I2673 — The sccache client configuration is derived from the selected offer, local disk first

✕BLOCKED wave 2 · p1 · implementation profile · runs alone

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

Objective

Emit the sccache environment for the chosen offer through majordomus env, local as level one and the offer as level two, with no hand-set variable.

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: RUSTC_WRAPPER=sccache is set by the user's ~/.cargo/config.toml with no remote; environment/shell.rs exports nothing about it.

Desired state

majordomus env exports the derived configuration when sccache is present and an offer is selected, local-only otherwise, and a diagnostic when sccache is absent; the committed .envrc is unchanged; a user's cargo config is never edited.

Scope

• apps/majordomus-cli/src/environment/
• docs/ENVIRONMENT.md

Out of scope

• Writing ~/.cargo/config.toml
• Distributed compilation

Dependencies

• I2670○READY A build-cache offer is a typed model and its selection is a pure, explained function
• I2672✕BLOCKED The offers and the selection are one read, projected to CLI, MCP, HTTP and OpenAPI

What waits on this

• I2676✕BLOCKED The build cache is verified and validated: failure paths, security and a real second-node hit

Acceptance criteria

• With an offer selected the exported variables name it and the local level and no secret is printed
• With no offer the client is local-only
• With the offer unhealthy at the moment the sccache server would start, the second level is left out and the compile succeeds: measured on 2026-10-13, a server started with a down store fails the compile (exit 2)
• A store that stops while the server runs leaves the compile correct (measured: a miss, exit 0)
• The installed sccache's multi-level support is read from the executable, not assumed
• Cross-checkout path normalisation is investigated and the finding recorded

Validation

• bin/majordomus plan validate
• MJ_TEST_JOBS=2 bash test/run.sh 3013_a_mesh_build_cache

Evidence required

• client_derivation_case
• sccache_multilevel_measured

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/I2673.yaml. Read it back with majordomus plan show I2673.