Thread text: a hidden message shows no sender or time

README.md

@@ -1013,8 +1013,8 @@ to an agent as context.
 The authenticated identity must be a participant of the *requested*
 message. Each message is preceded by a one-line separator with its sender
 and send time. Ancestors the caller is not a participant of appear as
-`[message not visible to you]` (a recipient added mid-thread cannot read
-what came before); non-text bodies appear as a `[non-text message: <type>,
+`--- hidden ---` and `[message not visible to you]`, with no sender or time
+(a recipient added mid-thread cannot read what came before); non-text bodies appear as a `[non-text message: <type>,
 <size> bytes]` placeholder. The walk is capped at 100 hops.
 
 **Response:** `200 OK`, `text/plain; charset=utf-8`.

internal/handlers/thread.go

@@ -230,21 +230,24 @@ type threadEntry struct {
 // renderThreadText renders the lineage as plain text, root at the top. Each
 // message gets a one-line separator with sender and send time; non-text
 // bodies and messages the caller may not read become placeholders, so the
-// chain's shape stays visible without leaking content.
+// chain's shape stays visible without leaking content. A message the caller
+// may not read shows neither its sender nor its time.
 func renderThreadText(entries []threadEntry) string {
 	var b strings.Builder
 	for i, e := range entries {
 		if i > 0 {
 			b.WriteString("\n\n")
 		}
+		if !e.Readable {
+			b.WriteString("--- hidden ---\n[message not visible to you]")
+			continue
+		}
 		ts := "draft"
 		if e.TimeSent != nil {
 			ts = time.Unix(int64(*e.TimeSent), 0).UTC().Format(time.RFC3339)
 		}
 		fmt.Fprintf(&b, "--- %s %s ---\n", e.From, ts)
 		switch {
-		case !e.Readable:
-			b.WriteString("[message not visible to you]")
 		case !e.Text:
 			fmt.Fprintf(&b, "[non-text message: %s, %d bytes]", e.Type, e.Size)
 		default:

internal/handlers/thread_test.go

@@ -28,6 +28,12 @@ func TestRenderThreadText(t *testing.T) {
 			t.Fatalf("missing %q in:\n%s", want, got)
 		}
 	}
+	if strings.Count(got, "@[email protected]") != 1 {
+		t.Fatalf("a message the caller cannot read must not name its sender:\n%s", got)
+	}
+	if !strings.Contains(got, "--- hidden ---\n[message not visible to you]") {
+		t.Fatalf("missing hidden placeholder in:\n%s", got)
+	}
 	if strings.Index(got, "root body") > strings.Index(got, "latest reply") {
 		t.Fatal("root must come first (top to bottom)")
 	}