diff --git a/src/main/daemon/daemon-pty-router.test.ts b/src/main/daemon/daemon-pty-router.test.ts
index 904b3703085..6b5afd62cb5 100644
--- a/src/main/daemon/daemon-pty-router.test.ts
+++ b/src/main/daemon/daemon-pty-router.test.ts
@@ -11,7 +11,8 @@ type AdapterMock = DaemonPtyAdapter & {
 function createAdapter(
   label: string,
   sessions: string[] = [],
-  reconcileResult?: { alive: string[]; killed: string[] }
+  reconcileResult?: { alive: string[]; killed: string[] },
+  opts: { listProcessesRejects?: boolean } = {}
 ): AdapterMock {
   const writes: { id: string; data: string }[] = []
   const dataListeners: ((payload: { id: string; data: string }) => void)[] = []
@@ -22,13 +23,16 @@ function createAdapter(
       sessions.push(id)
       return { id }
     }),
-    listProcesses: vi.fn(async () =>
-      sessions.map((id) => ({
+    listProcesses: vi.fn(async () => {
+      if (opts.listProcessesRejects) {
+        throw new Error('discovery failed')
+      }
+      return sessions.map((id) => ({
         id,
         cwd: '',
         title: label
       }))
-    ),
+    }),
     write: vi.fn((id: string, data: string) => {
       writes.push({ id, data })
     }),
@@ -218,6 +222,23 @@ describe('DaemonPtyRouter', () => {
     expect(onLegacyDrained).toHaveBeenCalledWith(legacy)
   })
 
+  it('does not drain an adapter when legacy discovery fails', async () => {
+    const current = createAdapter('current')
+    const legacy = createAdapter('legacy', ['legacy-session'], undefined, {
+      listProcessesRejects: true
+    })
+    const onLegacyDrained = vi.fn()
+    const router = new DaemonPtyRouter({ current, legacy: [legacy], onLegacyDrained })
+
+    await router.discoverLegacySessions()
+    router.sweepDrainedLegacyAdapters()
+    legacy.emitExit('legacy-session', 0)
+
+    expect(onLegacyDrained).not.toHaveBeenCalled()
+    await router.listProcesses()
+    expect(legacy.listProcesses).toHaveBeenCalledTimes(2)
+  })
+
   it('merges startup reconciliation and updates route mappings', async () => {
     const current = createAdapter('current', [], {
       alive: ['current-alive'],
diff --git a/src/main/daemon/daemon-pty-router.ts b/src/main/daemon/daemon-pty-router.ts
index bd5e2432f2b..61346a6155a 100644
--- a/src/main/daemon/daemon-pty-router.ts
+++ b/src/main/daemon/daemon-pty-router.ts
@@ -6,6 +6,7 @@ export class DaemonPtyRouter implements IPtyProvider {
   private legacy: DaemonPtyAdapter[]
   private sessionAdapters = new Map<string, DaemonPtyAdapter>()
   private unsubscribersByAdapter = new Map<DaemonPtyAdapter, (() => void)[]>()
+  private discoveryFailedAdapters = new Set<DaemonPtyAdapter>()
   private onLegacyDrained?: (adapter: DaemonPtyAdapter) => void
   private dataListeners: ((payload: { id: string; data: string }) => void)[] = []
   private exitListeners: ((payload: { id: string; code: number }) => void)[] = []
@@ -42,10 +43,12 @@ export class DaemonPtyRouter implements IPtyProvider {
     for (const adapter of this.legacy) {
       try {
         const sessions = await adapter.listProcesses()
+        this.discoveryFailedAdapters.delete(adapter)
         for (const session of sessions) {
           this.sessionAdapters.set(session.id, adapter)
         }
       } catch (error) {
+        this.discoveryFailedAdapters.add(adapter)
         console.warn('[daemon] Failed to discover legacy daemon sessions', error)
       }
     }
@@ -204,10 +207,15 @@ export class DaemonPtyRouter implements IPtyProvider {
   private drainLegacyAdapterIfEmpty(adapter: DaemonPtyAdapter): void {
     // Why: only previous-version adapters are cleaned up here. The current
     // daemon lifecycle must remain byte-identical when its sessions exit.
-    if (!this.legacy.includes(adapter) || this.hasActiveSessionsOn(adapter)) {
+    if (
+      !this.legacy.includes(adapter) ||
+      this.discoveryFailedAdapters.has(adapter) ||
+      this.hasActiveSessionsOn(adapter)
+    ) {
       return
     }
     this.legacy = this.legacy.filter((a) => a !== adapter)
+    this.discoveryFailedAdapters.delete(adapter)
     this.unsubscribeAdapter(adapter)
     this.onLegacyDrained?.(adapter)
   }