Adds apps/cli/src/cli/validators.ts — a small module of shape
validators (pubkey, pubkey prefix, message id, mesh slug) that return
discriminated results so callers can distinguish "shape is wrong"
(INVALID_ARGS exit) from "value is well-shaped, lookup failed"
(NOT_FOUND exit). Includes renderValidationError() for a consistent
three-tier error contract: what's wrong, what would be valid, closest
valid alternative.
First adopter is `claudemesh msg-status`:
- Validates id locally before opening WS — typos return immediately.
- Accepts 8-32 char prefixes (full ids are 32). Pastes that get
copy-truncated by the terminal still work.
- Distinct error messages for malformed input vs not-in-queue vs
ambiguous prefix; --json emits the structured shape.
Broker side: WS message_status handler validates idStr is 8-32
base62 before querying. Prefix lookups use LIKE 'prefix%' scoped to
the caller's mesh (no cross-mesh leak). Returns ambiguous_prefix
when more than one match.
Establishes the canonical pattern; rolling out to send / grant /
revoke / topic post --reply-to in subsequent patches.
80755dbf9b