diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5197964..8ebbe26 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,21 @@ All notable changes to PolterType are recorded here. The format is
 loosely based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and the project follows [Semantic Versioning](https://semver.org/).
 
+## [Unreleased]
+
+### macOS
+
+- **PolterType no longer blocks display / system sleep when the sound
+  output is HDMI (or DisplayPort).** The audio worker cached its
+  CoreAudio `OutputStream` for the whole life of the process once a
+  sound had played, and an open output stream on an HDMI device keeps
+  coreaudiod's power assertion alive — macOS then refuses to turn the
+  screen off or sleep, as if audio were playing forever. The worker
+  now releases the stream after 30 s without a sound command (the
+  existing `STREAM_IDLE_REFRESH` window) and reopens it lazily on the
+  next play; the ~20-50 ms reopen cost is hidden under the synth
+  tone's lead silence.
+
 ## [0.12.0] — the AI socket ships in the box
 
 ### Changed
@@ -62,7 +77,6 @@ and the project follows [Semantic Versioning](https://semver.org/).
   quotes. Still no automatic restart — a plug-in that crashes on
   startup would become a fork bomb, and the failure would go back to
   being invisible.
-
 ## [0.11.0] — plug-ins that run, and the first release Windows was actually held to
 
 Two blocks, and they meet in one place: the plug-in system landed in
diff --git a/crates/poltertype-core/src/audio/consts.rs b/crates/poltertype-core/src/audio/consts.rs
index 6992a55..c84c03e 100644
--- a/crates/poltertype-core/src/audio/consts.rs
+++ b/crates/poltertype-core/src/audio/consts.rs
@@ -2,8 +2,11 @@
 
 use std::time::Duration;
 
-/// Drop the cached `OutputStream` after this much idle time so the
-/// next play picks up the (possibly changed) default audio device.
+/// Drop the cached `OutputStream` after this much idle time. Two
+/// reasons: the next play picks up the (possibly changed) default
+/// audio device, and — critically on macOS with HDMI output — an
+/// idle open stream otherwise keeps coreaudiod's power assertion
+/// alive and blocks display/system sleep.
 /// 30 s is well above any plausible "pause-resume burst" cadence,
 /// so rapid hotkey use stays on the warm cached stream.
 pub(crate) const STREAM_IDLE_REFRESH: Duration = Duration::from_secs(30);
diff --git a/crates/poltertype-core/src/audio/mod.rs b/crates/poltertype-core/src/audio/mod.rs
index 1750ac4..352f6e4 100644
--- a/crates/poltertype-core/src/audio/mod.rs
+++ b/crates/poltertype-core/src/audio/mod.rs
@@ -26,6 +26,14 @@
 //! these handle "user just plugged in headphones" gracefully without
 //! paying the per-play cost during normal pause / resume bursts.
 //!
+//! The cached stream is also **released outright** after
+//! [`STREAM_IDLE_REFRESH`] with no commands. A permanently open
+//! CoreAudio output on an HDMI / DisplayPort device keeps
+//! coreaudiod's power assertion alive, which on macOS blocks display
+//! and system sleep ("app holds the audio focus" symptom). Letting
+//! go of the stream between plays costs one ~20-50 ms reopen, hidden
+//! under the synth's lead silence.
+//!
 //! Themes live in `<config-dir>/sound-themes/<name>/<event>.ogg`.
 //! Missing files are silent — we never crash because audio is absent.
 
diff --git a/crates/poltertype-core/src/audio/worker.rs b/crates/poltertype-core/src/audio/worker.rs
index d827236..ac696bb 100644
--- a/crates/poltertype-core/src/audio/worker.rs
+++ b/crates/poltertype-core/src/audio/worker.rs
@@ -8,11 +8,42 @@ use std::io::BufReader;
 use tracing::{debug, info, warn};
 
 pub(crate) fn run_worker(rx: crossbeam_channel::Receiver<AudioCmd>) {
-    info!("audio worker started (cached OutputStream + idle refresh)");
+    use crossbeam_channel::RecvTimeoutError;
+
+    info!("audio worker started (cached OutputStream + idle release)");
 
     let mut state = WorkerState::new();
 
-    while let Ok(cmd) = rx.recv() {
+    loop {
+        // Block indefinitely while there is no stream to release;
+        // only poll on a timeout while a stream is cached. Waiting
+        // with `recv_timeout` unconditionally would wake the worker
+        // every 30 s for the life of the process just to discover
+        // there is nothing to drop.
+        let cmd = if state.stream.is_some() {
+            match rx.recv_timeout(STREAM_IDLE_REFRESH) {
+                Ok(cmd) => cmd,
+                Err(RecvTimeoutError::Timeout) => {
+                    // No plays for a whole refresh window — release
+                    // the stream. A long-lived open CoreAudio output
+                    // on an HDMI / DisplayPort device keeps
+                    // coreaudiod's power assertion alive, which on
+                    // macOS blocks display sleep and system sleep.
+                    // Dropping the stream hands the device back and
+                    // costs only a ~20-50 ms reopen on the next sound
+                    // (cushioned by LEAD_SILENCE_MS).
+                    debug!("audio: idle timeout — releasing output stream");
+                    state.invalidate();
+                    continue;
+                }
+                Err(RecvTimeoutError::Disconnected) => break,
+            }
+        } else {
+            match rx.recv() {
+                Ok(cmd) => cmd,
+                Err(_) => break,
+            }
+        };
         match cmd {
             AudioCmd::Refresh {
                 theme_dir: d,