Harness Engineering: from CC to AI coding

/// Review a unified diff file and return structured findings.
#[tool(description = "Review a unified diff file for bugs, security issues, and code quality. Returns structured JSON findings with file, line, severity, and suggestions.")]
async fn review_diff(
    &self,
    Parameters(req): Parameters<ReviewDiffRequest>,
) -> String { ... }

pub struct ReviewDiffRequest {
    #[schemars(description = "Absolute path to a unified diff file (from git diff)")]
    pub diff_path: String,
    #[schemars(description = "Maximum total tokens across all files (default: 50000)")]
    pub max_tokens: Option<usize>,
    #[schemars(description = "Maximum tokens per file (default: 5000)")]
    pub max_file_tokens: Option<usize>,
}

pub struct ContextBudget {
    pub max_total_tokens: usize,
    pub max_file_tokens: usize,
    pub used_tokens: usize,
}

/// Try to consume tokens. Returns true if within budget, false otherwise.
pub fn try_consume(&mut self, tokens: usize) -> bool { ... }

/// Estimate token count from text using a conservative bytes/4 heuristic.
/// Uses byte length, not character count. For multi-byte UTF-8 content
/// (e.g., CJK), this overestimates, which is intentionally conservative.
pub fn estimate_tokens(text: &str) -> usize {
    (text.len() + 3) / 4
}