search_events fails on self-hosted Sentry (25.8.0): /events/validate/ returns 404 #1497

Summary

search_events always fails on self-hosted Sentry with an HTTP 404, because the tool unconditionally calls the event-validation endpoint GET /api/0/organizations/{organizationSlug}/events/validate/, which is not present on self-hosted Sentry 25.8.0.

The actual events endpoint GET /api/0/organizations/{organizationSlug}/events/ works fine, so only the pre-flight validation gate breaks the tool.

Environment

• @sentry/mcp-server version: 0.42.0 (current latest on npm)
• Transport: stdio
• Node: v24.18.0
• Sentry: self-hosted 25.8.0
• Command:

npx @sentry/mcp-server@latest --access-token=*** --host=sentry.example.com

• Auth token scopes: org:read, project:read, project:write, team:read, team:write, event:write

Steps to reproduce

1. Run the MCP server in stdio mode against a self-hosted Sentry instance (Sentry 25.8.0).
2. Call the search_events tool, for example:

{ "organizationSlug": "sentry", "dataset": "errors", "period": "1h", "fields": ["count()"] }

3. Observe the error.

Actual result

**Input Error**

There was an HTTP 404 error with your request to the Sentry API.

API error (404): API request failed: Not Found
. Please verify the parameters are correct.

Other tools (find_organizations, find_projects, search_issues, get_sentry_resource) work correctly against the same instance.

Root cause

The search_events handler calls validateEventsSearch(...) before executing the search, regardless of whether an embedded LLM/agent provider is configured. That validation issues a request to the events/validate/ path.

Reproduced directly against the same instance with a valid token:

GET /api/0/organizations/sentry/events/validate/?dataset=errors&query=&field=count()&statsPeriod=1h
  -> 404 Not Found

GET /api/0/organizations/sentry/events/
  -> 200 OK   (endpoint works)

GET /api/0/organizations/sentry/events/?field=count()&statsPeriod=1h
  -> 200 OK   -> {"data":[{"count()":4514}]}

So the events/validate/ endpoint simply does not exist on this self-hosted deployment/version, and the tool has no fallback: if (!lastValidation.valid) throw ... means a 404 during validation surfaces as an "Input Error" to the user.

Code path (from the published dist/index.cjs): the search_events handler calls validateEventsSearch(apiService, {...}); the underlying validateEvents method builds GET /organizations/${organizationSlug}/events/validate/?.... There is no self-hosted capability check around it.

Expected behavior

One of:

1. search_events should skip (or gracefully degrade) the validation step when the events/validate/ endpoint returns 404 / is unavailable (e.g. on self-hosted), and still run the actual search against /events/.
2. Or the tool should detect that validation is unsupported on the target host and proceed without it.
3. At minimum, a 404 from the validation endpoint should not be reported as a user-facing "Input Error" that blocks an otherwise-working search.

Notes

• The self-hosted --host skill filtering already drops seer; there appears to be no equivalent handling for endpoints that self-hosted Sentry does not expose.
• Direct API access to /events/ works, so this is purely an MCP-side validation incompatibility, not a token/permission issue.