diff --git a/src/hooks/team-session-events/team-lead-orphan-handler.test.ts b/src/hooks/team-session-events/team-lead-orphan-handler.test.ts
new file mode 100644
index 000000000..431ad1e5e
--- /dev/null
+++ b/src/hooks/team-session-events/team-lead-orphan-handler.test.ts
@@ -0,0 +1,169 @@
+/// <reference types="bun-types" />
+
+import { afterEach, describe, expect, mock, spyOn, test } from "bun:test"
+import { randomUUID } from "node:crypto"
+import { mkdtemp, mkdir, rm } from "node:fs/promises"
+import { tmpdir } from "node:os"
+import path from "node:path"
+
+import { TeamModeConfigSchema } from "../../config/schema/team-mode"
+import type { TeamModeConfig } from "../../config/schema/team-mode"
+import * as deleteTeamModule from "../../features/team-mode/team-runtime/delete-team"
+import {
+  clearTeamSessionRegistry,
+  registerTeamSession,
+} from "../../features/team-mode/team-session-registry"
+import type { RuntimeState } from "../../features/team-mode/types"
+import { loadRuntimeState, saveRuntimeState } from "../../features/team-mode/team-state-store/store"
+import { createTeamLeadOrphanHandler } from "./team-lead-orphan-handler"
+
+const temporaryDirectories: string[] = []
+
+async function createTemporaryBaseDir(): Promise<string> {
+  const baseDir = await mkdtemp(path.join(tmpdir(), "team-lead-orphan-handler-"))
+  temporaryDirectories.push(baseDir)
+  return baseDir
+}
+
+function createConfig(baseDir: string): TeamModeConfig {
+  return TeamModeConfigSchema.parse({ base_dir: baseDir, enabled: true })
+}
+
+function createRuntimeState(teamRunId: string): RuntimeState {
+  return {
+    version: 1,
+    teamRunId,
+    teamName: "team-alpha",
+    specSource: "project",
+    createdAt: 1,
+    status: "active",
+    leadSessionId: "lead-session",
+    members: [
+      {
+        name: "worker",
+        sessionId: "member-session",
+        agentType: "general-purpose",
+        status: "running",
+        pendingInjectedMessageIds: [],
+      },
+    ],
+    shutdownRequests: [],
+    bounds: {
+      maxMembers: 8,
+      maxParallelMembers: 4,
+      maxMessagesPerRun: 10000,
+      maxWallClockMinutes: 120,
+      maxMemberTurns: 500,
+    },
+  }
+}
+
+async function seedRuntimeState(runtimeState: RuntimeState, config: TeamModeConfig): Promise<void> {
+  await mkdir(path.join(config.base_dir ?? "", "runtime", runtimeState.teamRunId), { recursive: true })
+  await saveRuntimeState(runtimeState, config)
+}
+
+afterEach(async () => {
+  mock.restore()
+  clearTeamSessionRegistry()
+  await Promise.all(temporaryDirectories.splice(0).map(async (directoryPath) => {
+    await rm(directoryPath, { recursive: true, force: true })
+  }))
+})
+
+describe("createTeamLeadOrphanHandler", () => {
+  test("#given the deleted session matches the lead #when the orphan handler runs #then it marks the team orphaned and force-deletes the team", async () => {
+    // given
+    const baseDir = await createTemporaryBaseDir()
+    const config = createConfig(baseDir)
+    const teamRunId = randomUUID()
+    await seedRuntimeState(createRuntimeState(teamRunId), config)
+    const deleteTeamSpy = spyOn(deleteTeamModule, "deleteTeam")
+    deleteTeamSpy.mockResolvedValue({ removedLayout: true, removedWorktrees: [] })
+    const handler = createTeamLeadOrphanHandler(config)
+
+    // when
+    await handler({
+      event: {
+        type: "session.deleted",
+        properties: { info: { id: "lead-session" } },
+      },
+    })
+
+    // then
+    const runtimeState = await loadRuntimeState(teamRunId, config)
+    expect(runtimeState.status).toBe("orphaned")
+    expect(deleteTeamSpy).toHaveBeenCalledTimes(1)
+    expect(deleteTeamSpy).toHaveBeenCalledWith(teamRunId, config, undefined, undefined, { force: true })
+  })
+
+  test("#given the registry tracks a fresh lead session before disk state persists it #when the orphan handler runs #then it still marks the team orphaned and force-deletes it", async () => {
+    // given
+    const baseDir = await createTemporaryBaseDir()
+    const config = createConfig(baseDir)
+    const teamRunId = randomUUID()
+    await seedRuntimeState({
+      ...createRuntimeState(teamRunId),
+      leadSessionId: undefined,
+    }, config)
+    registerTeamSession("lead-session", {
+      teamRunId,
+      memberName: "lead",
+      role: "lead",
+    })
+    const deleteTeamSpy = spyOn(deleteTeamModule, "deleteTeam")
+    deleteTeamSpy.mockResolvedValue({ removedLayout: false, removedWorktrees: [] })
+    const handler = createTeamLeadOrphanHandler(config)
+
+    // when
+    await handler({
+      event: {
+        type: "session.deleted",
+        properties: { info: { id: "lead-session" } },
+      },
+    })
+
+    // then
+    const runtimeState = await loadRuntimeState(teamRunId, config)
+    expect(runtimeState.status).toBe("orphaned")
+    expect(deleteTeamSpy).toHaveBeenCalledTimes(1)
+    expect(deleteTeamSpy).toHaveBeenCalledWith(teamRunId, config, undefined, undefined, { force: true })
+  })
+
+  test("#given the registry points the lead session at the wrong teamRunId #when the orphan handler runs #then it falls back to disk lookup, orphans the correct team, and force-deletes it", async () => {
+    // given
+    const baseDir = await createTemporaryBaseDir()
+    const config = createConfig(baseDir)
+    const correctTeamRunId = randomUUID()
+    const wrongTeamRunId = randomUUID()
+    await seedRuntimeState(createRuntimeState(correctTeamRunId), config)
+    await seedRuntimeState({
+      ...createRuntimeState(wrongTeamRunId),
+      leadSessionId: "other-lead-session",
+    }, config)
+    registerTeamSession("lead-session", {
+      teamRunId: wrongTeamRunId,
+      memberName: "lead",
+      role: "lead",
+    })
+    const deleteTeamSpy = spyOn(deleteTeamModule, "deleteTeam")
+    deleteTeamSpy.mockResolvedValue({ removedLayout: false, removedWorktrees: [] })
+    const handler = createTeamLeadOrphanHandler(config)
+
+    // when
+    await handler({
+      event: {
+        type: "session.deleted",
+        properties: { info: { id: "lead-session" } },
+      },
+    })
+
+    // then
+    const correctRuntimeState = await loadRuntimeState(correctTeamRunId, config)
+    const wrongRuntimeState = await loadRuntimeState(wrongTeamRunId, config)
+    expect(correctRuntimeState.status).toBe("orphaned")
+    expect(wrongRuntimeState.status).toBe("active")
+    expect(deleteTeamSpy).toHaveBeenCalledTimes(1)
+    expect(deleteTeamSpy).toHaveBeenCalledWith(correctTeamRunId, config, undefined, undefined, { force: true })
+  })
+})
diff --git a/src/hooks/team-session-events/team-lead-orphan-handler.ts b/src/hooks/team-session-events/team-lead-orphan-handler.ts
new file mode 100644
index 000000000..e7b70b3d5
--- /dev/null
+++ b/src/hooks/team-session-events/team-lead-orphan-handler.ts
@@ -0,0 +1,108 @@
+import type { TeamModeConfig } from "../../config/schema/team-mode"
+import type { BackgroundManager } from "../../features/background-agent/manager"
+import { lookupTeamSession } from "../../features/team-mode/team-session-registry"
+import { loadRuntimeState, listActiveTeams, transitionRuntimeState } from "../../features/team-mode/team-state-store/store"
+import type { TmuxSessionManager } from "../../features/tmux-subagent/manager"
+import { log } from "../../shared/logger"
+
+type HookInput = { event: { type: string; properties?: unknown } }
+export type HookImpl = (input: HookInput) => Promise<void>
+
+function getDeletedSessionID(properties: unknown): string | undefined {
+  const record = properties as { info?: { id?: string } } | undefined
+  return record?.info?.id
+}
+
+async function findLeadTeamRunId(
+  deletedSessionID: string,
+  config: TeamModeConfig,
+): Promise<string | null> {
+  const registryEntry = lookupTeamSession(deletedSessionID)
+  if (registryEntry?.role === "lead") {
+    try {
+      const runtimeState = await loadRuntimeState(registryEntry.teamRunId, config)
+      if (runtimeState.leadSessionId === undefined || runtimeState.leadSessionId === deletedSessionID) {
+        return runtimeState.teamRunId
+      }
+    } catch (error) {
+      log("team lead orphan handler registry lookup failed", {
+        event: "team-mode-lead-orphan-handler-registry-error",
+        teamRunId: registryEntry.teamRunId,
+        deletedSessionID,
+        error: error instanceof Error ? error.message : String(error),
+      })
+    }
+  }
+
+  const activeTeams = await listActiveTeams(config)
+
+  for (const activeTeam of activeTeams) {
+    try {
+      const runtimeState = await loadRuntimeState(activeTeam.teamRunId, config)
+      if (runtimeState.leadSessionId === deletedSessionID) {
+        return runtimeState.teamRunId
+      }
+    } catch (error) {
+      log("team lead orphan handler skipped runtime", {
+        event: "team-mode-lead-orphan-handler-runtime-error",
+        teamRunId: activeTeam.teamRunId,
+        deletedSessionID,
+        error: error instanceof Error ? error.message : String(error),
+      })
+    }
+  }
+
+  return null
+}
+
+export function createTeamLeadOrphanHandler(
+  config: TeamModeConfig,
+  tmuxMgr?: TmuxSessionManager,
+  bgMgr?: BackgroundManager,
+): HookImpl {
+  return async ({ event }: HookInput): Promise<void> => {
+    if (event.type !== "session.deleted") return
+
+    const deletedSessionID = getDeletedSessionID(event.properties)
+    if (!deletedSessionID) return
+
+    try {
+      const teamRunId = await findLeadTeamRunId(deletedSessionID, config)
+      if (teamRunId === null) {
+        return
+      }
+
+      const runtimeState = await loadRuntimeState(teamRunId, config)
+      const nextRuntimeState = await transitionRuntimeState(runtimeState.teamRunId, (currentRuntimeState) => ({
+        ...currentRuntimeState,
+        status: "orphaned",
+      }), config)
+
+      log("team lead session deleted", {
+        event: "team-mode-lead-orphaned",
+        teamRunId: runtimeState.teamRunId,
+        teamName: runtimeState.teamName,
+        deletedSessionID,
+        previousStatus: runtimeState.status,
+        nextStatus: nextRuntimeState.status,
+      })
+
+      try {
+        const { deleteTeam } = await import("../../features/team-mode/team-runtime/delete-team")
+        await deleteTeam(teamRunId, config, tmuxMgr, bgMgr, { force: true })
+      } catch (deleteError) {
+        log("team lead orphan cleanup failed (non-fatal)", {
+          event: "team-mode-lead-orphan-cleanup-error",
+          teamRunId,
+          error: deleteError instanceof Error ? deleteError.message : String(deleteError),
+        })
+      }
+    } catch (error) {
+      log("team lead orphan handler failed", {
+        event: "team-mode-lead-orphan-handler-error",
+        deletedSessionID,
+        error: error instanceof Error ? error.message : String(error),
+      })
+    }
+  }
+}