fix(javascript): analyze sources containing empty string literals

A single legal empty literal such as `fetch('')`, `require('')`,
`bus.on('', f)`, `localStorage.getItem('')`, or `ipcMain.handle('', f)`
made the whole application analysis fail with `unreadable_output`: the
literal became an application-graph observation label, an artifact-local
identity key, or a semantic node label, all of which must be nonempty.

Normalize display at the two graph construction seams instead of at each
producer: `JavaScriptArtifactGraphAccumulator.addNode` and
`constructSemanticGraphNode` show the empty value as `""` via a shared
`javascriptDisplayText` helper. Observation and node properties keep the
exact empty value. This replaces the per-site `semanticNameLabel` calls.

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

src/application/JavaScriptApplicationEmptyLiterals.test.ts

@@ -0,0 +1,73 @@
+import { writeFile } from "node:fs/promises";
+import { join } from "node:path";
+
+import { expect, it } from "vitest";
+
+import { createTestTempDirectory } from "../../tests/fixtures/temporaryDirectory.js";
+import { javascriptApplicationAnalysisResultSchema } from "../domain/javascriptApplicationAnalysis.js";
+import { analyzeJavaScriptApplication } from "./JavaScriptApplicationService.js";
+
+const analyzeSource = async (source: string) => {
+  const inputPath = await createTestTempDirectory("rea-js-empty-literal-");
+  await writeFile(join(inputPath, "app.js"), `${source}\n`);
+  const result = await analyzeJavaScriptApplication({
+    input_path: inputPath,
+    format: "directory",
+  });
+  if (!result.ok)
+    throw new Error(`Expected analysis success: ${result.error.message}`);
+  return javascriptApplicationAnalysisResultSchema.parse(
+    result.value.normalized_result,
+  );
+};
+
+it.each([
+  "fetch('');",
+  "new WebSocket('');",
+  "navigator.serviceWorker.register('');",
+  "new Worker('');",
+  "const x = require('');",
+  "import y from ''; y();",
+  "import('');",
+  "localStorage.getItem('');",
+  "localStorage.setItem('', 1);",
+  "indexedDB.open('');",
+  "win.loadFile('');",
+  "win.loadURL('');",
+  "app.get('', handler);",
+  "process.on('', () => 1);",
+  "const { EventEmitter } = require('events'); new EventEmitter().on('', () => 1);",
+  "const { spawn } = require('child_process'); spawn('/bin/x').on('', () => 1);",
+  "const { ipcMain } = require('electron'); ipcMain.handle('', () => 1);",
+  "const { ipcRenderer } = require('electron'); ipcRenderer.invoke('');",
+  "const { contextBridge } = require('electron'); contextBridge.exposeInMainWorld('', {});",
+])("analyzes the legal empty string literal in %s", async (source) => {
+  await expect(analyzeSource(source)).resolves.toBeDefined();
+});
+
+it("displays empty literals as nonempty text while retaining exact values", async () => {
+  const output = await analyzeSource(
+    "fetch(''); fetch('/api'); process.on('', () => 1);",
+  );
+  const endpoints = output.graph.nodes
+    .filter(({ kind }) => kind === "endpoint")
+    .map(({ identity, observations }) => ({
+      key: identity.strategy === "artifact-local-key" ? identity.key : null,
+      labels: observations.map(({ label }) => label),
+      values: observations.map(({ properties }) => properties.value),
+    }));
+  expect(endpoints).toEqual(
+    expect.arrayContaining([
+      { key: '""', labels: ['""'], values: [""] },
+      { key: "/api", labels: ["/api"], values: ["/api"] },
+    ]),
+  );
+  expect(
+    output.semantic_graph?.nodes
+      .filter(({ kind }) => kind === "event")
+      .map(({ label, properties }) => ({
+        label,
+        eventName: properties.event_name,
+      })),
+  ).toEqual([{ label: '""', eventName: "" }]);
+});