AGENTS.md

Repository Guidelines

This file is the single source of truth for how humans and coding agents work in this repository. CLAUDE.md is a symlink to this file, so every agent reads the same instructions.

Project Structure

This is a Rust 2024 library crate rooted at Cargo.toml. It is both an ordinary library and a TinyBus module: the cdylib is the same code behind a JSON method.

src/
├── lib.rs              # crate docs + the entire public re-export surface
├── error/mod.rs        # compatibility exports of contract `Error` and `Result<T>`
├── credentials/        # the API key: redacted, deserialize-only
├── host/               # the `Host` trait (mod.rs) and the unified vocabulary
│   └── types.rs        #   every provider-independent type
├── bundle/             # an application's files, and reading them off disk
├── launch/             # the whole flow, in the one order that works
├── providers/
│   ├── mod.rs          # `ProviderKind`, `connect`, `connect_to`
│   └── vercel/         # one adapter: mod.rs (the `Host` impl),
│                       #   http.rs (status mapping), wire.rs (Vercel's shapes)
├── rpc/                # one JSON request in, one JSON result out
└── tinybus_module/     # TinyBus interface, ABI exports, and integration tests
crates/tinyhosts-bus/   # pure vocabulary, JSON envelopes and declarations
tests/                  # integration tests against the public API only
examples/               # runnable, compiled-in-CI usage examples
vendor/tinybus/         # pinned TinyBus host types and module SDK
docs/
├── specs/              # behavior and architecture specifications
├── plans/              # test-first implementation plans
└── adr/                # immutable architecture decision records

The model every provider is held to is docs/specs/unified-hosting-api.md; the reasoning behind it is ADR 2. Read both before changing the Host trait or the types in host/types.rs — they are a contract two other repositories depend on.

Four rules are load-bearing and must survive any change:

• A secret travels one way. Credentials has no Serialize; a listed environment variable has no value; a Database reports variable names, never a connection string. Do not add a getter, a Serialize, or a log line that breaks this.
• A capability a provider lacks returns Error::Unsupported. Never Ok.
• A provider state this crate does not model is carried through as DeploymentStatus::Other / Framework::Other, not mapped onto a known one.
• launch's order is the specification, not an implementation detail. The test that asserts the request sequence is the one that protects it.

Each feature area belongs in a focused module directory under src/. A module root explains the module, wires its pieces together, and exposes the smallest useful API. Move substantial type definitions into types.rs and put module-local unit tests in a sibling <module>_tests.rs, wired from the bottom of the module root with:

#[cfg(test)]
#[path = "mod_tests.rs"]
mod tests;

Do not write inline mod tests blocks in implementation files, do not name a test file test.rs, tests.rs or <module>_test.rs, and do not let a general-purpose utils.rs or helpers.rs grow — those are a symptom of a missing module. Prefer many small modules that each do one thing well over few broad ones.

Keep public exports centralized in src/lib.rs so downstream users have one predictable surface. Shared wire error variants live in crates/tinyhosts-bus/src/error/mod.rs; the implementation's src/error/mod.rs re-exports that vocabulary for compatibility. Return the crate-wide Result<T> from fallible public APIs.

Provider adapters

A new provider is a directory under src/providers/, a ProviderKind variant, and an arm in connect_to. Keep the three-file split the Vercel adapter uses: the Host implementation, the HTTP plumbing that owns status-to-error mapping in one place, and the provider's own request and response shapes. The provider's vocabulary stops at wire.rs; nothing above it should know the word readyState.

Test an adapter against a local mock of its REST API — never the live service and never a hand-written fake of Host, which would only confirm the behavior it was written to expect. Vercel::with_base_url exists for exactly this.

Build And Test

Run every command from the repository root. These four are the contract; CI runs exactly them, so a green local run should mean a green CI run.

cargo fmt --all -- --check
cargo clippy --workspace --all-targets --all-features -- -D warnings
cargo build --workspace --all-targets --all-features
cargo test --workspace --all-features

Supporting commands:

• cargo fmt --all — format before committing.
• cargo test <filter> — run a focused subset while iterating.
• cargo run --example basic — build a launch plan without sending it.
• cargo doc --no-deps --all-features — build the rustdoc CI also builds with RUSTDOCFLAGS="-D warnings".
• cargo test --doc — run doctests alone when editing documentation examples.

Never skip, ignore, or delete a failing test to make a command pass. Fix the root cause, or stop and report the blocker.

Coding Style

Use standard rustfmt output and Rust 2024 idioms. Do not hand-format around rustfmt, and do not add #[rustfmt::skip] without a comment explaining why.

• snake_case for modules, files, functions, methods, fields, and locals.
• PascalCase for types, traits, and enum variants; SCREAMING_SNAKE_CASE for constants and statics.
• Name things for what they are, not for their layer: RetryPolicy, not RetryHelper.
• Prefer small, typed APIs over stringly-typed ones. Accept &str and generic impl Into<String> at boundaries; return owned, concrete types.
• Keep the public surface minimal: default to private, and export deliberately from src/lib.rs.
• unsafe is forbidden crate-wide by the lint configuration in Cargo.toml. If a project genuinely needs it, relax the lint in its own commit and document every invariant with a // SAFETY: comment.

Errors

• One shared Error enum in the contract's src/error/mod.rs, built with thiserror and re-exported by the implementation's error module.
• Fallible public functions return Result<T>, the crate alias.
• Add a specific variant instead of stuffing context into a string; error messages are lowercase, without trailing punctuation.
• Do not unwrap(), expect(), or panic! in library code paths. They are fine in tests, examples, and genuinely unreachable states — where expect must carry a message explaining the invariant.
• Document a # Errors section on every public fallible function and a # Panics section on anything that can panic.

Dependencies

Adding a dependency is a design decision. Before adding one, check whether the standard library or an existing dependency already covers the need. When you do add one:

• pin a caret range (serde = "1"), not an exact version;
• enable only the features you need, with default-features = false when that meaningfully trims the tree;
• gate anything optional behind a Cargo feature, documented in Cargo.toml;
• leave a comment above the entry explaining why the crate is needed and what uses it — see the existing entries for the expected tone;
• prefer well-maintained crates with a compatible license.

Keep Cargo.lock committed; this crate ships a lockfile so CI and releases are reproducible.

Vendored dependencies

TinyBus is registered as the vendor/tinybus git submodule and pinned by its gitlink. It supplies the host types and module-side SDK required to build this crate's cdylib. Initialize it after cloning with:

git submodule update --init --recursive

Do not edit vendored code from the parent repository. Make TinyBus changes in its own repository, push them there, then update this repository's gitlink in a separate commit. Keep the exact path dependencies and minimal features unless a new module capability requires more.

Testing

• Module-local unit tests live in src/<feature>/mod_tests.rs and may touch private items.
• Integration tests live in tests/ and exercise only the public API — they are the regression suite for the crate's contract.
• Use descriptive, behavioral test names: rejects_an_empty_name, not test_greet_2.
• Cover the failure paths, not just the happy path. Every new error variant needs a test that produces it.
• For async behavior, standardize on one runtime (tokio as a dev-dependency for tests) rather than mixing runtimes.
• Tests must be deterministic and independent of network, wall-clock time, and execution order. Gate any live/network test behind a feature or an env var and name it live_* so it is easy to exclude.
• Maintain at least 90% line coverage in every source file. Add or update tests with every behavior change, and note any deliberately untested edge case in the pull request description.

Write the test first when fixing a bug: a failing test that reproduces the report, then the fix that turns it green.

Documentation

Write documentation for the reader who has never seen the code.

• Every public item gets a rustdoc comment. missing_docs is a warning that CI treats as an error.
• Start every mod.rs and *_tests.rs with a concise module-level //! description.
• src/lib.rs carries the crate-level overview: what the crate does, the primary entry points, and a short runnable example.
• Prefer concrete examples over vague description. Doc examples are compiled and run by cargo test, so they cannot drift.
• Complex modules must include a module-level README.md covering their design, public surface, and important operational constraints.
• Keep README.md, docs/, and module docs aligned with code changes in the same commit that changes behavior.
• Write accepted behavior and constraints in docs/specs/ before creating a linked, implementation-ordered plan in docs/plans/. Specs define what and why; plans define how and in what sequence.
• Keep every Markdown file, including this one, at 500 lines or fewer. When a topic outgrows that, split it into focused files and link them from the nearest README.md.

Git Workflow

• Never commit directly to main. Branch first, one branch per logical change.
• Do feature work in a git worktree so the main checkout stays clean.
• Commit subjects are concise and imperative: Add retry policy to the client. Keep the subject specific to the change and under ~72 characters.
• Make small, focused commits. Each commit should cover one logical change, build independently, and avoid mixing formatting, refactors, and behavior changes unless they are inseparable.
• Never commit secrets. .env is git-ignored; document new variables in .env.example with placeholder values.
• Never force-push a shared branch, rewrite published history, or bypass hooks with --no-verify.

Pull Requests

Open pull requests ready for review, not as drafts, unless the work genuinely must not merge yet. A pull request should:

• summarize what changed and why, in a few sentences;
• call out public API or behavior changes explicitly, or state "None";
• list the validation commands actually run, with their outcome;
• link the related issue;
• include updated tests, docs, and examples in the same change.

The template in .github/PULL_REQUEST_TEMPLATE.md encodes this checklist. Address review feedback by fixing it, and reply on each thread describing what changed. Do not resolve a thread whose feedback you have not addressed or explicitly declined with a reason.

Releases

Releases run from .github/workflows/release.yml via a manual workflow_dispatch with a patch / minor / major bump; current resumes an interrupted release after its version commit and tag exist. The workflow re-runs the full validation suite, computes the next version, updates Cargo.toml and Cargo.lock, commits and tags vX.Y.Z, builds the TinyBus module for every supported platform, pushes, and creates an immutable GitHub release with installable native packages.

Consequently:

• Do not hand-edit the version field in Cargo.toml; the release workflow owns it.
• Follow semantic versioning. Any change to the public surface that is not purely additive is a breaking change and needs a major bump (pre-1.0: a minor bump).
• The module must be packageable for every release target — main should always be green.

Agent Working Agreement

For automated contributors specifically:

1. Read before writing. Inspect the surrounding module and match its conventions, comment density, and idiom rather than importing a house style.
2. Verify, do not assume. Run the four contract commands and read their output before reporting a task complete. Report failures with the output; never claim a check passed that you did not run.
3. Stay in scope. Implement what was asked. Do not opportunistically refactor, reformat, upgrade dependencies, or "fix" unrelated code — raise it instead.
4. No placeholders in delivered code. No todo!(), no stubbed functions, no commented-out alternatives left behind. If something cannot be finished, say so explicitly.
5. Do not weaken the guardrails. Never add blanket #[allow(...)], relax a lint, mark a test #[ignore], or loosen CI to get a green run. Fix the cause.
6. Secrets stay out. Never read, echo, or commit .env contents, tokens, or credentials, and never paste them into a pull request or issue.
7. Ask only when blocked. Make routine judgment calls yourself; escalate only irreversible decisions or genuine forks with no clear default.

Tests live in *_tests.rs files

• Unit tests are never inline. Do not write a #[cfg(test)] mod tests { ... } block in a source file. Put the tests in a sibling <module>_tests.rs (mod_tests.rs beside a mod.rs, lib_tests.rs beside lib.rs) and declare it at the bottom of the module:

  #[cfg(test)]
  #[path = "foo_tests.rs"]
  mod tests;

• The test file starts with use super::*; and carries no #[cfg(test)] of its own. It is still a child module, so it reaches private items exactly as an inline module did.

• Name test files <module>_tests.rs; a second group for the same module is <module>_<topic>_tests.rs. Never test.rs, tests.rs or <module>_test.rs.

• Integration tests stay in the crate's tests/ directory.

• OpenHuman's scripts/externalize-inline-tests.mjs <repo-root> --write moves inline test modules out mechanically; without --write it only reports.