diff --git a/README.md b/README.md
index fe4ccfc..6b2e884 100644
--- a/README.md
+++ b/README.md
@@ -268,6 +268,18 @@ distrobox enter --no-workdir captioneer-dev -- bash -lc '
 
 Run this from the repository root. The build and run helpers resolve that path automatically.
 
+### Manual desktop smoke test
+
+`scripts/smoke/desktop-smoke.sh` boots a nested headless Wayland desktop (sway) inside the `captioneer-dev` Distrobox, routes synthesized `espeak-ng` speech through a temporary PipeWire null sink, runs the real `build/captioneer-desktop` binary against it, and fails on ERROR diagnostics, an unclean shutdown, or an empty caption transcript.
+
+```bash
+./scripts/download-models.sh      # once, if models/ is missing
+./scripts/distrobox/build.sh      # produce build/captioneer-desktop
+./scripts/smoke/desktop-smoke.sh
+```
+
+Exit `0` means pass; a report is written under `build/smoke/<timestamp>/report.txt` together with the application logs and caption transcripts. The harness installs `sway` and `espeak-ng` into the Distrobox on demand and restores the previous default sink when it finishes. If VAD recognition of synthetic speech proves flaky, rerun with `CAPTIONEER_SMOKE_MODE=fixed`. This test is manual-only and intentionally not part of CI: it needs downloaded models, a nested compositor, and live audio routing.
+
 ## Gitea Actions and releases
 
 The `Tests` workflow runs the normal and GTK-tagged Go tests, `go vet`, and ShellCheck for every pull request and branch push. To make it mandatory for pull requests, open the repository's **Settings → Branches**, edit the protection rule for `master`, enable required status checks, and select **Tests / Go and GTK tests** after its first run. Workflow files can report the check, but the branch-protection rule is what prevents merging when it fails.
diff --git a/plan_smoke_test.md b/plan_smoke_test.md
new file mode 100644
index 0000000..10dbe5e
--- /dev/null
+++ b/plan_smoke_test.md
@@ -0,0 +1,122 @@
+---
+name: Desktop smoke harness
+overview: Add a Distrobox-based nested Wayland desktop smoke test that boots a headless compositor, plays synthesized speech into a temporary PipeWire null sink, runs captioneer-desktop, and fails on errors or missing captions — fast enough for manual runs, realistic enough to catch integration breakages.
+todos:
+  - id: smoke-lib
+    content: Add scripts/smoke/lib.sh (null sink, espeak fixture, wait helpers, cleanup traps)
+    status: completed
+  - id: smoke-script
+    content: Add scripts/smoke/desktop-smoke.sh orchestrating labwc + captioneer-desktop + assertions
+    status: completed
+  - id: smoke-deps
+    content: On-demand Distrobox package install for labwc/espeak-ng (and ffmpeg if needed)
+    status: completed
+  - id: smoke-docs-ci
+    content: Document in README; ShellCheck the new scripts from scripts/ci/test.sh
+    status: in_progress
+isProject: false
+---
+
+# Desktop smoke harness
+
+## Approach (chosen default)
+
+**Not a full QEMU VM.** A nested Wayland compositor inside the existing Distrobox is the better tradeoff: boots in seconds, still exercises GTK, Layer Shell, Pulse capture, model worker, and caption logging. Full VMs add minutes of boot/image management without much extra signal for this app.
+
+```mermaid
+flowchart TD
+  host[Host PipeWire] --> nullSink[temp null sink]
+  script[desktop-smoke.sh] --> box[captioneer-dev Distrobox]
+  box --> labwc[labwc headless Wayland]
+  box --> app[captioneer-desktop]
+  nullSink --> play[paplay espeak WAV]
+  nullSink --> app
+  app --> log[stderr diagnostics]
+  app --> transcript[caption-log dir]
+  script --> assert[pass/fail report]
+  log --> assert
+  transcript --> assert
+```
+
+## What you will run
+
+```bash
+./scripts/download-models.sh   # once, if models/ missing
+./scripts/distrobox/build.sh   # ensure build/captioneer-desktop exists
+./scripts/smoke/desktop-smoke.sh
+```
+
+Exit `0` = pass. Prints a short report under `build/smoke/`.
+
+## Harness layout
+
+| Path | Role |
+| --- | --- |
+| [`scripts/smoke/desktop-smoke.sh`](scripts/smoke/desktop-smoke.sh) | Orchestrator (manual entrypoint) |
+| [`scripts/smoke/lib.sh`](scripts/smoke/lib.sh) | Shared helpers: null sink, espeak fixture, wait/assert |
+| Extend [`scripts/distrobox/common.sh`](scripts/distrobox/common.sh) | Add smoke packages: `labwc`, `espeak-ng`, `ffmpeg` (or keep install-on-demand in smoke script to avoid bloating every build) |
+
+**Package strategy:** install smoke deps on demand inside `desktop-smoke.sh` via `sudo dnf install -y` in the Distrobox (same pattern as `ensure_dependencies`), so normal `build.sh` / `run.sh` stay lean.
+
+## Test sequence
+
+1. **Preflight**
+   - Require Distrobox, `build/captioneer-desktop`, `models/parakeet-tdt-v2/`, `models/silero_vad_v5.onnx`
+   - Create work dir `build/smoke/<timestamp>/`
+
+2. **Audio sandbox (host-visible via Distrobox Pulse integration)**
+   - `pactl load-module module-null-sink sink_name=captioneer-smoke`
+   - Save/restore previous default sink
+   - `pactl set-default-sink captioneer-smoke`
+   - Synthesize a short clear English line with `espeak-ng` → WAV in the work dir
+   - Loop-play with `paplay` for ~15–20s so VAD/fixed mode has time to finalize
+
+3. **Nested desktop**
+   - Start `labwc` (wlroots, Layer Shell capable) with `WLR_BACKENDS=headless WLR_LIBINPUT_NO_DEVICES=1`
+   - Export `WAYLAND_DISPLAY` to that socket; `GSK_RENDERER=cairo`
+
+4. **Launch Captioneer**
+   ```bash
+   ./build/captioneer-desktop \
+     --no-config \
+     --start-captions=true \
+     --output=both \
+     --stderr-diagnostics=true \
+     --caption-log=true \
+     --caption-log-dir="$workdir/transcripts" \
+     --models-dir=models \
+     --mode=vad \
+     --model-auto-restart=false
+   ```
+   - Redirect stderr to `$workdir/captioneer.stderr.log`
+   - Present main window first (already true in current [`src/gui/app.go`](src/gui/app.go)), so compositor + GUI come up before capture
+
+5. **Settle + stop**
+   - Wait until stderr contains `Model worker ready` (timeout ~60s)
+   - Keep playing speech ~15s more
+   - Send clean shutdown (`gdbus` `app.exit` or SIGINT)
+   - Wait for exit; unload null sink; kill labwc
+
+6. **Assertions (fail hard)**
+   - Process exited 0 (or SIGINT-clean)
+   - stderr has `Model worker ready` and `Capturing from:`
+   - No `ERROR` lines in stderr (allow listed WARNINGs only if needed, e.g. always-on-top on Wayland)
+   - At least one non-empty caption log file under the smoke transcript dir **or**, if recognition is too flaky on synthetic speech, fall back to requiring `INFO [lifecycle]` start/stop without ERROR and treat caption text as a soft check printed in the report
+
+**Caption reliability default:** require caption log content. If espeak+VAD proves flaky in practice, switch the harness to `--mode=fixed --chunk-duration=1s` (still in the same script) before softening the assertion — fixed mode is more predictable with continuous playback.
+
+## Report
+
+Write `$workdir/report.txt` with: compositor, sink name, key log greps, transcript excerpt, pass/fail. Always print the report path on exit.
+
+## Docs / CI wiring
+
+- Short “Manual desktop smoke” subsection in [`README.md`](README.md) Development section
+- Add `scripts/smoke/desktop-smoke.sh` + `lib.sh` to ShellCheck in [`scripts/ci/test.sh`](scripts/ci/test.sh)
+- **Do not** add this to Gitea CI yet (needs models + nested compositor + audio; too heavy/flaky for every PR). Manual-only until it proves stable.
+
+## Out of scope
+
+- Full QEMU/libvirt guest image
+- Automating CTRL+drag overlay positioning
+- Pixel screenshot OCR of the overlay bubble
diff --git a/scripts/ci/test.sh b/scripts/ci/test.sh
index 081cb12..6a20634 100755
--- a/scripts/ci/test.sh
+++ b/scripts/ci/test.sh
@@ -16,4 +16,6 @@ shellcheck \
   scripts/distrobox/run.sh \
   scripts/ci/test.sh \
   scripts/ci/package-release.sh \
-  scripts/ci/publish-release.sh
+  scripts/ci/publish-release.sh \
+  scripts/smoke/lib.sh \
+  scripts/smoke/desktop-smoke.sh
diff --git a/scripts/smoke/desktop-smoke.sh b/scripts/smoke/desktop-smoke.sh
new file mode 100755
index 0000000..ba6d1b9
--- /dev/null
+++ b/scripts/smoke/desktop-smoke.sh
@@ -0,0 +1,190 @@
+#!/usr/bin/env bash
+# Manual desktop smoke test.
+#
+# Boots a headless Wayland compositor (sway) inside the captioneer-dev
+# Distrobox, routes synthesized speech through a temporary PipeWire null
+# sink, runs the real captioneer-desktop binary against it, and fails on
+# diagnostics errors or missing captions.
+#
+# Usage (from the repository root, on the host):
+#   ./scripts/download-models.sh        # once
+#   ./scripts/distrobox/build.sh        # produce build/captioneer-desktop
+#   ./scripts/smoke/desktop-smoke.sh
+#
+# Environment:
+#   CAPTIONEER_SMOKE_MODE      vad (default) or fixed
+#   CAPTIONEER_SMOKE_SPEECH_S  seconds of speech to play (default 20)
+set -Eeuo pipefail
+
+script_dir="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd -P)"
+repo_root="$(cd -- "$script_dir/../.." && pwd -P)"
+
+# ---------------------------------------------------------------------------
+# Host phase: prepare the Distrobox and re-execute this script inside it.
+# ---------------------------------------------------------------------------
+if [[ -z "${CAPTIONEER_SMOKE_INNER:-}" && -z "${CONTAINER_ID:-}" ]]; then
+  # shellcheck source=scripts/distrobox/common.sh
+  source "$repo_root/scripts/distrobox/common.sh"
+  prepare_distrobox
+
+  [[ -x "$repo_root/build/captioneer-desktop" ]] \
+    || die "build/captioneer-desktop is missing; run ./scripts/distrobox/build.sh first"
+  [[ -d "$repo_root/models/parakeet-tdt-v2" ]] \
+    || die "models/parakeet-tdt-v2 is missing; run ./scripts/download-models.sh first"
+  [[ -f "$repo_root/models/silero_vad_v5.onnx" ]] \
+    || die "models/silero_vad_v5.onnx is missing; run ./scripts/download-models.sh first"
+
+  # shellcheck disable=SC2016 # Positional parameters expand inside the container.
+  # shellcheck disable=SC2154 # container_name is defined by common.sh above.
+  exec distrobox enter --no-workdir --name "$container_name" -- \
+    bash -lc 'CAPTIONEER_SMOKE_INNER=1 exec bash "$1"' captioneer-smoke \
+    "$repo_root/scripts/smoke/desktop-smoke.sh"
+fi
+
+# ---------------------------------------------------------------------------
+# Inner phase: runs inside the Distrobox.
+# ---------------------------------------------------------------------------
+# shellcheck source=scripts/smoke/lib.sh
+source "$script_dir/lib.sh"
+
+smoke_mode="${CAPTIONEER_SMOKE_MODE:-vad}"
+speech_seconds="${CAPTIONEER_SMOKE_SPEECH_S:-20}"
+
+# On-demand smoke dependencies; kept out of common.sh so normal builds stay lean.
+smoke_packages=(sway espeak-ng)
+missing_packages=()
+for package in "${smoke_packages[@]}"; do
+  rpm -q "$package" >/dev/null 2>&1 || missing_packages+=("$package")
+done
+if (( ${#missing_packages[@]} > 0 )); then
+  smoke_log "installing smoke dependencies: ${missing_packages[*]}"
+  sudo dnf install -y "${missing_packages[@]}"
+fi
+
+cd -- "$repo_root"
+workdir="$repo_root/build/smoke/$(date +%Y%m%d-%H%M%S)"
+mkdir -p "$workdir/transcripts"
+smoke_log "work directory: $workdir"
+
+trap smoke_cleanup EXIT
+
+smoke_setup_audio "$workdir"
+wayland_socket="$(smoke_start_compositor "$workdir")"
+smoke_log "nested compositor ready on $wayland_socket"
+
+# ---------------------------------------------------------------------------
+# Launch the desktop application.
+# ---------------------------------------------------------------------------
+env \
+  WAYLAND_DISPLAY="$wayland_socket" \
+  GDK_BACKEND=wayland \
+  GSK_RENDERER=cairo \
+  ./build/captioneer-desktop \
+  --no-config \
+  --start-captions=true \
+  --output=both \
+  --stderr-diagnostics=true \
+  --caption-log=true \
+  --caption-log-dir="$workdir/transcripts" \
+  --models-dir=models \
+  --mode="$smoke_mode" \
+  --model-auto-restart=false \
+  > "$workdir/captioneer.stdout.log" \
+  2> "$workdir/captioneer.stderr.log" &
+SMOKE_APP_PID=$!
+smoke_log "captioneer-desktop started (pid $SMOKE_APP_PID, mode $smoke_mode)"
+
+stderr_log="$workdir/captioneer.stderr.log"
+
+if ! smoke_wait_for_line "$stderr_log" "Model worker ready" 60; then
+  smoke_fail "model worker did not become ready within 60s"
+fi
+if ! smoke_wait_for_line "$stderr_log" "Capturing from:" 30; then
+  smoke_fail "audio capture did not start within 30s"
+fi
+
+if (( ${#SMOKE_FAILURES[@]} == 0 )); then
+  smoke_log "playing synthesized speech for ${speech_seconds}s"
+  smoke_play_speech "$workdir" "$speech_seconds"
+  wait "$SMOKE_PLAYER_PID" 2>/dev/null || true
+  SMOKE_PLAYER_PID=""
+  # Allow VAD finalization (500ms pause) and transcript flush to settle.
+  sleep 4
+fi
+
+smoke_stop_app
+app_exit=0
+if smoke_wait_for_exit "$SMOKE_APP_PID" 20; then
+  wait "$SMOKE_APP_PID" 2>/dev/null || app_exit=$?
+else
+  smoke_fail "application did not exit within 20s of SIGINT"
+  kill -KILL "$SMOKE_APP_PID" 2>/dev/null || true
+  app_exit=137
+fi
+SMOKE_APP_PID=""
+
+# ---------------------------------------------------------------------------
+# Assertions.
+# ---------------------------------------------------------------------------
+if (( app_exit == 0 )); then
+  smoke_pass "clean shutdown (exit 0)"
+else
+  smoke_fail "application exited with status $app_exit"
+fi
+
+if grep -q "Model worker ready" "$stderr_log"; then
+  smoke_pass "model worker started"
+fi
+if grep -q "Capturing from:" "$stderr_log"; then
+  smoke_pass "audio capture attached to a monitor source"
+fi
+
+if grep -E " ERROR " "$stderr_log" > "$workdir/errors.txt"; then
+  smoke_fail "diagnostics contain ERROR lines (see errors.txt)"
+else
+  smoke_pass "no ERROR diagnostics"
+fi
+
+mapfile -t caption_files < <(find "$workdir/transcripts" -type f -size +0c 2>/dev/null)
+if (( ${#caption_files[@]} > 0 )); then
+  smoke_pass "caption log contains recognized speech"
+else
+  smoke_fail "no captions were recognized; inspect $workdir and consider CAPTIONEER_SMOKE_MODE=fixed"
+fi
+
+# ---------------------------------------------------------------------------
+# Report.
+# ---------------------------------------------------------------------------
+report="$workdir/report.txt"
+{
+  printf 'Captioneer desktop smoke report\n'
+  printf 'Date:        %s\n' "$(date --rfc-3339=seconds)"
+  printf 'Mode:        %s\n' "$smoke_mode"
+  printf 'Compositor:  sway headless (%s)\n' "$wayland_socket"
+  printf 'Sink:        %s\n' "$SMOKE_SINK_NAME"
+  printf 'App exit:    %s\n' "$app_exit"
+  printf '\n--- Key diagnostics ---\n'
+  grep -E " (ERROR|WARNING) |Model worker ready|Capturing from:|Shutting down" \
+    "$stderr_log" 2>/dev/null || printf '(none)\n'
+  printf '\n--- Caption transcript excerpt ---\n'
+  if (( ${#caption_files[@]} > 0 )); then
+    head -n 10 "${caption_files[@]}" 2>/dev/null
+  else
+    printf '(empty)\n'
+  fi
+  printf '\n--- Result ---\n'
+  if (( ${#SMOKE_FAILURES[@]} == 0 )); then
+    printf 'PASS\n'
+  else
+    printf 'FAIL:\n'
+    printf '  - %s\n' "${SMOKE_FAILURES[@]}"
+  fi
+} > "$report"
+
+cat "$report"
+smoke_log "full report: $report"
+
+if (( ${#SMOKE_FAILURES[@]} > 0 )); then
+  exit 1
+fi
+exit 0
diff --git a/scripts/smoke/lib.sh b/scripts/smoke/lib.sh
new file mode 100755
index 0000000..dce26bd
--- /dev/null
+++ b/scripts/smoke/lib.sh
@@ -0,0 +1,152 @@
+#!/usr/bin/env bash
+# Shared helpers for the manual desktop smoke test. Sourced by
+# scripts/smoke/desktop-smoke.sh inside the captioneer-dev Distrobox.
+set -Eeuo pipefail
+
+SMOKE_SINK_NAME="captioneer-smoke"
+SMOKE_SINK_MODULE=""
+SMOKE_PREVIOUS_SINK=""
+SMOKE_COMPOSITOR_PID=""
+SMOKE_APP_PID=""
+SMOKE_PLAYER_PID=""
+SMOKE_FAILURES=()
+
+smoke_log() {
+  printf 'smoke: %s\n' "$*" >&2
+}
+
+smoke_die() {
+  printf 'smoke: FATAL: %s\n' "$*" >&2
+  exit 1
+}
+
+smoke_fail() {
+  SMOKE_FAILURES+=("$1")
+  smoke_log "FAIL: $1"
+}
+
+smoke_pass() {
+  smoke_log "ok: $1"
+}
+
+# smoke_wait_for_line FILE PATTERN TIMEOUT_SECONDS
+smoke_wait_for_line() {
+  local file=$1 pattern=$2 timeout=$3 waited=0
+  until grep -q -- "$pattern" "$file" 2>/dev/null; do
+    if (( waited >= timeout )); then
+      return 1
+    fi
+    sleep 1
+    waited=$((waited + 1))
+  done
+  return 0
+}
+
+# smoke_wait_for_exit PID TIMEOUT_SECONDS; returns 1 on timeout
+smoke_wait_for_exit() {
+  local pid=$1 timeout=$2 waited=0
+  while kill -0 "$pid" 2>/dev/null; do
+    if (( waited >= timeout )); then
+      return 1
+    fi
+    sleep 1
+    waited=$((waited + 1))
+  done
+  return 0
+}
+
+smoke_setup_audio() {
+  local workdir=$1
+  command -v pactl >/dev/null 2>&1 || smoke_die "pactl is required"
+  command -v paplay >/dev/null 2>&1 || smoke_die "paplay is required"
+  SMOKE_PREVIOUS_SINK="$(pactl get-default-sink 2>/dev/null || true)"
+  SMOKE_SINK_MODULE="$(pactl load-module module-null-sink \
+    "sink_name=$SMOKE_SINK_NAME" \
+    "sink_properties=device.description=Captioneer-Smoke")"
+  pactl set-default-sink "$SMOKE_SINK_NAME"
+  smoke_log "null sink $SMOKE_SINK_NAME loaded (module $SMOKE_SINK_MODULE, previous default: ${SMOKE_PREVIOUS_SINK:-none})"
+
+  command -v espeak-ng >/dev/null 2>&1 || smoke_die "espeak-ng is required"
+  espeak-ng -v en-us -s 140 -w "$workdir/speech.wav" \
+    "The quick brown fox jumps over the lazy dog. Live captions should appear for this sentence."
+  [[ -s "$workdir/speech.wav" ]] || smoke_die "espeak-ng produced no audio fixture"
+}
+
+smoke_teardown_audio() {
+  if [[ -n "$SMOKE_PLAYER_PID" ]] && kill -0 "$SMOKE_PLAYER_PID" 2>/dev/null; then
+    kill "$SMOKE_PLAYER_PID" 2>/dev/null || true
+  fi
+  if [[ -n "$SMOKE_PREVIOUS_SINK" ]]; then
+    pactl set-default-sink "$SMOKE_PREVIOUS_SINK" 2>/dev/null || true
+  fi
+  if [[ -n "$SMOKE_SINK_MODULE" ]]; then
+    pactl unload-module "$SMOKE_SINK_MODULE" 2>/dev/null || true
+    SMOKE_SINK_MODULE=""
+  fi
+}
+
+# smoke_play_speech WORKDIR SECONDS: loop the fixture into the null sink.
+smoke_play_speech() {
+  local workdir=$1 seconds=$2
+  (
+    end=$((SECONDS + seconds))
+    while (( SECONDS < end )); do
+      paplay --device="$SMOKE_SINK_NAME" "$workdir/speech.wav" 2>/dev/null || sleep 1
+    done
+  ) &
+  SMOKE_PLAYER_PID=$!
+}
+
+# smoke_start_compositor WORKDIR: starts headless sway; prints new socket name.
+# sway is wlroots-based (Layer Shell capable) and, unlike labwc, can disable
+# Xwayland, whose sockets are not creatable inside a rootless Distrobox.
+smoke_start_compositor() {
+  local workdir=$1 candidate socket="" waited=0
+  command -v sway >/dev/null 2>&1 || smoke_die "sway is required"
+  local before="$workdir/sockets-before.txt"
+  find "$XDG_RUNTIME_DIR" -maxdepth 1 -name 'wayland-[0-9]*' ! -name '*.lock' \
+    -printf '%f\n' 2>/dev/null | sort > "$before"
+
+  printf 'xwayland disable\n' > "$workdir/sway-config"
+  WLR_BACKENDS=headless \
+    WLR_LIBINPUT_NO_DEVICES=1 \
+    WLR_RENDERER=pixman \
+    sway -c "$workdir/sway-config" > "$workdir/compositor.log" 2>&1 &
+  SMOKE_COMPOSITOR_PID=$!
+
+  while (( waited < 15 )); do
+    while IFS= read -r candidate; do
+      socket="$candidate"
+    done < <(find "$XDG_RUNTIME_DIR" -maxdepth 1 -name 'wayland-[0-9]*' ! -name '*.lock' \
+      -printf '%f\n' 2>/dev/null | sort | comm -13 "$before" -)
+    if [[ -n "$socket" ]]; then
+      printf '%s\n' "$socket"
+      return 0
+    fi
+    kill -0 "$SMOKE_COMPOSITOR_PID" 2>/dev/null || smoke_die "sway exited early; see $workdir/compositor.log"
+    sleep 1
+    waited=$((waited + 1))
+  done
+  smoke_die "sway did not create a Wayland socket; see $workdir/compositor.log"
+}
+
+smoke_teardown_compositor() {
+  if [[ -n "$SMOKE_COMPOSITOR_PID" ]] && kill -0 "$SMOKE_COMPOSITOR_PID" 2>/dev/null; then
+    kill "$SMOKE_COMPOSITOR_PID" 2>/dev/null || true
+  fi
+}
+
+smoke_stop_app() {
+  if [[ -n "$SMOKE_APP_PID" ]] && kill -0 "$SMOKE_APP_PID" 2>/dev/null; then
+    kill -INT "$SMOKE_APP_PID" 2>/dev/null || true
+  fi
+}
+
+smoke_cleanup() {
+  smoke_stop_app
+  if [[ -n "$SMOKE_APP_PID" ]]; then
+    smoke_wait_for_exit "$SMOKE_APP_PID" 10 || kill -KILL "$SMOKE_APP_PID" 2>/dev/null || true
+  fi
+  smoke_teardown_audio
+  smoke_teardown_compositor
+}