fix: preview edits through configured backend

src/agents/sessions/tools/edit-diff.ts

@@ -423,6 +423,11 @@ export interface EditDiffError {
   error: string;
 }
 
+export interface EditDiffOperations {
+  readFile: (absolutePath: string) => Promise<Buffer | string>;
+  access: (absolutePath: string) => Promise<void>;
+}
+
 /**
  * Compute the diff for one or more edit operations without applying them.
  * Used for preview rendering in the TUI before the tool executes.
@@ -431,13 +436,18 @@ export async function computeEditsDiff(
   path: string,
   edits: Edit[],
   cwd: string,
+  operations?: EditDiffOperations,
 ): Promise<EditDiffResult | EditDiffError> {
   const absolutePath = resolveToCwd(path, cwd);
 
   try {
     // Check if file exists and is readable
     try {
-      await access(absolutePath, constants.R_OK);
+      if (operations) {
+        await operations.access(absolutePath);
+      } else {
+        await access(absolutePath, constants.R_OK);
+      }
     } catch (error: unknown) {
       const errorMessage =
         error instanceof Error && "code" in error
@@ -447,7 +457,11 @@ export async function computeEditsDiff(
     }
 
     // Read the file
-    const rawContent = await readFile(absolutePath, "utf-8");
+    const rawContentResult = operations
+      ? await operations.readFile(absolutePath)
+      : await readFile(absolutePath, "utf-8");
+    const rawContent =
+      typeof rawContentResult === "string" ? rawContentResult : rawContentResult.toString("utf-8");
 
     // Strip BOM before matching (LLM won't include invisible BOM in oldText)
     const { text: content } = stripBom(rawContent);

src/agents/sessions/tools/edit.test.ts

@@ -1,8 +1,15 @@
 import fs from "node:fs/promises";
 import os from "node:os";
 import path from "node:path";
-import { afterEach, describe, expect, it } from "vitest";
-import { createEditTool, type EditOperations } from "./edit.js";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import type { Theme } from "../../modes/interactive/theme/theme.js";
+import { createEditTool, createEditToolDefinition, type EditOperations } from "./edit.js";
+
+const testTheme = {
+  bg: (_name: string, text: string) => text,
+  bold: (text: string) => text,
+  fg: (_name: string, text: string) => text,
+} as Theme;
 
 describe("edit tool", () => {
   let tmpDir = "";
@@ -125,4 +132,40 @@ describe("edit tool", () => {
       text: `Successfully replaced 2 block(s) in ${filePath}.`,
     });
   });
+
+  it("renders previews through custom edit operations", async () => {
+    const readFile = vi.fn(async () => Buffer.from("remote original\n"));
+    const operations: EditOperations = {
+      access: async () => {},
+      readFile,
+      writeFile: async () => {},
+    };
+    const tool = createEditToolDefinition("/workspace", { operations });
+    const args = {
+      path: "remote.txt",
+      edits: [{ oldText: "remote original", newText: "remote changed" }],
+    };
+    const context = {
+      args,
+      argsComplete: true,
+      cwd: "/workspace",
+      executionStarted: false,
+      expanded: false,
+      invalidate: vi.fn(),
+      isError: false,
+      isPartial: false,
+      lastComponent: undefined,
+      showImages: false,
+      state: {},
+      toolCallId: "call-preview",
+    };
+
+    const component = tool.renderCall?.(args, testTheme, context);
+    await vi.waitFor(() => expect(context.invalidate).toHaveBeenCalled());
+
+    expect(readFile).toHaveBeenCalledWith(path.join("/workspace", "remote.txt"));
+    expect((component as { preview?: { diff?: string } } | undefined)?.preview?.diff).toContain(
+      "remote changed",
+    );
+  });
 });

src/agents/sessions/tools/edit.ts

@@ -471,7 +471,7 @@ export function createEditToolDefinition(
       if (context.argsComplete && previewInput && !component.preview && !component.previewPending) {
         component.previewPending = true;
         const requestKey = argsKey;
-        void computeEditsDiff(previewInput.path, previewInput.edits, context.cwd).then(
+        void computeEditsDiff(previewInput.path, previewInput.edits, context.cwd, ops).then(
           (preview) => {
             if (component.previewArgsKey === requestKey) {
               setEditPreview(component, preview, requestKey);