fix: NoisePrototypeBank degeneracy guard — fix flaky smart-extractor-branches test

src/noise-prototypes.ts

@@ -83,6 +83,23 @@ export class NoisePrototypeBank {
         }
         this.builtinCount = this.vectors.length;
         this._initialized = true;
+
+        // Degeneracy check: if all prototype vectors are nearly identical, the
+        // embedding model does not produce discriminative outputs (e.g. a
+        // deterministic mock that ignores text).  In that case the noise bank
+        // would flag every input as noise, so we disable ourselves.
+        if (this.vectors.length >= 2) {
+            const sim = cosine(this.vectors[0], this.vectors[1]);
+            if (sim > 0.98) {
+                this.debugLog(
+                    `noise-prototype-bank: degenerate embeddings detected (pairwise cosine=${sim.toFixed(4)}), disabling noise filter`,
+                );
+                this._initialized = false;
+                this.vectors = [];
+                return;
+            }
+        }
+
         this.debugLog(
             `noise-prototype-bank: initialized with ${this.builtinCount} built-in prototypes`,
         );