scientific(membership): classify longitudinal observation support without atomistic collapse #640

Scientific / DDD finding

membership_core::classify_membership_design currently classifies one shared EventTime. Topic-lineage and other longitudinal consumers instead evaluate each modeled observation at its own event time. Re-running the single-instant classifier inside those consumers would duplicate Membership-domain truth; collapsing the observation set to one synthetic instant would be scientifically wrong.

The owner contract must classify a set of (MemberId, EventTime) observation coordinates directly from MembershipNetwork, preserving the same closed design vocabulary already owned by Membership: Nested, CrossClassified, MultipleMembership, CrossClassifiedMultipleMembership, HeterogeneousClassification, and HeterogeneousClassificationMultipleMembership.

This is needed by release issue #638 / Draft #639, but the implementation belongs here in the Membership bounded context. #639 must consume a released/pinned owner contract or an ordinary protected-main landing; it must not copy this classifier.

Required RED

Add owner-side contract tests proving that observation support is classified across the actual event time of each observation:

1. one member may leave/re-enter or change contextual assignments over time without the consumer selecting one global as_of instant;
2. locally single-classified observations that span different roles across the observation support are HeterogeneousClassification, not Nested;
3. a local cross-classified observation plus a separate local multiple-membership observation yields CrossClassifiedMultipleMembership;
4. a partial-weight/same-role multi-group observation remains MultipleMembership even when other observations are nested;
5. any requested observation with no active membership at its own event time fails closed rather than disappearing from the support;
6. an empty observation support fails closed.

The API should use opaque MemberId + EventTime coordinates only. Do not add HR/person truth, caller-asserted design labels, normalization, pseudo-row duplication, or estimator arithmetic.

Acceptance

• TDD RED first, then minimal Rust owner repair;
• public rustdoc and error semantics are explicit;
• all new branches are covered and existing single-instant classification remains unchanged;
• feat(membership): add owner-issued single-membership admission #605 remains the canonical owner vehicle unless a verified successor inherits every valid delta;
• release(contract): publish immutable temporal-analysis contract for Orgmetra consumers #638/fix(release): bind fail-closed reconstructable topic-lineage results (#638) #639 receive only an owner-path handoff until this contract lands normally;
• exact-head Rust/rustdoc/coverage/security/CodeQL/Semgrep plus qualifying independent review before protected merge;
• no source copy, force push, destructive rebase, self-approval, skip/xfail, or gate weakening.

Protected base at finding time: main@a243f18da4a4ca8a8d068c39922537f1f8ed6ad0. Canonical Membership owner PR at finding time: #605 c7defa251761f104e51a614cbba14f9f952bec58.