I2670 — A build-cache offer is a typed model and its selection is a pure, explained function

○READY wave 0 · p1 · implementation profile · runs alone

Part of development-runtime — The runtime has a development surface.

Objective

Model an offer (protocol, provider, scope, non-secret endpoint, bucket, priority, capacity, health) and select among offers deterministically with the reason.

Why

The owner, 2026-10-13, with full clearance: set up MinIO, an sccache server and every mesh node, verified and validated. The cluster compiles the same Rust on every machine from a cold cache; two declared offload hosts were under their disk minimum that day. See ADR 0157.

Current state

Measured on master b29cf4e487 on 2026-10-13: no build-cache, S3 or minio concept exists in source, schema or docs; sccache appears only in the container build (deploy/render.rs) and ADRs 0055 and 0139.

Desired state

A typed Offer and a select() that ranks healthy, scope, priority, headroom, round-trip time and node id, and returns the choice with the passed-over candidates; no offer is a normal answer; no secret field exists in the type.

Scope

• apps/majordomus-cli/src/mesh/build_cache/
• share/schemas/majordomus/mesh-declaration/

Out of scope

• Discovery transport: I2671
• Any command or endpoint: I2672

Dependencies

None. This issue is a root of the graph.

What waits on this

• I2671✕BLOCKED A provider offers its cache as a signed, expiring mesh record, and a stopped provider goes stale
• I2672✕BLOCKED The offers and the selection are one read, projected to CLI, MCP, HTTP and OpenAPI
• I2673✕BLOCKED The sccache client configuration is derived from the selected offer, local disk first
• I2674✕BLOCKED A node is provisioned as an S3 cache provider, idempotently, with no secret in the repository

Acceptance criteria

• Selection is deterministic for any ordering of the same offers
• A stale or unhealthy offer is never chosen over a healthy one and is listed as passed over
• No offers selects none and says so
• The serialized form cannot carry a credential

Validation

• bin/majordomus plan validate
• cargo test --manifest-path apps/majordomus-cli/Cargo.toml --lib mesh::build_cache

Evidence required

• build_cache_model_unit_tests

Evidence

None recorded. Every token above needs a command or an artifact behind it before this issue can be completed; narrative is refused.

Timeline

started

—

verified

—

completed

—

Those three fields, the evidence above and the state of the dependencies are all the status is made of. There is no status field to disagree with them.

Canonical record: .ai/repo/project/issues/I2670.yaml. Read it back with majordomus plan show I2670.