fix(server): canonicalize Antigravity file paths

apps/server/src/provider/AntigravityInstallation.test.ts

@@ -702,8 +702,9 @@ it.layer(NodeServices.layer)("Antigravity installation", (it) => {
         source: "managed",
         version: previousVersion,
       });
+      const canonicalExternalExecutable = yield* fs.realPath(externalExecutable);
       expect(yield* installation.resolve(externalExecutable)).toMatchObject({
-        executablePath: externalExecutable,
+        executablePath: canonicalExternalExecutable,
         source: "override",
         managedVersionDirectory: null,
       });
@@ -724,7 +725,7 @@ it.layer(NodeServices.layer)("Antigravity installation", (it) => {
       yield* installation.remove();
       expect(yield* installation.resolve()).toMatchObject({
         source: "path",
-        executablePath: externalExecutable,
+        executablePath: canonicalExternalExecutable,
       });
       const isolated = yield* makeHarness({ baseDir });
       expect(yield* isolated.installation.resolve().pipe(Effect.flip)).toMatchObject({
@@ -734,11 +735,11 @@ it.layer(NodeServices.layer)("Antigravity installation", (it) => {
         yield* isolated.installation.resolve(undefined, { PATH: externalDirectory }),
       ).toMatchObject({
         source: "path",
-        executablePath: externalExecutable,
+        executablePath: canonicalExternalExecutable,
       });
       expect(
         yield* isolated.installation.resolve("agy_acp_server.par", { PATH: externalDirectory }),
-      ).toMatchObject({ source: "override", executablePath: externalExecutable });
+      ).toMatchObject({ source: "override", executablePath: canonicalExternalExecutable });
     }),
   );
 

apps/server/src/provider/Layers/AntigravityAdapter.test.ts

@@ -882,6 +882,14 @@ it.layer(layer)("AntigravityAdapter", (it) => {
       }).pipe(Effect.flip);
       expect(escape._tag).toBe("AcpRequestError");
       expect(yield* fs.exists(path.join(outside, "escape.txt"))).toBe(false);
+      yield* fs.symlink(outside, path.join(cwd, "outside-link"));
+      const symlinkEscape = yield* write({
+        sessionId: nativeSessionId,
+        path: path.join(cwd, "outside-link", "nested", "escape.txt"),
+        content: "nope",
+      }).pipe(Effect.flip);
+      expect(symlinkEscape._tag).toBe("AcpRequestError");
+      expect(yield* fs.exists(path.join(outside, "nested", "escape.txt"))).toBe(false);
       const missing = yield* read({
         sessionId: nativeSessionId,
         path: path.join(cwd, "missing.txt"),

apps/server/src/provider/Layers/AntigravityAdapter.ts

@@ -196,6 +196,27 @@ function isInsideRoot(path: Path.Path, root: string, candidate: string): boolean
   return relative === "" || (!relative.startsWith("..") && !path.isAbsolute(relative));
 }
 
+const realPathWithMissingTail = Effect.fn("AntigravityAdapter.realPathWithMissingTail")(
+  function* (input: {
+    readonly fileSystem: FileSystem.FileSystem;
+    readonly path: Path.Path;
+    readonly candidate: string;
+  }) {
+    const missingSegments: Array<string> = [];
+    let current = input.candidate;
+    while (true) {
+      const real = yield* input.fileSystem.realPath(current).pipe(Effect.option);
+      if (Option.isSome(real)) {
+        return input.path.join(real.value, ...missingSegments.reverse());
+      }
+      const parent = input.path.dirname(current);
+      if (parent === current) return input.candidate;
+      missingSegments.push(input.path.basename(current));
+      current = parent;
+    }
+  },
+);
+
 /** Resolves an agent-supplied path and rejects anything outside the session roots. */
 const resolveClientFilePath = Effect.fn("AntigravityAdapter.resolveClientFilePath")(
   function* (input: {
@@ -207,9 +228,11 @@ const resolveClientFilePath = Effect.fn("AntigravityAdapter.resolveClientFilePat
     const { path } = input;
     const resolved = path.resolve(input.requestPath);
     // Follow symlinks on the parent so a link out of the workspace cannot escape it.
-    const parent = yield* input.fileSystem
-      .realPath(path.dirname(resolved))
-      .pipe(Effect.orElseSucceed(() => path.dirname(resolved)));
+    const parent = yield* realPathWithMissingTail({
+      fileSystem: input.fileSystem,
+      path,
+      candidate: path.dirname(resolved),
+    });
     const real = path.join(parent, path.basename(resolved));
     const roots = yield* Effect.forEach(input.allowedRoots, (root) =>
       input.fileSystem.realPath(root).pipe(Effect.orElseSucceed(() => root)),