ADR 0028 — M15 S7: the host services a compiler needs

Inherited from Nova. This is Nova's ADR 0028, which CeeSafe inherited at the fork (Nova v0.6.0; CeeSafe's Decision 0006). Its text is Nova's record and is not changed: read Nova and novac as the language and compiler CeeSafe forked from, .nova as .cee, and Nova's C names as CeeSafe's (spec/c-backend.md). Links to documents CeeSafe did not fork go to Nova's repository.

• Status: Accepted (project owner, 2026-10-30), every question as recommended (§5). The wording is the agent's. Implemented the same day (§6).
• Scope: M15 S7 (OD-35). These are the operating-system services novac build and its package commands use, which Nova's hosted library (type-system §26) lacks: a compiler written in Nova (OD-33) cannot do without them.

1. Context

The services novac itself uses (an audit of src/, 2026-10-30):

Service	Where novac uses it	Nova today (§26)
Run a program and capture its stdout and stderr, optionally with stdin	the C compiler and linker (Backend.C/CBackend.cs:252-290); tool discovery (CCompilers.cs:165)	Process.run: inherited stdio, exit status only
Read an environment variable	CC, PATH, NOVA_HOME, NOVA_INDEX, INCLUDE	none
Create and list directories	-o DIR for --emit c (Program.cs:586, :603, CBackend.cs:42); src/ of a package (Manifest.cs:271)	none
Whether a path exists, and what it is	manifests, the cache, fmt on a directory	none (File.open and look at the error)
A fresh temporary directory, removed afterwards	every build (Program.cs:614)	none
The working directory	package lookup (Manifest.FindDirectory), source paths (SourceText.SourcePath)	none

The CeeSafe port (P1, host-process probe) confirmed the rest works: writing a C file, running cc with an argument vector, its exit status, and reading the object back.

2. Options

	A. Built-in library API in lib/std and §26 (proposed)	B. C adapters in each program	C. A generic extern "C" POSIX binding
Safety	safe API; the runtime owns the unsafe parts	every program writes unsafe FFI	unsafe everywhere, and POSIX only
Portability	the runtime selects the platform (macOS, Linux, Windows, CosmoOS), as Process.run does (§26.6)	per program	none on Windows or CosmoOS
Interpreter	modelled, and refused in the sandbox	runs no C (§28.6)	runs no C

3. Proposed decision: A

Hosted-only functions (N0293 in freestanding code), blocking, with errors as IoError:

• Process.capture(program, arguments, input) -> Result<ProcessOutput, IoError>.
  • program: StringView is found on PATH; arguments: borrow Vector<StringView>; input: Slice<u8>? is written to the child's stdin, which is then closed (null: an empty stdin).
  • ProcessOutput is a built-in struct with status: i32, as Process.run reports it, plus stdout: Vector<u8> and stderr: Vector<u8>.
  • The runtime reads both pipes and writes stdin concurrently (poll on POSIX, overlapped pipes on Windows), so a child that fills one pipe cannot deadlock it.
  • Failures: allocation is OutOfMemory; the program not found is NotFound; arguments as for Process.run.
• Environment.variable(name: StringView) -> StringView?: the value as static text, like Process.argument (§26.1). It is null if absent or not valid UTF-8. Nova has no way to set a variable, so the text never changes under the program.
• Directory.create(path) -> Result<void, IoError> (one level; AlreadyExists if it exists) and Directory.remove(path) (an empty directory).
• Directory.list(path) -> Result<Vector<String>, IoError>: the entries' names, without . and .., sorted by byte value, so programs stay deterministic (c-backend §1's rule applied to I/O).
• Path.kind(path) -> Result<PathKind?, IoError>: File, Directory or Other, or null if nothing is there. It follows symbolic links.
• Directory.temporary() -> Result<String, IoError>: a new, empty, private directory, created atomically (mkdtemp) under the platform's temporary directory. The caller removes it.
• Directory.current() -> Result<String, IoError>.

Paths are StringViews, under the same rules as File.open: zero bytes and paths over 4,095 bytes are InvalidInput. The interpreter models these with .NET's APIs on macOS and Linux, and the sandbox (novac mcp, nova_run) refuses them all, as it refuses processes today.

4. Consequences

• Spec: type-system §26.7–§26.10, diagnostics (none new expected), and the runtime in runtime/hosted/nova_rt_io.c (POSIX and Windows) with CosmoOS's variants selected at compile time.
• Tests:
  • run-pass and run-fail programs for each function (a child writing more than a pipe's buffer to both streams; absent variables; sorted listing; temporary-directory cleanup);
  • InterpreterTests and McpTests for the sandbox;
  • the MSVC configuration for Windows;
  • c3.py in a CosmoOS guest for the spawn path.
• A compiler written in Nova (the CeeSafe port) can then implement build and package mode without C adapters.

5. Questions for the owner

1. Option A, with this API? (Recommended.)
2. Environment.variable as a StringView? of static text, rather than a copied String? (Recommended: it matches Process.argument, and nothing can change the environment.)
3. Directory.list: should a name that is not valid UTF-8 make the call fail with InvalidInput, or be skipped? (Recommended: fail. Skipping could make a compiler silently miss a source file.)
4. CosmoOS: implement Process.capture there in 0.4.0 (its spawn API needs pipe redirection; to be audited in CosmoOS's code), or report Other until a later release? (Recommended: audit first, and decide with the evidence.)
5. Windows: full parity in the same release? (Recommended: yes. novac's own Windows builds depend on these services.)

6. Implementation (2026-10-30)

• Q4 (CosmoOS), from the audit. CosmoOS's libc (libc/include/spawn.h, unistd.h, dirent.h, sys/stat.h, stdlib.h) has spawnvp with spawn_handle mappings, plus pipe, getenv, getcwd, opendir/readdir, stat, mkdir and rmdir, but no poll and no mkdtemp. So Process.capture is implemented there in this release. On every platform it routes the child's streams through files in a private temporary directory, not pipes, so nothing needs poll or threads to avoid a deadlock. The temporary directory is made by trying names until mkdir succeeds, which is atomic on every platform.
• One name changed. Path.kind is File.kind. A lib/std Path would break programs that declare their own: lib/std names cannot be redeclared in a hosted package (§38.5), and the corpus's run-pass/struct-nested.nova has one. Environment, Directory, PathKind, ProcessOutput and HostServices matched nothing in the repository, CeeSafe or the site's guide.
• Where it lives:
  • lib/std/host.nova, with its unsafe code behind documented contracts;
  • ten nova_host_* functions in runtime/hosted/nova_rt_io.c, for POSIX, CosmoOS and Windows, declared in rt.h;
  • two checker hooks, so Process.capture and File.kind call lib/std's HostServices;
  • the interpreter's models in Interpreter/HostServices.cs.
• Tests:
  • run-pass/host-services.nova, run in every C configuration and in the interpreter;
  • check-fail/host-services.nova;
  • HostServicesTests, where capture runs natively and in the interpreter with a child writing 300,000 bytes to each stream, and the sandbox refuses.
• CosmoOS, in a guest. c3.py --ssh builds integrations/cosmoos/c3/c3-host.nova for CosmoOS and runs it. The first run found that CosmoOS's S_ISDIR/S_ISREG test the stat record's st_type (a DT_* value), not st_mode (its sys/stat.h). The runtime selects st_type there.
• Not yet run: the Windows CreateProcess path. The CI's Windows job builds and runs the run corpus with MSVC, which covers everything but capture; HostServicesTests covers capture, but not on Windows.