fix(sync): a default import follows the module's default when an edit moves it (#2749)

An edit that changes which declaration a module exports as its default
(`export default A` becoming `export default B` while A stays, or the
default dropped) left every reference through a default import of it on
the old declaration. A sync moves other files' edges into a changed file
onto the node that replaces each target, and an `export default` statement
is no node, so no definition delta, failed-ref retry or importer walk saw
the change. A fresh index links the new default, or nothing.

- ReferenceResolver.changedDefaultExports: for each modified JS/TS module
  that unchanged files import by default or as a namespace (an imports edge
  into its file node named for the binding), compare what the whole-name
  references through those bindings resolved to with the module's default
  now (moduleDefaultExport, the lookup resolveViaImport makes). No file is
  read; a module forwarding its default samples 8 importers' edges.
- reopenReferencesThroughChangedDefaults (module-importers.ts): when one
  moved, the edges bound before this sync resolved anything go back for
  the sweep: through every binding that reads the default (importersOf
  seeded with `default`: default imports, { default as Y },
  require('./x').default, modules passing it on), the routers'
  `layout:<binding>` references, and into the old default's own members
  (typed receivers, inherited members).

Regression test sync-default-export-change.test.ts: 6 cases comparing the
synced graph with a fresh index of the final tree; all fail on main.
Fresh indexes are byte-identical on 8 repos.

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

CHANGELOG.md

@@ -274,6 +274,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 - In JavaScript and TypeScript, an import written from the app's root with a leading slash, like bigbluebutton's `import Icon from '/imports/ui/components/common/icon/component'`, now links to the file it names when the app's `tsconfig.json` or `jsconfig.json` maps it, as `"paths": { "/*": ["*"] }` does. Before, such an import was taken for a package, so the module looked unused and every name it imports linked by name instead, often to the wrong one of several components of the same name, or to nothing. Re-index projects that import this way after upgrading.
 - In JavaScript and TypeScript, a call whose callee is not a name, like an immediately invoked function `(() => { … })()`, a curried call such as `connect(mapState)(View)`, `handlers[type]()` or `(0, fn)()`, no longer stores the callee's whole source text as the name of a reference that nothing in the project can answer. A single immediately invoked function could leave its entire body in the index that way. The calls inside such a callee, and the inner call of a curried one, are still recorded. A call through parentheses, a cast or a non-null assertion, like `(fn)()`, `(fn as F)()` or `fn!()`, now links to `fn` exactly as `fn()` does, so a parameter named `fn` no longer links to a same-named property elsewhere in the project. In TypeScript, a call with type arguments behind an operator, like `!settings.get<boolean>('X')` or `void apiRequest<Status>()`, now links to what it calls, as `await load<T>()` already did.
 - In JavaScript, TypeScript, Python, Go, Rust, Java and Kotlin, a function named in the value of a top-level constant or variable, or of a class field, like `const routes = { home }`, `HANDLERS = {"home": home}`, a Go `map[string]func()` table, a Rust `static` list of functions, `static handlers = { click: onClick }`, a Java `List.of(Registry::home)` field or a Kotlin `listOf(::home)` property, is now referenced once, by the constant, variable, field or property that holds it. The file or class around it no longer also shows up as a second reference from the same place, so a function's callers and impact list each table once.
+- `codegraph sync` and the file watcher now follow an edit that changes which declaration a module exports as its default, like `export default A` becoming `export default B` while `A` stays, or the module dropping its default. References through `import Y from './x'`, `{ default as Y }`, `require('./x').default`, a barrel that passes the default on or a route that renders it as a layout, and calls on a value typed by it, now link to the new default, or stay unlinked, as a fresh index has them. Before, they kept pointing at the old declaration until the importing file changed or the project was indexed again.
 
 ## [1.6.2] - 2026-10-03
 

__tests__/sync-default-export-change.test.ts

@@ -0,0 +1,207 @@
+/**
+ * A sync re-links what a default import reads when the module's default changes.
+ *
+ * `import Y from './x'; new Y()` resolves to whatever `x` exports as its
+ * default. When an edit makes that another declaration (`export default A`
+ * becomes `export default B`) or stops exporting one, while the old default
+ * stays declared, a sync moved the edges other files made into `x` onto the
+ * node that replaces each old target. That is still `A`, so `new Y()` kept
+ * linking `A` where a full index links `B` (or nothing). An `export default`
+ * statement is no node, so neither the definition delta (CG-33) nor the
+ * failed-reference retry (#1240, #2450) saw it change.
+ *
+ * Each case indexes the first tree, edits it, syncs, and compares the graph
+ * with a full index of the final tree in a folder of its own (#2411).
+ */
+import { describe, it, expect, afterEach, vi } from 'vitest';
+import * as fs from 'fs';
+import * as os from 'os';
+import * as path from 'path';
+import CodeGraph from '../src/index';
+import { DatabaseConnection, getDatabasePath } from '../src/db';
+import { QueryBuilder } from '../src/db/queries';
+import { ReferenceResolver } from '../src/resolution';
+
+type Files = Record<string, string>;
+
+const run = '{ static create() { return 1; } run(): number { return 1; } }';
+
+/** Every way another file reaches `src/x.ts`'s default export, and a named import that must stay put. */
+const READERS: Files = {
+  'src/y.ts': "import Y from './x';\nexport function make(): unknown { return new Y(); }\nexport function build(): unknown { return Y.create(); }\nexport let held: Y | undefined;\n",
+  'src/w.ts': "import { default as W } from './x';\nexport function wrap(): unknown { return new W(); }\n",
+  'src/r.ts': "export function load(): unknown { const R = require('./x').default; return new R(); }\n",
+  'src/n.ts': "import { A } from './x';\nexport function named(): unknown { return new A(); }\n",
+  // A value typed by the default, and a subclass of it, reach its members by name only.
+  'src/t.ts': "import T from './x';\nexport function typed(v: T): number { return v.run(); }\n",
+  'src/s.ts': "import S from './x';\nexport class Sub extends S { go(): number { return this.run(); } }\n",
+};
+
+let roots: string[] = [];
+let graphs: CodeGraph[] = [];
+
+afterEach(() => {
+  vi.restoreAllMocks();
+  for (const graph of graphs) graph.close();
+  graphs = [];
+  for (const root of roots) fs.rmSync(root, { recursive: true, force: true });
+  roots = [];
+});
+
+function tempRoot(): string {
+  const root = fs.mkdtempSync(path.join(os.tmpdir(), 'cg-sync-default-'));
+  roots.push(root);
+  return root;
+}
+
+function write(root: string, files: Files): void {
+  for (const [file, text] of Object.entries(files)) {
+    fs.mkdirSync(path.dirname(path.join(root, file)), { recursive: true });
+    fs.writeFileSync(path.join(root, file), text);
+  }
+}
+
+async function index(root: string): Promise<CodeGraph> {
+  const graph = await CodeGraph.init(root, { index: true });
+  graphs.push(graph);
+  return graph;
+}
+
+/** Every edge by its ends' natural keys, and every reference left unresolved. */
+function stateOf(root: string, graph: CodeGraph): string[] {
+  const keys = new Map(
+    graph.getFiles()
+      .flatMap((file) => graph.getNodesInFile(file.path))
+      .map((n) => [n.id, `${n.kind} ${n.filePath}:${n.qualifiedName}:${n.startLine}`] as const)
+  );
+  const edges = graph.getOutgoingEdgesFrom([...keys.keys()])
+    .map((e) => `${e.kind} ${keys.get(e.source)} -> ${keys.get(e.target) ?? e.target} @${e.line}:${e.column} ${JSON.stringify(e.metadata ?? {})}`);
+  const db = DatabaseConnection.open(getDatabasePath(root));
+  try {
+    const refs = (db.getDb()
+      .prepare('SELECT reference_name, reference_kind, file_path, line, col, status, name_tail FROM unresolved_refs')
+      .all() as Array<Record<string, unknown>>)
+      .map((r) => `ref ${r.file_path}:${r.line}:${r.col} ${r.reference_kind} ${r.reference_name} ${r.status} ${r.name_tail}`);
+    return [...edges, ...refs].sort();
+  } finally {
+    db.close();
+  }
+}
+
+/** Where each reference to `refName` landed: `<source> -> <target kind> <file>::<qualified name>`. */
+function targetsOf(graph: CodeGraph, refName: string): string[] {
+  const ids = graph.getFiles().flatMap((file) => graph.getNodesInFile(file.path)).map((n) => n.id);
+  return graph.getOutgoingEdgesFrom(ids)
+    .filter((e) => e.metadata?.refName === refName && e.kind !== 'imports')
+    .map((e) => {
+      const target = graph.getNode(e.target)!;
+      return `${graph.getNode(e.source)!.name} -> ${target.kind} ${target.filePath}::${target.qualifiedName}`;
+    })
+    .sort();
+}
+
+/** Index `before`, write `after` over it, sync; return the graph and what a full index of `after` holds. */
+async function syncEdit(before: Files, after: Files): Promise<{ root: string; graph: CodeGraph; full: string[]; modified: number }> {
+  const root = tempRoot();
+  write(root, before);
+  const graph = await index(root);
+  write(root, after);
+  const result = await graph.sync();
+  const fullRoot = tempRoot();
+  write(fullRoot, { ...before, ...after });
+  const full = stateOf(fullRoot, await index(fullRoot));
+  return { root, graph, full, modified: result.filesModified };
+}
+
+describe('sync re-links default-import readers when the module default changes', () => {
+  it('when `export default` names another declaration', async () => {
+    const reopened = vi.spyOn(QueryBuilder.prototype, 'replaceResolutionEdgesWithUnresolvedRefs');
+    const before = { ...READERS, 'src/x.ts': `export class A ${run}\nexport class B ${run}\nexport default A;\n` };
+    const after = { 'src/x.ts': `export class A ${run}\nexport class B ${run}\nexport default B;\n` };
+    const { root, graph, full, modified } = await syncEdit(before, after);
+    expect(modified).toBe(1);
+    // What reads the default went back, and what reaches the old default's
+    // members; not the named import, which reads A as before.
+    expect(reopened.mock.calls.flatMap(([, refs]) => refs.map((ref) => ref.referenceName)).sort())
+      .toEqual(['R', 'S', 'T', 'W', 'Y', 'Y', 'Y.create', 'run', 'v.run']);
+    expect(targetsOf(graph, 'Y')).toEqual(['held -> class src/x.ts::B', 'make -> class src/x.ts::B']);
+    expect(targetsOf(graph, 'Y.create')).toEqual(['build -> method src/x.ts::B::create']);
+    expect(targetsOf(graph, 'W')).toEqual(['wrap -> class src/x.ts::B']);
+    expect(targetsOf(graph, 'R')).toEqual(['load -> class src/x.ts::B']);
+    expect(targetsOf(graph, 'v.run')).toEqual(['typed -> method src/x.ts::B::run']);
+    expect(targetsOf(graph, 'S')).toEqual(['Sub -> class src/x.ts::B']);
+    // The named import still reads A.
+    expect(targetsOf(graph, 'A')).toEqual(['named -> class src/x.ts::A']);
+    expect(stateOf(root, graph)).toEqual(full);
+    expect(graph.getPendingReferenceCount()).toBe(0);
+  }, 120_000);
+
+  it('when a route renders the default as its layout', async () => {
+    const root = (dflt: string): Files => ({
+      'src/root.tsx': `export function AppRoot() { return null; }\nexport function Shell() { return null; }\nexport default ${dflt};\n`,
+    });
+    const before = {
+      'package.json': JSON.stringify({ name: 'app', dependencies: { react: '^18', 'react-router-dom': '^6' } }),
+      'src/router.tsx': "import { createBrowserRouter } from 'react-router-dom';\nimport { default as AppRoot } from './root';\nimport { One } from './one';\n" +
+        "export const router = createBrowserRouter([\n  {\n    path: '/app',\n    element: <AppRoot />,\n    children: [{ path: 'one', element: <One /> }],\n  },\n]);\n",
+      'src/one.tsx': 'export function One() { return null; }\n',
+      ...root('AppRoot'),
+    };
+    const { root: dir, graph, full } = await syncEdit(before, root('Shell'));
+    expect(targetsOf(graph, 'layout:AppRoot').every((t) => t.endsWith('::Shell'))).toBe(true);
+    expect(stateOf(dir, graph)).toEqual(full);
+  }, 120_000);
+
+  it('when the default declaration moves to another class', async () => {
+    const before = { ...READERS, 'src/x.ts': `export default class A ${run}\nexport class B ${run}\n` };
+    const after = { 'src/x.ts': `export default class B ${run}\nexport class A ${run}\n` };
+    const { root, graph, full } = await syncEdit(before, after);
+    expect(targetsOf(graph, 'Y')).toEqual(['held -> class src/x.ts::B', 'make -> class src/x.ts::B']);
+    expect(stateOf(root, graph)).toEqual(full);
+  }, 120_000);
+
+  it('when the module stops exporting a default', async () => {
+    // Without `src/n.ts`: `{ A }` names a class exported only as the default,
+    // which no import of it reaches, so only a name match ever linked it.
+    const defaultReaders = Object.fromEntries(Object.entries(READERS).filter(([file]) => file !== 'src/n.ts'));
+    const before = { ...defaultReaders, 'src/x.ts': `export const VERSION = 1;\nclass A ${run}\nexport default A;\n` };
+    const after = { 'src/x.ts': `export const VERSION = 1;\nclass A ${run}\n` };
+    const { root, graph, full } = await syncEdit(before, after);
+    expect(targetsOf(graph, 'Y')).toEqual([]);
+    expect(stateOf(root, graph)).toEqual(full);
+  }, 120_000);
+
+  it('when a module forwards another module\'s default', async () => {
+    const lib = (from: string): Files => ({ 'src/lib/index.ts': `export { default } from './${from}';\n` });
+    const before = {
+      'src/lib/a.ts': `export default class A ${run}\n`,
+      'src/lib/b.ts': `export default class B ${run}\n`,
+      'src/y.ts': "import Y from './lib';\nexport function make(): unknown { return new Y(); }\n",
+      ...lib('a'),
+    };
+    const { root, graph, full } = await syncEdit(before, lib('b'));
+    expect(targetsOf(graph, 'Y')).toEqual(['make -> class src/lib/b.ts::B']);
+    expect(stateOf(root, graph)).toEqual(full);
+  }, 120_000);
+
+  it('and puts nothing back when an edit leaves the default alone', async () => {
+    const moved = vi.spyOn(ReferenceResolver.prototype, 'changedDefaultExports');
+    const before = {
+      ...READERS,
+      'src/x.ts': `export class A ${run}\nexport class B ${run}\nexport default A;\n`,
+      // A default that is an alias: a call through it links the function it names.
+      'src/alias.ts': 'function impl(): number { return 1; }\nconst go = impl;\nexport default go;\n',
+      'src/use-alias.ts': "import start from './alias';\nexport function call(): number { return start(); }\n",
+    };
+    const after = {
+      'src/x.ts': `export class A { static create() { return 2; } run(): number { return 2; } }\nexport class B ${run}\nexport default A;\n`,
+      'src/alias.ts': 'function impl(): number { return 2; }\nconst go = impl;\nexport default go;\n',
+    };
+    const { root, graph, full } = await syncEdit(before, after);
+    expect(targetsOf(graph, 'start')).toEqual(['call -> function src/alias.ts::impl']);
+    expect(moved).toHaveBeenCalledTimes(1);
+    expect(moved.mock.results[0]!.value).toEqual([]);
+    expect(targetsOf(graph, 'Y')).toEqual(['held -> class src/x.ts::A', 'make -> class src/x.ts::A']);
+    expect(stateOf(root, graph)).toEqual(full);
+  }, 120_000);
+});

src/db/queries.ts

@@ -3106,7 +3106,7 @@ export class QueryBuilder {
    */
   getCrossFileIncomingEdgesWithTarget(
     filePath: string
-  ): Array<Edge & { targetName: string; targetKind: NodeKind; sourceFilePath: string; sourceLanguage: Language }> {
+  ): Array<Edge & { edgeId: number; targetName: string; targetKind: NodeKind; sourceFilePath: string; sourceLanguage: Language }> {
     const sql = `SELECT e.*, tgt.name AS target_name, tgt.kind AS target_kind,
         src.file_path AS source_file_path, src.language AS source_language
       FROM edges e
@@ -3120,6 +3120,7 @@ export class QueryBuilder {
     >;
     return rows.map(row => ({
       ...rowToEdge(row),
+      edgeId: row.id,
       targetName: row.target_name,
       targetKind: row.target_kind,
       sourceFilePath: row.source_file_path,
@@ -3162,6 +3163,43 @@ export class QueryBuilder {
     }));
   }
 
+  /**
+   * The resolution edges into `targetIds` — every edge into one of them but
+   * `contains` and synthesized (`provenance='heuristic'`) ones — with the
+   * source file and language a resurrection needs and the file of each target.
+   */
+  getResolutionEdgesInto(
+    targetIds: readonly string[]
+  ): Array<Edge & { edgeId: number; sourceFilePath: string; sourceLanguage: Language; targetFilePath: string }> {
+    const out: Array<Edge & { edgeId: number; sourceFilePath: string; sourceLanguage: Language; targetFilePath: string }> = [];
+    const unique = [...new Set(targetIds)];
+    for (let i = 0; i < unique.length; i += SQLITE_PARAM_CHUNK_SIZE) {
+      const chunk = unique.slice(i, i + SQLITE_PARAM_CHUNK_SIZE);
+      const placeholders = chunk.map(() => '?').join(',');
+      const rows = this.db
+        .prepare(
+          `SELECT e.*, src.file_path AS source_file_path, src.language AS source_language, tgt.file_path AS target_file_path
+             FROM edges e
+             JOIN nodes src ON src.id = e.source
+             JOIN nodes tgt ON tgt.id = e.target
+            WHERE e.target IN (${placeholders})
+              AND e.kind != 'contains'
+              AND (e.provenance IS NULL OR e.provenance != 'heuristic')`
+        )
+        .all(...chunk) as Array<EdgeRow & { source_file_path: string; source_language: Language; target_file_path: string }>;
+      for (const row of rows) {
+        out.push({
+          ...rowToEdge(row),
+          edgeId: row.id,
+          sourceFilePath: row.source_file_path,
+          sourceLanguage: row.source_language,
+          targetFilePath: row.target_file_path,
+        });
+      }
+    }
+    return out;
+  }
+
   /**
    * The row ids of the failed references of `filePath` that import one of
    * `modules` or are written through one of `names` (see {@link THROUGH_NAMES}).

src/index.ts

@@ -54,7 +54,7 @@ import {
   ResolutionResult,
 } from './resolution';
 import { hasSynthesisPattern, isJsxChildCandidate } from './resolution/callback-synthesizer';
-import { createImportReader, reopenReferencesThroughAddedFiles, reopenReferencesThroughBarrels, reopenReferencesThroughDeclaredPackages } from './resolution/module-importers';
+import { createImportReader, reopenReferencesThroughAddedFiles, reopenReferencesThroughBarrels, reopenReferencesThroughChangedDefaults, reopenReferencesThroughDeclaredPackages } from './resolution/module-importers';
 import { GraphTraverser, GraphQueryManager } from './graph';
 import { findNamedCopybooks, type NamedCopybook } from './graph/cobol-copybooks';
 import { ContextBuilder, createContextBuilder } from './context';
@@ -1186,6 +1186,18 @@ export class CodeGraph {
               this.queries, importReader, this.projectRoot, result.changedFilePaths, edgesBeforeResolution
             );
             if (process.env.CODEGRAPH_SYNTH_TIMINGS && declared > 0) console.error(`[phase-timing] sync-declared-packages: ${declared} refs re-opened`);
+
+            // An edited module whose default export moved to another
+            // declaration, or went away, while the old one stayed declared:
+            // `new Y()` after `import Y from './x'` kept the old one, the node
+            // that replaced its target, and no name this sync's files carry
+            // changed. Read off the edges into the edited modules; an edit
+            // that leaves the default alone re-opens nothing.
+            const tDefaults = Date.now();
+            const movedDefaults = this.resolver.changedDefaultExports(modified, result.changedFilePaths, edgesBeforeResolution);
+            const throughDefaults = movedDefaults.length === 0 ? 0
+              : reopenReferencesThroughChangedDefaults(this.queries, importReader, movedDefaults, edgesBeforeResolution);
+            if (process.env.CODEGRAPH_SYNTH_TIMINGS) console.error(`[phase-timing] sync-default-exports: ${Date.now() - tDefaults}ms (${movedDefaults.length} defaults moved, ${throughDefaults} refs re-opened)`);
           } else {
             // No git info — use batched resolution to avoid OOM
             const unresolvedCount = this.queries.getUnresolvedReferencesCount();

src/resolution/import-resolver.ts

@@ -4430,6 +4430,31 @@ function localTypeBinding(receiver: string, ref: UnresolvedRef, context: Resolut
   return mappings.find((m) => m.localName === head);
 }
 
+/**
+ * The declaration a default import of `filePath` written in `language` binds
+ * — `X` in `import X from './x'` or `{ default as X }` — followed through the
+ * modules the file forwards its default from, or undefined when it has none.
+ * The lookup resolveViaImport makes for that binding, memoized with it.
+ */
+export function moduleDefaultExport(filePath: string, language: Language, context: ResolutionContext): Node | undefined {
+  return findExportedSymbol(filePath, { isDefault: true, isNamespace: false, exportedName: 'default', memberName: null }, language, context, new Set());
+}
+
+/** A `.js`/`.ts`-family file, the modules whose default an `export default` statement or the first exported declaration names. */
+export function isJsFamilyFile(filePath: string): boolean {
+  return JS_FAMILY_FILE.test(filePath);
+}
+
+/**
+ * Whether the name of an `imports` reference into a module's own file node is
+ * a binding the importing file holds on the module — `Y` of `import Y from
+ * './x'`, `{ default as Y }` or `import * as Y` — rather than the path it
+ * imports the module by.
+ */
+export function isModuleBindingName(name: string): boolean {
+  return IDENTIFIER.test(name);
+}
+
 const IDENTIFIER = /^[A-Za-z_$][\w$]*$/;
 /** The receiver of a direct member reference: `store` of `store.get`, none of `store.get().then` or `a.b.c`. */
 const MEMBER_RECEIVER = /^([A-Za-z_$][\w$]*)\.[A-Za-z_$][\w$]*$/;

src/resolution/index.ts

@@ -35,7 +35,7 @@ import { clearCppIncluderMemos } from './cpp-includers';
 import { clearCFeatureVariantMemos } from './c-feature-variants';
 import { clearAmbientModuleMemos, ambientModuleDeclarations } from './ambient-modules';
 import { matchShopifyThemeFile } from './shopify-themes';
-import { resolveViaImport, resolvePhpImportedStaticCall, resolvePhpQualifiedClassRef, resolveTsQualifiedTypeRef, resolveJvmImport, extractImportMappings, extractReExports, loadCppIncludeDirs, isPhpIncludePathRef, isCobolCopybookRef, isNixPathImportRef, isDartImportRef, isLuaRequireRef, isJsPathImportRef, isBoundToOutOfRepoImport, reachesAmbientModule, importBindingTail, clearImportResolverMemos, resolveImportPath, isExternalImport, ESM_IMPORT_LANGUAGES, jsModuleFile, pythonRootFingerprint, pythonReopenScope, pythonPackageImporters } from './import-resolver';
+import { resolveViaImport, resolvePhpImportedStaticCall, resolvePhpQualifiedClassRef, resolveTsQualifiedTypeRef, resolveJvmImport, extractImportMappings, extractReExports, loadCppIncludeDirs, isPhpIncludePathRef, isCobolCopybookRef, isNixPathImportRef, isDartImportRef, isLuaRequireRef, isJsPathImportRef, isBoundToOutOfRepoImport, reachesAmbientModule, importBindingTail, clearImportResolverMemos, resolveImportPath, isExternalImport, ESM_IMPORT_LANGUAGES, jsModuleFile, pythonRootFingerprint, pythonReopenScope, pythonPackageImporters, moduleDefaultExport, isJsFamilyFile, isModuleBindingName } from './import-resolver';
 import { ResolverPool, minRefsForPool, shouldEngageAdaptively } from './resolver-pool';
 import { resolveAliasBinding } from './alias-binding';
 import { detectFrameworks, getResolvingFrameworks } from './frameworks';
@@ -89,6 +89,13 @@ const CHAIN_SHAPE = /^(.+)\(\)\.(\w+)$/;
 /** PHP `$this->prop->method()` encoded as `this->prop.method` — no `()`, so CHAIN_SHAPE misses it. */
 const PHP_PROP_SHAPE = /^this->\w+\.\w+$/;
 
+/**
+ * How many files that import a changed module by default a sync reads the
+ * edges of, when the module forwards its default from another file, to see
+ * whether they still land on it (changedDefaultExports).
+ */
+const DEFAULT_READER_SAMPLE_FILES = 8;
+
 /**
  * Cache size limits. Each per-resolver cache is bounded so memory
  * stays flat on large codebases (20k+ files). Sizes were chosen to
@@ -2897,6 +2904,72 @@ export class ReferenceResolver {
     return this.queries.reopenFailedReferences(rowIds) + refs.length;
   }
 
+  /**
+   * The edited modules among `modifiedFilePaths` whose default export moved:
+   * an edit made `export default A` into `export default B`, or took the
+   * default away, while `A` stayed declared. A sync moves the edges other
+   * files made into a changed file onto the node that replaces each target, so
+   * `new Y()` after `import Y from './x'` kept `A` where a full index links
+   * `B`. An `export default` statement is no node, so neither the definition
+   * delta nor a failed-reference retry sees it change.
+   *
+   * The default a module had is read off the edges into it, with no file read:
+   * a default or namespace import of it is an `imports` edge into its file
+   * node named for the binding, and a whole-name reference through that
+   * binding (`Y`, not `Y.run`) that resolved through the import names exactly
+   * its default (a namespace binding's `NS` names the file). Only edges bound
+   * before this sync resolved anything count (up to `resolvedUpToEdgeId`), and
+   * only from files it left alone. A module that forwards its default from
+   * another file (`export { default } from './impl'`) has those edges there,
+   * so a few of its importers' are read instead. An edit that leaves the
+   * default alone, nearly every one, finds them all still on it. Each module
+   * comes with the declarations its default was (`was`), as those edges say.
+   */
+  changedDefaultExports(
+    modifiedFilePaths: readonly string[],
+    changedFilePaths: readonly string[],
+    resolvedUpToEdgeId: number,
+  ): Array<{ path: string; language: Language; was: string[] }> {
+    const fresh = new Set(changedFilePaths);
+    const moved: Array<{ path: string; language: Language; was: string[] }> = [];
+    for (const filePath of modifiedFilePaths) {
+      if (!isJsFamilyFile(filePath)) continue;
+      const bindings = new Map<string, Set<string>>();
+      for (const i of this.queries.getImportsInto(`file:${filePath}`, filePath)) {
+        if (i.refName === null || fresh.has(i.filePath) || !isModuleBindingName(i.refName)) continue;
+        const names = bindings.get(i.filePath) ?? new Set<string>();
+        names.add(i.refName);
+        bindings.set(i.filePath, names);
+      }
+      if (bindings.size === 0) continue;
+      const language = this.queries.getFileByPath(filePath)?.language;
+      if (!language) continue;
+      const readsDefault = (e: Edge & { edgeId: number; sourceFilePath: string }): boolean => {
+        const name = e.metadata?.refName;
+        return typeof name === 'string' && e.metadata?.resolvedBy === 'import' && e.edgeId <= resolvedUpToEdgeId &&
+          !e.target.startsWith('file:') && bindings.get(e.sourceFilePath)?.has(name) === true;
+      };
+      let readers: Array<Edge & { edgeId: number; sourceFilePath: string; sourceLanguage: Language }> =
+        this.queries.getCrossFileIncomingEdgesWithTarget(filePath).filter(readsDefault);
+      if (readers.length === 0) {
+        const now = moduleDefaultExport(filePath, language, this.context);
+        if (!now || now.filePath === filePath) continue;
+        readers = [...bindings].slice(0, DEFAULT_READER_SAMPLE_FILES)
+          .flatMap(([file, names]) => this.queries.getResolutionEdgesThrough(file, [...names]))
+          .filter(readsDefault);
+      }
+      const was = new Set<string>();
+      for (const e of readers) {
+        const now = moduleDefaultExport(filePath, e.sourceLanguage, this.context);
+        // A call that lands on an alias binding goes on to the callable it names (resolveOne).
+        if (now && (e.target === now.id || (e.kind === 'calls' && resolveAliasBinding(now, null, this.context)?.id === e.target))) continue;
+        was.add(e.target);
+      }
+      if (was.size > 0) moved.push({ path: filePath, language, was: [...was] });
+    }
+    return moved;
+  }
+
   /**
    * Whether a failed import could name one of `files`, the files a sync just
    * added: the test the import retry puts a crowded key's imports to

src/resolution/module-importers.ts

@@ -237,6 +237,41 @@ export function reopenReferencesThroughDeclaredPackages(
   return reopenEdges(queries, bindings, (e) => e.edgeId <= resolvedUpToEdgeId) + queries.reopenFailedReferences(failed);
 }
 
+/**
+ * Re-open, for the sync's sweep, what reads the default of any of `files`
+ * when it moved: an edit made `export default A` into `export default B`, or
+ * took the default away, while `A` stayed declared (`was`, see
+ * ReferenceResolver.changedDefaultExports). `new Y()` after `import Y from
+ * './x'` kept `A`, the node that replaced its old target. The edges bound
+ * before this sync resolved anything (up to `resolvedUpToEdgeId`) go back:
+ * - those through every binding that reads the default: a default import,
+ *   `{ default as Y }`, `require('./x').default`, the names a module passes it
+ *   on as (`export { default as Y } from './x'`), and a route rendering one
+ *   as its layout (`layout:Y`). A named import reads what it did, and a
+ *   default import's own edge links the module's file, which stays;
+ * - those into the members `A` declares, wherever they are written: a value
+ *   typed by the binding reaches them by their own name (`document.delete()`
+ *   with `document: Document`, a subclass's `this.add`). `A` itself is reached
+ *   through a binding, the default's or a named import's, which reads it still.
+ * Returns the number re-opened.
+ */
+export function reopenReferencesThroughChangedDefaults(
+  queries: QueryBuilder,
+  reader: ImportReader,
+  files: ReadonlyArray<{ path: string; language: Language; was: readonly string[] }>,
+  resolvedUpToEdgeId: number,
+): number {
+  const stays = (e: Edge & { edgeId: number }): boolean => e.edgeId <= resolvedUpToEdgeId && !e.target.startsWith('file:');
+  const bindings = bindingsOf(importersOf(queries, files, reader, [], new Set(['default'])), reader);
+  // React, Vue and Angular routers write a layout a route renders as `layout:<name>`.
+  for (const entry of bindings.values()) entry.names.push(...entry.names.map((name) => `layout:${name}`));
+  const reopened = reopenEdges(queries, bindings, stays);
+  const was = [...new Set(files.flatMap((file) => file.was))];
+  const members = was.length === 0 ? [] : queries.getOutgoingEdgesFrom(was, ['contains']).map((edge) => edge.target);
+  if (members.length === 0) return reopened;
+  return reopened + reopenEdgeList(queries, queries.getResolutionEdgesInto(members).filter(stays));
+}
+
 /** The languages a barrel a lazy route reads through is written in: the ES-module family. */
 const BARREL_LANGUAGES = new Set<Language>(['typescript', 'tsx', 'javascript', 'jsx']);
 
@@ -386,18 +421,20 @@ function reopenModuleEdges(queries: QueryBuilder, outranked: readonly OutrankedI
  * The files with an import statement naming one of `files`, or one of the
  * modules re-exporting from them, other than `files` themselves (going away,
  * or just resolved with the others in place); `outranked` imports name the
- * added file they now resolve to.
+ * added file they now resolve to. `names` limits what of `files` counts: all
+ * of it (null), or what they export under these names.
  */
 function importersOf(
   queries: QueryBuilder,
   files: ReadonlyArray<{ path: string; language: Language }>,
   reader: ImportReader,
   outranked: readonly OutrankedImport[] = [],
+  names: Set<string> | null = null,
 ): Importers {
   const importers: Importers = new Map();
   const changed = new Set(files.map((file) => file.path));
   const seen = new Set(changed);
-  let level: Module[] = files.filter((file) => BINDING_LANGUAGES.has(file.language)).map((file) => ({ ...file, passes: null }));
+  let level: Module[] = files.filter((file) => BINDING_LANGUAGES.has(file.language)).map((file) => ({ ...file, passes: names }));
   for (let depth = 1; level.length > 0; depth++) {
     // Per importer found here, its statements naming each module of the level.
     const naming = new Map<string, { language: Language; statements: Array<{ source: string; module: Module; onlyName?: string }> }>();
@@ -596,7 +633,7 @@ function bindingsOf(importers: Importers, reader: ImportReader): Map<string, { m
 function reopenEdges(
   queries: QueryBuilder,
   bindings: Map<string, { names: string[] }>,
-  keep: (e: { edgeId: number; targetFilePath: string }) => boolean,
+  keep: (e: Edge & { edgeId: number; targetFilePath: string }) => boolean,
 ): number {
   const edgeIds: number[] = [];
   const refs: UnresolvedReference[] = [];
@@ -614,6 +651,27 @@ function reopenEdges(
   return refs.length;
 }
 
+/**
+ * Swap `edges` for their references, one per reference: a conditional's arms
+ * are edges of one call. Returns how many references went back.
+ */
+function reopenEdgeList(queries: QueryBuilder, edges: ReadonlyArray<Edge & { edgeId: number; sourceFilePath: string; sourceLanguage: Language }>): number {
+  const edgeIds: number[] = [];
+  const refs: UnresolvedReference[] = [];
+  const sites = new Set<string>();
+  for (const edge of edges) {
+    const ref = resurrectRefFromDroppedEdge(edge);
+    if (!ref) continue;
+    edgeIds.push(edge.edgeId);
+    const site = `${ref.fromNodeId}\0${ref.referenceName}\0${ref.line}\0${ref.column}`;
+    if (sites.has(site)) continue;
+    sites.add(site);
+    refs.push(ref);
+  }
+  if (edgeIds.length > 0) queries.replaceResolutionEdgesWithUnresolvedRefs(edgeIds, refs);
+  return refs.length;
+}
+
 /** A Python file's module as a path: `shop/models.py` → 'shop/models', `shop/__init__.py` → 'shop'. Null for a top-level `__init__.py`. */
 function pythonModuleOfFile(filePath: string): string | null {
   if (!filePath.endsWith('.py') || filePath === '__init__.py') return null;