Add AGENTS.md contributor guide + CLAUDE.md pointer

AGENTS.md

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+# AGENTS.md — dinghy contributor guide
+
+IMPORTANT: Read this file in full before starting any work on the project.
+
+dinghy cross-builds, tests and runs Rust on remote devices, emulators and phones.
+
+## Overview
+- **`cargo-dinghy/`** — the CLI (`cargo dinghy …`). Parses args, selects a platform +
+  device, and dispatches: `runner` (ship a prebuilt exe to a device and run it), cargo
+  passthrough (`build`/`test`/…), `run-with`, and the `devices` / `all-devices` /
+  `all-platforms` listings.
+- **`dinghy-lib/`** — the engine. Key modules:
+  - `config` — parses `.dinghy.toml` (platforms, ssh/script devices, test data).
+  - `lib` — `Dinghy::probe` assembles platforms + devices from the managers; the core
+    `Platform` / `Device` / `PlatformManager` traits and `Build` / `Runnable` / `SetupArgs`.
+  - `platform/regular_platform` — cross-toolchain platform: sets up CC/linker/sysroot,
+    strips, cross-builds.
+  - `toolchain` — resolves a cross toolchain into CC/AR/linker/pkg-config/shim env.
+  - `host` — the native (host) platform.
+  - `android` — NDK platform + `adb` device transport.
+  - `apple` — iOS/tvOS/watchOS devices + simulators (macOS only), via xcode.
+  - `ssh` — remote-board transport (rsync + ssh).
+  - `script` — device driven by a user-supplied script.
+  - `plugin` — auto-detects `cargo-dinghy-*` executables as device/platform providers.
+  - `overlay` — pkg-config overlays (extra libraries onto the sysroot).
+  - `project` — cargo-metadata wrapper (target dir, workspace root).
+- **`dinghy-build/`** — helpers for a cross-built crate's own `build.rs` (env/sysroot).
+- **`dinghy-test/`** — test-time helpers (locate test data) for crates using dinghy.
+- **`test-ws/`** — fixture workspace exercised by dinghy's tests.
+- **`legacy/`** — deprecated stub; use `cargo-dinghy`.
+
+## Contributing
+
+### Before you commit
+- Format with `cargo fmt --all`. The repo has a `rust-toolchain` file, so bare
+  `cargo fmt` uses the toolchain CI checks against — don't override it.
+- `cargo clippy --workspace` — don't add new warnings.
+
+### Commit messages
+- One short paragraph: what was wrong + the fix. Nothing else.
+- No consequence chains ("X broke Y broke Z"), no "Result:/Symptom:" sections,
+  no bullet lists of every place the bug surfaced.
+
+### Inline comments
+- Default to NONE. Names carry the meaning. A comment signals a hidden
+  constraint / invariant / workaround — not narration.
+- Never describe the diff or history ("used to be X", "previously…"). Comments
+  describe current code only.
+- No section-banner comments; split into functions instead.
+
+### Doc comments (`///` / `//!`)
+- DO add a concise one on public / non-trivial items — public fns, traits,
+  config structs. State what it is, its contract, and valid inputs.
+- Same anti-narration rule: document the current contract, not benchmarks,
+  perf numbers, issue numbers, or history ("Measured on…", "Regression:…").
+
+### Pull requests
+- Open with a 1–2 sentence summary of what and why.
+- Follow-up questions and review replies are handled by a HUMAN, not the bot.
+  The maintainer wants to talk to the author, not prompt an LLM.

CLAUDE.md

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+AGENTS.md