fix(agent): support async onLoopDetected callbacks and prevent orphaned tool_use events

- Await onLoopDetected callback result so async functions work correctly
  instead of silently falling through to 'continue'
- Move loop detection before yielding tool_use events so terminate mode
  never emits tool_use without a matching tool_result

src/agent/runner.ts

@@ -310,14 +310,13 @@ export class AgentRunner {
           yield { type: 'text', data: turnText } satisfies StreamEvent
         }
 
-        // Announce each tool-use block the model requested.
+        // Extract tool-use blocks for detection and execution.
         const toolUseBlocks = extractToolUseBlocks(response.content)
-        for (const block of toolUseBlocks) {
-          yield { type: 'tool_use', data: block } satisfies StreamEvent
-        }
 
         // ------------------------------------------------------------------
-        // Step 2.5: Loop detection — check before executing tools.
+        // Step 2.5: Loop detection — check before yielding tool_use events
+        // so that terminate mode doesn't emit orphaned tool_use without
+        // matching tool_result.
         // ------------------------------------------------------------------
         let injectWarning = false
         let injectWarningKind: 'tool_repetition' | 'text_repetition' = 'tool_repetition'
@@ -331,7 +330,7 @@ export class AgentRunner {
             options.onWarning?.(info.detail)
 
             const action = typeof loopAction === 'function'
-              ? loopAction(info)
+              ? await loopAction(info)
               : loopAction
 
             if (action === 'terminate') {
@@ -363,6 +362,12 @@ export class AgentRunner {
           break
         }
 
+        // Announce each tool-use block the model requested (after loop
+        // detection, so terminate mode never emits unpaired events).
+        for (const block of toolUseBlocks) {
+          yield { type: 'tool_use', data: block } satisfies StreamEvent
+        }
+
         // ------------------------------------------------------------------
         // Step 4: Execute all tool calls in PARALLEL.
         //

src/types.ts

@@ -254,10 +254,10 @@ export interface LoopDetectionConfig {
    * - `'warn'`      — inject a "you appear stuck" message, give the LLM one
    *                    more chance; terminate if the loop persists (default)
    * - `'terminate'` — stop the run immediately
-   * - `function`    — custom callback; return `'continue'`, `'inject'`, or
-   *                    `'terminate'` to control the outcome
+   * - `function`    — custom callback (sync or async); return `'continue'`,
+   *                    `'inject'`, or `'terminate'` to control the outcome
    */
-  readonly onLoopDetected?: 'warn' | 'terminate' | ((info: LoopDetectionInfo) => 'continue' | 'inject' | 'terminate')
+  readonly onLoopDetected?: 'warn' | 'terminate' | ((info: LoopDetectionInfo) => 'continue' | 'inject' | 'terminate' | Promise<'continue' | 'inject' | 'terminate'>)
 }
 
 /** Diagnostic payload emitted when a loop is detected. */