import crypto from "node:crypto";
import { promises as fs } from "node:fs";
import type { SubagentLifecycleHookRunner } from "../plugins/hooks.js";
import { isValidAgentId, normalizeAgentId, parseAgentSessionKey } from "../routing/session-key.js";
import {
  normalizeLowercaseStringOrEmpty,
  normalizeOptionalString,
} from "../shared/string-coerce.js";
import type { BootstrapContextMode } from "./bootstrap-files.js";
import {
  mapToolContextToSpawnedRunMetadata,
  normalizeSpawnedRunMetadata,
  resolveSpawnedWorkspaceInheritance,
} from "./spawned-context.js";
import {
  decodeStrictBase64,
  materializeSubagentAttachments,
  type SubagentAttachmentReceiptFile,
} from "./subagent-attachments.js";
import { resolveSubagentCapabilities } from "./subagent-capabilities.js";
import { getSubagentDepthFromSessionStore } from "./subagent-depth.js";
import { countActiveRunsForSession, registerSubagentRun } from "./subagent-registry.js";
import { resolveSubagentSpawnAcceptedNote } from "./subagent-spawn-accepted-note.js";
export {
  SUBAGENT_SPAWN_ACCEPTED_NOTE,
  SUBAGENT_SPAWN_SESSION_ACCEPTED_NOTE,
} from "./subagent-spawn-accepted-note.js";
import {
  resolveConfiguredSubagentRunTimeoutSeconds,
  resolveSubagentModelAndThinkingPlan,
  splitModelRef,
} from "./subagent-spawn-plan.js";
import {
  ADMIN_SCOPE,
  AGENT_LANE_SUBAGENT,
  DEFAULT_SUBAGENT_MAX_SPAWN_DEPTH,
  buildSubagentSystemPrompt,
  callGateway,
  emitSessionLifecycleEvent,
  getGlobalHookRunner,
  loadConfig,
  mergeSessionEntry,
  normalizeDeliveryContext,
  pruneLegacyStoreKeys,
  resolveAgentConfig,
  resolveDisplaySessionKey,
  resolveGatewaySessionStoreTarget,
  resolveInternalSessionKey,
  resolveMainSessionAlias,
  resolveSandboxRuntimeStatus,
  updateSessionStore,
  isAdminOnlyMethod,
} from "./subagent-spawn.runtime.js";
import {
  SUBAGENT_SPAWN_MODES,
  SUBAGENT_SPAWN_SANDBOX_MODES,
  type SpawnSubagentMode,
  type SpawnSubagentSandboxMode,
} from "./subagent-spawn.types.js";

export { SUBAGENT_SPAWN_MODES, SUBAGENT_SPAWN_SANDBOX_MODES } from "./subagent-spawn.types.js";
export type { SpawnSubagentMode, SpawnSubagentSandboxMode } from "./subagent-spawn.types.js";

export { decodeStrictBase64 };

type SubagentSpawnDeps = {
  callGateway: typeof callGateway;
  getGlobalHookRunner: () => SubagentLifecycleHookRunner | null;
  loadConfig: typeof loadConfig;
  updateSessionStore: typeof updateSessionStore;
};

const defaultSubagentSpawnDeps: SubagentSpawnDeps = {
  callGateway,
  getGlobalHookRunner,
  loadConfig,
  updateSessionStore,
};

let subagentSpawnDeps: SubagentSpawnDeps = defaultSubagentSpawnDeps;

export type SpawnSubagentParams = {
  task: string;
  label?: string;
  agentId?: string;
  model?: string;
  thinking?: string;
  runTimeoutSeconds?: number;
  thread?: boolean;
  mode?: SpawnSubagentMode;
  cleanup?: "delete" | "keep";
  sandbox?: SpawnSubagentSandboxMode;
  lightContext?: boolean;
  expectsCompletionMessage?: boolean;
  attachments?: Array<{
    name: string;
    content: string;
    encoding?: "utf8" | "base64";
    mimeType?: string;
  }>;
  attachMountPath?: string;
};

export type SpawnSubagentContext = {
  agentSessionKey?: string;
  agentChannel?: string;
  agentAccountId?: string;
  agentTo?: string;
  agentThreadId?: string | number;
  agentGroupId?: string | null;
  agentGroupChannel?: string | null;
  agentGroupSpace?: string | null;
  requesterAgentIdOverride?: string;
  /** Explicit workspace directory for subagent to inherit (optional). */
  workspaceDir?: string;
};

export type SpawnSubagentResult = {
  status: "accepted" | "forbidden" | "error";
  childSessionKey?: string;
  runId?: string;
  mode?: SpawnSubagentMode;
  note?: string;
  modelApplied?: boolean;
  error?: string;
  attachments?: {
    count: number;
    totalBytes: number;
    files: Array<{ name: string; bytes: number; sha256: string }>;
    relDir: string;
  };
};

export { splitModelRef } from "./subagent-spawn-plan.js";

async function updateSubagentSessionStore(
  storePath: string,
  mutator: Parameters<typeof updateSessionStore>[1],
) {
  return await subagentSpawnDeps.updateSessionStore(storePath, mutator);
}

async function callSubagentGateway(
  params: Parameters<typeof callGateway>[0],
): Promise<Awaited<ReturnType<typeof callGateway>>> {
  // Subagent lifecycle requires methods spanning multiple scope tiers
  // (sessions.patch / sessions.delete → admin, agent → write).  When each call
  // independently negotiates least-privilege scopes the first connection pairs
  // at a lower tier and every subsequent higher-tier call triggers a
  // scope-upgrade handshake that headless gateway-client connections cannot
  // complete interactively, causing close(1008) "pairing required" (#59428).
  //
  // Only admin-only methods are pinned to ADMIN_SCOPE; other methods (e.g.
  // "agent" → write) keep their least-privilege scope so that the gateway does
  // not treat the caller as owner (senderIsOwner) and expose owner-only tools.
  const scopes = params.scopes ?? (isAdminOnlyMethod(params.method) ? [ADMIN_SCOPE] : undefined);
  return await subagentSpawnDeps.callGateway({
    ...params,
    ...(scopes != null ? { scopes } : {}),
  });
}

function readGatewayRunId(response: Awaited<ReturnType<typeof callGateway>>): string | undefined {
  if (!response || typeof response !== "object") {
    return undefined;
  }
  const { runId } = response as { runId?: unknown };
  return typeof runId === "string" && runId ? runId : undefined;
}

function loadSubagentConfig() {
  return subagentSpawnDeps.loadConfig();
}

async function persistInitialChildSessionRuntimeModel(params: {
  cfg: ReturnType<typeof loadConfig>;
  childSessionKey: string;
  resolvedModel?: string;
}): Promise<string | undefined> {
  const { provider, model } = splitModelRef(params.resolvedModel);
  if (!model) {
    return undefined;
  }
  try {
    const target = resolveGatewaySessionStoreTarget({
      cfg: params.cfg,
      key: params.childSessionKey,
    });
    await updateSubagentSessionStore(target.storePath, (store) => {
      pruneLegacyStoreKeys({
        store,
        canonicalKey: target.canonicalKey,
        candidates: target.storeKeys,
      });
      store[target.canonicalKey] = mergeSessionEntry(store[target.canonicalKey], {
        model,
        ...(provider ? { modelProvider: provider } : {}),
      });
    });
    return undefined;
  } catch (err) {
    return err instanceof Error ? err.message : typeof err === "string" ? err : "error";
  }
}

function sanitizeMountPathHint(value?: string): string | undefined {
  const trimmed = normalizeOptionalString(value);
  if (!trimmed) {
    return undefined;
  }
  // Prevent prompt injection via control/newline characters in system prompt hints.
  // eslint-disable-next-line no-control-regex
  if (/[\r\n\u0000-\u001F\u007F\u0085\u2028\u2029]/.test(trimmed)) {
    return undefined;
  }
  if (!/^[A-Za-z0-9._\-/:]+$/.test(trimmed)) {
    return undefined;
  }
  return trimmed;
}

async function cleanupProvisionalSession(
  childSessionKey: string,
  options?: {
    emitLifecycleHooks?: boolean;
    deleteTranscript?: boolean;
  },
): Promise<void> {
  try {
    await callSubagentGateway({
      method: "sessions.delete",
      params: {
        key: childSessionKey,
        emitLifecycleHooks: options?.emitLifecycleHooks === true,
        deleteTranscript: options?.deleteTranscript === true,
      },
      timeoutMs: 10_000,
    });
  } catch {
    // Best-effort cleanup only.
  }
}

async function cleanupFailedSpawnBeforeAgentStart(params: {
  childSessionKey: string;
  attachmentAbsDir?: string;
  emitLifecycleHooks?: boolean;
  deleteTranscript?: boolean;
}): Promise<void> {
  if (params.attachmentAbsDir) {
    try {
      await fs.rm(params.attachmentAbsDir, { recursive: true, force: true });
    } catch {
      // Best-effort cleanup only.
    }
  }
  await cleanupProvisionalSession(params.childSessionKey, {
    emitLifecycleHooks: params.emitLifecycleHooks,
    deleteTranscript: params.deleteTranscript,
  });
}

function resolveSpawnMode(params: {
  requestedMode?: SpawnSubagentMode;
  threadRequested: boolean;
}): SpawnSubagentMode {
  if (params.requestedMode === "run" || params.requestedMode === "session") {
    return params.requestedMode;
  }
  // Thread-bound spawns should default to persistent sessions.
  return params.threadRequested ? "session" : "run";
}

function summarizeError(err: unknown): string {
  if (err instanceof Error) {
    return err.message;
  }
  if (typeof err === "string") {
    return err;
  }
  return "error";
}

async function ensureThreadBindingForSubagentSpawn(params: {
  hookRunner: SubagentLifecycleHookRunner | null;
  childSessionKey: string;
  agentId: string;
  label?: string;
  mode: SpawnSubagentMode;
  requesterSessionKey?: string;
  requester: {
    channel?: string;
    accountId?: string;
    to?: string;
    threadId?: string | number;
  };
}): Promise<{ status: "ok" } | { status: "error"; error: string }> {
  const hookRunner = params.hookRunner;
  if (!hookRunner?.hasHooks("subagent_spawning")) {
    return {
      status: "error",
      error:
        "thread=true is unavailable because no channel plugin registered subagent_spawning hooks.",
    };
  }

  try {
    const result = await hookRunner.runSubagentSpawning(
      {
        childSessionKey: params.childSessionKey,
        agentId: params.agentId,
        label: params.label,
        mode: params.mode,
        requester: params.requester,
        threadRequested: true,
      },
      {
        childSessionKey: params.childSessionKey,
        requesterSessionKey: params.requesterSessionKey,
      },
    );
    if (result?.status === "error") {
      const error = result.error.trim();
      return {
        status: "error",
        error: error || "Failed to prepare thread binding for this subagent session.",
      };
    }
    if (result?.status !== "ok" || !result.threadBindingReady) {
      return {
        status: "error",
        error:
          "Unable to create or bind a thread for this subagent session. Session mode is unavailable for this target.",
      };
    }
    return { status: "ok" };
  } catch (err) {
    return {
      status: "error",
      error: `Thread bind failed: ${summarizeError(err)}`,
    };
  }
}

export async function spawnSubagentDirect(
  params: SpawnSubagentParams,
  ctx: SpawnSubagentContext,
): Promise<SpawnSubagentResult> {
  const task = params.task;
  const label = params.label?.trim() || "";
  const requestedAgentId = params.agentId?.trim();

  // Reject malformed agentId before normalizeAgentId can mangle it.
  // Without this gate, error-message strings like "Agent not found: xyz" pass
  // through normalizeAgentId and become "agent-not-found--xyz", which later
  // creates ghost workspace directories and triggers cascading cron loops (#31311).
  if (requestedAgentId && !isValidAgentId(requestedAgentId)) {
    return {
      status: "error",
      error: `Invalid agentId "${requestedAgentId}". Agent IDs must match [a-z0-9][a-z0-9_-]{0,63}. Use agents_list to discover valid targets.`,
    };
  }
  const modelOverride = params.model;
  const thinkingOverrideRaw = params.thinking;
  const requestThreadBinding = params.thread === true;
  const sandboxMode = params.sandbox === "require" ? "require" : "inherit";
  const spawnMode = resolveSpawnMode({
    requestedMode: params.mode,
    threadRequested: requestThreadBinding,
  });
  if (spawnMode === "session" && !requestThreadBinding) {
    return {
      status: "error",
      error: 'mode="session" requires thread=true so the subagent can stay bound to a thread.',
    };
  }
  const cleanup =
    spawnMode === "session"
      ? "keep"
      : params.cleanup === "keep" || params.cleanup === "delete"
        ? params.cleanup
        : "keep";
  const expectsCompletionMessage = params.expectsCompletionMessage !== false;
  const requesterOrigin = normalizeDeliveryContext({
    channel: ctx.agentChannel,
    accountId: ctx.agentAccountId,
    to: ctx.agentTo,
    threadId: ctx.agentThreadId,
  });
  const hookRunner = subagentSpawnDeps.getGlobalHookRunner();
  const cfg = loadSubagentConfig();

  // When agent omits runTimeoutSeconds, use the config default.
  // Falls back to 0 (no timeout) if config key is also unset,
  // preserving current behavior for existing deployments.
  const runTimeoutSeconds = resolveConfiguredSubagentRunTimeoutSeconds({
    cfg,
    runTimeoutSeconds: params.runTimeoutSeconds,
  });
  let modelApplied = false;
  let threadBindingReady = false;
  const { mainKey, alias } = resolveMainSessionAlias(cfg);
  const requesterSessionKey = ctx.agentSessionKey;
  const requesterInternalKey = requesterSessionKey
    ? resolveInternalSessionKey({
        key: requesterSessionKey,
        alias,
        mainKey,
      })
    : alias;
  const requesterDisplayKey = resolveDisplaySessionKey({
    key: requesterInternalKey,
    alias,
    mainKey,
  });

  const callerDepth = getSubagentDepthFromSessionStore(requesterInternalKey, { cfg });
  const maxSpawnDepth =
    cfg.agents?.defaults?.subagents?.maxSpawnDepth ?? DEFAULT_SUBAGENT_MAX_SPAWN_DEPTH;
  if (callerDepth >= maxSpawnDepth) {
    return {
      status: "forbidden",
      error: `sessions_spawn is not allowed at this depth (current depth: ${callerDepth}, max: ${maxSpawnDepth})`,
    };
  }

  const maxChildren = cfg.agents?.defaults?.subagents?.maxChildrenPerAgent ?? 5;
  const activeChildren = countActiveRunsForSession(requesterInternalKey);
  if (activeChildren >= maxChildren) {
    return {
      status: "forbidden",
      error: `sessions_spawn has reached max active children for this session (${activeChildren}/${maxChildren})`,
    };
  }

  const requesterAgentId = normalizeAgentId(
    ctx.requesterAgentIdOverride ?? parseAgentSessionKey(requesterInternalKey)?.agentId,
  );
  const requireAgentId =
    resolveAgentConfig(cfg, requesterAgentId)?.subagents?.requireAgentId ??
    cfg.agents?.defaults?.subagents?.requireAgentId ??
    false;
  if (requireAgentId && !requestedAgentId?.trim()) {
    return {
      status: "forbidden",
      error:
        "sessions_spawn requires explicit agentId when requireAgentId is configured. Use agents_list to see allowed agent ids.",
    };
  }
  const targetAgentId = requestedAgentId ? normalizeAgentId(requestedAgentId) : requesterAgentId;
  if (targetAgentId !== requesterAgentId) {
    const allowAgents =
      resolveAgentConfig(cfg, requesterAgentId)?.subagents?.allowAgents ??
      cfg?.agents?.defaults?.subagents?.allowAgents ??
      [];
    const allowAny = allowAgents.some((value) => value.trim() === "*");
    const normalizedTargetId = normalizeLowercaseStringOrEmpty(targetAgentId);
    const allowSet = new Set(
      allowAgents
        .filter((value) => value.trim() && value.trim() !== "*")
        .map((value) => normalizeLowercaseStringOrEmpty(normalizeAgentId(value))),
    );
    if (!allowAny && !allowSet.has(normalizedTargetId)) {
      const allowedText = allowSet.size > 0 ? Array.from(allowSet).join(", ") : "none";
      return {
        status: "forbidden",
        error: `agentId is not allowed for sessions_spawn (allowed: ${allowedText})`,
      };
    }
  }
  const childSessionKey = `agent:${targetAgentId}:subagent:${crypto.randomUUID()}`;
  const requesterRuntime = resolveSandboxRuntimeStatus({
    cfg,
    sessionKey: requesterInternalKey,
  });
  const childRuntime = resolveSandboxRuntimeStatus({
    cfg,
    sessionKey: childSessionKey,
  });
  if (!childRuntime.sandboxed && (requesterRuntime.sandboxed || sandboxMode === "require")) {
    if (requesterRuntime.sandboxed) {
      return {
        status: "forbidden",
        error:
          "Sandboxed sessions cannot spawn unsandboxed subagents. Set a sandboxed target agent or use the same agent runtime.",
      };
    }
    return {
      status: "forbidden",
      error:
        'sessions_spawn sandbox="require" needs a sandboxed target runtime. Pick a sandboxed agentId or use sandbox="inherit".',
    };
  }
  const childDepth = callerDepth + 1;
  const spawnedByKey = requesterInternalKey;
  const childCapabilities = resolveSubagentCapabilities({
    depth: childDepth,
    maxSpawnDepth,
  });
  const targetAgentConfig = resolveAgentConfig(cfg, targetAgentId);
  const plan = resolveSubagentModelAndThinkingPlan({
    cfg,
    targetAgentId,
    targetAgentConfig,
    modelOverride,
    thinkingOverrideRaw,
  });
  if (plan.status === "error") {
    return {
      status: "error",
      error: plan.error,
    };
  }
  const { resolvedModel, thinkingOverride } = plan;
  const patchChildSession = async (patch: Record<string, unknown>): Promise<string | undefined> => {
    try {
      await callSubagentGateway({
        method: "sessions.patch",
        params: { key: childSessionKey, ...patch },
        timeoutMs: 10_000,
      });
      return undefined;
    } catch (err) {
      return err instanceof Error ? err.message : typeof err === "string" ? err : "error";
    }
  };

  const initialChildSessionPatch: Record<string, unknown> = {
    spawnDepth: childDepth,
    subagentRole: childCapabilities.role === "main" ? null : childCapabilities.role,
    subagentControlScope: childCapabilities.controlScope,
    ...plan.initialSessionPatch,
  };

  const initialPatchError = await patchChildSession(initialChildSessionPatch);
  if (initialPatchError) {
    return {
      status: "error",
      error: initialPatchError,
      childSessionKey,
    };
  }
  if (resolvedModel) {
    const runtimeModelPersistError = await persistInitialChildSessionRuntimeModel({
      cfg,
      childSessionKey,
      resolvedModel,
    });
    if (runtimeModelPersistError) {
      try {
        await callSubagentGateway({
          method: "sessions.delete",
          params: { key: childSessionKey, emitLifecycleHooks: false },
          timeoutMs: 10_000,
        });
      } catch {
        // Best-effort cleanup only.
      }
      return {
        status: "error",
        error: runtimeModelPersistError,
        childSessionKey,
      };
    }
    modelApplied = true;
  }
  if (requestThreadBinding) {
    const bindResult = await ensureThreadBindingForSubagentSpawn({
      hookRunner,
      childSessionKey,
      agentId: targetAgentId,
      label: label || undefined,
      mode: spawnMode,
      requesterSessionKey: requesterInternalKey,
      requester: {
        channel: requesterOrigin?.channel,
        accountId: requesterOrigin?.accountId,
        to: requesterOrigin?.to,
        threadId: requesterOrigin?.threadId,
      },
    });
    if (bindResult.status === "error") {
      try {
        await callSubagentGateway({
          method: "sessions.delete",
          params: { key: childSessionKey, emitLifecycleHooks: false },
          timeoutMs: 10_000,
        });
      } catch {
        // Best-effort cleanup only.
      }
      return {
        status: "error",
        error: bindResult.error,
        childSessionKey,
      };
    }
    threadBindingReady = true;
  }
  const mountPathHint = sanitizeMountPathHint(params.attachMountPath);

  let childSystemPrompt = buildSubagentSystemPrompt({
    requesterSessionKey,
    requesterOrigin,
    childSessionKey,
    label: label || undefined,
    task,
    acpEnabled: cfg.acp?.enabled !== false && !childRuntime.sandboxed,
    childDepth,
    maxSpawnDepth,
  });

  let retainOnSessionKeep = false;
  let attachmentsReceipt:
    | {
        count: number;
        totalBytes: number;
        files: SubagentAttachmentReceiptFile[];
        relDir: string;
      }
    | undefined;
  let attachmentAbsDir: string | undefined;
  let attachmentRootDir: string | undefined;
  const materializedAttachments = await materializeSubagentAttachments({
    config: cfg,
    targetAgentId,
    attachments: params.attachments,
    mountPathHint,
  });
  if (materializedAttachments && materializedAttachments.status !== "ok") {
    await cleanupProvisionalSession(childSessionKey, {
      emitLifecycleHooks: threadBindingReady,
      deleteTranscript: true,
    });
    return {
      status: materializedAttachments.status,
      error: materializedAttachments.error,
    };
  }
  if (materializedAttachments?.status === "ok") {
    retainOnSessionKeep = materializedAttachments.retainOnSessionKeep;
    attachmentsReceipt = materializedAttachments.receipt;
    attachmentAbsDir = materializedAttachments.absDir;
    attachmentRootDir = materializedAttachments.rootDir;
    childSystemPrompt = `${childSystemPrompt}\n\n${materializedAttachments.systemPromptSuffix}`;
  }

  const bootstrapContextMode: BootstrapContextMode | undefined = params.lightContext
    ? "lightweight"
    : undefined;

  const childTaskMessage = [
    `[Subagent Context] You are running as a subagent (depth ${childDepth}/${maxSpawnDepth}). Results auto-announce to your requester; do not busy-poll for status.`,
    spawnMode === "session"
      ? "[Subagent Context] This subagent session is persistent and remains available for thread follow-up messages."
      : undefined,
    `[Subagent Task]: ${task}`,
  ]
    .filter((line): line is string => Boolean(line))
    .join("\n\n");

  const toolSpawnMetadata = mapToolContextToSpawnedRunMetadata({
    agentGroupId: ctx.agentGroupId,
    agentGroupChannel: ctx.agentGroupChannel,
    agentGroupSpace: ctx.agentGroupSpace,
    workspaceDir: ctx.workspaceDir,
  });
  const spawnedMetadata = normalizeSpawnedRunMetadata({
    spawnedBy: spawnedByKey,
    ...toolSpawnMetadata,
    workspaceDir: resolveSpawnedWorkspaceInheritance({
      config: cfg,
      targetAgentId,
      // For cross-agent spawns, ignore the caller's inherited workspace;
      // let targetAgentId resolve the correct workspace instead.
      explicitWorkspaceDir:
        targetAgentId !== requesterAgentId ? undefined : toolSpawnMetadata.workspaceDir,
    }),
  });
  const spawnLineagePatchError = await patchChildSession({
    spawnedBy: spawnedByKey,
    ...(spawnedMetadata.workspaceDir ? { spawnedWorkspaceDir: spawnedMetadata.workspaceDir } : {}),
  });
  if (spawnLineagePatchError) {
    await cleanupFailedSpawnBeforeAgentStart({
      childSessionKey,
      attachmentAbsDir,
      emitLifecycleHooks: threadBindingReady,
      deleteTranscript: true,
    });
    return {
      status: "error",
      error: spawnLineagePatchError,
      childSessionKey,
    };
  }

  const childIdem = crypto.randomUUID();
  let childRunId: string = childIdem;
  try {
    const {
      spawnedBy: _spawnedBy,
      workspaceDir: _workspaceDir,
      ...publicSpawnedMetadata
    } = spawnedMetadata;
    const response = await callSubagentGateway({
      method: "agent",
      params: {
        message: childTaskMessage,
        sessionKey: childSessionKey,
        channel: requesterOrigin?.channel,
        to: requesterOrigin?.to ?? undefined,
        accountId: requesterOrigin?.accountId ?? undefined,
        threadId: requesterOrigin?.threadId != null ? String(requesterOrigin.threadId) : undefined,
        idempotencyKey: childIdem,
        deliver: false,
        lane: AGENT_LANE_SUBAGENT,
        extraSystemPrompt: childSystemPrompt,
        thinking: thinkingOverride,
        timeout: runTimeoutSeconds,
        label: label || undefined,
        ...(bootstrapContextMode
          ? {
              bootstrapContextMode,
              bootstrapContextRunKind: "default" as const,
            }
          : {}),
        ...publicSpawnedMetadata,
      },
      timeoutMs: 10_000,
    });
    const runId = readGatewayRunId(response);
    if (runId) {
      childRunId = runId;
    }
  } catch (err) {
    if (attachmentAbsDir) {
      try {
        await fs.rm(attachmentAbsDir, { recursive: true, force: true });
      } catch {
        // Best-effort cleanup only.
      }
    }
    let emitLifecycleHooks = false;
    if (threadBindingReady) {
      const hasEndedHook = hookRunner?.hasHooks("subagent_ended") === true;
      let endedHookEmitted = false;
      if (hasEndedHook) {
        try {
          await hookRunner?.runSubagentEnded(
            {
              targetSessionKey: childSessionKey,
              targetKind: "subagent",
              reason: "spawn-failed",
              sendFarewell: true,
              accountId: requesterOrigin?.accountId,
              runId: childRunId,
              outcome: "error",
              error: "Session failed to start",
            },
            {
              runId: childRunId,
              childSessionKey,
              requesterSessionKey: requesterInternalKey,
            },
          );
          endedHookEmitted = true;
        } catch {
          // Spawn should still return an actionable error even if cleanup hooks fail.
        }
      }
      emitLifecycleHooks = !endedHookEmitted;
    }
    // Always delete the provisional child session after a failed spawn attempt.
    // If we already emitted subagent_ended above, suppress a duplicate lifecycle hook.
    try {
      await callSubagentGateway({
        method: "sessions.delete",
        params: {
          key: childSessionKey,
          deleteTranscript: true,
          emitLifecycleHooks,
        },
        timeoutMs: 10_000,
      });
    } catch {
      // Best-effort only.
    }
    const messageText = summarizeError(err);
    return {
      status: "error",
      error: messageText,
      childSessionKey,
      runId: childRunId,
    };
  }

  try {
    registerSubagentRun({
      runId: childRunId,
      childSessionKey,
      controllerSessionKey: requesterInternalKey,
      requesterSessionKey: requesterInternalKey,
      requesterOrigin,
      requesterDisplayKey,
      task,
      cleanup,
      label: label || undefined,
      model: resolvedModel,
      workspaceDir: spawnedMetadata.workspaceDir,
      runTimeoutSeconds,
      expectsCompletionMessage,
      spawnMode,
      attachmentsDir: attachmentAbsDir,
      attachmentsRootDir: attachmentRootDir,
      retainAttachmentsOnKeep: retainOnSessionKeep,
    });
  } catch (err) {
    if (attachmentAbsDir) {
      try {
        await fs.rm(attachmentAbsDir, { recursive: true, force: true });
      } catch {
        // Best-effort cleanup only.
      }
    }
    try {
      await callSubagentGateway({
        method: "sessions.delete",
        params: {
          key: childSessionKey,
          deleteTranscript: true,
          emitLifecycleHooks: threadBindingReady,
        },
        timeoutMs: 10_000,
      });
    } catch {
      // Best-effort cleanup only.
    }
    return {
      status: "error",
      error: `Failed to register subagent run: ${summarizeError(err)}`,
      childSessionKey,
      runId: childRunId,
    };
  }

  if (hookRunner?.hasHooks("subagent_spawned")) {
    try {
      await hookRunner.runSubagentSpawned(
        {
          runId: childRunId,
          childSessionKey,
          agentId: targetAgentId,
          label: label || undefined,
          requester: {
            channel: requesterOrigin?.channel,
            accountId: requesterOrigin?.accountId,
            to: requesterOrigin?.to,
            threadId: requesterOrigin?.threadId,
          },
          threadRequested: requestThreadBinding,
          mode: spawnMode,
        },
        {
          runId: childRunId,
          childSessionKey,
          requesterSessionKey: requesterInternalKey,
        },
      );
    } catch {
      // Spawn should still return accepted if spawn lifecycle hooks fail.
    }
  }

  // Emit lifecycle event so the gateway can broadcast sessions.changed to SSE subscribers.
  emitSessionLifecycleEvent({
    sessionKey: childSessionKey,
    reason: "create",
    parentSessionKey: requesterInternalKey,
    label: label || undefined,
  });

  return {
    status: "accepted",
    childSessionKey,
    runId: childRunId,
    mode: spawnMode,
    note: resolveSubagentSpawnAcceptedNote({
      spawnMode,
      agentSessionKey: ctx.agentSessionKey,
    }),
    modelApplied: resolvedModel ? modelApplied : undefined,
    attachments: attachmentsReceipt,
  };
}

export const __testing = {
  setDepsForTest(overrides?: Partial<SubagentSpawnDeps>) {
    subagentSpawnDeps = overrides
      ? {
          ...defaultSubagentSpawnDeps,
          ...overrides,
        }
      : defaultSubagentSpawnDeps;
  },
};
