Add AGENTS.md development guide for AI coding agents

AGENTS.md

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+# AGENTS.md - CKB Light Client Development Guide
+
+This guide provides essential information for AI coding agents working in the ckb-light-client repository.
+
+## Project Overview
+
+CKB light client reference implementation based on RFC 44 and RFC 45. This is a Rust workspace project with both native (Rust) and WebAssembly (Wasm) targets.
+
+**Workspace Structure:**
+- `light-client-lib/` - Core library (native + wasm, `ckb-light-client-lib`)
+- `light-client-bin/` - CLI binary (native only, `ckb-light-client`)
+- `wasm/light-client-wasm/` - Wasm bindings
+- `wasm/light-client-db-worker/` - Database worker for browsers
+- `wasm/light-client-db-common/` - Common database code
+- `wasm/light-client-js/` - JavaScript/TypeScript wrapper
+
+**Rust Toolchain:** 1.92.0 (specified in `rust-toolchain`)
+
+## Build Commands
+
+### Native Rust
+```bash
+# Build all native targets
+make build
+cargo build
+
+# Build release
+cargo build --release
+
+# Build specific package
+cargo build -p ckb-light-client
+cargo build -p ckb-light-client-lib
+```
+
+### WebAssembly
+```bash
+# Install dependencies and build all wasm packages
+make build-wasm
+
+# Equivalent to:
+npm install
+npm run build -ws
+```
+
+## Testing
+
+### Run All Tests
+```bash
+# Run native tests using cargo-nextest (required)
+make test
+
+# Runs:
+cargo nextest run --hide-progress-bar --success-output immediate \
+  --failure-output immediate -p ckb-light-client-lib -p ckb-light-client
+```
+
+### Run Tests on macOS
+```bash
+# Use portable feature on macOS
+make test-portable
+
+# Runs with feature flag:
+cargo nextest run --features portable ...
+```
+
+### Run Single Test
+```bash
+# Run a specific test by name
+cargo nextest run -p <package-name> <test-name>
+
+# Examples:
+cargo nextest run -p ckb-light-client-lib test_verify_blocks_proof
+cargo nextest run -p ckb-light-client synchronizer::tests
+```
+
+### Run Wasm Tests
+```bash
+# Run wasm-pack tests for browser environment
+make test-wasm
+
+# Runs:
+wasm-pack test --node ./wasm/light-client-db-common/
+```
+
+### JavaScript/TypeScript Tests
+```bash
+# Run tests in wasm workspace packages
+npm test -ws
+
+# Or for specific package:
+cd wasm/light-client-js && npm test
+```
+
+## Linting & Formatting
+
+### Format Check
+```bash
+# Check formatting (CI mode)
+make fmt
+
+# Runs:
+cargo fmt --all --check
+
+# Auto-fix formatting
+cargo fmt --all
+```
+
+### Clippy Linting
+```bash
+# Run clippy with warnings as errors
+make clippy
+
+# This runs two separate checks:
+# 1. Wasm targets
+cargo clippy --target wasm32-unknown-unknown \
+  -p light-client-wasm -p ckb-light-client-lib \
+  -p light-client-db-common -p light-client-db-worker \
+  --locked -- --deny warnings
+
+# 2. Native targets
+cargo clippy -p ckb-light-client --locked -- --deny warnings
+```
+
+## Code Style Guidelines
+
+### Imports
+- Group imports by: std library, external crates, internal crates
+- Use explicit imports rather than glob imports
+- Example from codebase:
+  ```rust
+  use std::{fmt, result};
+
+  use thiserror::Error;
+
+  use crate::storage;
+  ```
+
+### Error Handling
+- Use `thiserror` for error types
+- Define custom error enums with `#[derive(Error, Debug)]`
+- Use descriptive error messages with `#[error("...")]`
+- Create custom `Result<T>` type aliases:
+  ```rust
+  pub type Result<T> = result::Result<T, Error>;
+  ```
+- Provide helper methods for error construction:
+  ```rust
+  impl Error {
+      pub fn config<T: fmt::Display>(inner: T) -> Self {
+          Self::Config(inner.to_string())
+      }
+  }
+  ```
+
+### Types and Conversions
+- Implement `From` trait for type conversions between internal and external types
+- Use `#[serde(rename_all = "snake_case")]` for JSON serialization
+- Use `#[cfg(target_arch = "wasm32")]` for platform-specific code
+- Example:
+  ```rust
+  impl From<ScriptType> for storage::ScriptType {
+      fn from(st: ScriptType) -> Self {
+          match st {
+              ScriptType::Lock => Self::Lock,
+              ScriptType::Type => Self::Type,
+          }
+      }
+  }
+  ```
+
+### Naming Conventions
+- Use `snake_case` for functions, variables, and modules
+- Use `PascalCase` for types, structs, enums, and traits
+- Use `SCREAMING_SNAKE_CASE` for constants
+- Prefer descriptive names over abbreviations
+
+### Modules and Organization
+- Keep module declarations in `lib.rs` or `main.rs`
+- Use `mod.rs` files for module organization
+- Separate concerns: protocols, storage, utils, service, error
+
+### Testing
+- Place unit tests in the same file or dedicated `tests` submodule
+- Use `#[cfg(test)]` attribute for test-only code
+- Use `#[macro_use]` for test macros when needed
+- Integration tests go in workspace package's `tests/` directory
+
+### Documentation
+- Add doc comments for public APIs
+- Use `///` for documentation comments
+- Include examples in doc comments when helpful
+
+### Conditional Compilation
+- Use `#[cfg(not(target_arch = "wasm32"))]` for native-only code (e.g., RocksDB)
+- Use `#[cfg(target_arch = "wasm32")]` for wasm-only code (e.g., IndexedDB)
+- Keep platform-specific code isolated in separate modules when possible
+
+### Warnings
+- CI enforces `-D warnings` (all warnings treated as errors)
+- Use `#![allow(clippy::mutable_key_type)]` sparingly and only when justified
+- Address clippy warnings rather than silencing them
+
+## Development Workflow
+
+1. Make code changes
+2. Run `cargo fmt --all` to format code
+3. Run `make clippy` to check for lints
+4. Run `make test` (or `make test-portable` on macOS) for native tests
+5. Run `make test-wasm` if touching wasm code
+6. For wasm changes, run `npm test -ws` for JS/TS tests
+
+## CI Configuration
+
+The project uses GitHub Actions (`.github/workflows/ci.yaml`):
+- Runs on: Ubuntu, macOS, Windows
+- Steps: Format check, Clippy, Native tests, Wasm tests, Code coverage
+- All warnings treated as errors with `RUSTFLAGS: -D warnings`