Loop detector silently fails without math.js — should warn or error

[zntznt]

Problem

detectLoops (js/loops.js:52-69) calls evalFormula to probe formula signs. When math.js is not available (CLI without npm install), evalFormula returns 0 for all expressions using math.js functions (max(), min(), round(), etc.). The probe returns null (no measurable influence), the formula edge is silently dropped, and the loop table is incomplete with no error.

This is currently masked by the legacy new Function() fallback handling simple arithmetic but NOT math.js-specific functions. After #42 removes the legacy fallback, the problem extends to ALL arithmetic — even simple formulas like 10 - gold return 0 without math.js, making the loop detector silently useless in the CLI.

Fix

Add a guard at the top of detectLoops():

function detectLoops(diagram, opts = {}) {
  if (typeof math === 'undefined' || !math.compile) {
    console.warn('detectLoops: math.js not available; loop detection will be incomplete. npm install mathjs.');
  }
  // ... existing code ...
}

In the browser, math.js is always loaded so this only fires in CLI/test without npm install. The warning is actionable rather than silently producing wrong results.

Dependencies

Best applied after #42 (legacy evalFormula removal) since that makes the math.js dependency explicit.

Effort

~10 minutes. 1 file (js/loops.js). 3 lines added.

[zntznt]

Implementation Order

This is Phase 2 · Step 2.2 — implement after #42.

Priority: MODERATE
Phase: 2 (Correctness)
Order: 6 of 10
Depends on: #42 (makes the math.js dependency explicit after evalFormula legacy fallback is removed)
Effort: ~10 minutes