Lab 02: Error Receipts and Tracing

Goal

Add structured errors and tracing to lab-01, implementing the Receipt Pattern.

Requirements

1. Structured Errors

In core/src/error.rs:

• Define CoreError enum with thiserror
• Include structured fields (e.g., NotFound { id: String })
• Add #[error("...")] messages

2. Receipt Pattern

Create Receipt<T> type:

pub enum Receipt<T> {
    Accepted(T),
    Rejected { reason: String },
    Quarantined { id: String, reason: String },
}

Operations return Receipt<T>, not just Result<T, E>.

3. Tracing Spans

Add tracing to core operations:

#[tracing::instrument(skip(self))]
pub fn process_request(&self, req: Request) -> Receipt<Response> {
    // ...
}

Add nested spans showing lifecycle.

4. CLI Integration

• Initialize tracing subscriber with EnvFilter
• Run operations that succeed/fail/quarantine
• Show tracing output for all three paths

Done When

• Errors include structured fields
• Operations return typed receipts
• Tracing shows nested spans for request lifecycle
• You can see different receipt types in tracing output

Example Output

INFO core: processing request id="req-123"
WARN core: validation failed reason="invalid format" id="req-123"
INFO core: request quarantined id="req-123"

Resources

• icn/crates/icn-core/src/error.rs
• icn/crates/icn-ledger/src/ledger.rs (quarantine pattern)
• tracing crate docs