# ENC-ASL-CORE-INDEX ADDENDUM: Federation Encoding

Base spec: `tier1/enc-asl-core-index.md`

Status: Merged into `tier1/enc-asl-core-index.md`

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## 1. Purpose

This addendum defines **on-disk encoding changes** required to support the **Federation Specification**:

* Domain identifiers for artifacts and index entries
* Visibility flags for internal vs published state
* Backward-compatible update to existing index records
* Integration with existing block, segment, and tombstone layouts

It ensures **deterministic reconstruction** across domains while preserving index lookup semantics.

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## 2. New Fields for Index Records

Each **ArtifactIndexRecord** is extended to include **federation metadata**:

| Field               | Type                     | Description                                                                                         |
| ------------------- | ------------------------ | --------------------------------------------------------------------------------------------------- |
| `DomainID`          | uint32 / opaque          | Unique domain identifier for the artifact. Must match the domain in which the artifact was created. |
| `Visibility`        | uint8 (enum)             | Visibility status of the artifact: `0 = internal`, `1 = published`.                                 |
| `CrossDomainSource` | optional uint32 / opaque | DomainID of original domain if the artifact is imported from another domain; `NULL` if local.       |

**Encoding Notes:**

* `DomainID` and `Visibility` are **always present** in index records, even for legacy artifacts (legacy default: internal, local domain).
* `CrossDomainSource` is **optional**; present only for imported artifacts.
* Existing `(BlockID, offset, length)` mapping is unchanged.

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## 3. Segment Header Updates

Each segment now includes:

* `SegmentDomainID` (uint32 / opaque): domain owning this segment
* `SegmentVisibility` (uint8): maximum visibility of all artifacts in the segment (`internal` or `published`)
* Optional: `FederationVersion` (uint8) to allow backward-compatible upgrades

This allows **fast filtering** of visible segments during lookup in federated domains.

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## 4. Tombstone Encoding

* Tombstones include `DomainID` and `Visibility` fields to ensure **deterministic shadowing** across domains.
* Shadowing rules:

  * A tombstone in domain A only shadows artifacts in domain A.
  * Published artifacts cannot be accidentally shadowed by internal artifacts from another domain.

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## 5. Block Records

No change to `(BlockID, offset, length)` itself; however:

* Blocks supporting **published artifacts** are considered **cross-domain safe**.
* Optional **DomainID metadata** may be stored with blocks to speed up GC and federation operations.
* Addressing and segment packing rules are unchanged.

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## 6. Lookup and Reconstruction Rules

* When reconstructing **CURRENT in a domain**:

  1. Filter segments and records by `DomainID` and `Visibility`.
  2. Include artifacts with `DomainID = local` or `Visibility = published`.
  3. Include imported artifacts by following `CrossDomainSource`.
  4. Apply standard shadowing and tombstone rules per domain.

* Determinism and immutability guarantees remain identical to single-domain ENC-ASL-CORE-INDEX.

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## 7. Backward Compatibility

* Legacy segments without federation fields are treated as:

  * `DomainID = local domain`
  * `Visibility = internal`
* Lookup semantics automatically ignore artifacts from other domains until explicitly migrated.
* Federation fields are **forward-compatible**; versioning in segment headers allows safe upgrades.

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## 8. Normative Invariants

1. **DomainID presence:** Every index record must include a `DomainID`.
2. **Visibility correctness:** Published artifacts are always visible to other domains; internal artifacts are not.
3. **CrossDomainSource integrity:** Imported artifacts retain immutable reference to original domain.
4. **Deterministic encoding:** Serialization of index records and segments must be identical across platforms for the same snapshot + log.
5. **Backward compatibility:** Legacy records are interpreted safely with default federation metadata.

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## 9. Summary

This addendum updates **ENC-ASL-CORE-INDEX** to support **federation**:

* Adds `DomainID`, `Visibility`, and optional `CrossDomainSource` to index records
* Updates segment headers for fast domain/visibility filtering
* Ensures deterministic lookup, reconstruction, and shadowing rules per domain
* Maintains backward compatibility with legacy segments

It integrates federation metadata **without altering the underlying block or artifact encoding**, preserving deterministic execution and PEL provenance.