terminal: rename set_window_title effect to title_changed

The effect callback no longer receives the title string directly.
Instead, the handler stores the title in terminal state via setTitle
before invoking the callback, so consumers query it through
handler.terminal.getTitle(). This removes the redundant parameter
and keeps the effect signature consistent with the new terminal
title field. Tests now verify terminal state directly rather than
tracking the title through the callback.

src/terminal/stream_terminal.zig

@@ -40,8 +40,10 @@ pub const Handler = struct {
         /// during the lifetime of the call.
         write_pty: ?*const fn (*Handler, [:0]const u8) void,
 
-        /// Called when the window title is set via OSC 2.
-        set_window_title: ?*const fn (*Handler, []const u8) void,
+        /// Called when the terminal title changes via escape sequences
+        /// (e.g. OSC 0/2). The new title can be queried via
+        /// handler.terminal.getTitle().
+        title_changed: ?*const fn (*Handler) void,
 
         /// No effects means that the stream effectively becomes readonly
         /// that only affects pure terminal state and ignores all side
@@ -49,7 +51,7 @@ pub const Handler = struct {
         pub const readonly: Effects = .{
             .bell = null,
             .write_pty = null,
-            .set_window_title = null,
+            .title_changed = null,
         };
     };
 
@@ -194,7 +196,7 @@ pub const Handler = struct {
 
             // Effect-based handlers
             .bell => self.bell(),
-            .window_title => self.setWindowTitle(value.title),
+            .window_title => self.windowTitle(value.title),
             .request_mode => self.requestMode(value.mode),
             .request_mode_unknown => self.requestModeUnknown(value.mode, value.ansi),
 
@@ -239,9 +241,24 @@ pub const Handler = struct {
         func(self, data);
     }
 
-    inline fn setWindowTitle(self: *Handler, title: []const u8) void {
-        const func = self.effects.set_window_title orelse return;
-        func(self, title);
+    inline fn windowTitle(self: *Handler, title_raw: []const u8) void {
+        // Prevent DoS attacks by limiting title length.
+        const max_title_len = 1024;
+        const title = if (title_raw.len > max_title_len) title: {
+            log.warn("title length {d} exceeds max length {d}, truncating", .{
+                title_raw.len,
+                max_title_len,
+            });
+            break :title title_raw[0..max_title_len];
+        } else title_raw;
+
+        self.terminal.setTitle(title) catch |err| {
+            log.warn("error setting title err={}", .{err});
+            return;
+        };
+
+        const func = self.effects.title_changed orelse return;
+        func(self);
     }
 
     fn requestMode(self: *Handler, mode: modes.Mode) void {
@@ -1178,25 +1195,23 @@ test "window_title effect is called" {
     defer t.deinit(testing.allocator);
 
     const S = struct {
-        var last_title: ?[]const u8 = null;
-        fn setWindowTitle(handler: *Handler, title: []const u8) void {
-            _ = handler;
-            if (last_title) |old| testing.allocator.free(old);
-            last_title = testing.allocator.dupe(u8, title) catch null;
+        var title_changed_count: usize = 0;
+        fn titleChanged(_: *Handler) void {
+            title_changed_count += 1;
         }
     };
-    S.last_title = null;
-    defer if (S.last_title) |t2| testing.allocator.free(t2);
+    S.title_changed_count = 0;
 
     var handler: Handler = .init(&t);
-    handler.effects.set_window_title = &S.setWindowTitle;
+    handler.effects.title_changed = &S.titleChanged;
 
     var s: Stream = .initAlloc(testing.allocator, handler);
     defer s.deinit();
 
     // Set window title via OSC 2
     s.nextSlice("\x1b]2;Hello World\x1b\\");
-    try testing.expectEqualStrings("Hello World", S.last_title.?);
+    try testing.expectEqualStrings("Hello World", t.getTitle().?);
+    try testing.expectEqual(@as(usize, 1), S.title_changed_count);
 }
 
 test "window_title effect not called without callback" {
@@ -1209,6 +1224,9 @@ test "window_title effect not called without callback" {
     // Should not crash when no callback is set
     s.nextSlice("\x1b]2;Hello World\x1b\\");
 
+    // Title should still be set on terminal state
+    try testing.expectEqualStrings("Hello World", t.getTitle().?);
+
     // Terminal should still be functional
     s.nextSlice("Test");
     const str = try t.plainString(testing.allocator);
@@ -1221,23 +1239,21 @@ test "window_title effect with empty title" {
     defer t.deinit(testing.allocator);
 
     const S = struct {
-        var last_title: ?[]const u8 = null;
-        fn setWindowTitle(handler: *Handler, title: []const u8) void {
-            _ = handler;
-            if (last_title) |old| testing.allocator.free(old);
-            last_title = testing.allocator.dupe(u8, title) catch null;
+        var title_changed_count: usize = 0;
+        fn titleChanged(_: *Handler) void {
+            title_changed_count += 1;
         }
     };
-    S.last_title = null;
-    defer if (S.last_title) |t2| testing.allocator.free(t2);
+    S.title_changed_count = 0;
 
     var handler: Handler = .init(&t);
-    handler.effects.set_window_title = &S.setWindowTitle;
+    handler.effects.title_changed = &S.titleChanged;
 
     var s: Stream = .initAlloc(testing.allocator, handler);
     defer s.deinit();
 
     // Set empty window title
     s.nextSlice("\x1b]2;\x1b\\");
-    try testing.expectEqualStrings("", S.last_title.?);
+    try testing.expect(t.getTitle() == null);
+    try testing.expectEqual(@as(usize, 1), S.title_changed_count);
 }

src/termio/stream_handler.zig

@@ -1002,7 +1002,7 @@ pub const StreamHandler = struct {
         // Set the title on the terminal state. We ignore any errors since
         // we can continue to operate just fine without it.
         self.terminal.setTitle(title) catch |err| {
-            log.warn("error setting title in terminal state: {e}", .{err});
+            log.warn("error setting title in terminal state: {}", .{err});
         };
 
         @memcpy(buf[0..title.len], title);