feat(javascript): retain queryable static route inventories (#6019)

src/domain/javascript/javascriptRouteResultBudget.ts

@@ -0,0 +1,51 @@
+import { jsonValueByteLength } from "../jsonValueByteLength.js";
+import type { JsonValue } from "../jsonValue.js";
+import type { JavaScriptRouteSourceFacts } from "./javascriptRouteFacts.js";
+
+/**
+ * Admit this optional facet inside the enclosing result's actual remaining
+ * serialized bytes. The serialization owner supplies the space after all
+ * existing facts and this member's key/colon/comma; no worker protocol lives here.
+ * Omission means even a capacity envelope cannot fit, never an empty measurement.
+ */
+export const fitJavaScriptRouteSourceFacts = (
+  facts: JavaScriptRouteSourceFacts,
+  availableBytes: number,
+): JavaScriptRouteSourceFacts | undefined => {
+  if (availableBytes <= 0) return undefined;
+  if (jsonValueByteLength(facts, availableBytes) <= availableBytes)
+    return facts;
+  const result: JavaScriptRouteSourceFacts = {
+    candidates: [],
+    unresolved: [],
+    capacity: {
+      kind: "result-bytes",
+      limit_bytes: availableBytes,
+      preceding_work_capacity:
+        facts.capacity === null
+          ? null
+          : facts.capacity.kind === "route-work-or-facts"
+            ? facts.capacity
+            : facts.capacity.preceding_work_capacity,
+    },
+  };
+  let bytes = jsonValueByteLength(result, availableBytes);
+  if (bytes > availableBytes) return undefined;
+  const append = <T extends JsonValue>(
+    source: readonly T[],
+    output: T[],
+  ): void => {
+    for (const fact of source) {
+      const added =
+        jsonValueByteLength(fact, availableBytes - bytes) +
+        (output.length === 0 ? 0 : 1);
+      if (bytes + added > availableBytes) break;
+      output.push(fact);
+      bytes += added;
+    }
+  };
+  // Preserve uncertainty before route candidates when a prefix must be returned.
+  append(facts.unresolved, result.unresolved);
+  append(facts.candidates, result.candidates);
+  return result;
+};