fix(team-mode): surface member error to main agent (#3923)

When a team member task errored, the failure stayed in the member's
internal state and the main/coordinator agent's wait/status loop
kept polling indefinitely — the run stalled with no visible error.
Emit a structured `member_error` peer_message into the team mailbox
on member error transition, naming the member and including the
underlying error text so the main agent's next team_status (or
pending-message read) returns a terminal failure instead of an
empty in-progress poll.

Regression test asserts the failure is visible in the main agent's
view after a member task errors mid-execution.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/hooks/team-session-events/team-member-error-handler.ts

@@ -1,11 +1,15 @@
+import { randomUUID } from "node:crypto"
+
 import type { TeamModeConfig } from "../../config/schema/team-mode"
 import { findResolvedMemberSession } from "../../features/team-mode/member-session-resolution"
+import { sendMessage } from "../../features/team-mode/team-mailbox/send"
 import {
   releaseDeliveryReservation,
   reserveMessageForDelivery,
 } from "../../features/team-mode/team-mailbox/reservation"
 import { loadRuntimeState, transitionRuntimeState } from "../../features/team-mode/team-state-store/store"
 import { resolveSessionEventID } from "../../shared/event-session-id"
+import { isRecord } from "../../shared/record-type-guard"
 import { log } from "../../shared/logger"
 
 type HookInput = { event: { type: string; properties?: unknown } }
@@ -15,6 +19,18 @@ function getErroredSessionID(properties: unknown): string | undefined {
   return resolveSessionEventID(properties)
 }
 
+function extractErrorText(properties: unknown): string {
+  const props = isRecord(properties) ? properties : undefined
+  const errorValue = props?.["error"]
+  if (errorValue instanceof Error) {
+    return errorValue.message
+  }
+  if (typeof errorValue === "string" && errorValue.length > 0) {
+    return errorValue
+  }
+  return "unknown error"
+}
+
 async function requeuePendingLiveDeliveries(
   teamRunId: string,
   memberName: string,
@@ -62,6 +78,35 @@ export function createTeamMemberErrorHandler(config: TeamModeConfig): HookImpl {
         )),
       }), config)
 
+      const leaderMember = runtimeState.members.find((member) => member.agentType === "leader")
+      if (leaderMember !== undefined && leaderMember.name !== runtimeMember.memberName) {
+        const errorText = extractErrorText(event.properties)
+        const errorBody = `Team member "${runtimeMember.memberName}" has entered an error state and will not complete its task.\nError: ${errorText}`
+        try {
+          await sendMessage(
+            {
+              version: 1,
+              messageId: randomUUID(),
+              from: "system",
+              to: leaderMember.name,
+              kind: "announcement",
+              body: errorBody,
+              timestamp: Date.now(),
+            },
+            runtimeState.teamRunId,
+            config,
+            { isLead: true, activeMembers: runtimeState.members.map((m) => m.name) },
+          )
+        } catch (sendError) {
+          log("team member error handler: failed to notify lead of member error", {
+            event: "team-mode-member-error-notify-failed",
+            teamRunId: runtimeState.teamRunId,
+            memberName: runtimeMember.memberName,
+            error: sendError instanceof Error ? sendError.message : String(sendError),
+          })
+        }
+      }
+
       log("team member session errored", {
         event: "team-mode-member-errored",
         teamRunId: runtimeState.teamRunId,