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247_tinygo-wasm-build.md

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id 2606110517
title tinygo wasm build under the 8 MiB budget
status ✅
model sonnet
summary Make `tinygo build -target wasm ./cmd/mdsmith-wasm` succeed and fit the plan-215/218 ≤ 8 MiB budget by isolating the four standard-library calls tinygo's wasm target lacks — os.Chmod, os.SameFile, os.Symlink, filepath.EvalSymlinks — behind build-tagged seams per package, then un-skip the size budget test and flip the CI tinygo-wasm job to enforcing.
depends-on
240

tinygo wasm build under the 8 MiB budget

Goal

Make tinygo build -target wasm ./cmd/mdsmith-wasm compile. The artifact must fit the plan-215/218 budget of 8 MiB.

Context

This is the one remaining criterion from plan 240. Dropping cuelang.org/go cleared two earlier walls. The sync.Map.CompareAndDelete swap cleared a third. The tinygo build still fails.

The failure is not size. It is four standard-library calls tinygo's wasm target does not implement. Each one is reached transitively from pkg/mdsmith.

The real build attempt under tinygo 0.39.0 named this inventory:

The standard GOOS=js wasm path must stay unchanged. Only the tinygo build needs the seams.

Tasks

  1. Add a build-tagged seam per package for each missing call. A non-tinygo file keeps the current body. A tinygo file supplies the variant. Pick the variant semantics per call site.

  2. For os.Chmod on a freshly written index or fixed file, the tinygo variant is a no-op. The wasm host has no POSIX mode bits. Skipping the chmod degrades nothing the engine reads back.

  3. For os.SameFile and the symlink calls in internal/githooks, the tinygo variant degrades. The hook-install path is not reachable from the wasm surface. The variant returns a "not supported" error.

  4. For os.Symlink and filepath.EvalSymlinks in internal/schema, internal/lsp, and the cross-file rules, the tinygo variant skips symlink resolution. The wasm sandbox has no symlinks. An identity resolution is correct there.

  5. Un-skip TestTinyGoWASMArtifactSizeBudget in cmd/mdsmith-wasm/size_test.go. Replace the known-failure skip with the size assertion against maxTinyGoWASMBytes.

  6. Flip the tinygo-wasm job in .github/workflows/ci.yml to enforcing. Remove continue-on-error: true. Remove the comment that points here.

  7. Update the engine-api page and plan 218. Record the tinygo build as CI-verified, not scheduled.

Acceptance Criteria

  • tinygo build -target wasm ./cmd/mdsmith-wasm succeeds with tinygo 0.39.0.
  • The tinygo artifact is at or under 8 MiB. TestTinyGoWASMArtifactSizeBudget asserts it rather than skipping.
  • The standard GOOS=js wasm build is unchanged. TestWASMArtifactSizeBudget still passes.
  • The CI tinygo-wasm job enforces the build. A regression fails the PR.
  • No call site loses its standard-library behaviour on a non-tinygo build.
  • Plan 240, plan 218, and the engine-api page read truthfully. The tinygo build is verified, not pending.
  • go test ./... and go run ./cmd/mdsmith check . pass.

See also