Cursor `sessionStart` blocks on startup work, increasing risk of dropped `additional_context`

[Jerry-Terrasse]

Component

Plugin

Description

Summary

The Cursor plugin's sessionStart implementation unnecessarily increases the chance of losing the initial Mem0 context due to a known Cursor race condition.

Cursor has already confirmed that sessionStart runs asynchronously and additional_context may be silently dropped if the initial composer/request is created first:

• https://forum.cursor.com/t/sessionstart-hook-output-is-accepted-and-merged-but-the-injected-context-does-not-reach-agent-window/157141/5

Mem0 currently waits for the entire [on_session_start.sh](https://github.com/mem0ai/mem0/blob/main/integrations/mem0-plugin/scripts/on_session_start.sh) before returning anything to Cursor:

TEXT=$("$SCRIPT_DIR/on_session_start.sh" 2>/dev/null || echo "")
jq -cn --arg ctx "$TEXT" '{additional_context:$ctx}'

See [on_session_start_cursor.sh](https://github.com/mem0ai/mem0/blob/main/integrations/mem0-plugin/scripts/on_session_start_cursor.sh).

Steps to Reproduce

1. Install the official Mem0 Cursor plugin.
2. Start a new agent session and immediately submit the first prompt.
3. Repeat several times, especially with non-trivial Mem0 API latency.

on_session_start.sh synchronously performs several operations before it exits, including a Mem0 API request for memory count:

urllib.request.urlopen(req, timeout=5)

and session timeline generation with another timeout:

perl -e 'alarm 5; exec @ARGV' python3 "$SCRIPT_DIR/session_timeline.py"

Only after all of this completes can on_session_start_cursor.sh return additional_context.

Expected Behavior

The essential session context, especially:

Mem0 Active | user=... | project=... | branch=...

should reach the first agent turn reliably.

Actual Behavior

The hook can successfully generate the context, but the first response occasionally behaves as if it was never injected.

This is consistent with Cursor's confirmed sessionStart race condition. Mem0's synchronous network/enrichment work makes the timing window substantially larger.

A simple mitigation would be to keep the critical path local: resolve user, project, and branch, immediately return additional_context, and move memory count, timeline generation, auto-import, telemetry, etc. to background work.

Related Cursor reports:

• https://forum.cursor.com/t/sessionstart-hook-output-is-accepted-and-merged-but-the-injected-context-does-not-reach-agent-window/157141
• https://forum.cursor.com/t/sessionstart-hook-additional-context-is-never-injected-into-agents-initial-system-context/158452

Environment

• mem0 version: latest v2.0.17
• Cursor: 3.14.27
• OS: Linux