`get_observation_context` resolved scope by fetching every session name the
observer has a membership record in, then expanding that list into
`session_name IN (...)` twice in one statement — once in the CTE and once in
the outer select. That puts psycopg's 65535-bind-parameter ceiling at roughly
32,765 sessions, and the count only ever grows: the loose membership
definition (`active_only=False`) counts sessions the peer has since left, so
leaving a session does not shrink the scope. A workspace with tens of
thousands of sessions for one peer produced a statement the driver could not
serialize at all.
Two new helpers in `crud.message` express the observer half as a correlated
EXISTS over `session_peers`. Scope now costs two bind parameters regardless of
membership size, and the membership query disappears (two round trips become
one). The `session_peers` primary key is `(workspace_name, session_name,
peer_name)`, so the correlated probe is an exact-match index hit.
The caller-supplied allowlist stays an IN clause — it is route-capped at 1000
entries and carries none of the unbounded-growth risk. `resolve_session_scope`
is left in place: three other callers still need the materialized list,
including `_search_messages_external`, which sends session names to the vector
store as a filter payload and cannot take SQL.
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
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