fix: list a subagent's background Bash commands (#1540)

Claude Code sends no `tool_use_result` with a subagent's tool results.
The adapter recognizes a background Bash command only from the
`backgroundTaskId` in that structured result, so it never recognized one
that a subagent started. The command's terminal was reported exited
(code 0) as soon as the result came, while the command kept running, and
the command was missing from the subagent's `state_update.background`.

The real SDK stream (CLI 2.1.318) for a subagent running `sleep 30` in
the background:

```
task_started  task_id=beure6fer task_type=local_bash tool_use_id=toolu_018M… owned_by_subagent=true is_backgrounded=true
user          parent_tool_use_id=toolu_01HY… tool_result for toolu_018M…, no tool_use_result
```

The local transcripts agree: none of the 35 subagent background Bash
results across CLI 2.1.293 to 2.1.318 has a `toolUseResult`.

When a Bash result has no structured task id, the adapter now uses the
live background `local_bash` task whose `task_started` named that Bash
call. The existing subagent test now sends the stream the CLI sends. It
fails without the fix.

src/acp-agent.ts

@@ -8502,6 +8502,18 @@ export class ClaudeAcpAgent {
                 content,
                 toolUseResult,
                 session.toolUseCache,
+                (toolUseId) => {
+                  for (const [taskId, task] of session.liveBackgroundTasks) {
+                    if (
+                      task.parentToolUseId === toolUseId &&
+                      task.taskType === "local_bash" &&
+                      task.backgrounded
+                    ) {
+                      return taskId;
+                    }
+                  }
+                  return undefined;
+                },
               );
               if (backgroundBashTask) await asyncTasks.taskBackgrounded(backgroundBashTask);
               // The command's terminal runs until its task ends, unless the

src/async-tasks.ts

@@ -863,18 +863,29 @@ function recordPublished(task: AsyncTask, fields: Record<string, unknown>): void
  * Recovers a background Bash task from the structured `backgroundTaskId` of
  * its tool result. The text of a tool result never gives a task id: a
  * foreground command can print any text.
+ *
+ * Claude Code sends no `tool_use_result` with a subagent's tool results. For
+ * those, `startedTaskOf` gives the background `local_bash` task whose
+ * `task_started` named the Bash call, which comes before the result.
  */
 export function backgroundBashTaskFromToolResult(
   content: unknown,
   toolUseResult: unknown,
   toolUses: Record<string, { name: string; input: unknown }>,
+  startedTaskOf?: (toolUseId: string) => string | undefined,
 ): (AsyncTaskStarted & { taskId: string; toolCallId: string }) | undefined {
   if (!Array.isArray(content)) return undefined;
   const toolResults = content.flatMap(toolResultBlock);
   const bashResults = toolResults.filter((result) => toolUses[result.toolUseId]?.name === "Bash");
   if (bashResults.length === 0) return undefined;
 
-  const backgroundResults = structuredBackgroundResults(toolUseResult, toolUses);
+  let backgroundResults = structuredBackgroundResults(toolUseResult, toolUses);
+  if (backgroundResults.length === 0 && startedTaskOf) {
+    backgroundResults = bashResults.flatMap((result) => {
+      const taskId = result.isError ? undefined : startedTaskOf(result.toolUseId);
+      return taskId ? [{ taskId, toolUseId: result.toolUseId }] : [];
+    });
+  }
   const distinctTaskIds = new Set(backgroundResults.map((result) => result.taskId));
   if (distinctTaskIds.size !== 1) return undefined;
   const taskId = [...distinctTaskIds][0];

src/tests/acp-v2.test.ts

@@ -4510,10 +4510,13 @@ describe("ACP v2 requests that subagents make", () => {
           description: "make test",
           tool_use_id: "toolu_bg",
           parent_task_id: "agent-1",
+          owned_by_subagent: true,
           is_backgrounded: true,
           uuid: randomUUID(),
           session_id: options.sessionId,
         };
+        // As seen live (CLI 2.1.318): a subagent's tool result has no
+        // `tool_use_result`, so only the `task_started` above names the task.
         yield childMessage(options, {
           type: "user",
           message: {
@@ -4526,13 +4529,6 @@ describe("ACP v2 requests that subagents make", () => {
               },
             ],
           },
-          tool_use_result: {
-            stdout: "",
-            stderr: "",
-            interrupted: false,
-            isImage: false,
-            backgroundTaskId: "bg1",
-          },
         });
         yield taskEnd(options, "agent-1", "toolu_agent-1");
         yield level(options, [bash]);