Memory Hubness Gate

Guard the write path of vector/embedding memory against hubness poisoning: a record whose embedding sits near many unrelated query regions, so once inserted it becomes the nearest neighbor of queries it should never match. This skill makes the agent score every candidate write against a sentinel panel and quarantine hub-like candidates before they earn a place in the index — the memory-record-side sibling of skill-injection-guardian, which guards files.

Why

In this repo, writes into the Grove content-addressed store, chroma, and pgvector are cheap and frequent — memory-consolidation promotes session-retro traces to MEMORY.md, tool outputs and fetched passages get embedded, and self-authored notes append freely. Every one of those is a trust decision, not a free operation. Hubness is the high-dimensional geometry phenomenon where a few points dominate everyone's k-nearest-neighbor lists. An attacker can craft a STRANGER document that reads innocuous but embeds as a hub; the same failure appears accidentally when an over-general summary is written and then hijacks unrelated recalls. Read-side hardening guards what comes back; only admission screening guards what goes in.

Data classes touched

• memory records (public / project-internal). Every embedded write is in scope.
• STRANGER (externally-ingested: fetched passages, web tool outputs, community content — the sc-learn untrusted familiarity class) is the untrusted class. It may enter memory only through this gate and must not reach the live index without passing.
• never-surface clusters (private origins, Fox Companies IP, credentials, Center Camp trust rules). Boundary rule: a new record must NOT become the top-k neighbor of a sentinel that guards a never-surface cluster — that is poisoning that would route unrelated queries toward sensitive space. Any such candidate is quarantined regardless of other scores.

How

1. Panel. Maintain a fixed bank of ≥50 sentinel queries spanning ≥8 unrelated topic clusters that this memory serves, and include one guard sentinel per never-surface cluster above.
2. Familiarity. Classify the candidate HOME (self-authored: session-retro traces, consolidation output, repo-authored notes) vs STRANGER (externally-ingested). STRANGER gets full scrutiny; HOME a lighter check.
3. Fan-in. Embed the candidate. For each sentinel, mark a hit if the candidate would land in the sentinel's top-5 nearest neighbors OR cosine ≥ 0.55. Count the number of DISTINCT unrelated clusters it hits — the hub fan-in.
4. Verdict. Quarantine if fan-in spans ≥3 distinct unrelated clusters (HOME) or ≥2 (STRANGER); or if it hits any never-surface guard sentinel; or if the embedding cannot be computed. Otherwise admit.
5. Quarantine, never drop. Move the record to a quarantine store outside the live index, attached to the sentinels it dominated and its fan-in evidence. A human reviews. If the write was inside a convoy or the refinery-merge queue, escalate via mayor-coordinator rather than blocking silently.

Robustness rule

Judge by geometric effect — measured neighbor-domination over unrelated clusters — not by whether the record's text reads benign. A crafted hub is written to look innocuous. Do not admit on surface phrasing; admit only on measured low fan-in.

Confidence / failure model

This wraps a JUDGMENT over an embedding probe, not a deterministic guarantee. The sentinel panel is finite: a hub tuned to query regions absent from the panel slips through, so a passed record is lower risk, not clean. It reduces, does not eliminate, poisoning — the read-side gate (memory-use-warrant) stays the backstop. Default on any uncertainty — ambiguous fan-in, embedding failure, an unclassifiable familiarity — is quarantine (fail-closed), never silent admit.

When to skip

• Reading or recalling existing memory — that is memory-use-warrant's read-side gate.
• A HOME write that is a deterministic content-addressed dedup of an already-admitted record (identical hash) — no new geometry enters the index.
• Purely structural/metadata writes that carry no embedding vector.

Integration

• skill-injection-guardian — file-side sibling; this is the record-side sibling. Together with memory-use-warrant (read-side) they form a write/read memory-integrity family: guardian screens files, this screens writes, warrant screens reads.
• memory-consolidation — the primary place this gate runs, on the promote step.
• security-hygiene — the umbrella; this is its vector-memory-poisoning procedure.
• Grove content-addressed store / chroma / pgvector — the write path wrapped.
• mayor-coordinator — escalation target when a quarantine fires inside a convoy.