fix(GATE-005): harden helper trusted-input — argv separator + UUID v4 request_id

- apt build_plan: add POSIX '--' before user-derived name=version tokens
- dnf build_plan: add POSIX '--' before user-derived name-version token
- validate_mint_request: enforce canonical UUID v4 on request_id at intake
- RAF components/04: document '--' separator in pipeline step 7
- RAF security/05: document hardened argv contract + UUID v4 validation
- RAF flows/03: add stale banner (5 deviations from current code)

14 tests pass. Deferred: artifact_path staging root, name/version charset
regex (both need design decisions — see task file).

RAF/security/05-supply-chain-gate.md

@@ -165,8 +165,9 @@ The token extends the existing Ed25519 infrastructure rather than introducing ne
 - **Executor (`helper/`, privileged, Rust).** Verify validity window → resolve trusted key by
   `key_id` from a local pinned keyring → reconstruct `signed_message` → Ed25519 verify →
   verify each artifact's sha256 → replay-guard on `token_id` → exec exactly one operation via
-  argv (no shell, env stripped) → structured result + exit code. Fail-closed on every error
-  path. Auditable in one sitting.
+  argv (no shell, env stripped, POSIX `--` separator before user values) → structured result
+  + exit code. Fail-closed on every error path. `request_id` validated as canonical UUID v4
+  at intake (GATE-005). Auditable in one sitting.
 - **Kernel layer (where applicable).** Linux eBPF / Windows WDAC / macOS ESF deny
   package-manager execution except via the trusted executor. Defense-in-depth.