fix(ai-chat): drain stream on client disconnect to stop heap-OOM leak

The /api/ai-chat/stream and public-share streaming paths piped streamText
output to the client socket via pipeUIMessageStreamToResponse, whose only
reader is that socket. On a client disconnect (pervasive Safari/proxy
ECONNRESET), backpressure stalled the stream: the controller aborted the
turn but nothing drained it, so streamText's onFinish/onError/onAbort never
fired. Cleanup (close leased MCP clients, persist partial) never ran and the
whole per-turn object graph (history, per-request toolset closures, captured
steps, SDK buffers) stayed rooted — accumulating across turns until the
default ~2GB heap saturated and the process crashed with
"Ineffective mark-compacts near heap limit - JavaScript heap out of memory".

Add the AI SDK v6 documented remedy: fire-and-forget
`result.consumeStream({ onError })` right after streamText(), which removes
backpressure and drains the stream independently of the client socket so the
terminal callbacks always fire and the turn's memory is released even when the
client has gone away. Applied to both the authenticated and public-share
stream services.

Also add `--heapsnapshot-near-heap-limit=2` to the prod start script so any
residual leak dumps a heap snapshot near OOM for diagnosis (no effect on
normal operation). Heap size stays ops-tunable via NODE_OPTIONS.

- apps/server/src/core/ai-chat/ai-chat.service.ts
- apps/server/src/core/ai-chat/public-share-chat.service.ts
- apps/server/package.json

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

apps/server/package.json

@@ -11,7 +11,7 @@
     "start": "cross-env NODE_ENV=development nest start",
     "start:dev": "cross-env NODE_ENV=development nest start --watch",
     "start:debug": "cross-env NODE_ENV=development nest start --debug --watch",
-    "start:prod": "cross-env NODE_ENV=production node dist/main",
+    "start:prod": "cross-env NODE_ENV=production node --heapsnapshot-near-heap-limit=2 dist/main",
     "collab:prod": "cross-env NODE_ENV=production node dist/collaboration/server/collab-main",
     "collab:dev": "cross-env NODE_ENV=development node dist/collaboration/server/collab-main",
     "email:dev": "email dev -p 5019 -d ./src/integrations/transactional/emails",

apps/server/src/core/ai-chat/ai-chat.service.ts

@@ -535,6 +535,19 @@ export class AiChatService {
       },
       });
 
+      // Drain the stream independently of the client socket so the turn always
+      // runs to completion (or to its abort) and the terminal callbacks
+      // (onFinish/onError/onAbort) fire — releasing the per-turn object graph
+      // (history, the per-request toolset closures, captured steps, SDK buffers)
+      // and closing leased MCP clients. WITHOUT this, a client disconnect leaves
+      // the pipe's dead socket as the only reader; backpressure stalls the stream,
+      // the callbacks never run, and every dropped turn stays rooted in memory —
+      // the heap-OOM leak. consumeStream removes that backpressure (AI SDK v6
+      // "Handling client disconnects"). NOT awaited (fire-and-forget); the stream
+      // errors are already logged by the streamText `onError` callback above, so
+      // swallow here to avoid an unhandledRejection.
+      void result.consumeStream({ onError: () => undefined });
+
       // Stream the UI-message protocol straight to the hijacked Node response.
       // Without onError the AI SDK masks the cause ('An error occurred.') and the
       // UI shows a generic failure. Surface the real provider message instead.

apps/server/src/core/ai-chat/public-share-chat.service.ts

@@ -244,6 +244,15 @@ export class PublicShareChatService {
         },
       });
 
+      // Drain the stream independently of the client socket so the turn always
+      // runs to completion (or to its abort) even when the anonymous client
+      // disconnects — otherwise the dead socket is the only reader, backpressure
+      // stalls the stream, and the per-turn object graph stays rooted (heap-OOM
+      // leak). consumeStream removes that backpressure (AI SDK v6 "Handling
+      // client disconnects"). Fire-and-forget; stream errors are already logged
+      // by the streamText `onError` callback above.
+      void result.consumeStream({ onError: () => undefined });
+
       // Stream the UI-message protocol straight to the hijacked Node response.
       // Surface the real provider message (AI SDK error bodies never carry the
       // API key, so this is safe; we never dump the resolved config).