Derive Macro Event 

#[derive(Event)]
{
    // Attributes available to this derive:
    #[event]
    #[obs]
}

Derive macro for the Rust-first authoring path.

Container attributes:

• #[event(tier = "log" | "metric" | "trace" | "audit")]
• #[event(default_sev = "trace" | "debug" | "info" | "warn" | "error" | "fatal")]
• #[event(full_name = "myapp.v1.ObsXxx")] (defaults to <crate>.v1.<TypeName> derived from module_path!).

Field attributes:

• #[obs(label, cardinality = "low" | "medium" | "high" | "unbounded")]
• #[obs(attribute, classification = "internal" | "pii" | "secret")]
• #[obs(measurement)]
• #[obs(trace_id)], #[obs(span_id)], #[obs(parent_span_id)]
• #[obs(forensic)]

Lints (compile-time const _: () = { assert!(...) } blocks):

• L001 — every LABEL field must declare a Low or Medium cardinality.
• L002 — PII-classified fields must not be LABEL.
• L003 — SECRET-classified fields must not exist on LOG or AUDIT tier events.
• L011 — the type name must start with the workspace event prefix (default Obs).

See spec 12 § 3.4.