Implemented the Secret Passages + Hidden Room detection pass.

Changed:
[Edit.cshtml (line 36)](C:/Source/PlotLine/PlotLine/Views/FloorPlans/Edit.cshtml:36)Secret Passage and Hidden Passage now render as dashed route overlays instead of wall markers.
Hidden Door remains a wall/shared-edge marker and follows existing adjacency rules.
Hidden locations are detected from existing transition data: visible entrances count, windows/hidden doors/secret passages/hidden passages/blocked doors do not.
Hidden room tooltip now includes Hidden location: no visible entrance.

[site.css (line 4793)](C:/Source/PlotLine/PlotLine/wwwroot/css/site.css:4793)Added subtle hidden-location hatch styling.
Added dashed secret-route styling with dark-theme support.

[site.min.css](C:/Source/PlotLine/PlotLine/wwwroot/css/site.min.css)Synced minified CSS.

No database changes. No stored procedure changes. No Features concept added.

PlotLine/Views/FloorPlans/Edit.cshtml

@@ -32,7 +32,8 @@
             "blockeddoor" => "blocked-door",
             "exteriordoor" => "exterior-door",
             "stairs" or "stair" or "stairsup" or "stairsdown" => "stairs",
-            "passage" => "passage",
+            "passage" or "openpassage" => "passage",
+            "hiddenpassage" or "secretpassage" => "secret-route",
             _ => "other"
         };
     }
@@ -220,6 +221,7 @@
                                             data-location-id="@block.LocationID"
                                             data-location-name="@block.LocationName"
                                             data-location-path="@block.LocationPath"
+                                            data-location-title="@block.LocationPath"
                                             title="@block.LocationPath">
                                         <span class="floor-plan-block-label">@block.DisplayLabel</span>
                                         <span class="floor-plan-resize-handle" data-resize-handle aria-hidden="true"></span>
@@ -1530,6 +1532,7 @@
                 button.dataset.locationId = block.locationID || "";
                 button.dataset.locationName = block.locationName || "";
                 button.dataset.locationPath = block.locationPath || "";
+                button.dataset.locationTitle = block.locationPath || "";
                 button.title = block.locationPath || "";
                 button.innerHTML = `<span class="floor-plan-block-label"></span><span class="floor-plan-resize-handle" data-resize-handle aria-hidden="true"></span>`;
                 button.querySelector(".floor-plan-block-label").textContent = block.displayLabel || block.locationName || "New block";
@@ -1655,6 +1658,26 @@
                 return ["hiddenpassage", "openpassage", "secretpassage"].includes(normalizeTransitionType(type));
             }
 
+            function isSecretRouteTransition(type) {
+                return ["hiddenpassage", "secretpassage"].includes(normalizeTransitionType(type));
+            }
+
+            function isVisibleEntranceTransition(type) {
+                return [
+                    "door",
+                    "doubledoor",
+                    "frenchdoor",
+                    "frenchdoors",
+                    "slidingdoor",
+                    "slidingdoors",
+                    "exteriordoor",
+                    "archway",
+                    "openpassage",
+                    "stairsup",
+                    "stairsdown"
+                ].includes(normalizeTransitionType(type));
+            }
+
             function blocksTouchAlongEdge(a, b) {
                 const verticalTouch = a.x + a.w === b.x || b.x + b.w === a.x;
                 const verticalOverlap = a.y < b.y + b.h && b.y < a.y + a.h;
@@ -1874,6 +1897,44 @@
                 return { x: (minX + maxX) / 2, y: (minY + maxY) / 2 };
             }
 
+            function refreshHiddenLocationStyles(visibleBlocks) {
+                const visibleEntranceLocationIds = new Set();
+                editor.querySelectorAll("[data-transition-marker]").forEach(marker => {
+                    if (!isVisibleEntranceTransition(marker.dataset.transitionKind)) return;
+                    if (marker.dataset.fromLocationId) visibleEntranceLocationIds.add(marker.dataset.fromLocationId);
+                    if (marker.dataset.toLocationId) visibleEntranceLocationIds.add(marker.dataset.toLocationId);
+                });
+
+                visibleBlocks.forEach(item => {
+                    const locationId = item.block.dataset.locationId;
+                    const isHidden = !!locationId && !visibleEntranceLocationIds.has(locationId);
+                    item.block.classList.toggle("is-hidden-location", isHidden);
+                    const baseTitle = item.block.dataset.locationTitle || item.block.dataset.locationPath || item.block.dataset.locationName || "";
+                    item.block.title = isHidden
+                        ? `${baseTitle}${baseTitle ? "\n" : ""}Hidden location: no visible entrance`
+                        : baseTitle;
+                });
+            }
+
+            function renderSecretRoute(activePanel, marker, fromCenter, toCenter) {
+                if (!fromCenter || !toCenter) return;
+                const dx = toCenter.x - fromCenter.x;
+                const dy = toCenter.y - fromCenter.y;
+                const length = Math.sqrt(dx * dx + dy * dy);
+                if (length <= 0) return;
+
+                const route = document.createElement("span");
+                route.className = "floor-plan-secret-route";
+                route.dataset.secretRoute = marker.dataset.transitionMarker || "";
+                route.style.setProperty("--route-x", fromCenter.x);
+                route.style.setProperty("--route-y", fromCenter.y);
+                route.style.setProperty("--route-length", length);
+                route.style.setProperty("--route-angle", `${Math.atan2(dy, dx)}rad`);
+                route.title = marker.title || "";
+                route.setAttribute("aria-hidden", "true");
+                activePanel.querySelector("[data-floor-grid]")?.append(route);
+            }
+
             function sharedTransitionEdge(fromBlocks, toBlocks) {
                 let best = null;
                 fromBlocks.forEach(from => {
@@ -1931,9 +1992,21 @@
 
             function positionTransitions(activePanel, visibleBlocks) {
                 const markerPositions = [];
+                activePanel.querySelectorAll("[data-secret-route]").forEach(route => route.remove());
                 activePanel.querySelectorAll("[data-transition-marker]").forEach(marker => {
                     const fromBlocks = visibleBlocks.filter(item => item.block.dataset.locationId === marker.dataset.fromLocationId);
                     const toBlocks = visibleBlocks.filter(item => item.block.dataset.locationId === marker.dataset.toLocationId);
+                    const fromCenter = locationCenter(fromBlocks);
+                    const toCenter = locationCenter(toBlocks);
+
+                    if (isSecretRouteTransition(marker.dataset.transitionKind)) {
+                        marker.hidden = true;
+                        if (fromCenter && toCenter) {
+                            renderSecretRoute(activePanel, marker, fromCenter, toCenter);
+                        }
+                        return;
+                    }
+
                     if (fromBlocks.length === 0 || (!isStairTransition(marker.dataset.transitionKind) && toBlocks.length === 0)) {
                         marker.hidden = true;
                         return;
@@ -1943,8 +2016,6 @@
                         ? positionWithinLocation(fromBlocks, marker.dataset.positionWithinLocation)
                         : null;
                     const sharedEdge = stairPlacement ? null : sharedTransitionEdge(fromBlocks, toBlocks);
-                    const fromCenter = locationCenter(fromBlocks);
-                    const toCenter = locationCenter(toBlocks);
                     marker.hidden = false;
                     marker.classList.toggle("is-shared-edge", !!sharedEdge);
                     marker.classList.toggle("is-inside-location", !!stairPlacement);
@@ -2005,6 +2076,7 @@
                 if (!activePanel) return;
                 const visibleBlocks = refreshSharedWalls(activePanel);
                 positionTransitions(activePanel, visibleBlocks);
+                refreshHiddenLocationStyles(visibleBlocks);
                 let overlaps = false;
                 visibleBlocks.forEach(a => {
                     a.block.classList.remove("overlap");

PlotLine/wwwroot/css/site.css

@@ -4790,6 +4790,46 @@ body.dragging-location [data-drag-type="location"] {
   box-shadow: inset 0 0 0 2px rgba(180, 85, 68, .18);
 }
 
+.floor-plan-block.is-hidden-location {
+  background-image: repeating-linear-gradient(135deg, rgba(18, 51, 44, .08) 0, rgba(18, 51, 44, .08) 3px, transparent 3px, transparent 9px);
+  box-shadow: inset 0 0 0 1px rgba(43, 54, 49, .18);
+}
+
+.floor-plan-block.is-hidden-location.selected {
+  box-shadow: inset 0 0 0 1px rgba(43, 54, 49, .18), 0 0 0 3px rgba(47, 111, 99, .28);
+}
+
+.floor-plan-block.is-hidden-location.overlap {
+  box-shadow: inset 0 0 0 2px rgba(180, 85, 68, .18), inset 0 0 0 1px rgba(43, 54, 49, .18);
+}
+
+.floor-plan-secret-route {
+  border-top: 2px dashed rgba(69, 55, 42, .58);
+  height: 0;
+  left: calc(var(--route-x, 0) * var(--cell-size));
+  opacity: .72;
+  pointer-events: none;
+  position: absolute;
+  top: calc(var(--route-y, 0) * var(--cell-size));
+  transform: rotate(var(--route-angle, 0));
+  transform-origin: 0 50%;
+  width: calc(var(--route-length, 0) * var(--cell-size));
+  z-index: 3;
+}
+
+.floor-plan-secret-route::after {
+  background: rgba(255, 250, 242, .9);
+  border: 1px solid rgba(69, 55, 42, .5);
+  border-radius: 50%;
+  content: "";
+  height: 7px;
+  left: 50%;
+  position: absolute;
+  top: -5px;
+  transform: translateX(-50%);
+  width: 7px;
+}
+
 .floor-plan-transition-marker {
   align-items: center;
   --transition-marker-ink: #12332c;
@@ -5151,6 +5191,24 @@ body.dragging-location [data-drag-type="location"] {
   color: #f1f6f3;
 }
 
+[data-bs-theme="dark"] .floor-plan-block.is-hidden-location,
+.dark .floor-plan-block.is-hidden-location {
+  background-image: repeating-linear-gradient(135deg, rgba(244, 234, 220, .09) 0, rgba(244, 234, 220, .09) 3px, transparent 3px, transparent 9px);
+  box-shadow: inset 0 0 0 1px rgba(244, 234, 220, .2);
+}
+
+[data-bs-theme="dark"] .floor-plan-secret-route,
+.dark .floor-plan-secret-route {
+  border-top-color: rgba(244, 204, 160, .58);
+  opacity: .76;
+}
+
+[data-bs-theme="dark"] .floor-plan-secret-route::after,
+.dark .floor-plan-secret-route::after {
+  background: rgba(42, 35, 30, .95);
+  border-color: rgba(244, 204, 160, .55);
+}
+
 [data-bs-theme="dark"] .floor-plan-coordinate-label,
 .dark .floor-plan-coordinate-label {
   color: rgba(244, 234, 220, .46);