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reflections/2026-06-05-falsy-coercion.md

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+# Reflection: `||` vs `??` Falsy Coercion Bug
+
+> Date: 2026-06-05 | Severity: P1 | Recurrence: 2
+
+## Context
+Cross-Agent Certification (PR-30) — Fleet score ranking. Using `order[status] || 6` for certification ranking.
+
+## Root Cause
+JavaScript `||` operator treats `0` as falsy. When `order["healthy"] = 0`, `order["healthy"] || 6` evaluates to `6`, pushing healthy agents to bottom of ranking instead of top. The certification result was reversed — healthy fleets got low scores.
+
+## Fix
+Changed `order[status] || 6` → `order[status] ?? 6`. Nullish coalescing (`??`) only triggers on `null`/`undefined`, not on `0`.
+
+## Pattern Class
+**JS/TS Falsy Coercion Trap** — `||` treats `0`, `""`, `false` as falsy. Use `??` for numeric/boolean defaults.
+
+## Future Trigger
+- Any JS/TS code writing numeric defaults
+- Any ranking/scoring/ordering logic
+- Any code with `value || default` where value can legitimately be 0
+
+## Checklist
+- [ ] Grep all `||` in scoring/ranking/ordering code → replace with `??` if value can be 0
+- [ ] For all numeric defaults: `||` → `??`
+- [ ] Add `||` vs `??` check to JS/TS Domain Checklist
+
+## Recurrence Count
+2 — previously hit in Agent Evolution FK index scoring (same pattern: `count || 0` skipped real zeros)