Backport of #41549 to release/2026.1.
---
## Summary
Prevent information disclosure of topic existence by ensuring secondary
topic endpoints respect the 'detailed_404' security setting. The patch
implements a normalization handler for several TopicsController
actions—including post retrieval and notification updates—to return a
consistent 404 status code for inaccessible topics when the setting is
disabled.
## Source
- Patch Triage: https://patch.discourse.org/patch-triage/1384
Co-authored-by: discourse-patch-triage
<272280883+discourse-patch-triage[bot]@users.noreply.github.com>
Co-authored-by: Isaac Janzen <50783505+janzenisaac@users.noreply.github.com>
2727e4d7db
