diff --git a/src/main/runtime/runtime-terminal-orphan-session-adoption.test.ts b/src/main/runtime/runtime-terminal-orphan-session-adoption.test.ts
new file mode 100644
index 00000000000..71071b91193
--- /dev/null
+++ b/src/main/runtime/runtime-terminal-orphan-session-adoption.test.ts
@@ -0,0 +1,80 @@
+import { expect, it } from 'vitest'
+import { LOCAL_EXECUTION_HOST_ID } from '../../shared/execution-host'
+import { makePaneKey } from '../../shared/stable-pane-id'
+import type { RuntimeTerminalOrphanAdoptionRequest } from '../../shared/runtime-types'
+import { collectLayoutLeafIdsInOrder } from '../../shared/workspace-layout/terminal-pane-tree'
+import {
+  GIT_KEY,
+  addWorkspace,
+  emptySession,
+  leaf
+} from '../../shared/workspace-layout/workspace-layout-session.test-fixture'
+import { buildRuntimeTerminalOrphanSession } from './runtime-terminal-orphan-session-adoption'
+import type { RuntimePtyWorktreeRecord } from './runtime-terminal-state-records'
+
+const TAB = 'tab-1'
+const HEALTHY = leaf(1)
+const ORPHAN = leaf(2)
+
+function adopt(existingLeaves: [string, string?][]) {
+  const session = addWorkspace(emptySession(), GIT_KEY, [
+    { id: 'group-1', tabs: [{ id: TAB, leaves: existingLeaves }] }
+  ])
+  const claim = {
+    terminal: 'terminal-orphan',
+    ptyId: 'pty-orphan',
+    incarnationId: 'incarnation-orphan',
+    tabId: TAB,
+    leafId: ORPHAN
+  }
+  const topology: NonNullable<RuntimeTerminalOrphanAdoptionRequest['topology']> = {
+    tabs: [
+      {
+        tabId: TAB,
+        root: { type: 'leaf', leafId: ORPHAN },
+        activeLeafId: ORPHAN,
+        expandedLeafId: null
+      }
+    ],
+    groups: [{ id: 'group-1', activeTabId: TAB, tabOrder: [TAB] }]
+  }
+  const request: RuntimeTerminalOrphanAdoptionRequest = {
+    worktree: GIT_KEY,
+    expectedTopologyRevision: 0,
+    claims: [claim],
+    topology
+  }
+  return buildRuntimeTerminalOrphanSession({
+    hostId: LOCAL_EXECUTION_HOST_ID,
+    session,
+    sessionWorktreeId: GIT_KEY,
+    worktreeId: GIT_KEY,
+    request,
+    validated: [
+      {
+        claim,
+        // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the tab already exists, so the builder never reads the PTY record.
+        pty: {} as RuntimePtyWorktreeRecord,
+        paneKey: makePaneKey(TAB, ORPHAN)
+      }
+    ],
+    topologyTabsById: new Map(topology.tabs.map((tab) => [tab.tabId, tab])),
+    topologyGroups: topology.groups,
+    getDisplayTitle: () => null
+  })
+}
+
+it('keeps the healthy sibling pane and its PTY when one split pane is recovered', () => {
+  const layout = adopt([[HEALTHY, 'pty-healthy']]).terminalLayoutsByTabId[TAB]
+
+  expect(collectLayoutLeafIdsInOrder(layout?.root)).toEqual([HEALTHY, ORPHAN])
+  expect(layout?.ptyIdsByLeafId).toEqual({ [HEALTHY]: 'pty-healthy', [ORPHAN]: 'pty-orphan' })
+  expect(layout?.activeLeafId).toBe(ORPHAN)
+})
+
+it('keeps the saved split when it already holds the recovered pane', () => {
+  const layout = adopt([[HEALTHY, 'pty-healthy'], [ORPHAN]]).terminalLayoutsByTabId[TAB]
+
+  expect(collectLayoutLeafIdsInOrder(layout?.root)).toEqual([HEALTHY, ORPHAN])
+  expect(layout?.ptyIdsByLeafId).toEqual({ [HEALTHY]: 'pty-healthy', [ORPHAN]: 'pty-orphan' })
+})
diff --git a/src/main/runtime/runtime-terminal-orphan-session-adoption.ts b/src/main/runtime/runtime-terminal-orphan-session-adoption.ts
index 7ca492c3032..6696e3ce18f 100644
--- a/src/main/runtime/runtime-terminal-orphan-session-adoption.ts
+++ b/src/main/runtime/runtime-terminal-orphan-session-adoption.ts
@@ -6,6 +6,11 @@ import { nameBasedLoadContext } from '../../shared/workspace-layout/workspace-la
 import { saveWorkspaceLayout } from '../../shared/workspace-layout/workspace-layout-save'
 import type { WorkspaceSessionState } from '../../shared/workspace-session-state-types'
 import { collectPersistedTerminalLeafIds } from './mobile-session-layout-projection'
+import {
+  collectLayoutLeafIdsInOrder,
+  removeLayoutLeaf
+} from '../../shared/workspace-layout/terminal-pane-tree'
+import type { TerminalPaneLayoutNode } from '../../shared/terminal-tab-types'
 import type { RuntimePtyWorktreeRecord } from './runtime-terminal-state-records'
 import { mergeTerminalOrphanGroupLayout } from './terminal-orphan-topology'
 import { canonicalizeTerminalSessionWorktreeId } from './workspace-session-worktree-id'
@@ -62,7 +67,7 @@ export function buildRuntimeTerminalOrphanSession(args: {
     next.terminalLayoutsByTabId[claim.tabId] = topologyTab
       ? {
           ...existingLayout,
-          root: topologyTab.root,
+          root: mergeAdoptedTopologyRoot(existingLayout?.root ?? null, topologyTab.root),
           activeLeafId: topologyTab.activeLeafId,
           expandedLeafId: topologyTab.expandedLeafId,
           ptyIdsByLeafId: {
@@ -196,3 +201,29 @@ export function buildRuntimeTerminalOrphanSession(args: {
     loadWorkspaceLayoutWithoutReport(hostId, persisted, nameBasedLoadContext())
   )
 }
+
+/**
+ * The client's topology names only the panes it adopts; the tab's other panes keep their place
+ * beside them, so recovering one split never drops a healthy sibling.
+ */
+function mergeAdoptedTopologyRoot(
+  existingRoot: TerminalPaneLayoutNode | null,
+  adoptedRoot: TerminalPaneLayoutNode
+): TerminalPaneLayoutNode {
+  if (!existingRoot) {
+    return adoptedRoot
+  }
+  const existingLeafIds = collectLayoutLeafIdsInOrder(existingRoot)
+  const adoptedLeafIds = collectLayoutLeafIdsInOrder(adoptedRoot)
+  if (adoptedLeafIds.every((leafId) => existingLeafIds.includes(leafId))) {
+    return existingRoot
+  }
+  const siblings = adoptedLeafIds.reduce<TerminalPaneLayoutNode | null>(
+    (root, leafId) => removeLayoutLeaf(root, leafId),
+    existingRoot
+  )
+  if (!siblings) {
+    return adoptedRoot
+  }
+  return { type: 'split', direction: 'vertical', first: siblings, second: adoptedRoot }
+}