fix(javascript): leave empty application values unlabeled

A synthetic `""` label for an empty application-graph value could still
be matched by a literal `""` feature seed, which also matches the label of
a real two-quote value, so `trace_application_feature` combined
`fetch('')` with `fetch('""')`. Emit no label (`null`) for empty values;
the exact value stays in the identity and properties.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/application/JavaScriptApplicationEmptyLiterals.test.ts

@@ -5,6 +5,7 @@ import { expect, it } from "vitest";
 
 import { createTestTempDirectory } from "../../tests/fixtures/temporaryDirectory.js";
 import { javascriptApplicationAnalysisResultSchema } from "../domain/javascriptApplicationAnalysis.js";
+import { findApplicationFeatureSeeds } from "../domain/javascriptFeatureSeed.js";
 import { analyzeJavaScriptApplication } from "./JavaScriptApplicationService.js";
 
 const analyzeSource = async (
@@ -50,7 +51,7 @@ it.each([
   await expect(analyzeSource(source)).resolves.toBeDefined();
 });
 
-it("displays empty literals as nonempty text while retaining exact values", async () => {
+it("keeps exact values for empty literals without synthetic application labels", async () => {
   const output = await analyzeSource(
     "fetch(''); fetch('\"\"'); fetch('/api'); process.on('', () => 1);",
   );
@@ -61,11 +62,11 @@ it("displays empty literals as nonempty text while retaining exact values", asyn
       labels: observations.map(({ label }) => label),
       values: observations.map(({ properties }) => properties.value),
     }));
-  // The empty endpoint and a literal two-quote endpoint share display text
-  // but remain distinct nodes with exact identities.
+  // The empty endpoint has no display label, so it cannot be confused with
+  // a literal two-quote endpoint; both keep exact identities.
   expect(endpoints).toEqual(
     expect.arrayContaining([
-      { key: "", labels: ['""'], values: [""] },
+      { key: "", labels: [null], values: [""] },
       { key: '""', labels: ['""'], values: ['""'] },
       { key: "/api", labels: ["/api"], values: ["/api"] },
     ]),
@@ -128,3 +129,26 @@ it("keeps empty and two-quote source-map names distinct", async () => {
       .sort(),
   ).toEqual(["", '""']);
 });
+
+it("does not match an empty endpoint with a literal two-quote seed", async () => {
+  const output = await analyzeSource("fetch(''); fetch('\"\"');");
+  const endpoints = new Map(
+    output.graph.nodes
+      .filter(({ kind }) => kind === "endpoint")
+      .map((node) => [
+        node.node_id,
+        node.identity.strategy === "artifact-local-key"
+          ? node.identity.key
+          : null,
+      ]),
+  );
+  const matches = findApplicationFeatureSeeds(output.graph.nodes, {
+    kind: "string",
+    value: '""',
+    match: "exact",
+    case_sensitive: true,
+  }).filter(({ node_id: nodeId }) => endpoints.has(nodeId));
+  expect(matches.map(({ node_id: nodeId }) => endpoints.get(nodeId))).toEqual([
+    '""',
+  ]);
+});

src/application/JavaScriptArtifactGraphAccumulator.ts

@@ -4,7 +4,6 @@ import {
   type ApplicationEdge,
   type ApplicationNode,
 } from "../domain/javascriptApplicationGraph.js";
-import { javascriptDisplayText } from "../domain/javascriptAstValues.js";
 
 /** Deduplicate graph entities while retaining distinct evidence observations. */
 export class JavaScriptArtifactGraphAccumulator {
@@ -73,9 +72,10 @@ interface DisplayableNodeInput {
 
 /**
  * Static findings can carry legal empty strings, such as `fetch("")`,
- * `require("")`, or a source map's `sources: [""]`. Labels are nonempty display
- * text, so the empty value is shown as `""`. Identities and observation
- * properties keep the exact value, so distinct values never merge.
+ * `require("")`, or a source map's `sources: [""]`. Labels must be nonempty,
+ * so an empty value has no label rather than synthetic text that a real value
+ * could share; literal feature seeds match labels. Identities and observation
+ * properties keep the exact value.
  */
 const displayableNode = (
   input: DisplayableNodeInput,
@@ -83,9 +83,6 @@ const displayableNode = (
   ...input,
   observations: input.observations.map((observation) => ({
     ...observation,
-    label:
-      observation.label === null
-        ? null
-        : javascriptDisplayText(observation.label),
+    label: observation.label === "" ? null : observation.label,
   })),
 });