Generic vault context erase/verify and predecessor lineage

[censgate-coder]

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Summary

Additive, product-noun-free gateway APIs for platform ForgetMe(client):

• Optional vault.context_id alias on redact/restore (session_id unchanged; mismatch → 400)
• DELETE /v1/vault/context and POST /v1/vault/context/verify
• KV2 purge (all versions + metadata)
• POST /v1/credentials/predecessors with Authorization + X-Predecessor-Authorization
• Erase/verify walk current subject + transitive predecessor closure; echo lineage_revision / predecessor_count
• Default credential subject stays key:<sha256(api_key)> (no remapping)

No team/client/professional/ForgetMe types or docs.

Test plan

• cargo test -p redact-gateway (vault context, purge, predecessor register, rotation forget)
• Fixture names stay generic (caller-a, context-1)

[censgate-coder]

Sol Medium review (e6ed32b)

Verdict: CHANGES_REQUESTED (Important, no Critical)

1. Verify used get() (empty live mappings), so expired/soft-deleted KV2 history could report verified: true while ciphertext remained.
2. Predecessor register was a non-atomic read/compose/write; concurrent rotations could drop subjects or form cross-record cycles.
3. Lineage paths included the raw credential subject (OIDC emails can land in OpenBao audit URLs).
4. New erase/verify/predecessor bodies ignored unknown JSON fields (e.g. a foreign subject_id).

Addressed in 3dfc3d4 (DCO-signed): metadata exists(), tenant-graph CAS register, {prefix}/_lineage/{tenant} path, deny_unknown_fields on the new envelopes. Re-running Sol Medium on the new tip.

[censgate-coder]

Sol Medium re-review of 3dfc3d4 was still CHANGES_REQUESTED (2 Important):

1. Cached closures went stale when a child rotated after a parent had already registered (A→B then B→C left erase-as-A missing C).
2. {prefix}/_lineage/{tenant} collided with session_path(prefix, "_lineage", tenant).

4e372ac stores direct edges and walks the live closure on erase/verify, and moves lineage to {prefix}/_lineage/{tenant}/graph. Re-running Sol Medium.

[censgate-coder]

Sol Medium re-review of 4e372ac was still CHANGES_REQUESTED (1 Important): a descendant edge could expand an ancestor past the 32-subject bound, then erase/verify as that ancestor would 503. In-memory register could also keep the failed edge.

cf5a942 builds a candidate graph, validates every subject's closure, and commits only if all stay in bound / acyclic. Re-running Sol Medium.

[censgate-coder]

Sol Medium APPROVE on tip cf5a942.

All previously identified privacy, durability, verification, closure, and namespace issues are fixed with regression coverage. Ready to merge to main (operator). First commit e6ed32b is still not DCO-signed; follow-ups 3dfc3d4, 4e372ac, and cf5a942 are signed.