$ Lessons for Builders

while (session.active) {
  const userInput = await queryEngine.getInput();
  const toolCalls = await queryEngine.submit(userInput, {
    budget: session.remainingBudget,
    tools: toolPool.getAvailable(permissionContext),
  });

  for (const call of toolCalls) {
    // Sequential execution — no concurrency
    const result = await executionRegistry.route(call);
    session.transcript.append(result);
  }

  if (session.contextPressure > COMPACTION_THRESHOLD) {
    await session.compact(); // Preserve meaning, reduce tokens
  }
}

// Layer 1: Trust gate — is the user trusted at all?
if (!trustContext.verified) return MINIMAL_TOOLS;

// Layer 2: Deferred init — load expensive tools now
await toolPool.loadDeferred(mcpConnections, lspServers);

// Layer 3: Deny lists — block specific tools
const filtered = toolPool.filter({
  denyNames: ["rm", "format", "drop"],
  denyPrefixes: ["Dangerous", "Internal"],
});

// Layer 4: Per-tool safety — tool-level checks
// BashTool: destructive command warnings + preapproved list
// FileWriteTool: path validation
// AgentTool: restricted sub-agent toolsets

// Fork: child inherits parent context
const child = await forkSubagent({
  parentContext: session.transcript,
  tools: parentTools.subset(["FileReadTool", "GrepTool", "GlobTool"]),
  task: "Find all uses of deprecated API",
});

// Spawn: independent agent, clean slate
const worker = await spawnMultiAgent({
  tools: ["BashTool", "FileEditTool"],
  scratchpad: new Scratchpad(),
  task: "Refactor auth module",
  reportTo: coordinator,
});