git.stella-ops.org/docs/modules/concelier/link-not-merge-schema.md

# Link-Not-Merge (LNM) Observation & Linkset Schema

_Frozen v1 (add-only) — approved 2025-11-17 for CONCELIER-LNM-21-001/002/101._

## Goals
- Immutable storage of raw advisory observations per source/tenant.
- Deterministic linksets built from observations without merging or mutating originals.
- Stable across online/offline deployments; replayable from raw inputs.

## Status
- Frozen v1 as of 2025-11-17; further schema changes must go through ADR + sprint gating (CONCELIER-LNM-22x+).

## Observation document (Mongo JSON Schema excerpt)
```json
{
  "bsonType": "object",
  "required": ["_id","tenantId","source","advisoryId","affected","provenance","ingestedAt"],
  "properties": {
    "_id": {"bsonType": "objectId"},
    "tenantId": {"bsonType": "string"},
    "source": {"bsonType": "string", "description": "Adapter id, e.g., ghsa, nvd, cert-bund"},
    "advisoryId": {"bsonType": "string"},
    "title": {"bsonType": "string"},
    "summary": {"bsonType": "string"},
    "severities": {
      "bsonType": "array",
      "items": {"bsonType": "object", "required": ["system","score"],
        "properties": {"system":{"bsonType":"string"},"score":{"bsonType":"double"},"vector":{"bsonType":"string"}}}
    },
    "affected": {
      "bsonType": "array",
      "items": {"bsonType":"object","required":["purl"],
        "properties": {
          "purl": {"bsonType":"string"},
          "package": {"bsonType":"string"},
          "versions": {"bsonType":"array","items":{"bsonType":"string"}},
          "ranges": {"bsonType":"array","items":{"bsonType":"object",
            "required":["type","events"],
            "properties": {"type":{"bsonType":"string"},"events":{"bsonType":"array","items":{"bsonType":"object"}}}}},
          "ecosystem": {"bsonType":"string"},
          "cpe": {"bsonType":"array","items":{"bsonType":"string"}},
          "cpes": {"bsonType":"array","items":{"bsonType":"string"}}
        }
      }
    },
    "references": {"bsonType": "array", "items": {"bsonType":"string"}},
    "scopes": {"bsonType":"array","items":{"bsonType":"string"}},
    "relationships": {
      "bsonType": "array",
      "items": {"bsonType":"object","required":["type","source","target"],
        "properties": {
          "type":{"bsonType":"string"},
          "source":{"bsonType":"string"},
          "target":{"bsonType":"string"},
          "provenance":{"bsonType":"string"}
        }}
    },
    "weaknesses": {"bsonType":"array","items":{"bsonType":"string"}},
    "published": {"bsonType": "date"},
    "modified": {"bsonType": "date"},
    "provenance": {
      "bsonType": "object",
      "required": ["sourceArtifactSha","fetchedAt"],
      "properties": {
        "sourceArtifactSha": {"bsonType":"string"},
        "fetchedAt": {"bsonType":"date"},
        "ingestJobId": {"bsonType":"string"},
        "signature": {"bsonType":"object"}
      }
    },
    "ingestedAt": {"bsonType": "date"}
  }
}
```

### Observation invariants
- **Immutable:** no in-place updates; new revision → new document with `supersedesId` optional pointer.
- **Deterministic keying:** `_id` derived from `hash(tenantId|source|advisoryId|provenance.sourceArtifactSha)` to keep inserts idempotent in replay.
- **Normalization guardrails:** version ranges must be stored as raw-from-source; no inferred merges.

## Append-Only Contract (AOC) — LNM-21-004

The Aggregation-Only Contract (AOC) ensures observations are immutable after creation. This is enforced by `IAdvisoryObservationWriteGuard`.

### Write disposition rules
| Existing Hash | New Hash | Disposition | Action |
|--------------|----------|-------------|--------|
| null/empty | any | `Proceed` | Insert new observation |
| X | X (identical) | `SkipIdentical` | Idempotent re-insert, no write |
| X | Y (different) | `RejectMutation` | Reject with `AppendOnlyViolationException` |

### Supersession model
When an advisory source publishes a revised version of an advisory:
1. A **new observation** is created with its own unique `observationId` and `contentHash`.
2. The new observation MAY carry a `supersedesId` pointing to the previous observation.
3. The **original observation remains immutable** — it is never updated or deleted.
4. Linksets are rebuilt to include all non-superseded observations; superseded observations remain queryable for audit but excluded from active linkset aggregation.

### Implementation checklist (LNM-21-004)
- [x] `IAdvisoryObservationWriteGuard` interface with `ValidateWrite(observation, existingContentHash)` method.
- [x] `AdvisoryObservationWriteGuard` implementation enforcing append-only semantics.
- [x] `AppendOnlyViolationException` for mutation rejections.
- [x] DI registration via `AddConcelierAocGuards()` extension.
- [x] Unit tests covering Proceed/SkipIdentical/RejectMutation scenarios.
- [x] Legacy merge logic deprecated with `[Obsolete]` and gated by `NoMergeEnabled` feature flag (defaults to `true`).
- [x] Roslyn analyzer `StellaOps.Concelier.Analyzers.NoMergeApiAnalyzer` emits warnings for merge API usage.

## Linkset document
```json
{
  "bsonType":"object",
  "required":["_id","tenantId","advisoryId","source","observations","createdAt"],
  "properties":{
    "_id":{"bsonType":"objectId"},
    "tenantId":{"bsonType":"string"},
    "advisoryId":{"bsonType":"string"},
    "source":{"bsonType":"string"},
    "observations":{"bsonType":"array","items":{"bsonType":"objectId"}},
    "normalized": {
      "bsonType":"object",
      "properties":{
        "purls":{"bsonType":"array","items":{"bsonType":"string"}},
        "versions":{"bsonType":"array","items":{"bsonType":"string"}},
        "ranges": {"bsonType":"array","items":{"bsonType":"object"}},
        "severities": {"bsonType":"array","items":{"bsonType":"object"}}
      }
    },
    "confidence": {"bsonType":"double", "description":"Optional correlation confidence (0–1)"},
    "conflicts": {"bsonType":"array","items":{"bsonType":"object",
      "required":["field","reason"],
      "properties":{
        "field":{"bsonType":"string"},
        "reason":{"bsonType":"string"},
        "values":{"bsonType":"array","items":{"bsonType":"string"}},
        "sourceIds":{"bsonType":"array","items":{"bsonType":"string"}}
      }}},
    "createdAt":{"bsonType":"date"},
    "builtByJobId":{"bsonType":"string"},
    "provenance": {"bsonType":"object","properties":{
      "observationHashes":{"bsonType":"array","items":{"bsonType":"string"}},
      "toolVersion" : {"bsonType":"string"},
      "policyHash" : {"bsonType":"string"}
    }}
  }
}
```

### Linkset invariants
- Built from a set of observation IDs; never overwrites observations.
- Carries the hash list of source observations for audit/replay.
- Deterministic sort: observations sorted by `source, advisoryId, fetchedAt` before hashing.
- Conflicts are additive only and now carry optional `sourceIds[]` to trace which upstream sources produced divergent values.

## Indexes (Mongo)
- Observations: `{ tenantId:1, source:1, advisoryId:1, provenance.fetchedAt:-1 }` (compound for ingest); `{ provenance.sourceArtifactSha:1 }` unique to avoid dup writes.
- Linksets: `{ tenantId:1, advisoryId:1, source:1 }` unique; `{ observations:1 }` sparse for reverse lookups.

## Collections
- `advisory_observations` — raw per-source docs (immutable).
- `advisory_linksets` — derived normalized aggregates with observation pointers and hashes.

## Determinism & replay
- Replay rebuild: order observations by fetchedAt, recompute linkset hash list, ensure byte-identical linkset JSON.
- All timestamps UTC ISO-8601; no server-local time.
- String normalization: lowercase `source`, trim/normalize PURLs, stable sort arrays.

## Sample documents
See `docs/samples/lnm/observation-ghsa.json` and `docs/samples/lnm/linkset-ghsa.json` (added with this draft) for concrete payloads.

## Approval path
1) Architecture + Concelier Core review this document.
2) If accepted, freeze JSON Schema and roll into `src/Concelier/__Libraries/StellaOps.Concelier.Storage.Mongo` migrations.
3) Update consumers (policy/CLI/export) to read from linksets only; deprecate Merge endpoints.

---
Tracking: CONCELIER-LNM-21-001/002/101; Sprint 110 blockers (Concelier/Excititor waves).