diff --git a/apps/server/src/project/AgentSessionScanner.test.ts b/apps/server/src/project/AgentSessionScanner.test.ts
index ce1830b8c5710..0844e3cd71834 100644
--- a/apps/server/src/project/AgentSessionScanner.test.ts
+++ b/apps/server/src/project/AgentSessionScanner.test.ts
@@ -22,11 +22,13 @@ import * as FileSystem from "effect/FileSystem";
 import * as Layer from "effect/Layer";
 import * as Option from "effect/Option";
 import * as Path from "effect/Path";
+import * as Queue from "effect/Queue";
 import * as Schema from "effect/Schema";
 import * as Stream from "effect/Stream";
 import * as TestClock from "effect/testing/TestClock";
 
 import * as ServerConfig from "../config.ts";
+import * as ProcessRunner from "../processRunner.ts";
 import * as ProjectStore from "../orchestration-v2/ProjectStore.ts";
 import * as ServerSettings from "../serverSettings.ts";
 import * as AgentSessionScanner from "./AgentSessionScanner.ts";
@@ -56,10 +58,16 @@ interface ScannerTestInput {
   readonly importedWorkspaceRoots?: ReadonlyArray<string>;
   readonly configBaseDir?: string;
   readonly providerInstances?: ContractServerSettings["providerInstances"];
+  readonly processRunner?: Layer.Layer<ProcessRunner.ProcessRunner>;
 }
 
 const layerScannerTest = (input: ScannerTestInput) =>
-  AgentSessionScanner.layer.pipe(
+  (input.processRunner === undefined
+    ? AgentSessionScanner.layer
+    : Layer.effect(AgentSessionScanner.AgentSessionScanner, AgentSessionScanner.make).pipe(
+        Layer.provide(input.processRunner),
+      )
+  ).pipe(
     Layer.provide(
       Layer.mergeAll(
         ServerSettings.layerTest({
@@ -1959,11 +1967,38 @@ describe.skipIf(HostProcess.Platform.defaultValue() === "win32")(
           });
         }
 
+        // The deadline fires for every read still in flight, so on a slow runner the
+        // neighbours' `cat` children must have exited before the clock moves.
+        const neighbourConfigs = new Set(
+          [repos[0], repos[2]].map((repo) => path.join(repo, ".git", "config")),
+        );
+        const finishedNeighbourReads = yield* Queue.unbounded<string>();
+        const processRunner = Layer.effect(
+          ProcessRunner.ProcessRunner,
+          Effect.gen(function* () {
+            const runner = yield* ProcessRunner.ProcessRunner;
+            return ProcessRunner.ProcessRunner.of({
+              run: (input) => {
+                const filePath = input.args.at(-1) ?? "";
+                return neighbourConfigs.has(filePath)
+                  ? runner
+                      .run(input)
+                      .pipe(Effect.ensuring(Queue.offer(finishedNeighbourReads, filePath)))
+                  : runner.run(input);
+              },
+            });
+          }),
+        ).pipe(Layer.provide(ProcessRunner.layer), Layer.provide(NodeServices.layer));
+
         for (let attempt = 1; attempt <= 2; attempt++) {
-          const scan = yield* Effect.forkChild(runScan({ claudeHomePath, codexHomePath }));
+          const scan = yield* Effect.forkChild(
+            runScan({ claudeHomePath, codexHomePath, processRunner }),
+          );
           const result = yield* Effect.scoped(
             Effect.gen(function* () {
               yield* awaitGateReader(path.join(repos[1], ".git", "config"));
+              yield* Queue.take(finishedNeighbourReads);
+              yield* Queue.take(finishedNeighbourReads);
               yield* TestClock.adjust("2 seconds");
               return yield* Fiber.join(scan);
             }),