diff --git a/src/hooks/team-session-events/team-member-error-handler.test.ts b/src/hooks/team-session-events/team-member-error-handler.test.ts
new file mode 100644
index 000000000..8d1418929
--- /dev/null
+++ b/src/hooks/team-session-events/team-member-error-handler.test.ts
@@ -0,0 +1,172 @@
+/// <reference types="bun-types" />
+
+import { afterEach, describe, expect, 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 {
+  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 { createTeamMemberErrorHandler } from "./team-member-error-handler"
+
+const temporaryDirectories: string[] = []
+
+async function createTemporaryBaseDir(): Promise<string> {
+  const baseDir = await mkdtemp(path.join(tmpdir(), "team-member-error-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 () => {
+  clearTeamSessionRegistry()
+  await Promise.all(temporaryDirectories.splice(0).map(async (directoryPath) => {
+    await rm(directoryPath, { recursive: true, force: true })
+  }))
+})
+
+describe("createTeamMemberErrorHandler", () => {
+  test("marks the matching member errored without changing team status", async () => {
+    // given
+    const baseDir = await createTemporaryBaseDir()
+    const config = createConfig(baseDir)
+    const teamRunId = randomUUID()
+    await seedRuntimeState(createRuntimeState(teamRunId), config)
+    const handler = createTeamMemberErrorHandler(config)
+
+    // when
+    await handler({
+      event: {
+        type: "session.error",
+        properties: { sessionID: "member-session", error: new Error("boom") },
+      },
+    })
+
+    // then
+    const runtimeState = await loadRuntimeState(teamRunId, config)
+    expect(runtimeState.status).toBe("active")
+    expect(runtimeState.members[0]?.status).toBe("errored")
+  })
+
+  test("marks the member errored during the spawn race when the registry tracks the fresh session before disk state persists it", async () => {
+    // given
+    const baseDir = await createTemporaryBaseDir()
+    const config = createConfig(baseDir)
+    const teamRunId = randomUUID()
+    await seedRuntimeState({
+      ...createRuntimeState(teamRunId),
+      members: [
+        {
+          name: "worker",
+          agentType: "general-purpose",
+          status: "running",
+          pendingInjectedMessageIds: [],
+        },
+      ],
+    }, config)
+    registerTeamSession("member-session", {
+      teamRunId,
+      memberName: "worker",
+      role: "member",
+    })
+    const handler = createTeamMemberErrorHandler(config)
+
+    // when
+    await handler({
+      event: {
+        type: "session.error",
+        properties: { sessionID: "member-session", error: new Error("boom") },
+      },
+    })
+
+    // then
+    const runtimeState = await loadRuntimeState(teamRunId, config)
+    expect(runtimeState.status).toBe("active")
+    expect(runtimeState.members[0]?.status).toBe("errored")
+  })
+
+  test("falls back to disk lookup when the registry points the member session at the wrong teamRunId", 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),
+      members: [
+        {
+          name: "worker",
+          sessionId: "other-session",
+          agentType: "general-purpose",
+          status: "running",
+          pendingInjectedMessageIds: [],
+        },
+      ],
+    }, config)
+    registerTeamSession("member-session", {
+      teamRunId: wrongTeamRunId,
+      memberName: "worker",
+      role: "member",
+    })
+    const handler = createTeamMemberErrorHandler(config)
+
+    // when
+    await handler({
+      event: {
+        type: "session.error",
+        properties: { sessionID: "member-session", error: new Error("boom") },
+      },
+    })
+
+    // then
+    const correctRuntimeState = await loadRuntimeState(correctTeamRunId, config)
+    const wrongRuntimeState = await loadRuntimeState(wrongTeamRunId, config)
+    expect(correctRuntimeState.members[0]?.status).toBe("errored")
+    expect(wrongRuntimeState.members[0]?.status).toBe("running")
+  })
+})
diff --git a/src/hooks/team-session-events/team-member-error-handler.ts b/src/hooks/team-session-events/team-member-error-handler.ts
new file mode 100644
index 000000000..89dc67601
--- /dev/null
+++ b/src/hooks/team-session-events/team-member-error-handler.ts
@@ -0,0 +1,53 @@
+import type { TeamModeConfig } from "../../config/schema/team-mode"
+import { findResolvedMemberSession } from "../../features/team-mode/member-session-resolution"
+import { loadRuntimeState, transitionRuntimeState } from "../../features/team-mode/team-state-store/store"
+import { log } from "../../shared/logger"
+
+type HookInput = { event: { type: string; properties?: unknown } }
+export type HookImpl = (input: HookInput) => Promise<void>
+
+function getErroredSessionID(properties: unknown): string | undefined {
+  const record = properties as { sessionID?: string } | undefined
+  return record?.sessionID
+}
+
+export function createTeamMemberErrorHandler(config: TeamModeConfig): HookImpl {
+  return async ({ event }: HookInput): Promise<void> => {
+    if (event.type !== "session.error") return
+
+    const erroredSessionID = getErroredSessionID(event.properties)
+    if (!erroredSessionID) return
+
+    try {
+      const runtimeMember = await findResolvedMemberSession(erroredSessionID, config, "team member error handler")
+      if (runtimeMember === null) {
+        return
+      }
+
+      const runtimeState = await loadRuntimeState(runtimeMember.teamRunId, config)
+      await transitionRuntimeState(runtimeState.teamRunId, (currentRuntimeState) => ({
+        ...currentRuntimeState,
+        members: currentRuntimeState.members.map((member) => (
+          member.name === runtimeMember.memberName
+            ? { ...member, status: "errored" }
+            : member
+        )),
+      }), config)
+
+      log("team member session errored", {
+        event: "team-mode-member-errored",
+        teamRunId: runtimeState.teamRunId,
+        teamName: runtimeState.teamName,
+        memberName: runtimeMember.memberName,
+        sessionID: erroredSessionID,
+        runtimeStatus: runtimeState.status,
+      })
+    } catch (error) {
+      log("team member error handler failed", {
+        event: "team-mode-member-error-handler-error",
+        sessionID: erroredSessionID,
+        error: error instanceof Error ? error.message : String(error),
+      })
+    }
+  }
+}