLog bytes.Buffer
+	if err := client.UploadFile(ctx, tmpPath, 0o600, params.Payload, &uploadLog); err != nil {
+		return api.GuestSessionSendResult{}, fmt.Errorf("upload payload: %w", err)
+	}
+	sendScript := fmt.Sprintf(
+		"set -euo pipefail\ncat %s >> %s\nrm -f %s\n",
+		guestShellQuote(tmpPath),
+		guestShellQuote(guestSessionStdinPipePath(session.ID)),
+		guestShellQuote(tmpPath),
+	)
+	var sendLog bytes.Buffer
+	if err := client.RunScript(ctx, sendScript, &sendLog); err != nil {
+		return api.GuestSessionSendResult{}, fmt.Errorf("send to session: %w: %s", err, strings.TrimSpace(sendLog.String()))
+	}
+	return api.GuestSessionSendResult{Session: session, BytesWritten: len(params.Payload)}, nil
+}
+
 func (d *Daemon) BeginGuestSessionAttach(ctx context.Context, params api.GuestSessionAttachBeginParams) (api.GuestSessionAttachBeginResult, error) {
 	vm, err := d.FindVM(ctx, params.VMIDOrName)
 	if err != nil {