feat(ai): agent runtime tool-use loop with event streaming

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/ai/agent/runtime.js

@@ -0,0 +1,58 @@
+// 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 };
+}