Scope memberships carry observe_others=true, so every scope counted against
SESSION_OBSERVERS_LIMIT (default 10) — capping scopes-per-session at the limit
minus the session's real observers, and reporting the failure as
`400 Cannot create session <name> with 11 observers. ... Observers are peers
with 'observe_others' set to true.` on a membership call. Wrong on three counts:
the ceiling is undocumented and contradicts RFC §5.1 ("sessions belong to any
number of scopes"), the message describes session creation, and it leaks the
word "observer" through a facade whose entire job is hiding observers (RFC
goal 5). The limit exists to bound per-observer deriver fan-out for real peers;
a scope costs document rows, not LLM calls (RFC §5.2), so it does not belong in
that budget.
Excluded from both halves of the check in `_get_or_add_peers_to_session`: the
incoming names via a flag-based lookup, existing memberships via a correlated
NOT EXISTS on `scope_peer_clause()` — the same pattern the replacement and
removal paths already use, so the exclusion holds regardless of concurrent
scope creation. The early `count_observers_in_config(session.peer_names)` check
in `get_or_create_session` is left alone: `peer_names` cannot contain a scope,
and `scopes` is a separate field.
`reject_scope_peers` is split into a `scope_peer_names()` query helper plus a
two-line raiser so the observer count reuses the authoritative name-AND-flag
predicate instead of growing a third copy of it. Still costs nothing on the
common path — no reserved-prefix name in the input means no query at all.
Also caps `SessionCreate.scopes` at 100, matching `ScopeSessionsAdd.session_ids`.
This belongs in the same commit: the observer limit was the only thing bounding
that list, so removing it turns an unbounded `scopes` array into a peer row and
a membership row per element, committed — the single-request path to the
cardinality anti-pattern RFC §8 warns about. Partly answers OQ6: no per-session
cap, 100 per request.
Tests: a session joins SESSION_OBSERVERS_LIMIT + 2 scopes through both the
facade and session creation; real observers over the limit still 400, so the
carve-out cannot quietly disable the limit; 101 scopes is a 422.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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