[DEP-02] Three concurrent `rand` major versions + RUSTSEC-2026-0097 across all of them

[intendednull]

Commit: 2f26d91 · Finding: DEP-02

Problem

cargo tree -d shows rand in three concurrent majors:

• rand 0.8.5 — crates/crypto/Cargo.toml, crates/agent/Cargo.toml
• rand 0.9.2 — crates/identity/Cargo.toml
• rand 0.10.0 — via rmcp in willow-agent

cargo audit reports RUSTSEC-2026-0097 (unsoundness when a custom logger calls rand::rng()) across all three. The unsoundness is real but not direct RCE; the bigger issue is security-critical code paths (crypto key gen vs identity) use non-interoperable rand majors.

Fix

• Add rand = "0.9" to [workspace.dependencies] in the root Cargo.toml.
• Switch crates/crypto and crates/identity to the workspace version.
• Accept rand 0.10 in transitive rmcp path (MCP transport only, not key material) until rmcp upgrades.
• Re-run cargo audit to confirm unsoundness advisory is no longer pinned to willow-authored crates.