diff --git a/apps/server/src/provider/Layers/CodexAdapter.test.ts b/apps/server/src/provider/Layers/CodexAdapter.test.ts
index f7c6036885d9dd73920a9af329aa6a03d94621ef..48aff6cd707e74361eb3cda1d92a8e69d332506e 100644
--- a/apps/server/src/provider/Layers/CodexAdapter.test.ts
+++ b/apps/server/src/provider/Layers/CodexAdapter.test.ts
@@ -448,6 +448,54 @@ sessionErrorLayer("CodexAdapterLive session errors", (it) => {
     }),
   );
 
+  it.effect("passes image attachments to Codex by path instead of base64", () =>
+    Effect.gen(function* () {
+      const adapter = yield* CodexAdapter;
+      const threadId = asThreadId("thread-image-attachment");
+      yield* adapter.startSession({
+        provider: ProviderDriverKind.make("codex"),
+        threadId,
+        runtimeMode: "full-access",
+      });
+      const runtime = sessionRuntimeFactory.lastRuntime;
+      NodeAssert.ok(runtime);
+      runtime.sendTurnImpl.mockClear();
+
+      const serverConfig = yield* ServerConfig;
+      const attachmentsDir = serverConfig.attachmentsDir;
+      const attachmentId = "attachment-local-image-1";
+      const attachmentPath = NodePath.join(attachmentsDir, `${attachmentId}.png`);
+      NodeFS.writeFileSync(attachmentPath, Buffer.alloc(4, 0x89));
+
+      try {
+        yield* adapter.sendTurn({
+          threadId,
+          input: "Use this image.",
+          attachments: [
+            {
+              type: "image",
+              id: attachmentId,
+              name: "generated.png",
+              mimeType: "image/png",
+              sizeBytes: NodeFS.statSync(attachmentPath).size,
+            },
+          ],
+        });
+
+        const input = runtime.sendTurnImpl.mock.calls[0]?.[0];
+        NodeAssert.ok(input);
+        NodeAssert.deepStrictEqual(input.attachments, [
+          {
+            type: "localImage",
+            path: attachmentPath,
+          },
+        ]);
+      } finally {
+        NodeFS.rmSync(attachmentPath, { force: true });
+      }
+    }),
+  );
+
   it.effect("passes configured launch args into the session runtime", () => {
     const runtimeFactory = makeRuntimeFactory();
     const layer = Layer.effect(
diff --git a/apps/server/src/provider/Layers/CodexAdapter.ts b/apps/server/src/provider/Layers/CodexAdapter.ts
index b43755736ca3106caf031a23cb7fd2306a4338c2..ba61d14f5cf56ca4c2025f82151f3e11de8d9389 100644
--- a/apps/server/src/provider/Layers/CodexAdapter.ts
+++ b/apps/server/src/provider/Layers/CodexAdapter.ts
@@ -36,7 +36,6 @@ import * as NodeCrypto from "node:crypto";
 import * as Crypto from "effect/Crypto";
 import * as Exit from "effect/Exit";
 import * as Fiber from "effect/Fiber";
-import * as FileSystem from "effect/FileSystem";
 import * as Queue from "effect/Queue";
 import * as Schema from "effect/Schema";
 import * as Scope from "effect/Scope";
@@ -67,6 +66,7 @@ import {
   makeCodexSessionRuntime,
   type CodexSessionRuntimeError,
   type CodexSessionRuntimeOptions,
+  type CodexSessionRuntimeSendTurnInput,
   type CodexSessionRuntimeShape,
 } from "./CodexSessionRuntime.ts";
 import { type EventNdjsonLogger, makeEventNdjsonLogger } from "./EventNdjsonLogger.ts";
@@ -2218,7 +2218,6 @@ export const makeCodexAdapter = Effect.fn("makeCodexAdapter")(function* (
   options?: CodexAdapterLiveOptions,
 ) {
   const boundInstanceId = options?.instanceId ?? ProviderInstanceId.make("codex");
-  const fileSystem = yield* FileSystem.FileSystem;
   const childProcessSpawner = yield* ChildProcessSpawner.ChildProcessSpawner;
   const crypto = yield* Crypto.Crypto;
   const serverConfig = yield* Effect.service(ServerConfig);
@@ -2491,27 +2490,18 @@ export const makeCodexAdapter = Effect.fn("makeCodexAdapter")(function* (
         detail: `Invalid attachment id '${attachment.id}'.`,
       });
     }
-    const bytes = yield* fileSystem.readFile(attachmentPath).pipe(
-      Effect.mapError(
-        (cause) =>
-          new ProviderAdapterRequestError({
-            provider: PROVIDER,
-            method: "turn/start",
-            detail: `Failed to read attachment file: ${cause.message}.`,
-            cause,
-          }),
-      ),
-    );
     return {
-      type: "image" as const,
-      url: `data:${attachment.mimeType};base64,${Buffer.from(bytes).toString("base64")}`,
+      type: "localImage" as const,
+      path: attachmentPath,
     };
   });
 
   const sendTurn: CodexAdapterShape["sendTurn"] = Effect.fn("sendTurn")(function* (input) {
-    // Codex ingests images only. Anything else would be base64-encoded as an
-    // image and rejected or misread; generic files reach the agent through the
-    // path line ProviderService puts in the prompt.
+    // Codex ingests images only. Anything else would be inlined as an image
+    // and rejected or misread; generic files reach the agent through the path
+    // line ProviderService puts in the prompt. Images are passed by path
+    // instead of base64 so the turn/start request does not scale with file
+    // size; the CLI reads the file itself.
     const codexAttachments = yield* Effect.forEach(
       (input.attachments ?? []).filter((attachment) => attachment.type === "image"),
       (attachment) => resolveAttachment(input, attachment),
diff --git a/apps/server/src/provider/Layers/CodexSessionRuntime.test.ts b/apps/server/src/provider/Layers/CodexSessionRuntime.test.ts
index c14dca7ccd1918584a8dac80c9754f70fb5c2af0..ec113ab7c521cc6c2ff02d9cd40e3d4ad568c4c2 100644
--- a/apps/server/src/provider/Layers/CodexSessionRuntime.test.ts
+++ b/apps/server/src/provider/Layers/CodexSessionRuntime.test.ts
@@ -179,8 +179,8 @@ describe("buildTurnStartParams", () => {
         runtimeMode: "full-access",
         attachments: [
           {
-            type: "image",
-            url: { secret } as unknown as string,
+            type: "localImage",
+            path: { secret } as unknown as string,
           },
         ],
       }).pipe(Effect.flip),
@@ -248,8 +248,8 @@ describe("buildTurnStartParams", () => {
         interactionMode: "default",
         attachments: [
           {
-            type: "image",
-            url: "data:image/png;base64,abc",
+            type: "localImage",
+            path: "/tmp/generated.png",
           },
         ],
       }),
@@ -268,8 +268,8 @@ describe("buildTurnStartParams", () => {
           text: "Implement it",
         },
         {
-          type: "image",
-          url: "data:image/png;base64,abc",
+          type: "localImage",
+          path: "/tmp/generated.png",
         },
       ],
       model: "gpt-5.3-codex",
diff --git a/apps/server/src/provider/Layers/CodexSessionRuntime.ts b/apps/server/src/provider/Layers/CodexSessionRuntime.ts
index c26d6ae446d8c7a2784c853a4251b9a3993a45f8..c8aa069cb2b70f596f34b094bbcae20ca54ab395 100644
--- a/apps/server/src/provider/Layers/CodexSessionRuntime.ts
+++ b/apps/server/src/provider/Layers/CodexSessionRuntime.ts
@@ -186,8 +186,8 @@ export interface CodexSessionRuntimeOptions {
 export interface CodexSessionRuntimeSendTurnInput {
   readonly input?: string;
   readonly attachments?: ReadonlyArray<{
-    readonly type: "image";
-    readonly url: string;
+    readonly type: "localImage";
+    readonly path: string;
   }>;
   readonly model?: string;
   readonly serviceTier?: CodexServiceTier | undefined;
@@ -614,8 +614,8 @@ export function buildTurnStartParams(input: {
   readonly runtimeMode: RuntimeMode;
   readonly prompt?: string;
   readonly attachments?: ReadonlyArray<{
-    readonly type: "image";
-    readonly url: string;
+    readonly type: "localImage";
+    readonly path: string;
   }>;
   readonly model?: string;
   readonly serviceTier?: CodexServiceTier;