Current Dependencies (Auto-Injected)

!grep -A 100 '^\[dependencies\]' Cargo.toml 2>/dev/null | head -30 || echo "No Cargo.toml found"

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Ecosystem Integration

Layer 2: Design Choices

Core Question

What's the right crate for this job, and how should it integrate?

Before adding dependencies:

• Is there a standard solution?
• What's the maintenance status?
• What's the API stability?

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Integration Decision → Implementation

Need	Choice	Crates
Serialization	Derive-based	serde, serde_json
Async runtime	tokio or async-std	tokio (most popular)
HTTP client	Ergonomic	reqwest
HTTP server	Modern	axum, actix-web
Database	SQL or ORM	sqlx, diesel
CLI parsing	Derive-based	clap
Error handling	App vs lib	anyhow, thiserror
Logging	Facade	tracing, log

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Thinking Prompt

Before adding a dependency:

1. Is it well-maintained?

   • Recent commits?
   • Active issue response?
   • Breaking changes frequency?

2. What's the scope?

   • Do you need the full crate or just a feature?
   • Can feature flags reduce bloat?

3. How does it integrate?

   • Trait-based or concrete types?
   • Sync or async?
   • What bounds does it require?

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Trace Up ↑

To domain constraints (Layer 3):

"Which HTTP framework should I use?"
    ↑ Ask: What are the performance requirements?
    ↑ Check: domain-web (latency, throughput needs)
    ↑ Check: Team expertise (familiarity with framework)

Question	Trace To	Ask
Framework choice	domain-*	What constraints matter?
Library vs build	domain-*	What's the deployment model?
API design	domain-*	Who are the consumers?

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Trace Down ↓

To implementation (Layer 1):

"Integrate external crate"
    ↓ m04-zero-cost: Trait bounds and generics
    ↓ m06-error-handling: Error type compatibility

"FFI integration"
    ↓ unsafe-checker: Safety requirements
    ↓ m12-lifecycle: Resource cleanup

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Quick Reference

Language Interop

Integration	Crate/Tool	Use Case
C/C++ → Rust	bindgen	Auto-generate bindings
Rust → C	cbindgen	Export C headers
Python ↔ Rust	pyo3	Python extensions
Node.js ↔ Rust	napi-rs	Node addons
WebAssembly	wasm-bindgen	Browser/WASI

Cargo Features

Feature	Purpose
[features]	Optional functionality
default = [...]	Default features
feature = "serde"	Conditional deps
[workspace]	Multi-crate projects

Error Code Reference

Error	Cause	Fix
E0433	Can't find crate	Add to Cargo.toml
E0603	Private item	Check crate docs
Feature not enabled	Optional feature	Enable in features
Version conflict	Incompatible deps	cargo update or pin
Duplicate types	Different crate versions	Unify in workspace

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Crate Selection Criteria

Criterion	Good Sign	Warning Sign
Maintenance	Recent commits	Years inactive
Community	Active issues/PRs	No response
Documentation	Examples, API docs	Minimal docs
Stability	Semantic versioning	Frequent breaking
Dependencies	Minimal, well-known	Heavy, obscure

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Anti-Patterns

Anti-Pattern	Why Bad	Better
extern crate	Outdated (2018+)	Just use
#[macro_use]	Global pollution	Explicit import
Wildcard deps *	Unpredictable	Specific versions
Too many deps	Supply chain risk	Evaluate necessity
Vendoring everything	Maintenance burden	Trust crates.io

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Related Skills

When	See
Error type design	m06-error-handling
Trait integration	m04-zero-cost
FFI safety	unsafe-checker
Resource management	m12-lifecycle