update CLAUDE.md

Author: GiggleLiu

CLAUDE.md

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+# CLAUDE.md
+
+## Project Overview
+Rust library for NP-hard problem reductions. Implements computational problems with reduction rules for transforming between equivalent formulations.
+
+## Build & Test
+```bash
+make test        # Run all tests
+make clippy      # Lint
+make export-graph  # Regenerate reduction graph
+make paper         # Build Typst paper
+make mdbook        # Build and serve mdBook documentation
+make coverage      # Generate coverage report
+```
+
+## Architecture
+
+### Core Modules
+- `src/models/` - Problem implementations (SAT, Graph, Set, Optimization categories)
+- `src/rules/` - Reduction rules + inventory registration
+- `src/solvers/` - BruteForce solver, ILP solver (feature-gated)
+- `src/traits/` - `Problem`, `ConstraintSatisfactionProblem`, `ReduceTo<T>` traits
+- `src/registry/` - Compile-time reduction metadata collection
+
+### Reduction System
+```rust
+// Implement ReduceTo<TargetProblem> for SourceProblem
+impl ReduceTo<TargetProblem> for SourceProblem {
+    type Result = ReductionSourceToTarget;
+    fn reduce_to(&self) -> Self::Result { ... }
+}
+
+// Register with inventory for automatic discovery
+inventory::submit! { ReductionEntry { source_name, target_name, ... } }
+```
+
+### Key Patterns
+- Problems parameterized by weight type `W` (i32, f64)
+- `ReductionResult` provides `target_problem()` and `extract_solution()`
+- Graph types: SimpleGraph, GridGraph, UnitDiskGraph, Hypergraph
+
+## Adding Reductions
+See GitHub Issue #3 for detailed coding rules:
+1. Create `src/rules/<source>_<target>.rs` with inventory registration
+2. Add closed-loop test (create instance -> reduce -> solve -> extract -> verify)
+3. Document in `docs/paper/reductions.typ`
+4. Regenerate graph with `cargo run --example export_graph --all-features`
+
+## Coverage Requirement
+New code must have >95% test coverage:
+```bash
+cargo tarpaulin --all-features --skip-clean --ignore-tests -- <module_name>
+```