fix: address review-work round 2 findings

- MCP teardown race: add shutdownGeneration counter to prevent
  in-flight connections from resurrecting after disconnectAll
- MCP multi-key disconnect race: replace disconnectedSessions Set
  with generation-based Map to track per-session disconnect events
- MCP clients: check shutdownGeneration in stdio/http client
  creators before inserting into state.clients
- BackgroundManager: call clearTaskHistoryWhenParentTasksGone after
  timer-based task removal in scheduleTaskRemoval and notifyParentSession
- BackgroundManager: clean completedTaskSummaries when parent has
  no remaining tasks
- Plugin dispose: remove duplicate tmuxSessionManager.cleanup call
  since BackgroundManager.shutdown already handles it via onShutdown

src/features/background-agent/manager.ts

@@ -1149,6 +1149,7 @@ export class BackgroundManager {
     if (!parentSessionID) return
     if (this.getTasksByParentSession(parentSessionID).length > 0) return
     this.taskHistory.clearSession(parentSessionID)
+    this.completedTaskSummaries.delete(parentSessionID)
   }
 
   private scheduleTaskRemoval(taskId: string): void {
@@ -1170,6 +1171,7 @@ export class BackgroundManager {
           SessionCategoryRegistry.remove(task.sessionID)
         }
         log("[background-agent] Removed completed task from memory:", taskId)
+        this.clearTaskHistoryWhenParentTasksGone(task?.parentSessionID)
       }
     }, TASK_CLEANUP_DELAY_MS)
 

src/features/skill-mcp-manager/cleanup.ts

@@ -95,7 +95,7 @@ export async function disconnectSession(state: SkillMcpManagerState, sessionID:
     }
   }
   if (hasPendingForSession) {
-    state.disconnectedSessions.add(sessionID)
+    state.disconnectedSessions.set(sessionID, (state.disconnectedSessions.get(sessionID) ?? 0) + 1)
   }
   const keysToRemove: string[] = []
 
@@ -125,6 +125,7 @@ export async function disconnectSession(state: SkillMcpManagerState, sessionID:
 }
 
 export async function disconnectAll(state: SkillMcpManagerState): Promise<void> {
+  state.shutdownGeneration++
   stopCleanupTimer(state)
   unregisterProcessCleanup(state)
 

src/features/skill-mcp-manager/connection-race.test.ts

@@ -73,12 +73,13 @@ function createState(): SkillMcpManagerState {
   const state: SkillMcpManagerState = {
     clients: new Map(),
     pendingConnections: new Map(),
-    disconnectedSessions: new Set(),
+    disconnectedSessions: new Map(),
     authProviders: new Map(),
     cleanupRegistered: false,
     cleanupInterval: null,
     cleanupHandlers: [],
     idleTimeoutMs: 5 * 60 * 1000,
+    shutdownGeneration: 0,
   }
 
   trackedStates.push(state)
@@ -145,11 +146,11 @@ describe("getOrCreateClient disconnect race", () => {
     const state = createState()
     const info = createClientInfo("session-a")
     const clientKey = createClientKey(info)
-    state.disconnectedSessions.add(info.sessionID)
+    state.disconnectedSessions.set(info.sessionID, 1)
 
     const client = await getOrCreateClient({ state, clientKey, info, config: stdioConfig })
 
-    expect(state.disconnectedSessions.has(info.sessionID)).toBe(false)
+    expect(state.disconnectedSessions.has(info.sessionID)).toBe(true)
     expect(state.clients.get(clientKey)?.client).toBe(client)
     expect(createdClients[0]?.close).not.toHaveBeenCalled()
   })
@@ -163,3 +164,51 @@ describe("getOrCreateClient disconnect race", () => {
     expect(state.clients.size).toBe(0)
   })
 })
+
+describe("getOrCreateClient disconnectAll race", () => {
+  it("#given pending connection #when disconnectAll() is called before connection completes #then client is not added to state.clients", async () => {
+    const state = createState()
+    const info = createClientInfo("session-a")
+    const clientKey = createClientKey(info)
+    const pendingConnect = createDeferred<void>()
+    pendingConnects.push(pendingConnect)
+
+    const clientPromise = getOrCreateClient({ state, clientKey, info, config: stdioConfig })
+    expect(state.pendingConnections.has(clientKey)).toBe(true)
+
+    await disconnectAll(state)
+    pendingConnect.resolve(undefined)
+
+    await expect(clientPromise).rejects.toThrow(/connection completed after shutdown/)
+    expect(state.clients.has(clientKey)).toBe(false)
+  })
+})
+
+describe("getOrCreateClient multi-key disconnect race", () => {
+  it("#given 2 pending connections for session A #when disconnectSession(A) before both complete #then both old connections are rejected", async () => {
+    const state = createState()
+    const infoKey1 = createClientInfo("session-a")
+    const infoKey2 = { ...createClientInfo("session-a"), serverName: "server-2" }
+    const clientKey1 = createClientKey(infoKey1)
+    const clientKey2 = `${infoKey2.sessionID}:${infoKey2.skillName}:${infoKey2.serverName}`
+    const pendingConnect1 = createDeferred<void>()
+    const pendingConnect2 = createDeferred<void>()
+    pendingConnects.push(pendingConnect1)
+    pendingConnects.push(pendingConnect2)
+
+    const promise1 = getOrCreateClient({ state, clientKey: clientKey1, info: infoKey1, config: stdioConfig })
+    const promise2 = getOrCreateClient({ state, clientKey: clientKey2, info: infoKey2, config: stdioConfig })
+    expect(state.pendingConnections.size).toBe(2)
+
+    await disconnectSession(state, "session-a")
+
+    pendingConnect1.resolve(undefined)
+    await expect(promise1).rejects.toThrow(/disconnected during MCP connection setup/)
+
+    pendingConnect2.resolve(undefined)
+    await expect(promise2).rejects.toThrow(/disconnected during MCP connection setup/)
+
+    expect(state.clients.has(clientKey1)).toBe(false)
+    expect(state.clients.has(clientKey2)).toBe(false)
+  })
+})

src/features/skill-mcp-manager/connection.ts

@@ -14,7 +14,6 @@ export async function getOrCreateClient(params: {
   config: ClaudeCodeMcpServer
 }): Promise<Client> {
   const { state, clientKey, info, config } = params
-  state.disconnectedSessions.delete(info.sessionID)
 
   const existing = state.clients.get(clientKey)
   if (existing) {
@@ -31,6 +30,9 @@ export async function getOrCreateClient(params: {
   const expandedConfig = expandEnvVarsInObject(config)
   let currentConnectionPromise!: Promise<Client>
   currentConnectionPromise = (async () => {
+    const disconnectGenAtStart = state.disconnectedSessions.get(info.sessionID) ?? 0
+    const shutdownGenAtStart = state.shutdownGeneration
+
     const client = await createClient({ state, clientKey, info, config: expandedConfig })
 
     const isStale = state.pendingConnections.has(clientKey) && state.pendingConnections.get(clientKey) !== currentConnectionPromise
@@ -39,7 +41,13 @@ export async function getOrCreateClient(params: {
       throw new Error(`Connection for "${info.sessionID}" was superseded by a newer connection attempt.`)
     }
 
-    if (state.disconnectedSessions.has(info.sessionID)) {
+    if (state.shutdownGeneration !== shutdownGenAtStart) {
+      try { await client.close() } catch {}
+      throw new Error(`Shutdown occurred during MCP connection for "${info.sessionID}"`)
+    }
+
+    const currentDisconnectGen = state.disconnectedSessions.get(info.sessionID) ?? 0
+    if (currentDisconnectGen > disconnectGenAtStart) {
       await forceReconnect(state, clientKey)
       throw new Error(`Session "${info.sessionID}" disconnected during MCP connection setup.`)
     }

src/features/skill-mcp-manager/disconnect-cleanup.test.ts

@@ -18,12 +18,13 @@ function createState(): SkillMcpManagerState {
   const state: SkillMcpManagerState = {
     clients: new Map(),
     pendingConnections: new Map(),
-    disconnectedSessions: new Set(),
+    disconnectedSessions: new Map(),
     authProviders: new Map(),
     cleanupRegistered: false,
     cleanupInterval: null,
     cleanupHandlers: [],
     idleTimeoutMs: 5 * 60 * 1000,
+    shutdownGeneration: 0,
   }
 
   trackedStates.push(state)

src/features/skill-mcp-manager/http-client.ts

@@ -24,6 +24,7 @@ function redactUrl(urlStr: string): string {
 
 export async function createHttpClient(params: SkillMcpClientConnectionParams): Promise<Client> {
   const { state, clientKey, info, config } = params
+  const shutdownGenAtStart = state.shutdownGeneration
 
   if (!config.url) {
     throw new Error(`MCP server "${info.serverName}" is configured for HTTP but missing 'url' field.`)
@@ -72,6 +73,12 @@ export async function createHttpClient(params: SkillMcpClientConnectionParams):
     )
   }
 
+  if (state.shutdownGeneration !== shutdownGenAtStart) {
+    try { await client.close() } catch {}
+    try { await transport.close() } catch {}
+    throw new Error(`MCP server "${info.serverName}" connection completed after shutdown`)
+  }
+
   const managedClient = {
     client,
     transport,

src/features/skill-mcp-manager/manager.ts

@@ -10,12 +10,13 @@ export class SkillMcpManager {
   private readonly state: SkillMcpManagerState = {
     clients: new Map(),
     pendingConnections: new Map(),
-    disconnectedSessions: new Set(),
+    disconnectedSessions: new Map(),
     authProviders: new Map(),
     cleanupRegistered: false,
     cleanupInterval: null,
     cleanupHandlers: [],
     idleTimeoutMs: 5 * 60 * 1000,
+    shutdownGeneration: 0,
   }
 
   private getClientKey(info: SkillMcpClientInfo): string {

src/features/skill-mcp-manager/stdio-client.ts

@@ -14,6 +14,7 @@ function getStdioCommand(config: ClaudeCodeMcpServer, serverName: string): strin
 
 export async function createStdioClient(params: SkillMcpClientConnectionParams): Promise<Client> {
   const { state, clientKey, info, config } = params
+  const shutdownGenAtStart = state.shutdownGeneration
 
   const command = getStdioCommand(config, info.serverName)
   const args = config.args ?? []
@@ -55,6 +56,12 @@ export async function createStdioClient(params: SkillMcpClientConnectionParams):
     )
   }
 
+  if (state.shutdownGeneration !== shutdownGenAtStart) {
+    try { await client.close() } catch {}
+    try { await transport.close() } catch {}
+    throw new Error(`MCP server "${info.serverName}" connection completed after shutdown`)
+  }
+
   const managedClient = {
     client,
     transport,

src/features/skill-mcp-manager/types.ts

@@ -51,12 +51,13 @@ export interface ProcessCleanupHandler {
 export interface SkillMcpManagerState {
   clients: Map<string, ManagedClient>
   pendingConnections: Map<string, Promise<Client>>
-  disconnectedSessions: Set<string>
+  disconnectedSessions: Map<string, number>
   authProviders: Map<string, McpOAuthProvider>
   cleanupRegistered: boolean
   cleanupInterval: ReturnType<typeof setInterval> | null
   cleanupHandlers: ProcessCleanupHandler[]
   idleTimeoutMs: number
+  shutdownGeneration: number
 }
 
 export interface SkillMcpClientConnectionParams {