Reduce idle wakeups via event-driven loop

docs/architecture.md

@@ -28,17 +28,18 @@ Architect is a terminal multiplexer displaying 9 interactive sessions in a 3×3
 
 ## Runtime Flow
 
-**main.zig** owns application lifetime, window sizing, PTY/session startup, configuration persistence, and the frame loop. Each frame it:
+**main.zig** owns application lifetime, window sizing, PTY/session startup, configuration persistence, and the frame loop. Each iteration it:
 
-1. Polls SDL events and scales coordinates to render space.
-2. Builds a lightweight `UiHost` snapshot and lets `UiRoot` handle events first.
-3. Runs remaining app logic (terminal input, resizing, keyboard shortcuts).
-4. Runs `xev` loop iteration for async process exit detection.
-5. Processes output from all sessions and drains async notifications.
+1. Computes a wait deadline (0ms when work is pending, ~16ms during inertia, up to 500ms when idle) and blocks on `SDL_WaitEventTimeout`.
+2. SDL events include user events posted by a dedicated IO thread (xev) whenever a PTY has data or a child exits.
+3. Builds a lightweight `UiHost` snapshot and lets `UiRoot` handle events first.
+4. Runs remaining app logic (terminal input, resizing, keyboard shortcuts).
+5. Processes PTY output only for sessions marked “ready” by the IO thread, then flushes queued stdin.
 6. Updates UI components and drains `UiAction` queue.
 7. Advances animation state if transitioning.
-8. Calls `renderer.render` for the scene, then `ui.render` for overlays, then presents.
-9. Sleeps based on idle/active frame targets (~16ms active, ~50ms idle).
+8. Calls `renderer.render` for the scene, then `ui.render` for overlays, then presents—only when something is dirty/animating.
+
+The IO-facing work is isolated on a dedicated xev thread: it watches all PTY masters for readability and process exits, then posts SDL user events that wake the main loop. Access to the xev loop is serialized with a mutex when (re)registering watchers during spawns or restarts.
 
 **renderer/render.zig** draws only the *scene*:
 - Terminal cell content with HarfBuzz-shaped text runs

src/c.zig

@@ -56,6 +56,8 @@ pub const SDL_FillSurfaceRect = c_import.SDL_FillSurfaceRect;
 pub const SDL_BlitSurface = c_import.SDL_BlitSurface;
 pub const SDL_GetError = c_import.SDL_GetError;
 pub const SDL_PollEvent = c_import.SDL_PollEvent;
+pub const SDL_WaitEventTimeout = c_import.SDL_WaitEventTimeout;
+pub const SDL_PushEvent = c_import.SDL_PushEvent;
 pub const SDL_Delay = c_import.SDL_Delay;
 pub const SDL_StartTextInput = c_import.SDL_StartTextInput;
 pub const SDL_StopTextInput = c_import.SDL_StopTextInput;
@@ -79,6 +81,7 @@ pub const SDL_EVENT_MOUSE_MOTION = c_import.SDL_EVENT_MOUSE_MOTION;
 pub const SDL_EVENT_MOUSE_WHEEL = c_import.SDL_EVENT_MOUSE_WHEEL;
 pub const SDL_EVENT_WINDOW_RESIZED = c_import.SDL_EVENT_WINDOW_RESIZED;
 pub const SDL_EVENT_WINDOW_MOVED = c_import.SDL_EVENT_WINDOW_MOVED;
+pub const SDL_EVENT_USER = c_import.SDL_EVENT_USER;
 pub const SDL_EVENT_DROP_BEGIN = c_import.SDL_EVENT_DROP_BEGIN;
 pub const SDL_EVENT_DROP_FILE = c_import.SDL_EVENT_DROP_FILE;
 pub const SDL_EVENT_DROP_TEXT = c_import.SDL_EVENT_DROP_TEXT;
@@ -96,6 +99,9 @@ pub const SDL_SCANCODE_END = c_import.SDL_SCANCODE_END;
 pub const SDL_KMOD_MODE = c_import.SDL_KMOD_MODE;
 pub const SDL_SCANCODE_AC_HOME = c_import.SDL_SCANCODE_AC_HOME;
 pub const SDL_SCANCODE_AC_END = c_import.SDL_SCANCODE_AC_END;
+pub const SDL_DisplayID = c_import.SDL_DisplayID;
+pub const SDL_GetPrimaryDisplay = c_import.SDL_GetPrimaryDisplay;
+pub const SDL_GetDisplayBounds = c_import.SDL_GetDisplayBounds;
 
 pub const SDL_SetTextureScaleMode = c_import.SDL_SetTextureScaleMode;
 pub const SDL_SCALEMODE_LINEAR = c_import.SDL_SCALEMODE_LINEAR;