diff --git a/gitnexus/bench/import-target/baselines.json b/gitnexus/bench/import-target/baselines.json
index 4c8e75f9f..0dac29cea 100644
--- a/gitnexus/bench/import-target/baselines.json
+++ b/gitnexus/bench/import-target/baselines.json
@@ -164,7 +164,7 @@
         "files_small": 8000,
         "files_large": 32000,
         "path_segments": 14,
-        "probe": "github.com/org/repo0/pkg/util"
+        "probe": "example.com/mod/repo0/pkg/util"
       },
       "_measured": {
         "collide_ms": 7.15,
diff --git a/gitnexus/bench/import-target/measure.mjs b/gitnexus/bench/import-target/measure.mjs
index 61aed7775..aaf61ec83 100644
--- a/gitnexus/bench/import-target/measure.mjs
+++ b/gitnexus/bench/import-target/measure.mjs
@@ -2016,8 +2016,8 @@ const HEAP_PROBE_TARGET = {
   // budgeted ones above: a spelling `uniqueTarget` already mints for that language, and
   // one that MISSES, so the reading is the index and the cascade runs to the
   // end. Chosen from the miss family that reaches furthest into each cascade:
-  //   - `go` takes the GOPATH fallback, one `filesDirectlyInPkgDir` per path
-  //     segment, which is the leg that forces `PackageDirIndex`;
+  //   - `go` names a missing package inside GO_MODULE, which reaches the
+  //     package-directory lookup and forces `PackageDirIndex`;
   //   - `dart` is an external package, so BOTH candidate paths miss and both
   //     walk the basename bucket to completion;
   //   - `kotlin` misses in `suffixByStem`, the map its four-tier cascade builds;
@@ -2028,7 +2028,7 @@ const HEAP_PROBE_TARGET = {
   //     `javascript` and `c` arms they are excluded as duplicates OF, so the
   //     bound compares like with like. `vue`'s is bare rather than `@/…`
   //     because the alias branch rewrites to `src/` and would resolve.
-  go: 'github.com/org/repo0/pkg/util',
+  go: 'example.com/mod/repo0/pkg/util',
   dart: 'package:ext0/src/thing.dart',
   kotlin: 'com.ghost0.deep.Missing',
   cobol: 'VENDOR0',
diff --git a/gitnexus/src/core/ingestion/languages/go/import-target.ts b/gitnexus/src/core/ingestion/languages/go/import-target.ts
index 847af0c09..14d9e2d48 100644
--- a/gitnexus/src/core/ingestion/languages/go/import-target.ts
+++ b/gitnexus/src/core/ingestion/languages/go/import-target.ts
@@ -16,9 +16,9 @@ import { perFileSet } from '../../import-resolvers/per-file-set.js';
  * IMPORTS edge fanout AND binding materialization for every exported symbol in
  * the package.
  *
- * Strategy (first match wins):
- *   1. go.mod-based: strip module prefix, match package directory
- *   2. Non-go.mod / GOPATH: progressively shorter directory suffixes
+ * Strategy:
+ *   1. With go.mod: resolve only imports owned by that module
+ *   2. Without go.mod / GOPATH: progressively shorter directory suffixes
  */
 export function resolveGoImportTarget(
   targetRaw: string,
@@ -30,11 +30,14 @@ export function resolveGoImportTarget(
 
   const goModule = resolutionConfig as GoModuleConfig | undefined;
 
-  // 1) go.mod-based: strip module prefix, match directory
-  if (
-    goModule != null &&
-    (targetRaw === goModule.modulePath || targetRaw.startsWith(`${goModule.modulePath}/`))
-  ) {
+  // 1) go.mod is authoritative: only this module's exact path or subpackages
+  //    can name files in the workspace. Standard-library and third-party
+  //    imports must not fall through to the suffix matcher below.
+  if (goModule != null) {
+    const ownedByModule =
+      targetRaw === goModule.modulePath || targetRaw.startsWith(`${goModule.modulePath}/`);
+    if (!ownedByModule) return null;
+
     const relativePkg =
       targetRaw === goModule.modulePath ? '' : targetRaw.slice(goModule.modulePath.length + 1); // e.g. "internal/models"
     const files =
@@ -42,6 +45,7 @@ export function resolveGoImportTarget(
         ? findRootPackageFiles(allFilePaths)
         : findAllFilesInPkgDir(allFilePaths, relativePkg);
     if (files.length > 0) return files;
+    return null;
   }
 
   // 2) Non-go.mod / GOPATH: progressively shorter directory suffixes.
@@ -66,10 +70,9 @@ function isGoPackageFile(normalized: string): boolean {
  * Package index over the file set, memoized on the Set's identity (#2877).
  *
  * Every leg above used to walk all of `allFilePaths`, and the GOPATH fallback
- * walks once per path segment — so a single unresolved import (which is most of
- * them: stdlib and third-party module paths run the whole cascade to completion
- * before returning null) cost several full workspace scans, making resolution
- * O(imports × files).
+ * walks once per path segment — so without go.mod a single unresolved stdlib or
+ * third-party import ran the whole cascade before returning null and cost
+ * several full workspace scans, making resolution O(imports × files).
  *
  * The orchestrator hands the same Set to every import in a pass, so the index
  * is built once per run. `resolveGoImportTarget` must therefore never copy the
diff --git a/gitnexus/test/integration/go-import-index-reuse.test.ts b/gitnexus/test/integration/go-import-index-reuse.test.ts
index ac798e471..44cd9dec5 100644
--- a/gitnexus/test/integration/go-import-index-reuse.test.ts
+++ b/gitnexus/test/integration/go-import-index-reuse.test.ts
@@ -60,10 +60,8 @@ describe('Go import resolution — index reuse across imports (#2877)', () => {
     const resolved: (string | readonly string[] | null)[] = [];
 
     for (let i = 0; i < 200; i++) {
-      // Three shapes that between them reach every leg: the module-relative
-      // package leg, the root-package leg, and a third-party path that misses
-      // and so runs the whole GOPATH suffix cascade to completion — the case
-      // that used to cost one full workspace scan per path segment.
+      // Three module-mode shapes: the module-relative package leg, the
+      // root-package leg, and a third-party path rejected by the go.mod gate.
       resolved.push(
         resolveImportTarget('example.com/mod/internal/models', FROM_FILE, files, GO_MODULE),
       );
@@ -83,6 +81,19 @@ describe('Go import resolution — index reuse across imports (#2877)', () => {
     expect(resolved[2]).toBeNull();
   });
 
+  it('rejects foreign and stdlib imports before building the package index', () => {
+    const files = buildWorkspace(300);
+
+    for (let i = 0; i < 200; i++) {
+      expect(
+        resolveImportTarget(`github.com/vendor/dep${i}/sub`, FROM_FILE, files, GO_MODULE),
+      ).toBeNull();
+      expect(resolveImportTarget('fmt', FROM_FILE, files, GO_MODULE)).toBeNull();
+    }
+
+    expect(files.scans).toBe(0);
+  });
+
   it('a distinct file set gets its own index (no stale cross-run reuse)', () => {
     expectDistinctFileSetsGetOwnIndex({
       resolveImportTarget,
diff --git a/gitnexus/test/unit/scope-resolution/external-import-conformance.test.ts b/gitnexus/test/unit/scope-resolution/external-import-conformance.test.ts
index b7dd03473..42dbf9799 100644
--- a/gitnexus/test/unit/scope-resolution/external-import-conformance.test.ts
+++ b/gitnexus/test/unit/scope-resolution/external-import-conformance.test.ts
@@ -326,7 +326,6 @@ const CASES: ReadonlyMap<SupportedLanguages, ConformanceCase> = new Map([
  */
 const KNOWN_GAPS: ReadonlyMap<SupportedLanguages, string> = new Map<SupportedLanguages, string>([
   [SupportedLanguages.Kotlin, '`org.junit.Assert` -> `src/main/kotlin/vendor/Assert.kt`'],
-  [SupportedLanguages.Go, '`github.com/vendor/dep/internal/models` -> `internal/models/user.go`'],
   [SupportedLanguages.Ruby, '`rails/generators` -> `lib/generators.rb`'],
   [SupportedLanguages.PHP, '`Vendor\\Ghost\\Missing` -> `lib/Legacy/Missing.php`'],
   [SupportedLanguages.Dart, '`package:http/http.dart` -> `lib/http.dart`'],
diff --git a/gitnexus/test/unit/scope-resolution/go/go-imports.test.ts b/gitnexus/test/unit/scope-resolution/go/go-imports.test.ts
index 1e1e715b3..c3e4eac26 100644
--- a/gitnexus/test/unit/scope-resolution/go/go-imports.test.ts
+++ b/gitnexus/test/unit/scope-resolution/go/go-imports.test.ts
@@ -126,6 +126,31 @@ describe('Go import target resolution', () => {
     ]);
   });
 
+  it.each(['github.com/vendor/dep/internal/models', 'fmt', 'example.com/modular/internal/models'])(
+    'rejects imports outside the go.mod module: %s',
+    (targetRaw) => {
+      const result = resolveGoImportTarget(
+        targetRaw,
+        'main.go',
+        new Set(['internal/models/user.go', 'main.go']),
+        { modulePath: 'example.com/mod' },
+      );
+
+      expect(result).toBeNull();
+    },
+  );
+
+  it('treats a semantic import-version suffix as part of the module path', () => {
+    const result = resolveGoImportTarget(
+      'example.com/mod/v2/internal/models',
+      'cmd/app/main.go',
+      new Set(['internal/models/user.go']),
+      { modulePath: 'example.com/mod/v2' },
+    );
+
+    expect(result).toEqual(['internal/models/user.go']);
+  });
+
   it('rejects single-segment GOPATH suffix that collides with a local dir', () => {
     // "github.com/other/team/pkg" suffix-stripped would eventually
     // reach "pkg" which matches the local pkg/ dir — but we require
diff --git a/gitnexus/test/unit/scope-resolution/import-target-index-parity.test.ts b/gitnexus/test/unit/scope-resolution/import-target-index-parity.test.ts
index 311ca8aa2..560a5daca 100644
--- a/gitnexus/test/unit/scope-resolution/import-target-index-parity.test.ts
+++ b/gitnexus/test/unit/scope-resolution/import-target-index-parity.test.ts
@@ -99,16 +99,17 @@ function legacyResolveGoImportTarget(
   modulePath: string | undefined,
 ): string | readonly string[] | null {
   if (!targetRaw) return null;
-  if (
-    modulePath !== undefined &&
-    (targetRaw === modulePath || targetRaw.startsWith(`${modulePath}/`))
-  ) {
+  if (modulePath !== undefined) {
+    const ownedByModule = targetRaw === modulePath || targetRaw.startsWith(`${modulePath}/`);
+    if (!ownedByModule) return null;
+
     const relativePkg = targetRaw === modulePath ? '' : targetRaw.slice(modulePath.length + 1);
     const files =
       relativePkg === ''
         ? legacyFindRootPackageFiles(allFilePaths)
         : legacyFindAllFilesInPkgDir(allFilePaths, relativePkg);
     if (files.length > 0) return files;
+    return null;
   }
   const parts = targetRaw.split('/').filter(Boolean);
   for (let i = 0; i < parts.length - 1; i++) {
@@ -717,7 +718,7 @@ describe('import-target index hoist — output parity with the pre-change scans'
     for (let repo = 0; repo < 40; repo++) {
       const go = corpus(repo, '.go', 6 + (repo % 25));
       for (const t of GO_TARGETS) {
-        if (resolveGoImportTarget(t, 'main.go', go, { modulePath: 'example.com/mod' }) !== null) {
+        if (resolveGoImportTarget(t, 'main.go', go) !== null) {
           hits.go++;
         }
       }
@@ -782,7 +783,7 @@ describe('import-target index hoist — built once per file set, not once per im
   it('go builds one index for many imports (#2877)', () => {
     const files = countingCorpus(1, '.go');
     for (let i = 0; i < 200; i++) {
-      resolveGoImportTarget(`github.com/org/repo${i}/pkg`, 'main.go', files, {
+      resolveGoImportTarget(`example.com/mod/repo${i}/pkg`, 'main.go', files, {
         modulePath: 'example.com/mod',
       });
     }