Allow custom C++/Java compiler executable (#21)

[HamzaHassanain]

Summary

Closes #21.

The C++ compiler executable was hardcoded to g++ in compileCPP. It is now resolved in this order:

1. POLYMAN_CXX environment variable
2. compiler.cpp in Config.json
3. g++

The same applies to Java: POLYMAN_JAVAC, then compiler.javac, then javac.

An optional compiler.flags array appends extra flags to every C++ compile, so g++-15 with -std=c++23 works without touching the system default compiler.

{
  "compiler": {
    "cpp": "g++-15",
    "flags": ["-O2", "-std=c++23"]
  }
}

POLYMAN_CXX=clang++ polyman verify

The block is local only and never sent to Polygon (Polygon uses sourceType). Executables are shell-quoted so absolute paths with spaces work.

Changes

• src/helpers/utils.ts: resolveCppCompiler, resolveCppFlags, resolveJavaCompiler; compileCPP/compileJava use them.
• src/types.d.ts: new CompilerConfig type and optional compiler field on ConfigFile.
• Docs: template/instructions/config.md, GUIDE.md, README.md.
• Tests: tests/helpers/utils.test.ts covers default, config, env precedence, blank/malformed values, flags passthrough, and quoting.

Verification

• npm run build, npm run lint, npm run format:check, npm test (779 tests) all pass.
• Smoke-tested POLYMAN_CXX pointing at a wrapper script against dist/; the wrapper was invoked and the binary ran.

🤖 Generated with Claude Code

https://claude.ai/code/session_01GpqwzMj4fWWDcyfAT6WWq9