diff --git a/extensions/shared/child-session.ts b/extensions/shared/child-session.ts
index e37fc3f5..9e0f8033 100644
--- a/extensions/shared/child-session.ts
+++ b/extensions/shared/child-session.ts
@@ -173,9 +173,6 @@ function packageSourceValue(source: PackageSource) {
 
 const CHILD_DISABLED_OPENPI_EXTENSION =
   "-extensions/git-info/index.ts" as const;
-const OPENPI_GIT_INFO_EXTENSION_PATH = realpathSync.native(
-  fileURLToPath(new URL("../git-info/index.ts", import.meta.url)),
-);
 
 function canonicalExistingPath(value: string) {
   try {
@@ -185,15 +182,38 @@ function canonicalExistingPath(value: string) {
   }
 }
 
+/**
+ * ENOENT means git-info is truly absent (trimmed fork, partial install):
+ * nothing to exclude. Any other failure (permissions, symlink loops) means we
+ * cannot verify the Git-polling extension is present, so fail closed instead
+ * of running a child with an unverifiable extension.
+ */
+export function resolveGitInfoPathOrThrow(
+  resolve: (value: string) => string = realpathSync.native,
+): string | undefined {
+  try {
+    return resolve(
+      fileURLToPath(new URL("../git-info/index.ts", import.meta.url)),
+    );
+  } catch (error) {
+    if ((error as NodeJS.ErrnoException).code === "ENOENT") return undefined;
+    throw error;
+  }
+}
+
 function excludeOpenPiGitInfoExtension(
   resources: LoadExtensionsResult,
+  resolve: (value: string) => string = realpathSync.native,
 ): LoadExtensionsResult {
+  const gitInfoPath = resolveGitInfoPathOrThrow(resolve);
+  // undefined = absent (ENOENT): nothing to exclude. Non-ENOENT failures
+  // throw from resolveGitInfoPathOrThrow and fail child creation upstream.
+  if (gitInfoPath === undefined) return resources;
   return {
     ...resources,
     extensions: resources.extensions.filter(
       (extension) =>
-        canonicalExistingPath(extension.resolvedPath) !==
-        OPENPI_GIT_INFO_EXTENSION_PATH,
+        canonicalExistingPath(extension.resolvedPath) !== gitInfoPath,
     ),
   };
 }
diff --git a/tests/extensions/shared/child-session.test.ts b/tests/extensions/shared/child-session.test.ts
index 4ef5daeb..4864fc9a 100644
--- a/tests/extensions/shared/child-session.test.ts
+++ b/tests/extensions/shared/child-session.test.ts
@@ -13,7 +13,7 @@ import { syncBuiltinESMExports } from "node:module";
 import { tmpdir } from "node:os";
 import * as path from "node:path";
 import test from "node:test";
-import { fileURLToPath } from "node:url";
+import { fileURLToPath, pathToFileURL } from "node:url";
 import {
   createAgentSession,
   DefaultPackageManager,
@@ -34,6 +34,7 @@ import {
   createChildResources,
   type DisposableChildSession,
   effectiveChildToolAllowlist,
+  resolveGitInfoPathOrThrow,
   resolveStandaloneChildProjectTrust,
   shutdownAndDisposeChildSession,
 } from "../../../extensions/shared/child-session.ts";
@@ -1470,3 +1471,31 @@ test("every registered package tool is classified child-safe or excluded (fail-c
     );
   }
 });
+
+test("git-info exclusion: ENOENT degrades, other errors fail closed", async () => {
+  const enoent: NodeJS.ErrnoException = new Error("no such file");
+  enoent.code = "ENOENT";
+  // Absent (ENOENT) -> undefined, so nothing is excluded.
+  assert.equal(
+    resolveGitInfoPathOrThrow(() => {
+      throw enoent;
+    }),
+    undefined,
+  );
+  // Present -> the real path is returned for exclusion matching.
+  assert.equal(
+    resolveGitInfoPathOrThrow(() => "/repo/extensions/git-info/index.ts"),
+    "/repo/extensions/git-info/index.ts",
+  );
+  // Unverifiable (non-ENOENT) -> must throw, not silently degrade.
+  const eacces: NodeJS.ErrnoException = new Error("permission denied");
+  eacces.code = "EACCES";
+  assert.throws(
+    () =>
+      resolveGitInfoPathOrThrow(() => {
+        throw eacces;
+      }),
+    (error: unknown) => (error as NodeJS.ErrnoException).code === "EACCES",
+    "non-ENOENT realpath failures must fail closed",
+  );
+});