feat(statusfile): render the ambient drift line when idle

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

internal/statusfile/statusfile.go

@@ -34,12 +34,15 @@ func DefaultPath() (string, error) {
 }
 
 // Render produces the single status line for the harness envelope, dispatching
-// on the active mode. An idle harness ("") renders "idle"; an unknown kind
-// renders a generic fallback so a future mode degrades gracefully rather than
-// rendering nothing.
-func Render(env mode.Envelope, now time.Time) string {
+// on the active mode. An idle harness ("") renders the ambient coaching line as
+// "⚠ <line>" when one is present, else "idle"; an unknown kind renders a generic
+// fallback so a future mode degrades gracefully.
+func Render(env mode.Envelope, ambientLine string, now time.Time) string {
 	switch env.ActiveMode {
 	case "":
+		if line := strings.TrimSpace(ambientLine); line != "" {
+			return "⚠ " + line
+		}
 		return "idle"
 	case "focus":
 		st, ok := env.Mode.(focus.State)
@@ -121,22 +124,24 @@ func remaining(st focus.State, now time.Time) string {
 	return fmt.Sprintf("%dm", mins)
 }
 
-// Writer periodically renders the harness envelope and writes it to a file,
-// rewriting only when the line changes.
+// Writer periodically renders the harness envelope (plus the ambient line) and
+// writes it to a file, rewriting only when the line changes.
 type Writer struct {
-	path  string
-	state func() mode.Envelope
-	now   func() time.Time
-	wake  chan struct{}
+	path    string
+	state   func() mode.Envelope
+	ambient func() string
+	now     func() time.Time
+	wake    chan struct{}
 
 	last  string
 	wrote bool
 }
 
-// NewWriter builds a Writer for path, reading the harness envelope via the given
-// accessor (typically harness.State).
-func NewWriter(path string, state func() mode.Envelope) *Writer {
-	return &Writer{path: path, state: state, now: time.Now, wake: make(chan struct{}, 1)}
+// NewWriter builds a Writer for path, reading the harness envelope via state and
+// the ambient coaching line via ambient (either may be supplied; a nil ambient
+// is treated as "" by write).
+func NewWriter(path string, state func() mode.Envelope, ambient func() string) *Writer {
+	return &Writer{path: path, state: state, ambient: ambient, now: time.Now, wake: make(chan struct{}, 1)}
 }
 
 // Wake asks the writer to re-render now rather than at the next tick. It is the
@@ -174,14 +179,18 @@ func (w *Writer) Run(ctx context.Context) {
 }
 
 func (w *Writer) write() {
-	line := Render(w.state(), w.now())
-	if w.wrote && line == w.last {
+	line := ""
+	if w.ambient != nil {
+		line = w.ambient()
+	}
+	rendered := Render(w.state(), line, w.now())
+	if w.wrote && rendered == w.last {
 		return
 	}
-	if err := os.WriteFile(w.path, []byte(line), 0o644); err != nil {
+	if err := os.WriteFile(w.path, []byte(rendered), 0o644); err != nil {
 		log.Printf("statusfile: write %s: %v", w.path, err)
 		return
 	}
-	w.last = line
+	w.last = rendered
 	w.wrote = true
 }