fix(wasm): provide C stdlib for tree-sitter, fix playground abort

[jeanclawdbotdamn]

Summary

Fixes the playground showing "Error: abort" on every validation.

Root cause: PR #39 added JS shims for tree-sitter's C stdlib imports, but malloc returning 0 (NULL) caused tree-sitter to call abort() when allocating memory.

Fix: Provide real #[no_mangle] C stdlib implementations in Rust (crates/truss-wasm/lib.rs):

• Memory functions (malloc/calloc/realloc/free): route to Rust's global allocator with an 8-byte size-prefix header so free/realloc can reconstruct the Layout
• I/O stubs (fprintf/snprintf/vsnprintf/fwrite/fputc/fclose/clock): no-op — tree-sitter declares but never calls these in the validation path
• abort: triggers wasm32::unreachable trap

The linker resolves these at build time, so the generated JS will no longer contain import * from "env". Removes the now-unnecessary env.js shim and import map from PR #39.

Files changed

File	Change
crates/truss-wasm/lib.rs	Add wasm_compat module with 12 C stdlib implementations
playground/env.js	Deleted (no longer needed)
playground/index.html	Remove import map
.github/workflows/pages.yml	Remove env.js copy step

Test plan

• CI passes (WASM build must succeed with the new #[no_mangle] symbols)
• After Pages deploy: open playground, type YAML, validation runs without abort
• Verify import * from "env" no longer appears in generated truss_wasm.js

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 77.65%. Comparing base (ee4fc67) to head (603e88d).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #40   +/-   ##
=======================================
  Coverage   77.65%   77.65%           
=======================================
  Files          50       50           
  Lines        4408     4408           
=======================================
  Hits         3423     3423           
  Misses        985      985           

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