diff --git a/scripts/package-boundaries.json b/scripts/package-boundaries.json
index 9a82fa11e..29476fb6f 100644
--- a/scripts/package-boundaries.json
+++ b/scripts/package-boundaries.json
@@ -426,7 +426,8 @@
       "src/ui/rightPanelRail.js",
       "src/ui/panelMeasurement.js",
       "src/ui/panelRailGeometry.js",
-      "src/panelStackLayout.js"
+      "src/panelStackLayout.js",
+      "src/ui/panelAccordion.js"
     ],
     "external": []
   },
@@ -874,7 +875,8 @@
       "src/ui/statusText.js",
       "src/ui/statusBadge.js",
       "src/scopeMaskPolicy.js",
-      "src/visualStylePolicy.js"
+      "src/visualStylePolicy.js",
+      "src/ui/panelAccordion.js"
     ],
     "external": ["cesium"]
   },
@@ -2810,7 +2812,8 @@
       "src/ui/statusBadge.js",
       "src/sceneCommandRelease.js",
       "src/scopeMaskPolicy.js",
-      "src/visualStylePolicy.js"
+      "src/visualStylePolicy.js",
+      "src/ui/panelAccordion.js"
     ],
     "external": [
       "hls.js",
@@ -3603,7 +3606,8 @@
       "src/i18n/locales/ru.json",
       "src/i18n/locales/uk.json",
       "src/i18n/locales/zh-CN.json",
-      "src/i18n/locales/zh-Hant.json"
+      "src/i18n/locales/zh-Hant.json",
+      "src/ui/panelAccordion.js"
     ],
     "external": []
   },
diff --git a/src/rightRailPolicy.test.mjs b/src/rightRailPolicy.test.mjs
index dde4c64be..89e5b4d73 100644
--- a/src/rightRailPolicy.test.mjs
+++ b/src/rightRailPolicy.test.mjs
@@ -4,16 +4,21 @@ import { readFileSync } from 'node:fs';
 import test from 'node:test';
 import { shouldExpandGlobalContextPanel } from './rightRailPolicy.js';
 
-test('desktop side rails hide collapsed panels in every HUD layout, never on phones', () => {
+test('desktop side rails hide collapsed panels in every HUD layout, never on phones or beside Cockpit', () => {
   const right = readFileSync(new URL('./ui/rightPanelRail.js', import.meta.url), 'utf8');
   const left = readFileSync(new URL('./ui/leftPanelRail.js', import.meta.url), 'utf8');
   const css = readStylesheet(new URL('../style.css', import.meta.url));
   for (const ui of [right, left]) {
     assert.match(ui, /const isMobile = windowRef\.matchMedia\('\(max-width: 720px\)'\)\.matches/);
-    assert.match(ui, /const exclusive = !isMobile;/);
     assert.match(ui, /if \(exclusive && panel\.classList\.contains\('collapsed'\)\)\s*panel\.setAttribute\('aria-hidden', 'true'\)/);
     assert.doesNotMatch(ui, /hud\.variant === 'cyber'/);
   }
+  assert.match(right, /const exclusive = !isMobile;/);
+  // Cockpit keeps its collapsed Data Layers strip, which its layout aligns to.
+  assert.match(
+    left,
+    /const exclusive =\s*!isMobile && !documentRef\?\.body\?\.classList\?\.contains\('cockpit-mode'\);/,
+  );
   assert.match(css, /#right-context-rail\.layout-exclusive > \[data-panel-id\]\.collapsed \{/);
   assert.match(css, /#left-panel-stack\.layout-exclusive > \[data-panel-id\]\.collapsed \{/);
 });
diff --git a/src/ui/leftPanelRail.js b/src/ui/leftPanelRail.js
index a0de82746..d9930676a 100644
--- a/src/ui/leftPanelRail.js
+++ b/src/ui/leftPanelRail.js
@@ -5,6 +5,7 @@ import {
   resolvePanelStackCorridor,
 } from '../panelStackLayout.js';
 import { measurePanelNaturalHeight } from './panelMeasurement.js';
+import { settleSideAccordion } from './panelAccordion.js';
 
 /**
  * Measure and place the left panel rail for one synchronous layout pass.
@@ -60,35 +61,26 @@ export function layoutLeftPanelRail({
     stack.style.removeProperty('--left-stack-centered-height');
     stack.classList.remove('layout-exclusive');
     stack.dataset.layoutMode = 'mobile';
+    settleSideAccordion({ panels, enabled: false, onCollapse });
     for (const panel of panels) {
-      if (panel.classList.contains('accordion-collapsed')) {
-        panel.classList.remove('collapsed', 'accordion-collapsed');
-        onCollapse(panel);
-      }
       panel.removeAttribute('aria-hidden');
       panel.style.removeProperty('--left-panel-allocated-height');
     }
     return;
   }
 
-  // One panel is open per desktop side and the panel rail lists the others,
-  // so collapsed panels are hidden. Normalize restored state without
-  // overwriting saved panel preferences.
-  const expandedBeforeAccordion = panels.filter(
-    (panel) => !panel.classList.contains('collapsed'),
-  );
-  const accordionOwner =
-    expandedBeforeAccordion.find((panel) => panel.id === preferredPanelId) ||
-    expandedBeforeAccordion.find((panel) =>
-      panel.contains(documentRef?.activeElement),
-    ) ||
-    expandedBeforeAccordion[0];
-  for (const panel of expandedBeforeAccordion) {
-    if (panel === accordionOwner) continue;
-    panel.classList.add('collapsed', 'accordion-collapsed');
-    onCollapse(panel);
-  }
-  const exclusive = !isMobile;
+  // One panel is open per desktop side, and the panel rail lists the others,
+  // so collapsed panels are hidden. Cockpit keeps its collapsed Data Layers
+  // strip, which its layout aligns to, and shows no rail.
+  settleSideAccordion({
+    panels,
+    enabled: true,
+    preferredPanelId,
+    documentRef,
+    onCollapse,
+  });
+  const exclusive =
+    !isMobile && !documentRef?.body?.classList?.contains('cockpit-mode');
   stack.classList.toggle('layout-exclusive', exclusive);
   const laidOutPanels = panels.filter(
     (panel) => !exclusive || !panel.classList.contains('collapsed'),
diff --git a/src/ui/panelAccordion.js b/src/ui/panelAccordion.js
new file mode 100644
index 000000000..5690bf71a
--- /dev/null
+++ b/src/ui/panelAccordion.js
@@ -0,0 +1,41 @@
+/**
+ * Keep one side panel open on desktop, and on phones put back the collapse
+ * this applied, since a sheet shows several panels at once. The owner is the
+ * most recently opened panel, then the one holding keyboard focus, then the
+ * first. `accordion-collapsed` marks the collapse as presentation only, so
+ * saved and shared preferences still report the panel as the user left it.
+ * @param {object} options
+ * @param {HTMLElement[]} options.panels The side's laid-out panels.
+ * @param {boolean} options.enabled Whether the one-panel rule applies.
+ * @param {string} [options.preferredPanelId] Most recently opened panel.
+ * @param {Document} [options.documentRef] Document supplying keyboard focus.
+ * @param {Function} options.onCollapse Update a panel's disclosure chrome.
+ */
+export function settleSideAccordion({
+  panels,
+  enabled,
+  preferredPanelId,
+  documentRef,
+  onCollapse,
+}) {
+  if (!enabled) {
+    for (const panel of panels) {
+      if (!panel.classList.contains('accordion-collapsed')) continue;
+      panel.classList.remove('collapsed', 'accordion-collapsed');
+      onCollapse(panel);
+    }
+    return;
+  }
+  const expanded = panels.filter(
+    (panel) => !panel.classList.contains('collapsed'),
+  );
+  const owner =
+    expanded.find((panel) => panel.id === preferredPanelId) ||
+    expanded.find((panel) => panel.contains(documentRef?.activeElement)) ||
+    expanded[0];
+  for (const panel of expanded) {
+    if (panel === owner) continue;
+    panel.classList.add('collapsed', 'accordion-collapsed');
+    onCollapse(panel);
+  }
+}
diff --git a/src/ui/panelChrome.js b/src/ui/panelChrome.js
index 459694967..8f8bd219f 100644
--- a/src/ui/panelChrome.js
+++ b/src/ui/panelChrome.js
@@ -421,14 +421,14 @@ export class PanelChrome {
     const wasAutoCollapsed =
       panelEl.classList.contains('layout-auto-collapsed') ||
       panelEl.classList.contains('accordion-collapsed');
-    // One panel is open per desktop side: a user opening a side panel owns
-    // the whole accordion, including peers that were only
-    // presentation-collapsed during a saved-state restore.
+    // One panel is open per desktop side: opening a side panel, whether the
+    // user asked or a feature revealed it (Street Level's viewer, a selected
+    // radio station), owns the whole accordion, including peers that were
+    // only presentation-collapsed during a saved-state restore.
     const sideStack = [this._leftPanelStack, this._rightPanelStack].find(
       (stack) => stack && panelEl.parentElement === stack,
     );
     if (
-      explicit &&
       !restore &&
       !nextCollapsed &&
       sideStack &&
@@ -460,7 +460,7 @@ export class PanelChrome {
           : null;
     const priorLeftOwner = this._panelLayout._leftStackPreferredPanelId;
     const priorRightOwner = this._panelLayout._rightStackPreferredPanelId;
-    if (explicit && !restore && !nextCollapsed && leftOwnerPanel) {
+    if (!restore && !nextCollapsed && leftOwnerPanel) {
       this._panelLayout._leftStackPreferredPanelId = leftOwnerPanel.id;
     } else if (
       explicit &&
@@ -470,7 +470,7 @@ export class PanelChrome {
     ) {
       this._panelLayout._leftStackPreferredPanelId = null;
     }
-    if (explicit && !restore && !nextCollapsed && rightOwnerPanel) {
+    if (!restore && !nextCollapsed && rightOwnerPanel) {
       this._panelLayout._rightStackPreferredPanelId = rightOwnerPanel.id;
     } else if (
       explicit &&
diff --git a/src/ui/panelRails.test.mjs b/src/ui/panelRails.test.mjs
index e7f0d07cf..291eaac6c 100644
--- a/src/ui/panelRails.test.mjs
+++ b/src/ui/panelRails.test.mjs
@@ -777,3 +777,17 @@ test('right layout ignores a hidden panel: no lane, no gap, no auto-collapse', (
     ) <= alone,
   );
 });
+
+test('left rail keeps collapsed panels shown beside Cockpit, still one open', () => {
+  const f = fixture('left');
+  f.options.documentRef.body = {
+    classList: { contains: (name) => name === 'cockpit-mode' },
+  };
+  f.expand(f.first, 250);
+  f.expand(f.second, 250);
+  f.options.preferredPanelId = f.second.id;
+  f.run();
+  assert.equal(f.first.classList.contains('accordion-collapsed'), true);
+  assert.equal(f.stack.classList.contains('layout-exclusive'), false);
+  assert.equal(f.first.getAttribute('aria-hidden'), undefined);
+});
diff --git a/src/ui/rightPanelRail.js b/src/ui/rightPanelRail.js
index 5afdce2b7..1dcd4460f 100644
--- a/src/ui/rightPanelRail.js
+++ b/src/ui/rightPanelRail.js
@@ -5,6 +5,7 @@ import {
 import { resolveHudRailLayout } from './panelRailGeometry.js';
 
 import { displayPanelScroller } from './displayPanelScroll.js';
+import { settleSideAccordion } from './panelAccordion.js';
 
 const pendingCollapseRetries = new WeakSet();
 
@@ -86,31 +87,16 @@ export function layoutRightPanelRail({
       onCollapse(panel);
     }
   }
-  // One panel is open per desktop side. Normalize restored state without
-  // overwriting saved panel preferences; this marker is distinct from
-  // Tactical's space-based collapse. Phones present the rail as tab sheets
-  // that show several panels at once.
+  // One panel is open per desktop side; this marker is distinct from
+  // Tactical's space-based collapse.
   const isMobile = windowRef.matchMedia('(max-width: 720px)').matches;
-  if (!isMobile) {
-    const expanded = panels.filter(
-      (panel) => !panel.classList.contains('collapsed'),
-    );
-    const owner =
-      expanded.find((panel) => panel.id === preferredPanelId) ||
-      expanded.find((panel) => panel.contains(documentRef?.activeElement)) ||
-      expanded[0];
-    for (const panel of expanded) {
-      if (panel === owner) continue;
-      panel.classList.add('collapsed', 'accordion-collapsed');
-      onCollapse(panel);
-    }
-  } else {
-    for (const panel of panels) {
-      if (!panel.classList.contains('accordion-collapsed')) continue;
-      panel.classList.remove('collapsed', 'accordion-collapsed');
-      onCollapse(panel);
-    }
-  }
+  settleSideAccordion({
+    panels,
+    enabled: !isMobile,
+    preferredPanelId,
+    documentRef,
+    onCollapse,
+  });
   // The desktop panel rail lists every panel, so collapsed ones are hidden.
   // Phones present the rail as tab sheets (mobileShell.js), which choose what
   // shows; hiding collapsed siblings would empty a sheet and its a11y tree.
diff --git a/src/ui/sidePanelDisclosure.test.mjs b/src/ui/sidePanelDisclosure.test.mjs
index 41b0977f7..7badbd464 100644
--- a/src/ui/sidePanelDisclosure.test.mjs
+++ b/src/ui/sidePanelDisclosure.test.mjs
@@ -97,3 +97,20 @@ test('restored preferences keep every saved panel open for the layout to normali
     } finally { globalThis.document = prior; }
   }
 });
+
+test('a feature revealing a side panel makes it the side owner', () => {
+  const f = fixture('tactical'), prior = globalThis.document;
+  globalThis.document = f.doc;
+  try {
+    f.owner.setPanelCollapsed('pp-toggles', false, { explicit: true });
+    f.claimed.length = 0;
+    // Street Level's viewer or a selected radio station opens its panel
+    // without an explicit user disclosure.
+    f.owner.setPanelCollapsed('radio-panel', false);
+    assert.equal(f.context.classList.contains('collapsed'), false);
+    assert.equal(f.display.classList.contains('collapsed'), true);
+    assert.equal(f.owner._panelLayout._rightStackPreferredPanelId, 'global-context-panel');
+    // Only a user's choice claims restoration lanes.
+    assert.deepEqual(f.claimed, []);
+  } finally { globalThis.document = prior; }
+});
diff --git a/src/ui/styles/cyber.css b/src/ui/styles/cyber.css
index 4dd7de5b3..b625b9f81 100644
--- a/src/ui/styles/cyber.css
+++ b/src/ui/styles/cyber.css
@@ -1674,6 +1674,13 @@
     flex: 0 0 auto;
   }
 
+  /* The panel rail lists the collapsed panels. */
+  :root[data-ui-theme='cyber']
+    #left-panel-stack.layout-focus.layout-exclusive
+    > [data-panel-id].collapsed {
+    display: none;
+  }
+
   :root[data-ui-theme='cyber']
     #left-panel-stack
     > :is(#data-panel, #scene-panel) {