Issue: Buffer Width Validation and Failure Atomicity 2026-08-20

issue022 [ ] Invalid buffer widths mutate or create invalid projection state

Status: Runtime fix verified by task037; user-visible confirmation remains pending.
Summary: ekp-justify-region accepts zero, negative, and non-integer widths without the string API's positive-integer validation. It clears the existing projection before a later type error, so a rejected request can destroy valid visible state.
Repro: In a justified buffer, call ekp-justify-region with 0, -1, 1.5, or "80".
Expected vs Actual: Expected a preflight signal with the old projection unchanged. Actual zero creates a span with width zero; a type error after a prior projection leaves no spans.
Related: ekp-buffer.el, ekp.el, task037.
Fix: ekp-justify-region now validates the width before font-lock or projection clearing.
Verification: Red/green focused ERT 1/1 and source-first full ERT 294/294.
Resolved At: Pending user-visible confirmation.
Resolved By: Developer implementation and verification.
Commit: Pending hardening commit.