feat: stream files as binary frames over WebSocket (#659)

Replace base64-in-JSON file transfers with binary WebSocket frames to
unblock the JS thread when assistant markdown messages contain images.
Receive cost (JSON.parse over multi-MB base64) and persist cost (base64
re-encode to disk) both removed.

- Split daemon-client `exploreFileSystem` into `listDirectory` + `readFile`;
  `readFile` returns `{ bytes, mime, size, modifiedAt }`. Encoding stays
  private to the seam.
- New `packages/server/src/shared/binary-frames/` module hosts terminal
  frames (moved from `terminal-stream-protocol.ts`) and new file-transfer
  opcodes (`FileBegin` / `FileChunk` / `FileEnd`) with request-id correlation.
- Add optional `acceptBinary` to `FileExplorerRequestSchema`. New daemons
  emit binary frames when set; legacy JSON path remains for old clients.
  Compat fallback lives only inside `readFile`.
- New `persistAttachmentFromBytes` writes bytes directly: native via
  `expo-file-system` `File.write(Uint8Array)`, web via Blob -> IndexedDB,
  desktop via new `write_attachment_bytes` IPC. `persistAttachmentFromBase64`
  removed.

packages/app/src/components/file-pane.tsx

@@ -1,5 +1,6 @@
 import React, { useMemo, useRef } from "react";
 import { useQuery } from "@tanstack/react-query";
+import type { FileReadResult } from "@server/client/daemon-client";
 import Markdown, { MarkdownIt } from "react-native-markdown-display";
 import {
   ActivityIndicator,
@@ -27,8 +28,9 @@ import { isWeb } from "@/constants/platform";
 import { createMarkdownStyles } from "@/styles/markdown-styles";
 import type { AttachmentMetadata } from "@/attachments/types";
 import { useAttachmentPreviewUrl } from "@/attachments/use-attachment-preview-url";
-import { persistAttachmentFromBase64 } from "@/attachments/service";
+import { persistAttachmentFromBytes } from "@/attachments/service";
 import { createPreviewAttachmentId, getFileNameFromPath } from "@/attachments/utils";
+import { explorerFileFromReadResult } from "@/file-explorer/read-result";
 
 interface CodeLineProps {
   tokens: HighlightToken[];
@@ -65,30 +67,34 @@ function formatFileSize({ size }: { size: number }): string {
   return `${(size / (1024 * 1024)).toFixed(1)} MB`;
 }
 
-async function createFilePanePreview(file: ExplorerFile | null): Promise<{
+async function createFilePanePreview(file: FileReadResult | null): Promise<{
   file: ExplorerFile | null;
   imageAttachment: AttachmentMetadata | null;
 }> {
-  if (!file || file.kind !== "image" || !file.content) {
-    return { file, imageAttachment: null };
+  if (!file) {
+    return { file: null, imageAttachment: null };
   }
 
-  const { content: _content, ...imageFile } = file;
-  const imageAttachment = await persistAttachmentFromBase64({
+  const explorerFile = explorerFileFromReadResult(file);
+  if (file.kind !== "image") {
+    return { file: explorerFile, imageAttachment: null };
+  }
+
+  const imageAttachment = await persistAttachmentFromBytes({
     id: createPreviewAttachmentId({
-      mimeType: file.mimeType ?? "image/png",
+      mimeType: file.mime,
       path: file.path,
       size: file.size,
       modifiedAt: file.modifiedAt,
-      contentLength: file.content.length,
+      contentLength: file.bytes.byteLength,
     }),
-    base64: file.content,
-    mimeType: file.mimeType,
+    bytes: file.bytes,
+    mimeType: file.mime,
     fileName: getFileNameFromPath(file.path),
   });
 
   return {
-    file: imageFile,
+    file: explorerFile,
     imageAttachment,
   };
 }
@@ -358,17 +364,21 @@ export function FilePane({
       if (!client || !normalizedWorkspaceRoot || !normalizedFilePath) {
         return { file: null as ExplorerFile | null, error: "Host is not connected" };
       }
-      const payload = await client.exploreFileSystem(
-        normalizedWorkspaceRoot,
-        normalizedFilePath,
-        "file",
-      );
-      const preview = await createFilePanePreview(payload.file ?? null);
-      return {
-        file: preview.file,
-        imageAttachment: preview.imageAttachment,
-        error: payload.error ?? null,
-      };
+      try {
+        const file = await client.readFile(normalizedWorkspaceRoot, normalizedFilePath);
+        const preview = await createFilePanePreview(file);
+        return {
+          file: preview.file,
+          imageAttachment: preview.imageAttachment,
+          error: null,
+        };
+      } catch (error) {
+        return {
+          file: null,
+          imageAttachment: null,
+          error: error instanceof Error ? error.message : "Failed to load file",
+        };
+      }
     },
     staleTime: 5_000,
     refetchOnMount: true,

packages/app/src/components/message.tsx

@@ -98,7 +98,7 @@ import { PlanCard } from "./plan-card";
 import { useToolCallSheet } from "./tool-call-sheet";
 import { ToolCallDetailsContent } from "./tool-call-details";
 import { useAttachmentPreviewUrl } from "@/attachments/use-attachment-preview-url";
-import { persistAttachmentFromBase64, persistAttachmentFromDataUrl } from "@/attachments/service";
+import { persistAttachmentFromBytes, persistAttachmentFromDataUrl } from "@/attachments/service";
 import type { DaemonClient } from "@server/client/daemon-client";
 import { isWeb, isNative } from "@/constants/platform";
 export type { InlinePathTarget } from "@/utils/inline-path";
@@ -760,25 +760,21 @@ function AssistantMarkdownImage({
         return null;
       }
 
-      const payload = await client.exploreFileSystem(resolution.cwd, resolution.path, "file");
-      if (payload.error) {
-        throw new Error(payload.error);
-      }
-      const file = payload.file;
-      if (!file || file.kind !== "image" || !file.content) {
+      const file = await client.readFile(resolution.cwd, resolution.path);
+      if (file.kind !== "image") {
         throw new Error("Image preview unavailable.");
       }
 
-      return await persistAttachmentFromBase64({
+      return await persistAttachmentFromBytes({
         id: createPreviewAttachmentId({
-          mimeType: file.mimeType ?? "image/png",
+          mimeType: file.mime,
           path: file.path || resolution.path,
           size: file.size,
           modifiedAt: file.modifiedAt,
-          contentLength: file.content.length,
+          contentLength: file.bytes.byteLength,
         }),
-        base64: file.content,
-        mimeType: file.mimeType,
+        bytes: file.bytes,
+        mimeType: file.mime,
         fileName: getFileNameFromPath(file.path || resolution.path),
       });
     },