diff --git a/src/tools/agent-teams/teammate-runtime.ts b/src/tools/agent-teams/teammate-runtime.ts
index 052a58c6..0a531412 100644
--- a/src/tools/agent-teams/teammate-runtime.ts
+++ b/src/tools/agent-teams/teammate-runtime.ts
@@ -18,6 +18,18 @@ function delay(ms: number): Promise<void> {
   return new Promise((resolve) => setTimeout(resolve, ms))
 }
 
+function resolveLaunchFailureMessage(status: string | undefined, error: string | undefined): string {
+  if (status === "error") {
+    return error ? `teammate_launch_failed:${error}` : "teammate_launch_failed"
+  }
+
+  if (status === "cancelled") {
+    return "teammate_launch_cancelled"
+  }
+
+  return "teammate_launch_timeout"
+}
+
 function buildLaunchPrompt(teamName: string, teammateName: string, userPrompt: string): string {
   return [
     `You are teammate "${teammateName}" in team "${teamName}".`,
@@ -87,17 +99,28 @@ export async function spawnTeammate(params: SpawnTeammateParams): Promise<TeamTe
 
     const start = Date.now()
     let sessionID = launched.sessionID
+    let latestStatus: string | undefined
+    let latestError: string | undefined
     while (!sessionID && Date.now() - start < 30_000) {
       await delay(50)
       const task = params.manager.getTask(launched.id)
+      latestStatus = task?.status
+      latestError = task?.error
+      if (task?.status === "error" || task?.status === "cancelled") {
+        throw new Error(resolveLaunchFailureMessage(task.status, task.error))
+      }
       sessionID = task?.sessionID
     }
 
+    if (!sessionID) {
+      throw new Error(resolveLaunchFailureMessage(latestStatus, latestError))
+    }
+
     const nextMember: TeamTeammateMember = {
       ...teammate,
       isActive: true,
       backgroundTaskID: launched.id,
-      ...(sessionID ? { sessionID } : {}),
+      sessionID,
     }
 
     const current = readTeamConfigOrThrow(params.teamName)
diff --git a/src/tools/agent-teams/teammate-tools.ts b/src/tools/agent-teams/teammate-tools.ts
index 062be025..f5c47f55 100644
--- a/src/tools/agent-teams/teammate-tools.ts
+++ b/src/tools/agent-teams/teammate-tools.ts
@@ -71,6 +71,14 @@ export function createForceKillTeammateTool(manager: BackgroundManager): ToolDef
     execute: async (args: Record<string, unknown>): Promise<string> => {
       try {
         const input = TeamForceKillInputSchema.parse(args)
+        const teamError = validateTeamName(input.team_name)
+        if (teamError) {
+          return JSON.stringify({ error: teamError })
+        }
+        const agentError = validateAgentName(input.agent_name)
+        if (agentError) {
+          return JSON.stringify({ error: agentError })
+        }
         const config = readTeamConfigOrThrow(input.team_name)
         const member = getTeamMember(config, input.agent_name)
         if (!member || !isTeammateMember(member)) {
@@ -78,7 +86,11 @@ export function createForceKillTeammateTool(manager: BackgroundManager): ToolDef
         }
 
         await cancelTeammateRun(manager, member)
-        writeTeamConfig(input.team_name, removeTeammate(config, input.agent_name))
+        const refreshedConfig = readTeamConfigOrThrow(input.team_name)
+        const refreshedMember = getTeamMember(refreshedConfig, input.agent_name)
+        if (refreshedMember && isTeammateMember(refreshedMember)) {
+          writeTeamConfig(input.team_name, removeTeammate(refreshedConfig, input.agent_name))
+        }
         resetOwnerTasks(input.team_name, input.agent_name)
 
         return JSON.stringify({ success: true, message: `${input.agent_name} stopped` })
@@ -99,9 +111,17 @@ export function createProcessShutdownTool(): ToolDefinition {
     execute: async (args: Record<string, unknown>): Promise<string> => {
       try {
         const input = TeamProcessShutdownInputSchema.parse(args)
+        const teamError = validateTeamName(input.team_name)
+        if (teamError) {
+          return JSON.stringify({ error: teamError })
+        }
         if (input.agent_name === "team-lead") {
           return JSON.stringify({ error: "cannot_shutdown_team_lead" })
         }
+        const agentError = validateAgentName(input.agent_name)
+        if (agentError) {
+          return JSON.stringify({ error: agentError })
+        }
 
         const config = readTeamConfigOrThrow(input.team_name)
         const member = getTeamMember(config, input.agent_name)
diff --git a/src/tools/agent-teams/tools.functional.test.ts b/src/tools/agent-teams/tools.functional.test.ts
index ab3cbbf9..00fd680b 100644
--- a/src/tools/agent-teams/tools.functional.test.ts
+++ b/src/tools/agent-teams/tools.functional.test.ts
@@ -76,6 +76,24 @@ function createMockManager(): MockManagerHandles {
   return { manager, launchCalls, resumeCalls, cancelCalls }
 }
 
+function createFailingLaunchManager(): BackgroundManager {
+  return {
+    launch: async () => ({ id: "bg-fail" }),
+    getTask: () => ({
+      id: "bg-fail",
+      parentSessionID: "ses-main",
+      parentMessageID: "msg-main",
+      description: "failed launch",
+      prompt: "prompt",
+      agent: "sisyphus-junior",
+      status: "error",
+      error: "launch failed",
+    }),
+    resume: async () => ({ id: "resume-unused" }),
+    cancelTask: async () => true,
+  } as unknown as BackgroundManager
+}
+
 function createContext(): TestToolContext {
   return {
     sessionID: "ses-main",
@@ -225,6 +243,26 @@ describe("agent-teams tools functional", () => {
     expect(payload.taskId).toBe(createdTask.id)
   })
 
+  test("rejects invalid task id input for task_get", async () => {
+    //#given
+    const { manager } = createMockManager()
+    const tools = createAgentTeamsTools(manager)
+    const context = createContext()
+
+    await executeJsonTool(tools, "team_create", { team_name: "core" }, context)
+
+    //#when
+    const result = await executeJsonTool(
+      tools,
+      "team_task_get",
+      { team_name: "core", task_id: "../../etc/passwd" },
+      context,
+    ) as { error?: string }
+
+    //#then
+    expect(result.error).toBe("task_id_invalid")
+  })
+
   test("spawn_teammate + send_message + force_kill_teammate execute end-to-end", async () => {
     //#given
     const { manager, launchCalls, resumeCalls, cancelCalls } = createMockManager()
@@ -342,4 +380,35 @@ describe("agent-teams tools functional", () => {
     expect(taskAfterKill.owner).toBeUndefined()
     expect(taskAfterKill.status).toBe("pending")
   })
+
+  test("rolls back teammate when launch fails", async () => {
+    //#given
+    const manager = createFailingLaunchManager()
+    const tools = createAgentTeamsTools(manager)
+    const context = createContext()
+    await executeJsonTool(tools, "team_create", { team_name: "core" }, context)
+
+    //#when
+    const spawnResult = await executeJsonTool(
+      tools,
+      "spawn_teammate",
+      {
+        team_name: "core",
+        name: "worker_1",
+        prompt: "Handle release prep",
+      },
+      context,
+    ) as { error?: string }
+
+    //#then
+    expect(spawnResult.error).toBe("teammate_launch_failed:launch failed")
+
+    //#when
+    const config = await executeJsonTool(tools, "read_config", { team_name: "core" }, context) as {
+      members: Array<{ name: string }>
+    }
+
+    //#then
+    expect(config.members.map((member) => member.name)).toEqual(["team-lead"])
+  })
 })