# sessionStart hook additional\_context is never injected into agent's initial system context **URL:** \ **Category:** Bug Reports\ **Tags:** context, hooks\ **Created:** [April 19, 2026, 5:55pm UTC](https://forum.cursor.com/t/sessionstart-hook-additional-context-is-never-injected-into-agents-initial-system-context/158452 "2026-04-19T17:55:26Z")\ **Posts on this page:** 1\ **Showing post:** 8
**Author:** ![Bogdan\_Parhomenko](https://avatars.discourse-cdn.com/v4/letter/b/ecccb3/32.png) [@Bogdan\_Parhomenko](https://forum.cursor.com/u/Bogdan_Parhomenko)\ **Post date:** [April 29, 2026, 8:50am UTC](https://forum.cursor.com/t/sessionstart-hook-additional-context-is-never-injected-into-agents-initial-system-context/158452/8 "2026-04-29T08:50:07Z")
Adding a massive +1 to this bug report. We are experiencing the exact same context-injection failure with the `postToolUse` hooks in v3.1.15. Just like you described for `sessionStart`, the `postToolUse` hook executes correctly and outputs the valid JSON schema for `additional_context`, but that context is completely discarded and never surfaces to the agent model. (As a side note, `postToolUse` is currently also suffering from entirely empty input payloads and intermittent firing, making the whole hooks system feel very fragile right now). It strongly appears that the core pipeline responsible for taking a hook’s stdout and actually injecting it into the Agent Window is broken across multiple hook types in this build. For any devs looking into this, here is the related thread detailing the exact same failure point for `postToolUse`: > [@Native postToolUse hooks accept and log additional\_context successfully, but the injected context is not surfaced to the model](https://forum.cursor.com/t/native-posttooluse-hooks-accept-and-log-additional-context-successfully-but-the-injected-context-is-not-surfaced-to-the-model/155689/11): > > Adding data points on Cursor 3.1.15 (macOS, 2026-04-21). The postToolUse input side also looks unpopulated, on the same path where the response is discarded — so even fixing the output plumbing wouldn’t be sufficient on its own. Hook script logs process.argv, CURSOR\_\* env vars, and stdin length on every invocation. Representative entries: [2026-04-21T21:53:59.071Z] spawn pid=25047 argv=[] env= [2026-04-21T21:53:59.077Z] stdin-end bytes=0 [2026-04-21T21:55:37.036Z] spawn pid=26394 argv=[] env… --- _[View the full topic](https://forum.cursor.com/t/sessionstart-hook-additional-context-is-never-injected-into-agents-initial-system-context/158452)._