feat(membership): recover nested ICC and refuse cross-classified collapse

[seonghobae]

Summary

ADR 0003 increment from protected main (40adac9 / #44). Review wait and queued Checks on #45 are local; this slice does not recreate psychometric_core (#49), compute_backend (#51), or encrypted mapping persistence (waits for #45 / 0008).

• CPU f64 unbalanced ANOVA recovers a known nested ICC (1/4) with computed RMSE versus that truth.
• Zero within-cluster residual recovers ICC 1; equal cluster means recover ICC 0.
• Cross-classified (two roles) and multiple-membership (two groups in one role) designs return NestedIccInapplicable.
• Empty, inactive, duplicate, unknown, singleton-only, and constant samples fail closed.
• No new migration (0007 remains owned by feat(persistence): retention deletion legal-hold SQL contracts (0007) #45).

Claim boundary

• Membership design gate and nested ICC only. Not a full MMMC/HLM/ESEM/DSEM fit, not causal identification, not a GDPR/SOC 2/CSAP claim.

Test plan

• RED: nested_icc_recovery_contract failed to compile (E0432/E0599) before the public API existed
• cargo test -p membership_core --offline --lib --tests --doc
• cargo clippy -p membership_core --all-targets --offline -- -D warnings
• python3 scripts/check_docstrings.py, check_workspace_contract.py, validate_documentation.py
• membership_core line coverage 188/188 and nightly branch coverage 50/50
• Exact-head CI; independent review

[coderabbitai]

Important

Review skipped

Draft detected.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 933af888-dbbc-4963-8b24-c73fee8eb63e

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}