Fuse: Instructions file for Codex

Fuse: contributor and agent guide

Fuse is one .NET tool (fuse) that keeps a warm Roslyn compilation of a repository and gives coding agents the errors their edits introduced, affected-test runs, and compact build output, through agent hooks and a three-tool MCP server. README.md describes the product, site/docs/index.html indexes the documentation, and site/docs/how-it-works.html describes how it works.

Layout

• src/Fuse: the only product project, packed as the Fuse dotnet tool. Its namespaces are layers; site/docs/architecture.html says which may use which, in what order to read them, and what its words mean. From the top:
  • Program.cs: parses the command line and picks a surface or the engine.
  • Hooks/, Mcp/, Harnesses/: fuse hook, fuse mcp, and fuse init with one class per harness.
  • Operations/: the check, test and build operations shared by every surface, and their output.
  • Engine/Client/: finds, starts and calls the engine.
  • Protocol/: the pipe's request and response records.
  • Engine/: the engine process: pipe server, request routing, preload, mapping results to Protocol.
  • Check/, Testing/: the check algorithm and test selection, each with a Model/ folder read first.
  • Changes/: which declarations differ between HEAD and the working tree.
  • Workspace/: the current and baseline Roslyn solutions.
  • Repo/, Graph/, Dotnet/: git and the working tree, MSBuild evaluation, child processes and their output parsers.
  • Paths/, Failures/, Telemetry/: RepoRoot and RepoPath, FuseException and ErrorCode, PhaseTimes and EngineLog.
• tests/Fuse.Tests: unit, engine and process tests over generated fixture repositories, and Architecture/NamespaceDependencyTests, which fails the build when a namespace uses one it may not.
• evals/Fuse.Evals: the correctness, selection and latency evals, and the chart renderer; results in evals/results.
• site/: the website at fuse.codes, static HTML deployed from main with no build step. Cloudflare Workers serves it as static assets, configured by wrangler.jsonc at the repository root.
  • index.html and 404.html: the home page and the not-found page.
  • docs/: all documentation, one page per file, with index.html as the overview.
  • assets/: style.css, the icons, og.png, and benefits.svg, which dotnet run --project evals/Fuse.Evals -c Release -- chart renders from evals/results.
  • _headers and _redirects: response headers, and redirects from addresses that moved.
  • robots.txt, sitemap.xml and llms.txt: for crawlers and agents.
• Documents outside site/docs/: only the files GitHub and the release workflow read, the README, CONTRIBUTING.md, SECURITY.md and CHANGELOG.md in the root, and CODE_OF_CONDUCT.md and SUPPORT.md in .github/.