// Tool-use loop. callModel + registry injected (no network here).
// Emits: { type:'tool', tool, args, status } | { type:'delta', text }
//        | { type:'draft', pending_change_id, summary }
// Returns: { text, toolTrace, draftIds, usage, stoppedOnGuard }
export async function runTurn({ callModel, registry, system, messages, ctx, onEvent, maxIterations = 6 }) {
  const convo = [...messages];
  const toolTrace = [];
  const draftIds = [];
  let usage = {};
  let stoppedOnGuard = false;

  for (let i = 0; i < maxIterations; i++) {
    const res = await callModel({
      system,
      messages: convo,
      tools: registry.toAnthropicTools(),
      onTextDelta: (t) => onEvent?.({ type: 'delta', text: t })
    });
    usage = res.usage || usage;

    if (!res.toolUses?.length) {
      return { text: res.text, toolTrace, draftIds, usage, stoppedOnGuard };
    }

    // Record the assistant turn (text + tool_use blocks) for the next round.
    convo.push({
      role: 'assistant',
      content: [
        ...(res.text ? [{ type: 'text', text: res.text }] : []),
        ...res.toolUses.map(t => ({ type: 'tool_use', id: t.id, name: t.name, input: t.input }))
      ]
    });

    const toolResults = [];
    for (const call of res.toolUses) {
      const tool = registry.getTool(call.name);
      let result;
      try {
        result = tool ? await tool.handler(call.input, ctx) : { error: `unknown tool ${call.name}` };
      } catch (e) {
        result = { error: String(e?.message || e) };
      }
      const status = result?.error ? 'error' : 'done';
      toolTrace.push({ tool: call.name, args: call.input, ok: !result?.error });
      onEvent?.({ type: 'tool', tool: call.name, args: call.input, status });
      if (result?.pending_change_id) {
        draftIds.push(result.pending_change_id);
        onEvent?.({ type: 'draft', pending_change_id: result.pending_change_id, summary: result.summary });
      }
      toolResults.push({ type: 'tool_result', tool_use_id: call.id, content: JSON.stringify(result) });
    }
    convo.push({ role: 'user', content: toolResults });

    if (i === maxIterations - 1) stoppedOnGuard = true;
  }

  return { text: '', toolTrace, draftIds, usage, stoppedOnGuard };
}