report the working directory to the terminal with OSC 7

Before each prompt gosh sends ESC ] 7 ; file://host/path BEL (host and
path percent-encoded), so terminals like GNOME Terminal open new tabs
and windows in the directory of the shell instead of the one gosh was
started in. Nothing is sent if stdout is not a terminal or TERM=dumb.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

main_test.go

@@ -1133,6 +1133,31 @@ func TestBuildPrompt_ColorEscapesControlCharacters(t *testing.T) {
 	}
 }
 
+func TestOSC7Sequence(t *testing.T) {
+	tests := []struct{ host, dir, want string }{
+		{"host", "/home/flow", "\x1b]7;file://host/home/flow\a"},
+		{"host", "/tmp/a b/ä", "\x1b]7;file://host/tmp/a%20b/%C3%A4\a"},
+		{"host", "/x%y#z?", "\x1b]7;file://host/x%25y%23z%3F\a"},
+		{"", "/", "\x1b]7;file:///\a"},
+	}
+	for _, tt := range tests {
+		if got := osc7Sequence(tt.host, tt.dir); got != tt.want {
+			t.Errorf("osc7Sequence(%q, %q) = %q, want %q", tt.host, tt.dir, got, tt.want)
+		}
+	}
+}
+
+func TestOSC7Sequence_EscapesControlCharacters(t *testing.T) {
+	got := osc7Sequence("ho/st\x07", "/evil\x07\x1b]0;title\x1b\\")
+	body := strings.TrimSuffix(strings.TrimPrefix(got, "\x1b]7;"), "\a")
+	if strings.ContainsAny(body, "\x07\x1b") {
+		t.Errorf("sequence contains control characters: %q", got)
+	}
+	if !strings.HasPrefix(body, "file://ho%2Fst%07/evil%07%1B") {
+		t.Errorf("unexpected encoding: %q", got)
+	}
+}
+
 func TestUseColor_NoColor(t *testing.T) {
 	t.Setenv("NO_COLOR", "1")
 	if useColor() {