## Why
Decimal IDs of up to three digits fit in a single token. Issuing shorter IDs first keeps identifiers compact in model context.
## What changed
Add `codex-utils-model-facing-id` with deterministic, seed-based ID generation. Each salt prefixes the displayed ID and derives a separate sequence from the session seed. The generator shuffles decimal pools, exhausting `000`–`999` before issuing six-digit suffixes, then expanding in groups of three digits.
Support serializable, versioned snapshots that resume at the next unissued ID, plus suffix-only formatting for protocols that supply their own prefix.
## Testing
Add integration tests for pool exhaustion, stable outputs across pool boundaries, serialization and restore, salt-based seed derivation, invalid snapshots, and wraparound after the last `u64` ordinal.
GitOrigin-RevId: 80ffbf861106980b731d34a61ca2b9448d3bbb0d
