112-typed-overlays-ride-the-existing-seam

Typed overlays ride the existing seam

Lifecycle approvedImplementation completeVerification unknownQualification unknown

Four proposals (effect contracts, budgets, dependency rationale, contract adapters) all want to attach typed data to a spec's units without changing what a unit is. The corpus already has the seam: declared extra frontmatter (spec 012), carried into the registry as `extraFrontmatter`. This states the contract an overlay keeps on that seam, pins what the engine does and does not promise about it (canonical values, not original bytes; a hash scope that is the declaring spec's, not every shard), and asserts it with several independent overlays in one corpus. No new unit kind, no engine enforcement, and no domain schemas.

Read the full pinned specification ↗

Relationships

depends on

012-declared-extra-frontmatter-passthrough

Claimed units

establishes

{
  "kind": "file",
  "path": "crates/spec-spine-core/tests/overlays.rs"
}

establishes

{
  "kind": "file",
  "path": "docs/overlay-contract.md"
}

extends

{
  "nature": "additive",
  "spec": "092-the-engine-ships-governance-not-an-environment",
  "unit": {
    "kind": "file",
    "path": "spec-spine.toml"
  }
}

Source headings

112: Typed overlays ride the existing seam
1. Purpose
1.1 Why the dependency is spec 012
1.2 What the reserved draft said that the engine does not do
2. Territory
3. Behavior
3.1 An overlay is a declared extra frontmatter key, and nothing else
3.2 The engine transports an overlay's value and never its meaning
3.3 The hash scope is the declaring spec
3.4 Declaring is what admits an overlay
3.5 Overlays coexist by namespacing, and the consumer owns the meaning
3.6 No verdict reads an overlay
3.7 What an overlay establishes, and what it does not
4. Out of scope
5. Resolved decisions
Verification

Frozen anchors

No frozen anchors declared.