Capability Invariant¶
Parent contract: Bluefly Engineering Execution Contract Parent doctrine: Convergence Doctrine Version: 1.0 Applies to: All roles. All platforms. All providers. All protocols. Authority: canonical
The Invariant¶
Every capability shall converge toward its smallest stable authority. Retention requires evidence. Absence of evidence is not justification for ownership.
This invariant applies uniformly across: - Platform providers: Apple, GitLab, Gas City, Docker, PostgreSQL, Kubernetes, Drupal, Cloudflare, Keycloak, 1Password - Protocol authorities: AG-UI, MCP, A2A, OpenTelemetry, OAuth 2.0, OpenID Connect, HTTP, Git, WebSocket, SSE - Any future provider, platform, or protocol Bluefly depends on
Three Corollaries¶
Corollary 1 — Temporary Ownership: A consumer may temporarily implement a capability its authority does not yet offer. The moment the authority's capability satisfies the required operational characteristics, the local implementation is reclassified as technical debt and SHALL be evaluated for removal.
Corollary 2 — Evidence Required for Retention: A pre-existing local implementation may be retained only if evidence is produced that the authority's current capability does not satisfy the operational requirement. Absence of evidence is not justification for retention.
Corollary 3 — Evaluation Is Mandatory; Removal Is Not Immediate: Debt classification guarantees tracking. It does not guarantee immediate removal. Removal is governed by the consumer's modernization timeline. The invariant requires evaluation, not instantaneous convergence.
Smallest Stable Authority¶
"Smallest stable authority" means the upstream entity that: 1. Owns the capability by design or specification 2. Publishes a stable contract (API, protocol, or specification) 3. Has an active maintenance and release lifecycle 4. Has no smaller upstream owner
Examples:
| Capability | Smallest Stable Authority | Why |
|---|---|---|
| State observation in Swift | Apple (@Observable) |
Apple owns the Swift runtime |
| Test authorship in Swift | Apple (Swift Testing) | Apple owns the Swift toolchain |
| Agent ↔ UI interaction events | AG-UI protocol | AG-UI defines the canonical specification |
| Tool invocation between agents | Anthropic (MCP) | MCP is the published standard |
| Telemetry: traces, metrics, logs | OpenTelemetry (OTLP) | OTEL is the vendor-neutral standard |
| Authentication and authorization | IETF (OAuth 2.0 / OIDC) | IETF defines the protocol |
| Container image format | OCI | OCI defines the specification |
| Source history | Git (libgit) | Git defines its own format |
Relationship to Convergence Doctrine¶
The Convergence Doctrine states:
"Bluefly composes upstream platforms rather than reimplementing them."
The Capability Invariant is the enforcement formulation of that doctrine: - The doctrine states the direction of travel. - The invariant states what constitutes a violation and what evidence is required to avoid it. - The invariant extends to protocol authorities — an area the original doctrine did not explicitly address.
Application by Governance Family¶
Each provider and protocol governance family applies this invariant within its own scope.
| Governance Family | Authority Type | Invariant Applied In |
|---|---|---|
standards/platforms/apple/APPLE-001 |
Platform Provider | §6 — Capability Invariant (references this document) |
standards/platforms/drupal/ |
Platform Provider | Convergence doctrine — align to Capability Invariant on next revision |
standards/protocols/ |
Protocol Authority | Each protocol's 001 document, §N — Capability Invariant |