[BUG] `/channels/<id>/messages/_search` fails intermittently on postgres after metadata change

[mgaffigan]

Repro:

1. Deploy channel on pg mirthdb
2. Make at least 5 calls to /channels/<id>/messages/_search to get the plan cached
3. Change the type of the metadata
4. Make the call to /channels/<id>/messages/_search again (repeatedly since it might be from a different pid)

Expected:

• the call succeeds

Actual:

• When the same pid is reused, the cache fails with HTTP 500
• PG Server records this error:

2026-09-21 04:51:50.195 UTC [79] ERROR:  cached plan must not change result type
2026-09-21 04:51:50.195 UTC [79] STATEMENT:  SELECT *
                        FROM D_MCM1
                        WHERE MESSAGE_ID = $1
                        AND METADATA_ID = $2