Vital Sign · Design Spec · m1nd-mcp (backend only)

Skeleton Coherence Vital Sign

A passive health signal that detects when a serving brain answers a request with a foreign skeleton — a skeleton whose slug does not belong to that brain. Born from a real incident where a brain bound to ~/m1nd served sk_keyvault_candidate for days with no alarm.

signal-only never blocks a read never blocks a write backend only · m1nd-ui/ untouched reuse, do not reinvent

1 · The one-line contract

Given the serving brain's identity (project_root basename, or a display name when present) and the store's skeleton (skeleton_id + block ids), return one of three honest answers:

Ok — slugs agree (after sanitization) Mismatch{expected_slug, found_slug} — foreign skeleton None / silent — empty store, no signal

ABSOLUTE: this is a vital sign, not a gate. It MUST NOT cause any read or write to fail, be refused, or change behavior. It only reports.

2 · The incident that made it necessary

A session bound to the root brain ~/m1nd kept answering system_blocks_snapshot with a store whose skeleton_id was sk_keyvault_candidate — a skeleton that belonged to a different project (keyvault). For days nothing surfaced the mismatch: the snapshot looked well-formed, the north packet read normally, no metric tripped.

The missing piece was a coherence check — the serving brain's identity vs. the served skeleton's slug — surfaced where operators and agents already look: the snapshot result and the orientation packet.

3 · The coherence check — reuse what already exists

The engine already exists and is already pub. The maker's job is to surface it, not to rewrite it. Verified present in the worktree:

// m1nd-mcp/src/skeleton_scan.rs:154
pub enum SkeletonCoherence {
    Ok,
    Mismatch { expected_slug: String, found_slug: String, reason: String },
}

// m1nd-mcp/src/skeleton_scan.rs:1473
pub fn skeleton_coherence(
    project_root: Option<&str>,
    display_name:  Option<&str>,
    skeleton:      Option<(&str, &[String])>,   // (skeleton_id, block_ids)
) -> Option<SkeletonCoherence>

3.1 · Rules the engine already encodes (do not re-implement)

Identity source: display_name wins when non-empty; else basename_of(project_root) (session.rs:519). Empty store ⇒ the whole call returns None ⇒ silent.
Expected slug = the SAME sanitizer that mints ids. Reuses the private sanitize_slug (skeleton_scan.rs:1512): lowercase, non-alphanumeric → _, trim leading/trailing _, empty → "repo". This is exactly what builds sk_<slug>_candidate at skeleton_scan.rs:489 and sb_<slug>_… block ids.
Skeleton acceptance: skeleton_id == "sk_<expected>" or skeleton_id.starts_with("sk_<expected>_"). So sk_m1nd_candidate matches expected m1nd — and sk_keyvault_candidate does not match expected m1nd.
Block acceptance: every block id must start with sb_<expected_slug>_; the first offender becomes the reason.
found_slug extraction: strip sk_ then _candidate; fall back to sanitize_slug(skeleton_id). So a sk_keyvault_candidate served by the m1nd brain yields Mismatch{expected_slug:"m1nd", found_slug:"keyvault"}.

Reuse-first (binding): there is exactly one slug sanitizer that matters — the one skeleton_scan uses to mint ids. The coherence engine already calls it. The surface code MUST call skeleton_coherence() and MUST NOT invent a parallel sanitizer; otherwise a future drift between mint-rule and check-rule silently re-opens the incident.

4 · Data flow — identity in, verdict out, surfaced twice

Serving brainproject_root
display_name?

›

Identitydisplay_name else basename_of(root)

›

sanitize_slug(reused) → expected_slug

›

skeleton_coherence()vs skeleton_id + sb_ ids

Noneempty store → no signal

›

Option<SkeletonCoherence>Ok · Mismatch · None

⇲

Surface Asystem_blocks_snapshot →
skeleton_coherence field

⇲

Surface Bnorth / orientation packet →
sickness line (on Mismatch)

5 · Surface A — `system_blocks_snapshot` result

Handler: handle_system_blocks_snapshot (system_blocks_handlers.rs:70). It already returns a READ-only JSON and already loads the store — the coherence field is computed from the same load, adding zero new I/O.

Before

{
  "present": true,
  "store_version": 1,
  "block_count": 3,
  "store": { … }
}

After

{
  "present": true,
  "store_version": 1,
  "block_count": 3,
  "skeleton_coherence": {
    "status": "mismatch",
    "expected_slug": "m1nd",
    "found_slug": "keyvault",
    "reason": "skeleton_id slug does not match …"
  },
  "store": { … }
}

Present + Ok: {"status":"ok"}.
Present + Mismatch: {"status":"mismatch", expected_slug, found_slug, reason} — names both slugs so the operator sees who-served-whose-skeleton.
Absent store: the field is omitted (or null) alongside the existing honest "no skeleton yet" — silent, no false alarm.
Inputs at the call site: identity from the serving brain's state.workspace_root (basename) / display name; skeleton_id + block ids from the loaded SystemBlockStore.

6 · Surface B — the sickness line in the north packet

The orientation packet is composed in the HTTP routing layer (the caller of project_brains::bootstrap, per project_brains.rs:242). When coherence is a Mismatch, append one sickness line to the packet the agent reads on orientation:

{
  "north": {
    …
    "skeleton_coherence": {
      "status": "sick",
      "expected_slug": "m1nd",
      "found_slug": "keyvault",
      "advice": "this brain is serving a foreign skeleton; rebind or re-ingest before trusting block scope"
    }
  }
}

Silent by default: the line appears only on Mismatch. Ok and empty-store add nothing — no noise on healthy brains.
Locate the site: grep the routing layer for where the orientation/north packet JSON is assembled right after bootstrap(); inject there. The packet is already built for every orientation — this is one extra field, conditionally.
Never aborts orientation: a sickness line is data, not an error. The packet still returns.

7 · RED battery (straight from the incident)

Four cases. Two are incident-specific and MUST be added as tests; two are covered by existing engine tests and are listed for completeness.

#	Serving brain identity	skeleton_id	block ids	Verdict	Why
1	`~/m1nd` → slug `m1nd`	sk_keyvault_candidate	sb_keyvault_…	Mismatch `{expected:"m1nd", found:"keyvault"}`	The incident. expected `m1nd`; the served slug is `keyvault`. Both named.
2	`~/m1nd` → slug `m1nd`	sk_m1nd_candidate	sb_m1nd_…	Ok	Own-root skeleton. Healthy baseline — no false alarm.
3	(no store)	—	—	Silent (None)	Empty store = no signal. Snapshot says "no skeleton yet"; packet omits the line.
4	`My-Repo` → slug `my_repo`	sk_my_repo_candidate	sb_my_repo_…	Ok	Sanitization is part of the rule: `My-Repo` → `my_repo`, and `sk_my_repo_candidate` starts with `sk_my_repo_`. No false positive.

Existing engine tests already proving the spine: skeleton_coherence_has_no_signal_without_a_skeleton, skeleton_coherence_reuses_scan_slug_rules (case 4 family), skeleton_coherence_reports_identity_and_block_mismatches — all in skeleton_scan.rs test module.

8 · File / location map for the maker

File	Role	Action
m1nd-mcp/src/skeleton_scan.rs	Engine: `SkeletonCoherence` enum (:154), `skeleton_coherence()` (:1473), `sanitize_slug` (:1512).	reuse No new sanitizer. Add the two incident tests (cases 1 & 4).
m1nd-mcp/src/system_blocks_handlers.rs	`handle_system_blocks_snapshot` (:70).	wire Compute coherence from the loaded store + brain identity; emit `skeleton_coherence`.
m1nd-mcp/src/* (routing)	Where the north/orientation packet is composed after `bootstrap()`.	wire On `Mismatch`, append the sickness line. Silent otherwise.
docs/ (snapshot + north surface)	Agent-facing doc describing the snapshot fields & the orientation packet.	doc gate Document the new field + sickness line.
m1nd-ui/**	The served web UI.	FORBIDDEN Do not touch. Backend signal only.

9 · Maker checklist & proof

Surface A: skeleton_coherence present on system_blocks_snapshot for the present:true arm; omitted/silent for the absent-store arm.
Surface B: sickness line in the north packet only on Mismatch; absent on Ok and empty.
Signal-only: no read or write path changes behavior based on coherence. (Assert in tests that a mismatched brain still serves the snapshot and still orients.)
RED battery cases 1 & 4 added as explicit tests; existing cases 2 & 3 stay green.
Agent-facing doc updated (snapshot field + sickness line) — satisfies the Agent Docs Gate.
Local gate green: cargo test -p m1nd-mcp --lib · cargo clippy -p m1nd-mcp --all-targets -- -D warnings · cargo fmt --check.
Commit as the repo's configured identity (Max Kle1nz <kleinz@cosmophonix.com>), English, no AI mentions, no push.

Design artifact for the l00p design-maker phase — Skeleton Coherence Vital Sign, m1nd-mcp. Grounded against the live worktree (skeleton_scan.rs, system_blocks_handlers.rs, project_brains.rs). Backend-only; m1nd-ui/ is out of scope.