diff --git a/src/main/runtime/orchestration/db-task-dispatch-lifecycle-guards.test.ts b/src/main/runtime/orchestration/db-task-dispatch-lifecycle-guards.test.ts
index f57bc0e55c6..3514f25a2ae 100644
--- a/src/main/runtime/orchestration/db-task-dispatch-lifecycle-guards.test.ts
+++ b/src/main/runtime/orchestration/db-task-dispatch-lifecycle-guards.test.ts
@@ -224,6 +224,38 @@ describe('Task/Dispatch lifecycle guards', () => {
     }
   )
 
+  it.each(['stop', 'abandon'] as const)(
+    '%s preserves a live worker sibling and lets it report',
+    (operation) => {
+      const database = createDatabase()
+      const task = database.createTask({ spec: `${operation} legacy worker split` })
+      const live = startWorker(database, task.id, `${operation}_live`)
+      sqliteFor(database).prepare("UPDATE tasks SET status = 'ready' WHERE id = ?").run(task.id)
+      const released = startWorker(database, task.id, `${operation}_released`)
+
+      if (operation === 'stop') {
+        expect(database.beginWorkerStop(released.dispatchId).disposition).toBe('stopping')
+        expect(database.settleWorkerStop(released.dispatchId).state).toBe('stopped')
+      } else {
+        expect(database.abandonWorkerDispatch(released.dispatchId).disposition).toBe('abandoned')
+      }
+
+      expect(database.getTask(task.id)?.status).toBe('dispatched')
+      expect(database.getDispatchContextById(live.dispatchId)?.status).toBe('dispatched')
+      expectCapability(database, live, true)
+      expect(
+        database.settleWorkerReport({
+          taskId: task.id,
+          dispatchId: live.dispatchId,
+          outcome: 'succeeded',
+          result: `${operation} sibling completed`
+        })
+      ).toEqual({ action: 'settled', outcome: 'succeeded', duplicate: false })
+      expect(database.getTask(task.id)?.status).toBe('completed')
+      expectCapability(database, live, false)
+    }
+  )
+
   it('rejects gate creation while a supervised worker remains active', () => {
     const database = createDatabase()
     const task = database.createTask({ spec: 'worker gate guard' })
diff --git a/src/main/runtime/orchestration/db.ts b/src/main/runtime/orchestration/db.ts
index 1f0f7528d4a..a89fc393d50 100644
--- a/src/main/runtime/orchestration/db.ts
+++ b/src/main/runtime/orchestration/db.ts
@@ -6414,7 +6414,7 @@ export class OrchestrationDb {
            WHERE id = ?`
         )
         .run(dispatchId)
-      this.db.prepare("UPDATE tasks SET status = 'blocked' WHERE id = ?").run(dispatch.task_id)
+      this.blockTaskWithoutActiveSibling(dispatch.task_id, dispatchId)
       this.closeQuestionsForDispatch(dispatchId)
       this.db.exec('COMMIT')
       return {
@@ -6592,7 +6592,7 @@ export class OrchestrationDb {
            WHERE id = ?`
         )
         .run(dispatchId)
-      this.db.prepare("UPDATE tasks SET status = 'blocked' WHERE id = ?").run(dispatch.task_id)
+      this.blockTaskWithoutActiveSibling(dispatch.task_id, dispatchId)
       this.closeQuestionsForDispatch(dispatchId)
       this.db.exec('COMMIT')
       return {
@@ -7316,6 +7316,26 @@ export class OrchestrationDb {
       .get(taskId) as DispatchContextRow | undefined
   }
 
+  private getActiveDispatchForTask(taskId: string): DispatchContextRow | undefined {
+    return this.db
+      .prepare(
+        "SELECT * FROM dispatch_contexts WHERE task_id = ? AND status IN ('pending', 'dispatched') ORDER BY rowid DESC LIMIT 1"
+      )
+      .get(taskId) as DispatchContextRow | undefined
+  }
+
+  private blockTaskWithoutActiveSibling(taskId: string, dispatchId: string): void {
+    this.db
+      .prepare(
+        `UPDATE tasks SET status = 'blocked'
+         WHERE id = ? AND NOT EXISTS (
+           SELECT 1 FROM dispatch_contexts
+           WHERE task_id = tasks.id AND id != ? AND status IN ('pending', 'dispatched')
+         )`
+      )
+      .run(taskId, dispatchId)
+  }
+
   getDispatchContextById(dispatchId: string): DispatchContextRow | undefined {
     return this.db.prepare('SELECT * FROM dispatch_contexts WHERE id = ?').get(dispatchId) as
       | DispatchContextRow
@@ -7586,7 +7606,7 @@ export class OrchestrationDb {
         reason: `inactive dispatch ${params.dispatchId}: it or task ${params.taskId} is already settled.`
       }
     }
-    const latest = this.getDispatchContext(params.taskId)
+    const latest = this.getActiveDispatchForTask(params.taskId)
     if (latest?.id !== params.dispatchId) {
       return {
         action: 'rejected',
@@ -7670,11 +7690,7 @@ export class OrchestrationDb {
   }
 
   failActiveDispatchForTask(taskId: string, error: string): DispatchContextRow | undefined {
-    const active = this.db
-      .prepare(
-        "SELECT * FROM dispatch_contexts WHERE task_id = ? AND status IN ('pending', 'dispatched') ORDER BY rowid DESC LIMIT 1"
-      )
-      .get(taskId) as DispatchContextRow | undefined
+    const active = this.getActiveDispatchForTask(taskId)
     return active ? this.failDispatch(active.id, error) : undefined
   }
 
diff --git a/src/main/runtime/rpc/methods/orchestration-send.test.ts b/src/main/runtime/rpc/methods/orchestration-send.test.ts
index 0462249bf32..afcac1d13ae 100644
--- a/src/main/runtime/rpc/methods/orchestration-send.test.ts
+++ b/src/main/runtime/rpc/methods/orchestration-send.test.ts
@@ -206,6 +206,50 @@ describe('orchestration RPC methods', () => {
       expect(result).toMatchObject({ lifecycle: { action: 'completed' } })
     })
 
+    it('fences a replacement process for a capability-less manual Dispatch', async () => {
+      setup()
+      const task = db.createTask({ spec: 'process-bound manual work' })
+      const dispatch = db.createDispatchContext(
+        task.id,
+        'term_worker',
+        'tab_worker:leaf_worker',
+        undefined,
+        'runtime_test:term_worker:1'
+      )
+      vi.mocked(runtime.getTerminalPaneKey).mockImplementation((handle) =>
+        handle === 'term_worker' ? 'tab_worker:leaf_worker' : coordinatorPaneKey
+      )
+      vi.mocked(runtime.getTerminalProcessIncarnation).mockReturnValue('runtime_test:term_worker:2')
+      const payload = JSON.stringify({
+        taskId: task.id,
+        dispatchId: dispatch.id,
+        outcome: 'succeeded'
+      })
+
+      const rejected = (await call('orchestration.send', {
+        from: 'term_worker',
+        subject: 'Done after replacement',
+        type: 'worker_done',
+        payload
+      })) as { lifecycle: { action: string; code: string } }
+
+      expect(rejected.lifecycle).toEqual({
+        action: 'rejected',
+        code: 'sender_not_assignee',
+        reason: `Dispatch ${dispatch.id} process incarnation is no longer current for its pane.`
+      })
+      expect(db.getTask(task.id)?.status).toBe('dispatched')
+
+      vi.mocked(runtime.getTerminalProcessIncarnation).mockReturnValue('runtime_test:term_worker:1')
+      const accepted = (await call('orchestration.send', {
+        from: 'term_worker',
+        subject: 'Done by assignee',
+        type: 'worker_done',
+        payload
+      })) as { lifecycle: { action: string } }
+      expect(accepted.lifecycle.action).toBe('completed')
+    })
+
     it('rejects an identity-less lifecycle send resolved through the coordinator handle', async () => {
       setup()
       const task = db.createTask({ spec: 'work' })
diff --git a/src/main/runtime/rpc/methods/orchestration.ts b/src/main/runtime/rpc/methods/orchestration.ts
index f52ee65da19..1b876fe1347 100644
--- a/src/main/runtime/rpc/methods/orchestration.ts
+++ b/src/main/runtime/rpc/methods/orchestration.ts
@@ -639,29 +639,42 @@ export const ORCHESTRATION_METHODS: RpcMethod[] = [
         const dispatch = routing.dispatchId
           ? db.getDispatchContextById(routing.dispatchId)
           : undefined
-        if ((msg.type === 'worker_done' || msg.type === 'heartbeat') && dispatch?.capability_hash) {
-          const authority = db.verifyDispatchCapability({
-            dispatchId: dispatch.id,
-            capability: orchestrationCapability,
-            paneKey: senderPaneKey,
-            processIncarnation:
-              attestedCaller?.processIncarnation ??
-              runtime.getTerminalProcessIncarnation(from) ??
-              undefined
-          })
+        const lifecycleMessage = msg.type === 'worker_done' || msg.type === 'heartbeat'
+        if (
+          lifecycleMessage &&
+          dispatch &&
+          (dispatch.capability_hash || dispatch.process_incarnation)
+        ) {
+          const processIncarnation =
+            attestedCaller?.processIncarnation ??
+            runtime.getTerminalProcessIncarnation(from) ??
+            undefined
+          const capabilityBacked = Boolean(dispatch.capability_hash)
+          const authority = capabilityBacked
+            ? db.verifyDispatchCapability({
+                dispatchId: dispatch.id,
+                capability: orchestrationCapability,
+                paneKey: senderPaneKey,
+                processIncarnation
+              })
+            : {
+                valid: db.isDispatchProcessCurrent({
+                  dispatchId: dispatch.id,
+                  paneKey: senderPaneKey ?? null,
+                  processIncarnation: processIncarnation ?? null
+                }),
+                reason: `Dispatch ${dispatch.id} process incarnation is no longer current for its pane.`
+              }
           if (!authority.valid) {
+            const code = capabilityBacked ? 'dispatch_capability_invalid' : 'sender_not_assignee'
             const rejection =
-              db.convertLifecycleMessageToRejection(
-                msg.id,
-                'dispatch_capability_invalid',
-                authority.reason
-              ) ?? msg
+              db.convertLifecycleMessageToRejection(msg.id, code, authority.reason) ?? msg
             runtime.notifyMessageArrived(rejection.to_handle, rejection.type)
             return {
               message: rejection,
               lifecycle: {
                 action: 'rejected',
-                code: 'dispatch_capability_invalid',
+                code,
                 reason: authority.reason
               }
             }