fix(javascript): retain assignment and nested-default destructuring

Share source identity and one iterative pattern walker across declarations and assignments. Traverse nested default targets without losing dependency paths, preserving existing scalar-default occurrence identities and conservative unresolved slots.

Validation: 405 focused tests across five files, including public CLI dependency Evidence. Refs #4609, #4604

src/application/javascript/JavaScriptSemanticGraphDestructuring.test.ts

@@ -0,0 +1,69 @@
+import { expect, it } from "vitest";
+import { graphForJavaScript } from "../../../tests/fixtures/javascriptSemanticGraph.js";
+
+it.each(
+  [
+    { pattern: "{ a: selected }", source: "{ a: 1 }", path: ["a"] },
+    { pattern: "[selected]", source: "[1]", path: ["0"] },
+    {
+      pattern: "{ a: [selected] = [] }",
+      source: "{ a: [1] }",
+      path: ["a", "0"],
+    },
+    {
+      pattern: "{ a: { b: selected } = {} }",
+      source: "{ a: { b: 1 } }",
+      path: ["a", "b"],
+    },
+    { pattern: "[[selected] = []]", source: "[[1]]", path: ["0", "0"] },
+  ].flatMap((pattern) =>
+    [false, true].map((assignment) => ({ ...pattern, assignment })),
+  ),
+)(
+  "retains source-property flow for $pattern, assignment=$assignment",
+  ({ pattern, source, path, assignment }) => {
+    const graph = graphForJavaScript(`
+      const source = ${source};
+      ${assignment ? `let selected; (${pattern} = source);` : `const ${pattern} = source;`}
+    `);
+    const target = graph.nodes.find(
+      (node) => node.kind === "binding" && node.label === "selected",
+    );
+    expect(target).toBeDefined();
+    const relations = graph.relations.filter(
+      (relation) =>
+        relation.relation === "destructures" &&
+        relation.target_node_id === target?.node_id,
+    );
+    expect(relations).toHaveLength(1);
+    expect(relations[0]?.resolution).toBe("resolved");
+    const slot = graph.nodes.find(
+      (node) => node.node_id === relations[0]?.source_node_id,
+    );
+    expect(slot?.properties.property_path).toEqual(path);
+  },
+);
+
+it.each(["{}", "unknownSource"])(
+  "keeps nested default source flow conservative for %s",
+  (source) => {
+    const graph = graphForJavaScript(
+      `const source = ${source}; const { a: [selected] = [1] } = source;`,
+    );
+    const target = graph.nodes.find(
+      (node) => node.kind === "binding" && node.label === "selected",
+    );
+    const relation = graph.relations.find(
+      (item) =>
+        item.relation === "destructures" &&
+        item.target_node_id === target?.node_id,
+    );
+    expect(relation).toMatchObject({ resolution: "candidate" });
+    expect(graph.unknowns).toContainEqual(
+      expect.objectContaining({
+        family: "object-flow",
+        relation_kinds: ["destructures"],
+      }),
+    );
+  },
+);