MEP-71 Phase 10. TargetPythonPackage emit

Status: LANDED (pending merge) as of 2026-05-30 00:27 (GMT+7). Implements the publish-direction artifact composer that turns a Mochi-side library into a PEP 517 source distribution, a pure-Python wheel, the bundled mochi_build PEP 517 backend, and a typed .pyi for downstream consumers.

Gate

The umbrella sentinel TestPhase10TargetPythonPackage in package3/python/pypackage/phase10_test.go is green. The sentinel:

• Builds a Package carrying a frozen record (Point with two int fields), an async function (fetch(string) -> Awaitable[string]), and a scalar module-level constant (VERSION: string).
• Validates the package via Package.Validate() (PEP 503 distribution name, PEP 440 version, non-empty Summary/License, Python-identifier export names).
• Renders both layouts via RenderSdist(p) and RenderWheel(p).
• Writes each layout to a t.TempDir() subdirectory via Layout.Write(dst) (mkdirall + 0644 file writes, sorted output).
• Asserts the sdist contains pyproject.toml, PKG-INFO, README.md, <module>/__init__.py, <module>/__init__.pyi, and mochi_build/__init__.py (the bundled PEP 517 backend).
• Asserts the wheel contains <module>/__init__.py, <module>/__init__.pyi, <dist>-<ver>.dist-info/METADATA, WHEEL, and RECORD.
• Asserts the .pyi re-emits the frozen record as a Python class, the async function as def fetch(arg0: str) -> Awaitable[str]: ..., the constant as VERSION: str, and pulls in the Awaitable typing import.
• Asserts the wheel RECORD carries sha256= lines for every artifact except RECORD itself (which is listed with empty hash and size per PEP 376).
• Asserts the bundled mochi_build/__init__.py exposes build_wheel, build_sdist, and dispatches to mochi pkg build.

Plus 38 unit tests (go test ./package3/python/pypackage/... -count=1) covering:

• PEP 503 distribution-name normalisation (-/digit/lowercase only, no leading or trailing -).
• PEP 426 module-name fallback (mochi-httpx -> mochi_httpx) plus an explicit Module override.
• Validate() error paths for empty Distribution / Version / Summary / License and for non-identifier export names.
• PyprojectTOML core fields and conditional omission of HomePage / authors / requires-python / dependencies.
• PKGInfo METADATA 2.1 headers (Name / Version / Summary / Home-page / Author / License / Requires-Python / Requires-Dist).
• WheelMetadata PEP 427 marker (Wheel-Version 1.0, Tag py3-none-any, Root-Is-Purelib true).
• InitPy re-exports mochi_runtime and populates __all__ in sorted export order.
• InitPYI rendering for func / record / interface / constant exports (sync + async methods, empty record + empty Protocol bodies).
• pyAnnotation for every typemap.Kind: scalars, list/set/map/tuple, Optional, Sum, Async, Stream, Callable, named record/interface (and Any fallback when name is empty), Ref, TypeVar, and the unknown-kind fallback.
• pyImportsFor minimal from typing import ... set computed by walking exports (Optional, Union, Awaitable, AsyncIterator, Callable, Protocol, Any).
• MochiBuildBackend carries build_wheel, build_sdist, prepare_metadata_for_build_wheel, and shells to mochi pkg build.
• RecordLine rendering (empty self-line vs hashed line) and HashBody determinism + base64-urlsafe-no-padding shape.
• Layout.Add overwrite semantics, sorted Paths(), Write mkdirall + empty-destination rejection.
• RenderSdist artifact set, README content, module-override propagation.
• RenderWheel artifact set, RECORD line format, RECORD determinism across two renders.

Files

• package3/python/pypackage/doc.go — package overview.
• package3/python/pypackage/package.go — Package, Export, ExportKind, Validate, ModuleName, PEP 503 / identifier validators.
• package3/python/pypackage/layout.go — Layout (flat path -> body map) with Add, sorted Paths, Write.
• package3/python/pypackage/render.go — PyprojectTOML, PKGInfo, WheelMetadata, InitPy, InitPYI, pyAnnotation, pyImportsFor, MochiBuildBackend, RecordEntry / RecordLine / HashBody.
• package3/python/pypackage/sdist.go — RenderSdist(p) (*Layout, error).
• package3/python/pypackage/wheel.go — RenderWheel(p) (*Layout, error) + RECORD synthesis.
• package3/python/pypackage/package_test.go — Package validators (12 cases).
• package3/python/pypackage/layout_test.go — Layout mechanics (4 cases).
• package3/python/pypackage/render_test.go — renderers + type lowering (18 cases).
• package3/python/pypackage/sdist_test.go — sdist composition (4 cases).
• package3/python/pypackage/wheel_test.go — wheel composition + RECORD (4 cases).
• package3/python/pypackage/phase10_test.go — umbrella sentinel.

Sub-phase decomposition

Phase 10 ships the in-memory artifact composer only. The actual archive packing (sdist .tar.gz and wheel .whl zip) and the surrounding CLI surface land as follow-ups so the umbrella gate stays subprocess-free and deterministic:

Sub-phase	Title	Status	Notes
10	Layout + renderers + mochi_build backend	LANDED (pending merge)	This PR.
10.1	Sdist tar.gz packer (deterministic mtimes, uid/gid 0)	NOT STARTED	Reproducible tarball + ZIP64-aware wheel packer.
10.2	mochi pkg build --target=python-package CLI verb	NOT STARTED	Drives RenderSdist / RenderWheel, copies output to --out=<dir>.
10.3	Mochi -> Package lowering	NOT STARTED	Walks a Mochi module's public surface and produces the Package value Phase 10 consumes.

Fixtures

Phase 10's surface is a renderer over the closed Phase 4 type table; it does not consume the 25-package corpus directly. The 10.3 sub-phase will exercise the fixture corpus when the Mochi-side surface walker lands.

Skip count

N/A. Phase 10 has no SkipReport surface; non-renderable surfaces are rejected by Validate() before any artifact is touched.

Cross-references

• MEP-71 spec §10 "Publish direction" for the normative artifact schema.
• Phase 8 for the consume-direction workspace synth that already covers mochi_runtime packaging.
• Phase 9 for the wrapper-sha256 pin Phase 10 will eventually surface in the published .dist-info.
• Phase 11 for the PyPI upload + Sigstore / PEP 740 attestation pipeline that consumes Phase 10's output.