The Build Process — compile and test as a dependency cascade

Decision (maintainer, 2026-08-30). A node repo is built by our own build runner and test runner, not by dotnet test over xUnit projects that reference a core source checkout. The runner is the platform's own container (mw-plugin-test, the image the platform BUILD produces), the verb is build, and the lane that starts it is one small workflow.

mw-plugin-test build <repo-root> [<package>... | all] [--module <dll>]... [--out <dir>] \
    [--report <file>] [--max-parallel <n>] [--case-timeout <s>] [--no-tests] [--source-sha <sha>]

The invariants

1. Build means compile AND run tests. They are one unit per package; there is no "it compiled" verdict without the tests, and no test run without the compile that produced its assembly.
2. A cascade, not a schedule. Every package has a result stream. A package observes the streams of the packages it requires and starts itself the moment the last one completes green. No level table, no topological list: the graph is the schedule, so packages with no edge between them build at the same time (bounded by --max-parallel), and a package with three dependencies starts the instant the slowest lands.
3. On red we break; on green we continue. A package whose dependency did not end green never starts: it completes at once as blocked by <dependency>, and that verdict cascades. A failure is reported exactly once, where it happened; everything above it reads "blocked by X", never a second, derived failure. A cycle is refused up front and named.
4. One execution per package, however many dependents. A package's stream is shared (PublishLast): the first subscriber starts the work, every later subscriber gets the same single result, and nothing is rebuilt because two packages both required it.
5. No mesh, no import. Sources are read from the git checkout on disk and composed into Roslyn compilations exactly as the portal composes them — the same skeleton, the same options, the image's /app as the reference set (NodeSetCompiler, the code path the portals run at runtime). Each package additionally compiles against the assemblies its dependency packages just emitted. Grains cannot carry a Roslyn workload; a build process can.
6. Input is one or many packages, or all. Naming packages selects them and their transitive requirements inside the repo, so a single package builds on freshly built dependencies rather than on nothing. all (the default) is the full rebuild — the platform-rebuild case, where every package must be re-proven against the new image.
7. Timings are part of the result. Every package carries when it became ready (its last dependency finished), when it started (a slot was free) and when it finished, plus the compile and test splits and per-type compile times. The report prints them, the critical path (the chain whose serial length is the wall-clock floor) and the parallel speed-up; --report writes it all as JSON, and the lane renders it into the job summary.
8. Fails red, never skips. The lane asserts its inputs first; an image that does not know the verb exits 2 and the step names the fix. Nobody reads a green that ran nothing.

Tests without a mesh

The in-mesh test convention is <Type>/Test/*.cs: static classes whose public static parameterless methods throw on failure, listed by a Tests layout area. The runner executes those methods straight from the emitted assembly in a collectible load context, each case timed and capped by --case-timeout. A case that takes a host (the layout-area aggregator, anything needing a hub) is counted and named as needs-mesh, never dropped; the gate (mw-plugin-test <root> --seed <out>) still runs those, seeded from the build's --out so nothing is compiled twice.

The parity flag

The portal reaches other packages' types by shared= source inclusion, never by referencing their emitted assemblies. This build references them (the maintainer's instruction: use the references the dependency packages produce). A type whose emitted assembly turns out to bind a dependency package's assembly is therefore green here on grounds the portal does not have, and the report marks it binds-dependency-assembly — visible in the table, not discovered as a CompileError in production.

What this replaces, and what it retires

• MeshWeaver.Fixture and the two TestBase assemblies are the platform's own test support. They live under test/ and are never packed or published (they were a NuGet package only because they once lived under src/). A node repo does not reference them and does not need a $(MeshWeaverRoot) source checkout to test: the platform is the image, pinned by digest.
• xUnit projects in node repos are the migration's subject. The measured shapes (core: 1,205 test files, 6,295 facts; 535 of those files mesh- or hub-based) convert mechanically once the runner offers one primitive — a per-class mesh factory replacing the MonolithMeshTestBase constructor — plus a log sink for ITestOutputHelper, loops for [Theory] rows and a classified skip. Substrate suites (Postgres via Testcontainers, Orleans TestingHost, HtmlRenderer) run in the runner process, never in a grain. Browser E2E stays a browser lane.

Where the pieces are