fix: buffer Docker log chunks into complete lines before SSE emit

Docker splits long stdout lines (e.g. stream-json tool_result events
with full file contents) across multiple log frames. Each fragment
fails JSON.parse in the frontend, displaying raw JSON blobs.

Backend: stream_output now buffers chunks and only emits complete
newline-delimited lines, so each SSE event is a parseable JSON line.

Frontend: parseStreamEvent suppresses text that looks like a JSON
fragment (starts with {, [, or ") as defense-in-depth.

Author: mariuspruvot

apps/api/src/helprs/modules/container/service.py

@@ -299,16 +299,28 @@ async def stream_output(
 ) -> AsyncIterator[str]:
     """Async generator yielding container log lines as SSE events.
 
-    Each event includes an incrementing ``id:`` field so that clients can
-    resume from the last received event via the ``offset`` query parameter
-    (number of events to skip).
+    Docker may split long stdout lines (e.g. stream-json tool_result
+    events with full file contents) across multiple log frames.  We
+    buffer chunks and only emit complete newline-delimited lines so
+    the frontend always receives valid, parseable JSON per SSE event.
+
+    Each event includes an incrementing ``id:`` field so that clients
+    can resume from the last received event via the ``offset`` query
+    parameter (number of events to skip).
     """
     event_id = 0
-    async for line in docker.container_logs(container_id, follow=True):
-        event_id += 1
-        if event_id <= offset:
-            continue
-        yield f"id: {event_id}\ndata: {line}\n\n"
+    buffer = ""
+    async for chunk in docker.container_logs(container_id, follow=True):
+        buffer += chunk
+        while "\n" in buffer:
+            line, buffer = buffer.split("\n", 1)
+            line = line.strip()
+            if not line:
+                continue
+            event_id += 1
+            if event_id <= offset:
+                continue
+            yield f"id: {event_id}\ndata: {line}\n\n"
 
 
 async def send_message(

apps/web/src/features/session/containerTypes.ts

@@ -57,7 +57,13 @@ export function parseStreamEvent(raw: string): { text: string; kind: TerminalLin
   try {
     event = JSON.parse(raw)
   } catch {
-    // Not JSON -- show as raw text
+    // Not JSON — if it looks like a truncated JSON fragment (from Docker
+    // log frame splitting), suppress it.  Only show genuinely non-JSON
+    // lines (git clone output, entrypoint messages, etc.).
+    const trimmed = raw.trimStart()
+    if (trimmed.startsWith('{') || trimmed.startsWith('[') || trimmed.startsWith('"')) {
+      return null
+    }
     return { text: raw, kind: 'text' }
   }