mcp: make agent mutations idempotent and retry-safe

[cristicretu]

Summary

• add strict request keys and a daemon-owned caller-scoped idempotency ledger
• coalesce concurrent duplicate mutations and retire caller generations safely
• preserve sticky outcome-uncertain results across panic, timeout, TTL, and eviction boundaries
• prevalidate embedded mutations and roll back created worktrees, branches, and PTYs on failure
• share typed control-error mapping across embedded and production MCP paths

Verification

• full diri-proto, diri-engine, and dirijor-mcp suites
• strict all-target Clippy
• concurrent replay, caller replacement, panic, timeout, rollback, and embedded parity tests
• formatting and lockfile checks clean