Type the audit-log decision field with a Decision enum

[luca-iachini]

What

Replace the bare i32 decision wire value in the audit log with a typed Decision enum, so producers and readers share one source of truth for the 1=ALLOW / 2=DENY / 3=ABORT mapping.

Producer (firma-sidecar)

• New firma_sidecar::audit::Decision (#[repr(u8)], Serialize_repr + Deserialize_repr). JSON wire stays numeric — no format change.
• Retyped AuditPayload.decision, ExecutionEvent.decision, DecisionOverride.decision, and AuditDecisionFields.decision_code from i32 to Decision.
• Dropped the DECISION_ALLOW/DENY/ABORT magic-int constants (pipeline + test copies).
• Proto boundary converts with as i32; signing hashes (decision as i32).to_string() so existing signatures stay byte-identical.

Reader (firma monitor)

• AuditLite.decision now decodes into AuditLiteDecision { Known(Decision), Unknown(i64) } via a custom Deserialize impl. Three states preserved: absent (None), present-but-unrecognized (Unknown → renders UNKNOWN), known. An off-range code never drops the whole record.
• Removed the duplicate PROTO_DECISION_* constants and the decision_label fn (now a Display impl).

Tests

• e2e tests/e2e/audit.rs consumes the production enum instead of a local copy.
• Added monitor coverage for unknown-code and absent-field cases.

Also regenerates Cargo.lock, which was stale on main (manifest 0.1.2, lock 0.1.1).

Invariants

Wire format unchanged, signatures unchanged, deterministic enforcement unaffected.

just check passes.

[codecov]

Codecov Report

❌ Patch coverage is 93.63636% with 7 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/firma/src/monitor/filters.rs	94.82%	2 Missing and 1 partial ⚠️
crates/firma-sidecar/src/audit.rs	0.00%	1 Missing ⚠️
crates/firma-sidecar/src/audit/sink/grpc.rs	0.00%	1 Missing ⚠️
crates/firma-sidecar/src/handler.rs	95.45%	1 Missing ⚠️
crates/firma/src/monitor/render.rs	75.00%	0 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

[LukeMathWalker]

Nice clean-up!