diff --git a/apps/server/src/mcp/McpToolAccess.ts b/apps/server/src/mcp/McpToolAccess.ts
index 9d99fb7da89e3..1eb4cf8c12f84 100644
--- a/apps/server/src/mcp/McpToolAccess.ts
+++ b/apps/server/src/mcp/McpToolAccess.ts
@@ -102,7 +102,7 @@ export const readsAsCaller = <P, A, E, R>(handle: (params: P) => Effect.Effect<A
 export const actsAsCaller = <P, A, E, R>(handle: (params: P) => Effect.Effect<A, E, R>) =>
   declare((params: P) =>
     requireThreadCaller.pipe(
-      Effect.flatMap(() => writingCaller),
+      Effect.andThen(writingCaller),
       Effect.flatMap(() => handle(params)),
     ),
   );
diff --git a/apps/server/src/telemetry/AnalyticsService.ts b/apps/server/src/telemetry/AnalyticsService.ts
index 54e3a3e6105d3..e88eaff9d079e 100644
--- a/apps/server/src/telemetry/AnalyticsService.ts
+++ b/apps/server/src/telemetry/AnalyticsService.ts
@@ -307,7 +307,7 @@ export const make = Effect.gen(function* () {
     ),
   );
 
-  yield* Effect.forever(Effect.sleep(FLUSH_INTERVAL_MS).pipe(Effect.flatMap(() => flushWhenDue)), {
+  yield* Effect.forever(Effect.sleep(FLUSH_INTERVAL_MS).pipe(Effect.andThen(flushWhenDue)), {
     disableYield: true,
   }).pipe(Effect.forkScoped);
 
diff --git a/packages/provider-acp/src/server/AcpSessionRuntime.ts b/packages/provider-acp/src/server/AcpSessionRuntime.ts
index 9253e799221cd..5a3a2ff0166e5 100644
--- a/packages/provider-acp/src/server/AcpSessionRuntime.ts
+++ b/packages/provider-acp/src/server/AcpSessionRuntime.ts
@@ -2005,7 +2005,7 @@ export const make = Effect.fn("AcpSessionRuntime.make")(function* (
     value: string | boolean,
   ): Effect.Effect<EffectAcpSchema.SetSessionConfigOptionResponse, EffectAcpErrors.AcpError> =>
     validateConfigOptionValue(configId, value).pipe(
-      Effect.flatMap(() => getStartedState),
+      Effect.andThen(getStartedState),
       Effect.flatMap((started) =>
         Ref.get(configOptionsRef).pipe(
           Effect.flatMap((configOptions) => {
diff --git a/tsconfig.base.json b/tsconfig.base.json
index 71b0ad793e9ef..f6215a4d0fbee 100644
--- a/tsconfig.base.json
+++ b/tsconfig.base.json
@@ -24,6 +24,7 @@
         "namespaceImportPackages": ["@effect/platform-node", "effect"],
         "effectFn": ["span", "inferred-span", "suggested-span"],
         "diagnosticSeverity": {
+          "flatMapIgnoredParamToAndThen": "error",
           "mapSomeToAsSome": "error",
           "unnecessaryPipeChain": "error",
           "effectFnOpportunity": "suggestion",