From bec5fdcf571f1b6f0b3248ac60b89eec6e1dbc1d Mon Sep 17 00:00:00 2001
From: Lucas Vinicius <lucas.oliv001@gmail.com>
Date: Mon, 22 Jun 2026 13:45:10 -0300
Subject: [PATCH] feat(run): forward child session events to NDJSON stream
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When the `task` tool spawns a subagent, its child session events are
published on the bus but filtered out of the parent NDJSON stream
(`opencode run --format json`). This makes `opencode run` unusable as
a headless runtime for multi-agent platforms that need real-time
visibility into subagent execution.

Two new event types are emitted in `--format json` mode:

- `subtask_delta` — streaming token delta from a child session
  (`childSessionID`, `partID`, `delta`)
- `subtask_event` — completed/updated part from a child session
  (`childSessionID`, `part`)

Child sessions are discovered when a `task` tool part transitions to
`running` and its metadata exposes `sessionId`. Only events from known
child sessions are forwarded; the filter is additive and does not affect
any existing event types.

Closes #33397
---
 packages/opencode/src/cli/cmd/run.ts | 29 +++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/packages/opencode/src/cli/cmd/run.ts b/packages/opencode/src/cli/cmd/run.ts
index fad09c3a7add..f2aa5737180c 100644
--- a/packages/opencode/src/cli/cmd/run.ts
+++ b/packages/opencode/src/cli/cmd/run.ts
@@ -680,6 +680,9 @@ export const RunCommand = effectCmd({
         async function loop(client: OpencodeClient, events: Awaited<ReturnType<typeof sdk.event.subscribe>>) {
           const toggles = new Map<string, boolean>()
           let error: string | undefined
+          // Track child session IDs spawned by the task tool so their events
+          // can be forwarded to the parent NDJSON stream.
+          const childSessionIDs = new Set<string>()
 
           for await (const event of events.stream) {
             if (
@@ -695,9 +698,33 @@ export const RunCommand = effectCmd({
               toggles.set("start", true)
             }
 
+            // Forward streaming token deltas from child sessions.
+            if (event.type === "message.part.delta") {
+              if (childSessionIDs.has(event.properties.sessionID)) {
+                emit("subtask_delta", {
+                  childSessionID: event.properties.sessionID,
+                  partID: event.properties.partID,
+                  delta: event.properties.delta,
+                })
+              }
+            }
+
             if (event.type === "message.part.updated") {
               const part = event.properties.part
-              if (part.sessionID !== sessionID) continue
+
+              // Register child session ID when a task tool starts running.
+              if (part.type === "tool" && part.tool === "task" && part.state.status === "running") {
+                const meta = (part.state as { metadata?: { sessionId?: string } }).metadata
+                if (meta?.sessionId) childSessionIDs.add(meta.sessionId)
+              }
+
+              // Forward completed/updated parts from child sessions.
+              if (part.sessionID !== sessionID) {
+                if (childSessionIDs.has(part.sessionID)) {
+                  emit("subtask_event", { childSessionID: part.sessionID, part })
+                }
+                continue
+              }
 
               if (part.type === "tool" && (part.state.status === "completed" || part.state.status === "error")) {
                 if (emit("tool_use", { part })) continue