diff --git a/packages/hosts/mcp/src/stdio-integration.test.ts b/packages/hosts/mcp/src/stdio-integration.test.ts
index db3b461b5..6d0aea108 100644
--- a/packages/hosts/mcp/src/stdio-integration.test.ts
+++ b/packages/hosts/mcp/src/stdio-integration.test.ts
@@ -1,6 +1,7 @@
 import { describe, expect, it } from "@effect/vitest";
 import { Client } from "@modelcontextprotocol/sdk/client/index.js";
 import { StdioClientTransport } from "@modelcontextprotocol/sdk/client/stdio.js";
+import { Effect } from "effect";
 import { mkdtempSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join, resolve } from "node:path";
@@ -10,35 +11,39 @@ const cliEntry = resolve(repoRoot, "apps/cli/src/main.ts");
 const testScope = resolve(repoRoot, "apps/local");
 
 describe("MCP stdio integration", () => {
-  it("execute tool returns result over stdio transport", async () => {
-    // Fresh temp dir so the test doesn't migrate against the developer's
-    // real ~/.executor/data.db.
-    const dataDir = mkdtempSync(join(tmpdir(), "executor-mcp-test-"));
-
-    const transport = new StdioClientTransport({
-      command: "bun",
-      args: ["run", cliEntry, "mcp", "--scope", testScope],
-      env: { ...process.env, EXECUTOR_DATA_DIR: dataDir },
-    });
+  it.effect("execute tool returns result over stdio transport", () =>
+    Effect.gen(function* () {
+      // Fresh temp dir so the test doesn't migrate against the developer's
+      // real ~/.executor/data.db.
+      const dataDir = mkdtempSync(join(tmpdir(), "executor-mcp-test-"));
+
+      const transport = new StdioClientTransport({
+        command: "bun",
+        args: ["run", cliEntry, "mcp", "--scope", testScope],
+        env: { ...process.env, EXECUTOR_DATA_DIR: dataDir },
+      });
 
-    const client = new Client({ name: "test-client", version: "1.0.0" }, { capabilities: {} });
+      const client = new Client({ name: "test-client", version: "1.0.0" }, { capabilities: {} });
 
-    await client.connect(transport);
+      yield* Effect.acquireRelease(
+        Effect.promise(() => client.connect(transport)),
+        () => Effect.promise(() => transport.close()),
+      );
 
-    try {
-      const { tools } = await client.listTools();
+      const { tools } = yield* Effect.promise(() => client.listTools());
       expect(tools.map((t) => t.name)).toContain("execute");
 
-      const result = await client.callTool({
-        name: "execute",
-        arguments: { code: "return 2+2" },
-      });
+      const result = yield* Effect.promise(() =>
+        client.callTool({
+          name: "execute",
+          arguments: { code: "return 2+2" },
+        }),
+      );
 
       const text = (result.content as Array<{ type: string; text: string }>)[0]?.text;
       expect(text).toContain("4");
       expect(result.isError).toBeFalsy();
-    } finally {
-      await transport.close();
-    }
-  }, 30_000);
+    }).pipe(Effect.scoped),
+    { timeout: 30_000 },
+  );
 });
diff --git a/tests/presets-reachable.test.ts b/tests/presets-reachable.test.ts
index 120e7603c..86c051a7e 100644
--- a/tests/presets-reachable.test.ts
+++ b/tests/presets-reachable.test.ts
@@ -62,10 +62,11 @@ describe("graphql presets are reachable endpoints", () => {
           const result = yield* introspect(preset.url).pipe(
             Effect.provide(FetchHttpClient.layer),
             Effect.map((r) => ({ ok: true as const, schema: r })),
-            Effect.catch((err) =>
+            Effect.catchTag("GraphqlIntrospectionError", (err) =>
               Effect.succeed({
                 ok: false as const,
-                message: String(err),
+                // oxlint-disable-next-line executor/no-unknown-error-message -- boundary: catchTag narrows to GraphqlIntrospectionError whose public contract includes message
+                message: err.message,
               }),
             ),
           );
diff --git a/tests/tools-cli.test.ts b/tests/tools-cli.test.ts
index d3931beb5..66a5b6940 100644
--- a/tests/tools-cli.test.ts
+++ b/tests/tools-cli.test.ts
@@ -34,6 +34,7 @@ describe("CLI tooling helpers", () => {
   it.effect("rejects non-object JSON input", () =>
     Effect.gen(function* () {
       const error = yield* parseJsonObjectInput('[1,2,3]').pipe(Effect.flip);
+      // oxlint-disable-next-line executor/no-unknown-error-message -- boundary: helper contract returns a native Error for CLI input parsing
       expect(error.message).toContain("must decode to a JSON object");
     }),
   );