diff --git a/CHANGELOG.md b/CHANGELOG.md
index 63fb58c..05fc0de 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,7 +5,27 @@ All notable DeckDoc changes are recorded here. The project follows
 
 ## [Unreleased]
 
-No unreleased changes.
+### Added
+
+- External-display blackout coverage for desktop mode (#29): `display_blackout.sh` now inspects
+  connected non-eDP connectors in a KWin session, matches each display's EDID against the stored
+  KWin output policy, and emits `EXTERNAL_BLACKOUT_SIGNATURE: FULLSCREEN_SYNC_POLICY_GAP`,
+  `SYNC_POLICY_UNDETERMINED` (policy unreadable — treated as unpinned, never as fixed), or
+  `SYNC_POLICY_ALREADY_PINNED` when a physical-black symptom is declared with a healthy deck-side
+  link — the discriminator for fullscreen adaptive-sync blanking on a monitor or dock chain. The
+  internal and external assessments are independent, so an extended desktop reports both.
+- A guarded `rem_external_display.sh` remediation behind the new `--fix-external-display-blackout`
+  flag: pins adaptive sync off (`kscreen-doctor vrrpolicy.never`) for connected external outputs
+  after desktop-session and symptom prechecks, with config backup and verification scoped to each
+  targeted output (live state and per-EDID persistence). Shares the internal-panel remediation's
+  no-power/brightness/clock-write contract; the pinned policy itself persists per-display by KWin
+  design and is reversible via `vrrpolicy.automatic` or the saved backup.
+
+### Fixed
+
+- A connected-but-disabled internal panel (docked, external-only setups) no longer claims the
+  internal `LIVE_RENDER_TO_PHYSICAL_SCANOUT_GAP` signature ahead of an active external display;
+  the panel must be enabled in the output configuration for that classification.
 
 ## [3.4.0] - 2026-07-21
 
diff --git a/deckdoc.sh b/deckdoc.sh
index 72044c0..6c1f255 100755
--- a/deckdoc.sh
+++ b/deckdoc.sh
@@ -5,6 +5,7 @@ umask 077
 FIX_MODE=false
 DISPLAY_BLACK_REPORTED=false
 DISPLAY_FIX_MODE=false
+EXTERNAL_DISPLAY_FIX_MODE=false
 PERSIST_DISPLAY_STABILITY=false
 for arg in "$@"; do
     case "$arg" in
@@ -14,6 +15,10 @@ for arg in "$@"; do
             DISPLAY_BLACK_REPORTED=true
             DISPLAY_FIX_MODE=true
             ;;
+        --fix-external-display-blackout)
+            DISPLAY_BLACK_REPORTED=true
+            EXTERNAL_DISPLAY_FIX_MODE=true
+            ;;
         --persist-display-stability)
             DISPLAY_BLACK_REPORTED=true
             DISPLAY_FIX_MODE=true
@@ -145,5 +150,15 @@ if [ "$DISPLAY_FIX_MODE" = true ]; then
     sync
 fi
 
+# External-display remediation targets the KWin desktop path, not gamescope; it
+# shares the explicit physical-black symptom gate with the internal-panel fix.
+if [ "$EXTERNAL_DISPLAY_FIX_MODE" = true ]; then
+    echo "" >> "${REPORT_FILE}"
+    echo "=== EXTERNAL DISPLAY REMEDIATION PHASE ===" >> "${REPORT_FILE}"
+    "${MODULES_DIR}/rem_external_display.sh" 2>&1 | "$REDACTOR" >> "${REPORT_FILE}"
+    echo "" >> "${REPORT_FILE}"
+    sync
+fi
+
 sync
 exit 0
diff --git a/modules/display_blackout.sh b/modules/display_blackout.sh
index e57568a..99c54ea 100755
--- a/modules/display_blackout.sh
+++ b/modules/display_blackout.sh
@@ -29,6 +29,7 @@ sync
 
 echo "--- DRM connector status ---"
 EDP_DIR=""
+EDP_ENABLED="not-exposed"
 for conn in "${SYS_ROOT}"/class/drm/*/status; do
     [ -f "$conn" ] || continue
     connector_dir=$(dirname "$conn")
@@ -38,6 +39,7 @@ for conn in "${SYS_ROOT}"/class/drm/*/status; do
     echo "  ${name}: status=${status}, enabled=${enabled}"
     if [ "$status" = "connected" ] && echo "$name" | grep -qi 'edp'; then
         EDP_DIR="$connector_dir"
+        EDP_ENABLED="$enabled"
     fi
 done
 
@@ -109,6 +111,54 @@ fi
 echo "  Active hardware planes with framebuffers: ${ACTIVE_PLANES}"
 sync
 
+echo "--- External display / desktop session (read-only) ---"
+SESSION_HOME=$(getent passwd "$SESSION_USER" 2>/dev/null | cut -d: -f6)
+KWIN_OUTPUT_CONFIG="${DECKDOC_KWIN_OUTPUT_CONFIG:-${SESSION_HOME}/.config/kwinoutputconfig.json}"
+KWIN_ACTIVE=false
+if [ "${DECKDOC_KWIN_ACTIVE:-auto}" = "auto" ]; then
+    if pgrep -x kwin_wayland >/dev/null 2>&1; then KWIN_ACTIVE=true; fi
+else
+    KWIN_ACTIVE="${DECKDOC_KWIN_ACTIVE}"
+fi
+echo "  KWin desktop session active: ${KWIN_ACTIVE}"
+EXTERNAL_CONNECTED=false
+ANY_VRR_UNPINNED=false
+ANY_VRR_UNKNOWN=false
+for conn in "${SYS_ROOT}"/class/drm/*/status; do
+    [ -f "$conn" ] || continue
+    connector_dir=$(dirname "$conn")
+    name=$(basename "$connector_dir")
+    case "$name" in *eDP*|*Writeback*) continue ;; esac
+    [ "$(read_value "$conn")" = "connected" ] || continue
+    EXTERNAL_CONNECTED=true
+    ext_edid_bytes=$(wc -c < "${connector_dir}/edid" 2>/dev/null || echo 0)
+    echo "  ${name}: connected, EDID=${ext_edid_bytes} bytes"
+    if [ -r "${connector_dir}/modes" ]; then head -3 "${connector_dir}/modes" | sed 's/^/  mode: /'; fi
+    # KWin persists per-display policy keyed by the EDID md5; match this
+    # connector against the session's stored output configuration. Track
+    # unpinned and unreadable states across every connector rather than a
+    # single last-writer flag so one pinned display cannot mask another.
+    vrr_policy=""
+    if [ "$ext_edid_bytes" -gt 0 ] && [ -r "$KWIN_OUTPUT_CONFIG" ] && command -v md5sum >/dev/null 2>&1; then
+        edid_hash=$(md5sum "${connector_dir}/edid" 2>/dev/null | cut -d' ' -f1)
+        vrr_policy=$(awk -v hash="$edid_hash" '
+            /"edidHash"/ { entry_hash = ($0 ~ hash) }
+            entry_hash && /"vrrPolicy"/ {
+                gsub(/[",]/, ""); print $2; exit
+            }
+        ' "$KWIN_OUTPUT_CONFIG" 2>/dev/null)
+    fi
+    if [ -n "$vrr_policy" ]; then
+        echo "  ${name}: stored vrrPolicy=${vrr_policy}"
+        if [ "$vrr_policy" != "Never" ]; then ANY_VRR_UNPINNED=true; fi
+    else
+        echo "  ${name}: stored sync policy could not be determined for this display."
+        ANY_VRR_UNKNOWN=true
+    fi
+done
+if [ "$EXTERNAL_CONNECTED" = "false" ]; then echo "  No external display connector is connected."; fi
+sync
+
 echo "--- Gamescope composition state ---"
 if [ "${DECKDOC_SKIP_GAMESCOPE:-0}" = "1" ]; then
     echo "  Skipped by test environment."
@@ -154,18 +204,50 @@ fi
 sync
 
 echo "--- Display-path assessment ---"
-if [ "$DISPLAY_BLACK_REPORTED" = "true" ] && [ -n "$EDP_DIR" ] && [ "$EDP_EDID_BYTES" -gt 0 ] && [ "$BACKLIGHT_LIT" = "true" ] && [ "$CRTC_ACTIVE" = "true" ]; then
-    echo "  BLACKOUT_SIGNATURE: LIVE_RENDER_TO_PHYSICAL_SCANOUT_GAP"
-    echo "  eDP link/EDID, backlight, and CRTC remain live while the physical panel is reported black."
-    if [ "$ACTIVE_PLANES" -gt 1 ]; then
-        echo "  Multi-plane scanout is active (${ACTIVE_PLANES} planes); test forced composition with --fix-display-blackout."
-    else
-        echo "  Single-plane composition is already active; continue panel-link/kernel investigation."
-    fi
-elif [ "$DISPLAY_BLACK_REPORTED" = "true" ]; then
-    echo "  BLACKOUT_SIGNATURE: PANEL_OR_MODESET_STATE_INCOMPLETE"
-    echo "  A panel-link, EDID, backlight, or CRTC check failed; forced composition is not automatically indicated."
-else
+if [ "$DISPLAY_BLACK_REPORTED" != "true" ]; then
     echo "  No physical-black symptom was declared. Use --display-black while it is present."
+else
+    # The internal and external assessments are independent facts: an extended
+    # desktop can have a live panel and an unpinned external display at once,
+    # and neither signature may shadow the other.
+    EXTERNAL_ASSESSED=false
+    if [ "$EXTERNAL_CONNECTED" = "true" ] && [ "$KWIN_ACTIVE" = "true" ]; then
+        # A user-visible external blank with a healthy deck-side connector state
+        # is the discriminator for a presentation-path or downstream fault: the
+        # kernel keeps scanning out while the monitor loses the picture. KWin
+        # engages adaptive sync and direct scanout only for fullscreen surfaces,
+        # which is why the desktop is stable and games are not.
+        EXTERNAL_ASSESSED=true
+        if [ "$ANY_VRR_UNPINNED" = "true" ]; then
+            echo "  EXTERNAL_BLACKOUT_SIGNATURE: FULLSCREEN_SYNC_POLICY_GAP"
+            echo "  External connector is live with adaptive sync not pinned off; the monitor or dock"
+            echo "  chain may blank on fullscreen VRR engagement. Test --fix-external-display-blackout."
+        elif [ "$ANY_VRR_UNKNOWN" = "true" ]; then
+            # An unreadable policy must never be reported as a confirmed fix;
+            # the safe direction is to recommend the reversible remediation.
+            echo "  EXTERNAL_BLACKOUT_SIGNATURE: SYNC_POLICY_UNDETERMINED"
+            echo "  The stored sync policy could not be read for at least one external display; treat"
+            echo "  it as unpinned and test --fix-external-display-blackout before deeper investigation."
+        else
+            echo "  EXTERNAL_BLACKOUT_SIGNATURE: SYNC_POLICY_ALREADY_PINNED"
+            echo "  Adaptive sync is already pinned off for every external display; continue dock-segment,"
+            echo "  cable, and monitor investigation (the deck-side link shows no fault)."
+        fi
+    fi
+    # A connected panel that is disabled in the output configuration (docked,
+    # lid use, external-only setups) still reports a lit backlight; it must not
+    # claim the blackout signature while inactive.
+    if [ -n "$EDP_DIR" ] && [ "$EDP_ENABLED" != "disabled" ] && [ "$EDP_EDID_BYTES" -gt 0 ] && [ "$BACKLIGHT_LIT" = "true" ] && [ "$CRTC_ACTIVE" = "true" ]; then
+        echo "  BLACKOUT_SIGNATURE: LIVE_RENDER_TO_PHYSICAL_SCANOUT_GAP"
+        echo "  eDP link/EDID, backlight, and CRTC remain live while the physical panel is reported black."
+        if [ "$ACTIVE_PLANES" -gt 1 ]; then
+            echo "  Multi-plane scanout is active (${ACTIVE_PLANES} planes); test forced composition with --fix-display-blackout."
+        else
+            echo "  Single-plane composition is already active; continue panel-link/kernel investigation."
+        fi
+    elif [ "$EXTERNAL_ASSESSED" != "true" ]; then
+        echo "  BLACKOUT_SIGNATURE: PANEL_OR_MODESET_STATE_INCOMPLETE"
+        echo "  A panel-link, EDID, backlight, or CRTC check failed; forced composition is not automatically indicated."
+    fi
 fi
 sync
diff --git a/modules/rem_external_display.sh b/modules/rem_external_display.sh
new file mode 100755
index 0000000..3648107
--- /dev/null
+++ b/modules/rem_external_display.sh
@@ -0,0 +1,147 @@
+#!/usr/bin/env bash
+set -uo pipefail
+
+echo "[REMEDIATION: External Display Blackout / Adaptive-Sync Pinning]"
+SYS_ROOT="${DECKDOC_SYS_ROOT:-/sys}"
+DECKDOC_DIR="${DECKDOC_DIR:-$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)}"
+REPORTED="${DECKDOC_DISPLAY_BLACK_REPORTED:-false}"
+
+SESSION_USER="${DECKDOC_SESSION_USER:-${SUDO_USER:-$(id -un)}}"
+if [ "$SESSION_USER" = "root" ]; then
+    SESSION_USER=$(loginctl list-users --no-legend 2>/dev/null | awk '$2 != "root" { print $2; exit }')
+fi
+SESSION_UID=$(id -u "$SESSION_USER" 2>/dev/null || echo "")
+SESSION_HOME=$(getent passwd "$SESSION_USER" 2>/dev/null | cut -d: -f6)
+KWIN_OUTPUT_CONFIG="${DECKDOC_KWIN_OUTPUT_CONFIG:-${SESSION_HOME}/.config/kwinoutputconfig.json}"
+
+run_session() {
+    if [ "$(id -un)" = "$SESSION_USER" ]; then
+        XDG_RUNTIME_DIR="/run/user/${SESSION_UID}" WAYLAND_DISPLAY="${WAYLAND_SOCKET}" "$@"
+    else
+        runuser -u "$SESSION_USER" -- env XDG_RUNTIME_DIR="/run/user/${SESSION_UID}" WAYLAND_DISPLAY="${WAYLAND_SOCKET}" "$@"
+    fi
+}
+
+echo "--- PRE_CHECK ---"
+if [ "$REPORTED" != "true" ]; then
+    echo "SKIPPED: Physical-black symptom was not explicitly reported."
+    echo "REMEDIATION_OUTCOME: SKIPPED (symptom not declared)"
+    exit 0
+fi
+if [ -z "$SESSION_USER" ] || [ -z "$SESSION_UID" ] || [ -z "$SESSION_HOME" ]; then
+    echo "FAILED: Could not resolve the active non-root desktop user."
+    echo "REMEDIATION_OUTCOME: FAILED (session user unresolved)"
+    exit 1
+fi
+if ! pgrep -x kwin_wayland >/dev/null 2>&1; then
+    echo "SKIPPED: No KWin desktop session is active. Use --fix-display-blackout for Game Mode."
+    echo "REMEDIATION_OUTCOME: SKIPPED (KWin inactive)"
+    exit 0
+fi
+if ! command -v kscreen-doctor >/dev/null 2>&1; then
+    echo "FAILED: kscreen-doctor is not available."
+    echo "REMEDIATION_OUTCOME: FAILED (kscreen-doctor missing)"
+    exit 1
+fi
+WAYLAND_SOCKET=""
+for sock in "/run/user/${SESSION_UID}"/wayland-*; do
+    [ -S "$sock" ] || continue
+    case "$sock" in *.lock) continue ;; esac
+    WAYLAND_SOCKET=$(basename "$sock")
+    break
+done
+if [ -z "$WAYLAND_SOCKET" ]; then
+    echo "FAILED: No Wayland socket found for the desktop session."
+    echo "REMEDIATION_OUTCOME: FAILED (no Wayland socket)"
+    exit 1
+fi
+EXTERNAL_OUTPUTS=""
+for conn in "${SYS_ROOT}"/class/drm/*/status; do
+    [ -f "$conn" ] || continue
+    connector_dir=$(dirname "$conn")
+    name=$(basename "$connector_dir")
+    case "$name" in *eDP*|*Writeback*) continue ;; esac
+    [ "$(cat "$conn" 2>/dev/null)" = "connected" ] || continue
+    # KWin names outputs without the DRM card prefix (card0-DP-1 -> DP-1).
+    EXTERNAL_OUTPUTS="${EXTERNAL_OUTPUTS} ${name#card*-}"
+done
+EXTERNAL_OUTPUTS="${EXTERNAL_OUTPUTS# }"
+if [ -z "$EXTERNAL_OUTPUTS" ]; then
+    echo "SKIPPED: No external display connector is connected."
+    echo "REMEDIATION_OUTCOME: SKIPPED (no external display)"
+    exit 0
+fi
+echo "PASS: KWin active, Wayland socket ${WAYLAND_SOCKET}, external output(s): ${EXTERNAL_OUTPUTS}"
+
+echo "--- BACKUP ---"
+BACKUP_DIR="${DECKDOC_DIR}/remediation_backups"
+mkdir -p "$BACKUP_DIR"
+STAMP=$(date +%s)
+if [ -r "$KWIN_OUTPUT_CONFIG" ]; then
+    cp -a "$KWIN_OUTPUT_CONFIG" "${BACKUP_DIR}/kwinoutputconfig.json.${STAMP}.bak"
+    echo "Saved pre-change output policy: ${BACKUP_DIR}/kwinoutputconfig.json.${STAMP}.bak"
+else
+    echo "NOTE: No existing KWin output configuration file to back up."
+fi
+run_session kscreen-doctor -o > "${BACKUP_DIR}/kscreen_pre_${STAMP}.txt" 2>&1 || true
+
+echo "--- EXECUTE ---"
+# Pinning adaptive sync off changes fullscreen VRR engagement only. It does not
+# change resolution, refresh rate, panel power, brightness, TDP, or GPU clocks.
+APPLIED=""
+for output in $EXTERNAL_OUTPUTS; do
+    if run_session kscreen-doctor "output.${output}.vrrpolicy.never" >/dev/null 2>&1; then
+        echo "Applied vrrpolicy=never on ${output}."
+        APPLIED="${APPLIED} ${output}"
+    else
+        echo "FAILED: kscreen-doctor rejected vrrpolicy change on ${output}."
+    fi
+done
+if [ -z "${APPLIED# }" ]; then
+    echo "REMEDIATION_OUTCOME: FAILED (no output accepted the policy)"
+    exit 1
+fi
+
+echo "--- VERIFY ---"
+sleep 1
+# Verification is scoped to each output this run actually changed; a policy
+# already pinned on some other display (or a stale per-EDID entry from an
+# earlier fix) must never satisfy the check for this one.
+LIVE_STATE=$(run_session kscreen-doctor -o 2>/dev/null | sed 's/\x1b\[[0-9;]*m//g')
+VERIFY_FAILED=false
+for output in $APPLIED; do
+    live_vrr=$(printf '%s\n' "$LIVE_STATE" | awk -v out="$output" '
+        /^Output:/ { in_block = ($3 == out) }
+        in_block && /^[[:space:]]*Vrr:/ { print $2; exit }')
+    if [ "$live_vrr" = "Never" ]; then
+        echo "PASS: ${output} reports adaptive sync pinned off in the live output state."
+    else
+        echo "FAILED: ${output} live state reports \"${live_vrr:-no policy}\" instead of a pinned sync policy."
+        VERIFY_FAILED=true
+    fi
+done
+if [ "$VERIFY_FAILED" = "true" ]; then
+    echo "REMEDIATION_OUTCOME: FAILED (live verification)"
+    exit 1
+fi
+for output in $APPLIED; do
+    edid_file=""
+    for candidate in "${SYS_ROOT}"/class/drm/card*-"${output}"/edid; do
+        [ -r "$candidate" ] && { edid_file="$candidate"; break; }
+    done
+    stored=""
+    if [ -n "$edid_file" ] && [ -r "$KWIN_OUTPUT_CONFIG" ] && command -v md5sum >/dev/null 2>&1; then
+        edid_hash=$(md5sum "$edid_file" 2>/dev/null | cut -d' ' -f1)
+        stored=$(awk -v hash="$edid_hash" '
+            /"edidHash"/ { entry_hash = ($0 ~ hash) }
+            entry_hash && /"vrrPolicy"/ { gsub(/[",]/, ""); print $2; exit }
+        ' "$KWIN_OUTPUT_CONFIG" 2>/dev/null)
+    fi
+    if [ "$stored" = "Never" ]; then
+        echo "PASS: ${output} policy persisted for this display's EDID (survives reboot, keyed to this display)."
+    else
+        echo "NOTE: ${output}: persistence not yet visible for this display's EDID; KWin may write it on session exit."
+    fi
+done
+echo "NOTE: Software cannot observe the monitor's panel; confirm blanking stops during fullscreen use."
+echo "REMEDIATION_OUTCOME: PARTIAL (sync policy pinned; physical confirmation required)"
diff --git a/tests/test_runner.sh b/tests/test_runner.sh
index 893029c..d650dee 100755
--- a/tests/test_runner.sh
+++ b/tests/test_runner.sh
@@ -75,10 +75,10 @@ echo ""
 echo "--- Test 5: Module count ---"
 MODULE_COUNT=$(ls -1 "${DECKDOC_DIR}"/modules/*.sh | wc -l)
 echo "  Total modules: ${MODULE_COUNT}"
-if [ "$MODULE_COUNT" -eq 21 ]; then
-    echo "  PASS: Expected 21 modules present (19 diagnostic + 2 remediation)."
+if [ "$MODULE_COUNT" -eq 22 ]; then
+    echo "  PASS: Expected 22 modules present (19 diagnostic + 3 remediation)."
 else
-    echo "  FAIL: Expected 21 modules, found ${MODULE_COUNT}."
+    echo "  FAIL: Expected 22 modules, found ${MODULE_COUNT}."
     exit 1
 fi
 
@@ -642,6 +642,116 @@ echo "--- Test 31: RyuDeck application diagnostics ---"
 "${DECKDOC_DIR}/tests/validate_ryudeck.sh"
 echo "  PASS: RyuDeck startup stalls, cache suspicion, renderer failure, rendering, and privacy remain distinct."
 
+# === Test 32: External fullscreen sync-policy signature ===
+echo ""
+echo "--- Test 32: External display sync-policy signature ---"
+EXT_ENV="${TEST_ENV}/external"
+mkdir -p "${EXT_ENV}/sys/class/drm/card0-eDP-1" \
+    "${EXT_ENV}/sys/class/drm/card0-DP-1" \
+    "${EXT_ENV}/sys/class/backlight/amdgpu_bl1" \
+    "${EXT_ENV}/debug/dri/0"
+printf 'connected\n' > "${EXT_ENV}/sys/class/drm/card0-eDP-1/status"
+printf 'disabled\n' > "${EXT_ENV}/sys/class/drm/card0-eDP-1/enabled"
+head -c 128 /dev/zero > "${EXT_ENV}/sys/class/drm/card0-eDP-1/edid"
+printf 'connected\n' > "${EXT_ENV}/sys/class/drm/card0-DP-1/status"
+printf 'enabled\n' > "${EXT_ENV}/sys/class/drm/card0-DP-1/enabled"
+printf '1920x1080\n' > "${EXT_ENV}/sys/class/drm/card0-DP-1/modes"
+printf 'external-display-edid-fixture' > "${EXT_ENV}/sys/class/drm/card0-DP-1/edid"
+printf '65535\n' > "${EXT_ENV}/sys/class/backlight/amdgpu_bl1/max_brightness"
+printf '9996\n' > "${EXT_ENV}/sys/class/backlight/amdgpu_bl1/brightness"
+printf '9996\n' > "${EXT_ENV}/sys/class/backlight/amdgpu_bl1/actual_brightness"
+printf '0\n' > "${EXT_ENV}/sys/class/backlight/amdgpu_bl1/bl_power"
+printf 'crtc[67]: crtc-0\n  active=1\n' > "${EXT_ENV}/debug/dri/0/state"
+EXT_EDID_HASH=$(md5sum "${EXT_ENV}/sys/class/drm/card0-DP-1/edid" | cut -d' ' -f1)
+printf '%s\n' \
+    '[ { "outputs": [ {' \
+    '    "connectorName": "DP-1",' \
+    "    \"edidHash\": \"${EXT_EDID_HASH}\"," \
+    '    "vrrPolicy": "Automatic"' \
+    '} ] } ]' > "${EXT_ENV}/kwinoutputconfig.json"
+EXT_REPORT="${EXT_ENV}/report.txt"
+DECKDOC_SYS_ROOT="${EXT_ENV}/sys" \
+DECKDOC_DEBUGFS_ROOT="${EXT_ENV}/debug" \
+DECKDOC_DISPLAY_BLACK_REPORTED=true \
+DECKDOC_KWIN_ACTIVE=true \
+DECKDOC_KWIN_OUTPUT_CONFIG="${EXT_ENV}/kwinoutputconfig.json" \
+DECKDOC_SKIP_JOURNAL=1 \
+DECKDOC_SKIP_GAMESCOPE=1 \
+    "${DECKDOC_DIR}/modules/display_blackout.sh" > "$EXT_REPORT"
+if grep -q 'EXTERNAL_BLACKOUT_SIGNATURE: FULLSCREEN_SYNC_POLICY_GAP' "$EXT_REPORT" && \
+   grep -q 'stored vrrPolicy=Automatic' "$EXT_REPORT"; then
+    echo "  PASS: Un-pinned external sync policy with a disabled panel is classified as a fullscreen sync gap."
+else
+    echo "  FAIL: External sync-policy gap was not classified correctly."
+    cat "$EXT_REPORT"
+    exit 1
+fi
+if grep -q 'BLACKOUT_SIGNATURE: LIVE_RENDER_TO_PHYSICAL_SCANOUT_GAP' "$EXT_REPORT"; then
+    echo "  FAIL: Disabled internal panel wrongly claimed the internal blackout signature."
+    exit 1
+else
+    echo "  PASS: Disabled internal panel does not shadow the external diagnosis."
+fi
+sed -i 's/"vrrPolicy": "Automatic"/"vrrPolicy": "Never"/' "${EXT_ENV}/kwinoutputconfig.json"
+DECKDOC_SYS_ROOT="${EXT_ENV}/sys" \
+DECKDOC_DEBUGFS_ROOT="${EXT_ENV}/debug" \
+DECKDOC_DISPLAY_BLACK_REPORTED=true \
+DECKDOC_KWIN_ACTIVE=true \
+DECKDOC_KWIN_OUTPUT_CONFIG="${EXT_ENV}/kwinoutputconfig.json" \
+DECKDOC_SKIP_JOURNAL=1 \
+DECKDOC_SKIP_GAMESCOPE=1 \
+    "${DECKDOC_DIR}/modules/display_blackout.sh" > "$EXT_REPORT"
+if grep -q 'EXTERNAL_BLACKOUT_SIGNATURE: SYNC_POLICY_ALREADY_PINNED' "$EXT_REPORT"; then
+    echo "  PASS: Pinned sync policy routes investigation to the downstream display chain."
+else
+    echo "  FAIL: Pinned sync policy was not recognized."
+    cat "$EXT_REPORT"
+    exit 1
+fi
+DECKDOC_SYS_ROOT="${EXT_ENV}/sys" \
+DECKDOC_DEBUGFS_ROOT="${EXT_ENV}/debug" \
+DECKDOC_DISPLAY_BLACK_REPORTED=true \
+DECKDOC_KWIN_ACTIVE=true \
+DECKDOC_KWIN_OUTPUT_CONFIG="${EXT_ENV}/does-not-exist.json" \
+DECKDOC_SKIP_JOURNAL=1 \
+DECKDOC_SKIP_GAMESCOPE=1 \
+    "${DECKDOC_DIR}/modules/display_blackout.sh" > "$EXT_REPORT"
+if grep -q 'EXTERNAL_BLACKOUT_SIGNATURE: SYNC_POLICY_UNDETERMINED' "$EXT_REPORT" && \
+   ! grep -q 'SYNC_POLICY_ALREADY_PINNED' "$EXT_REPORT"; then
+    echo "  PASS: An unreadable sync policy is reported as undetermined, never as already pinned."
+else
+    echo "  FAIL: Missing output policy was not classified as undetermined."
+    cat "$EXT_REPORT"
+    exit 1
+fi
+
+# === Test 33: External display remediation safety contract ===
+echo ""
+echo "--- Test 33: External display remediation safety contract ---"
+if grep -q 'kscreen-doctor "output.${output}.vrrpolicy.never"' "${DECKDOC_DIR}/modules/rem_external_display.sh" && \
+   grep -q 'REMEDIATION_OUTCOME: SKIPPED (symptom not declared)' "${DECKDOC_DIR}/modules/rem_external_display.sh" && \
+   grep -q 'REMEDIATION_OUTCOME: SKIPPED (KWin inactive)' "${DECKDOC_DIR}/modules/rem_external_display.sh" && \
+   grep -q 'rem_external_display.sh' "${DECKDOC_DIR}/deckdoc.sh" && \
+   grep -q -- '--fix-external-display-blackout' "${DECKDOC_DIR}/deckdoc.sh"; then
+    echo "  PASS: External sync-pinning remediation is present, gated, and wired to its own flag."
+else
+    echo "  FAIL: External display remediation is incomplete or unwired."
+    exit 1
+fi
+if grep -q 'in_block = ($3 == out)' "${DECKDOC_DIR}/modules/rem_external_display.sh" && \
+   grep -q 'entry_hash = ($0 ~ hash)' "${DECKDOC_DIR}/modules/rem_external_display.sh"; then
+    echo "  PASS: VERIFY scopes live and persisted checks to each targeted output, not the whole state."
+else
+    echo "  FAIL: VERIFY is not scoped per targeted output (PR #12-class unscoped verification)."
+    exit 1
+fi
+if grep -Eq '(tee|echo).*(brightness|bl_power|power_control|power_dpm|pp_od_clk_voltage)' "${DECKDOC_DIR}/modules/rem_external_display.sh"; then
+    echo "  FAIL: External display remediation contains a forbidden power/brightness/clock write."
+    exit 1
+else
+    echo "  PASS: External display remediation contains no panel-power, brightness, or clock writes."
+fi
+
 echo ""
 echo "========================================="
 echo "All DeckDoc tests completed successfully."