Worker thread + tray icon repaint fix

- processUtterance runs on a detached std.Thread; Qt event loop stays
  responsive during whisper/letta/melo (icon repaints, menu works)
- setState marshals to main thread via threading.async with thread-id check
- rapid double-click race guarded: state claimed before spawn
- icon: QPainter-drawn antialiased circle (dark rim, transparent bg) —
  bare pixmap.fill rendered blank on the KDE SNI host
- new qt libs: qbrush, qpainter, qrect, qt6zigthreading

👾 Generated with [Letta Code](https://letta.com)

Co-Authored-By: Letta Code <noreply@letta.com>

src/main.zig

@@ -14,6 +14,10 @@ const QAction = qt6.QAction;
 const QPixmap = qt6.QPixmap;
 const QIcon = qt6.QIcon;
 const QColor = qt6.QColor;
+const QPainter = qt6.QPainter;
+const QBrush = qt6.QBrush;
+const QRectF = qt6.QRectF;
+const threading = qt6.threading;
 const letta = @import("letta.zig");
 
 // ------------------------------------------------------------- constants ---
@@ -75,15 +79,39 @@ fn setLastUserText(text: []u8) void {
 var current_icon: ?QIcon = null;
 var current_pixmap: ?QPixmap = null;
 
-fn setState(next: State) void {
+var main_thread_id: std.Thread.Id = 0;
+var pending_state: State = .idle;
+
+/// Must run on the Qt main thread (touches QSystemTrayIcon / QPixmap).
+fn setStateMainThread(next: State) void {
     state = next;
 
+    // Circle icon drawn with QPainter — a bare pixmap.fill rendered blank
+    // on the KDE SNI host.
     const c = next.color();
     const color = QColor.new5(c[0], c[1], c[2]);
     defer color.delete();
+    const pen_color = QColor.new5(20, 20, 26);
+    defer pen_color.delete();
+    const transparent = QColor.new8("transparent");
+    defer transparent.delete();
 
     const pixmap = QPixmap.new2(128, 128);
-    pixmap.fill1(color);
+    pixmap.fill1(transparent);
+
+    const brush = QBrush.new3(color);
+    defer brush.delete();
+
+    const painter = QPainter.new();
+    _ = painter.begin(pixmap);
+    painter.setRenderHint(1); // Antialiasing
+    painter.setPen(pen_color);
+    painter.setBrush(brush);
+    const rect = QRectF.new6(16, 16, 96, 96);
+    defer rect.delete();
+    painter.drawEllipse(rect);
+    _ = painter.end();
+    painter.delete();
 
     const icon = QIcon.new2(pixmap);
 
@@ -99,6 +127,21 @@ fn setState(next: State) void {
     tray_icon.setToolTip(tip);
 }
 
+fn onStateFromWorker(_: ?*anyopaque) callconv(.c) void {
+    setStateMainThread(pending_state);
+}
+
+/// Thread-safe state transition: runs directly on the main thread, or
+/// marshals through Qt's event loop when called from the pipeline worker.
+fn setState(next: State) void {
+    if (std.Thread.getCurrentId() == main_thread_id) {
+        setStateMainThread(next);
+    } else {
+        pending_state = next;
+        threading.async(null, onStateFromWorker);
+    }
+}
+
 /// Play a WAV via pw-play (blocking; audio length). Fine for v1 — same
 /// thread already blocks on whisper/letta. UI-thread decoupling comes later.
 fn playWav(path: []const u8) void {
@@ -258,7 +301,16 @@ fn onTrayActivated(_: QSystemTrayIcon, reason: i32) callconv(.c) void {
         },
         .recording => {
             stopRecording();
-            processUtterance(); // chains transcribe -> infer -> speak -> re-listen
+            setState(.transcribing); // claim the pipeline slot before spawning
+            // Pipeline runs on a worker thread; the Qt event loop stays
+            // responsive (icon repaints, menu works) while whisper/letta/melo
+            // block. setState marshals back to the main thread.
+            const worker = std.Thread.spawn(.{}, processUtterance, .{}) catch |e| {
+                std.debug.print("inferon: failed to spawn worker: {s}\n", .{@errorName(e)});
+                setState(.error_backend);
+                return;
+            };
+            worker.detach();
         },
         // Clicks during the pipeline are no-ops now — states advance on their own.
         .transcribing, .thinking, .speaking => {},
@@ -347,6 +399,7 @@ pub fn main(init: std.process.Init) !void {
 
     setState(.idle);
     tray_icon.show();
+    main_thread_id = std.Thread.getCurrentId();
 
     // Own the whisper-server lifecycle: spawn AFTER the tray exists (setState
     // touches tray_icon). Create the log dir first.