feat(billing): add cch attestation for OAuth requests

.cspell/words.txt

@@ -1,4 +1,5 @@
 anthropic
+anthropics
 anyhow
 claudemd
 clippy
@@ -15,6 +16,7 @@ RAII
 ratatui
 replacen
 reqwest
+rfind
 rustls
 serde
 strum
@@ -23,3 +25,4 @@ thiserror
 tokio
 tracing
 venv
+xxhash

CLAUDE.md

@@ -7,42 +7,43 @@ oxide-code is a terminal-based AI coding assistant written in Rust, inspired by
 ### CLI
 
 ```bash
-ox # Start an interactive session
+ox # Start an interactive session
 ```
 
 ### Project Layout
 
 ```text
 .
-├── crates/oxide-code/ # Main binary crate
-├── docs/ # Roadmap and research notes
-└── target/ # Build output
+├── crates/oxide-code/ # Main binary crate
+├── docs/ # Roadmap and research notes
+└── target/ # Build output
 ```
 
 ### Crate Structure (`crates/oxide-code/src/`)
 
 ```text
 .
-├── client.rs # Client module root
+├── client.rs # Client module root
 ├── client/
-│ └── anthropic.rs # Anthropic Messages API streaming client
-├── config.rs # Configuration loading (env vars, model, base URL)
+│ ├── anthropic.rs # Anthropic Messages API streaming client
+│ └── billing.rs # Billing attribution header (fingerprint, cch attestation)
+├── config.rs # Configuration loading (env vars, model, base URL)
 ├── config/
-│ └── oauth.rs # Claude Code OAuth credentials (macOS Keychain + file), token refresh, file locking
-├── main.rs # CLI entry point, agent loop, async REPL
-├── message.rs # Conversation message types
-├── prompt.rs # System prompt builder (section assembly, static content)
+│ └── oauth.rs # Claude Code OAuth credentials (macOS Keychain + file), token refresh, file locking
+├── main.rs # CLI entry point, agent loop, async REPL
+├── message.rs # Conversation message types
+├── prompt.rs # System prompt builder (section assembly, static content)
 ├── prompt/
-│ ├── environment.rs # Runtime environment detection (platform, git, date)
-│ └── instructions.rs # Instruction file discovery and loading (CLAUDE.md, AGENTS.md)
-├── tool.rs # Tool trait, registry, definitions
+│ ├── environment.rs # Runtime environment detection (platform, git, date)
+│ └── instructions.rs # Instruction file discovery and loading (CLAUDE.md, AGENTS.md)
+├── tool.rs # Tool trait, registry, definitions
 └── tool/
- ├── bash.rs # Shell command execution with timeout
- ├── edit.rs # Exact string replacement in files
- ├── glob.rs # File pattern matching (glob)
- ├── grep.rs # Content search via regex
- ├── read.rs # File reading with line numbers and pagination
- └── write.rs # File writing with directory creation
+ ├── bash.rs # Shell command execution with timeout
+ ├── edit.rs # Exact string replacement in files
+ ├── glob.rs # File pattern matching (glob)
+ ├── grep.rs # Content search via regex
+ ├── read.rs # File reading with line numbers and pagination
+ └── write.rs # File writing with directory creation
 ```
 
 ## Coding Conventions

Cargo.toml

@@ -32,6 +32,7 @@ reqwest = { version = "0.12", default-features = false, features = [
 security-framework = "3"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
+sha2 = "0.10"
 tempfile = "3"
 time = { version = "0.3", features = ["local-offset"] }
 tokio = { version = "1", features = [
@@ -50,6 +51,7 @@ tracing-subscriber = { version = "0.3", default-features = false, features = [
  "env-filter",
  "fmt",
 ] }
+xxhash-rust = { version = "0.8", features = ["xxh64"] }
 
 [profile.release]
 lto = true

crates/oxide-code/Cargo.toml

@@ -23,10 +23,12 @@ regex.workspace = true
 reqwest.workspace = true
 serde.workspace = true
 serde_json.workspace = true
+sha2.workspace = true
 time.workspace = true
 tokio.workspace = true
 tracing.workspace = true
 tracing-subscriber.workspace = true
+xxhash-rust.workspace = true
 
 [target.'cfg(target_os = "macos")'.dependencies]
 security-framework.workspace = true

crates/oxide-code/src/client.rs

@@ -1 +1,2 @@
 pub mod anthropic;
+mod billing;