Wasm backend and WASI profile 0.1
The target ID is wasm; its runtime profile is wasi-preview1. Artifacts are WebAssembly 1 binary command modules exporting _start and memory. Imports are exclusively functions from wasi_snapshot_preview1. Binary emission belongs to the backend: it uses no WAT conversion, external assembler, LLVM, or other code-generation framework. Wasmtime executes the already-emitted modules.
Core remains unchanged and target independent. Backend-private instructions, value tags, memory offsets, calling conventions, and allocation headers are not Core operations or public language types. The Kelft encoder, lowering, and embedded runtime instructions provide the source implementation of this profile.
Values and ownership
Scalars use tagged integer values; aggregate handles carry 32-bit linear-memory offsets. Functions transfer owned by-value arguments and return owned values. Borrowing runtime helpers retain returned children; callers release temporaries. inout locations borrow a live root cell and own their evaluated-once path. Forwarding extends that path without escaping the root's lifetime.
Arrays use persistent radix-32 trees; maps iterate sorted key/value tuples. Structs, tuples, and variants contain immutable value slots. Mutations rebuild the affected path. Loop snapshots and match temporaries remain alive through their scopes and are released on exits, including early returns.
Strings are immutable UTF-8 views over reference-counted byte buffers. Concatenation may append beyond every existing view, but cannot modify an existing view's length or bytes. Slices retain backing storage. Buffers grow by copying when appending would overlap an existing value. The allocator reuses power-of-two size classes; storage strategies are private implementation choices.
Arithmetic, structural equality, UTF-8 validation, and language traps retain the language specification. Main's i32 return is an exit code in 0..255; other values trap with KRT_EXIT. Engine failures and resource exhaustion are infrastructure failures, not successful fixture evidence.
Host operations and paths
WASI paths use a POSIX guest namespace. Drivers map host directories to stable guest paths and preserve project-relative module identities. The profile initially supports directory capability roots within the explicit project root. The driver rejects roots outside that boundary; it never widens a preopen to make them work. File effects are compared using guest paths rather than host drive letters.
Filesystem calls resolve links and existing ancestors, check containment, and intersect external grants with the artifact's embedded maximum policy. Grants are denied by default. Read-only preopens are also enforced by the stock WASI implementation. Recoverable errors use the shared ENOENT/EACCES/EEXIST/ENOTDIR/ EISDIR/IO_ERROR vocabulary. Policy denial traps with KRT_CAPABILITY.
The trusted host supplies only KELFT_WASI_CAPABILITIES. Its private encoding is 1 followed by records: a kind byte (r, w, or c), decimal UTF-8 byte length, :, and the exact path bytes. r/w grant operation roots; c sets the logical working directory. Example: 1r8:/projectw7:/outputc8:/project. Source programs have no environment-reading or environment-writing primitive. No network, clock, randomness, arbitrary subprocess, or FFI API is exposed.
artifact_run returns DRIVER_REQUIRED in this profile. External execution uses the separate driver protocol, never proprietary Wasmtime imports. Direct compilation and deterministic Intent inspection need no driver API.
The default module memory maximum is 1 GiB. The trusted driver bounds execution time and captured output separately. Host-runtime resource failure withholds successful evidence. These bounds do not claim an operating-system sandbox for an external coding agent.
Source: public Kelft compiler, commit f567c21684362db37e0aa0a68e71e7614502c45a. Compiler 0.1.0-alpha.2; Core 0.1; Intent 0.2.