[Kayvan-Zahiri]

railway variable edit quotes ASCII spaces/tabs but leaves other whitespace unquoted. The reader uses Rust's Unicode-aware trim, so saving an unchanged document drops leading/trailing non-breaking, em, thin, narrow non-breaking and ideographic spaces, NEL, vertical tab and form feed. Whitespace-only values become empty. This produces unwanted pending variable updates; the CLI still requires confirmation before applying them.

Quote any value containing char::is_whitespace, matching the reader. Existing special-character escaping remains intact. Add a regression that writes and reads an edit document and checks the resulting variable diff across 32 cases: eight whitespace characters in leading, trailing, whitespace-only and embedded positions. Before, 24 boundary cases lose data; eight embedded controls are preserved. After, all round-trip and unchanged-diff assertions pass. All 16 variable-editor tests pass.

Validation on Rust/Cargo 1.98.0 with unchanged Cargo.lock:

• cargo test --locked: 1,890 passed, six ignored, across unit and CLI integration suites.
• cargo fmt --check, git diff --check and built CLI --version (5.71.0) pass.
• Required cargo lint-fix completes. Its unrelated rewrites were excluded from this change; final cargo clippy --locked --all-targets --all-features completes with existing warnings outside the changed lines. The only warning in this file concerns the unchanged render_variable_plan_plain at line 197.

The regression uses local temporary files and synthetic values. Broader integration tests use local fixtures; no Railway project variables or live credentials were used. No release build or hosted account behavior is claimed.