shockbot/mcp/delegate.ts

import { type } from "arktype";
import { Effort } from "../external.ts";
import type { Mode } from "../modes.ts";
import { markActivity } from "../utils/activity.ts";
import { log } from "../utils/cli.ts";
import { resolveSubagentInstructions } from "../utils/instructions.ts";
import type { ToolContext } from "./server.ts";
import { execute, tool } from "./shared.ts";

export const DelegateParams = type({
  mode: type.string.describe(
    "the name of the mode to delegate to (e.g., 'Build', 'Plan', 'Review', 'Fix', 'AddressReviews')"
  ),
  "effort?": Effort.describe(
    'effort level for the subagent: "mini" (low-effort and fast, only for simple tasks), "auto" (medium-effort, good for typical tasks that don\'t require significant reasoning), or "max" (high-effort, good for PR reviews and complex coding tasks)'
  ),
  "instructions?": type.string.describe(
    "optional additional context or instructions for the subagent — use this to pass results from earlier delegations or narrow the subagent's focus"
  ),
});

// exported for unit testing
export function resolveMode(modes: Mode[], modeName: string): Mode | null {
  return modes.find((m) => m.name.toLowerCase() === modeName.toLowerCase()) ?? null;
}

// cap subagent output to avoid bloating the orchestrator's context window.
// the orchestrator needs enough to understand what happened, not the full NDJSON stream.
const MAX_OUTPUT_CHARS = 20_000;

// exported for unit testing
export function truncateOutput(output: string | undefined): string | undefined {
  if (!output || output.length <= MAX_OUTPUT_CHARS) return output;
  const truncated = output.slice(-MAX_OUTPUT_CHARS);
  return `[truncated — showing last ${MAX_OUTPUT_CHARS} chars]\n${truncated}`;
}

export function DelegateTool(ctx: ToolContext) {
  return tool({
    name: "delegate",
    description:
      "Delegate a task to a subagent with a specific mode and effort level. The subagent runs as a separate process with the mode's step-by-step instructions.",
    parameters: DelegateParams,
    execute: execute(async (params) => {
      // guard: prevent subagent recursion
      if (ctx.toolState.delegationActive) {
        return {
          error:
            "delegation is not available inside a subagent. you are already running as a delegated subagent. complete the task directly using the available tools. do not attempt to delegate further. your last agent message will be passed to your supervisor and it will decide what to do next.",
        };
      }

      // resolve mode
      const selectedMode = resolveMode(ctx.modes, params.mode);
      if (!selectedMode) {
        const availableModes = ctx.modes.map((m) => m.name).join(", ");
        return {
          error: `mode "${params.mode}" not found. available modes: ${availableModes}`,
          availableModes: ctx.modes.map((m) => ({
            name: m.name,
            description: m.description,
          })),
        };
      }

      const effort = params.effort ?? "auto";

      // track state
      ctx.toolState.selectedMode = selectedMode.name;
      ctx.toolState.delegationActive = true;

      log.info(
        `» delegating to ${selectedMode.name} mode (effort=${effort})${params.instructions ? " with orchestrator instructions" : ""}`
      );

      // keep the process-level activity timeout alive while the subagent runs.
      // agent CLIs can have long silent thinking phases (>60s) with no stdout,
      // which would trigger the activity timeout. the overall run timeout (default 1h)
      // is the real safety net for stalled agents.
      const keepAliveInterval = setInterval(markActivity, 30_000);

      try {
        // build subagent payload with effort override
        const subagentPayload = { ...ctx.payload, effort };

        // build subagent instructions with mode prompt baked in
        const subagentInstructions = resolveSubagentInstructions({
          payload: subagentPayload,
          repo: ctx.repo,
          modes: ctx.modes,
          mode: selectedMode,
          orchestratorInstructions: params.instructions,
        });

        // spawn subagent — reuses same MCP server, same toolState
        const result = await ctx.agent.run({
          payload: subagentPayload,
          mcpServerUrl: ctx.mcpServerUrl,
          tmpdir: ctx.tmpdir,
          instructions: subagentInstructions,
        });

        log.info(`» delegation to ${selectedMode.name} completed (success=${result.success})`);

        return {
          success: result.success,
          mode: selectedMode.name,
          effort,
          output: truncateOutput(result.output),
          error: result.error,
        };
      } catch (err) {
        // normalize agent crashes into the same return shape as clean failures
        const errorMessage = err instanceof Error ? err.message : String(err);
        log.info(`» delegation to ${selectedMode.name} crashed: ${errorMessage}`);
        return {
          success: false,
          mode: selectedMode.name,
          effort,
          error: errorMessage,
        };
      } finally {
        clearInterval(keepAliveInterval);
        // always release the lock so the orchestrator can delegate again
        ctx.toolState.delegationActive = false;
      }
    }),
  });
}