feat(coding-agent): expose edit tool unified patch

closes #4821

packages/coding-agent/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Added
+
+- Added a standard unified patch to edit tool result details for SDK consumers ([#4821](https://github.com/earendil-works/pi/issues/4821)).
+
 ### Fixed
 
 - Fixed final bash tool cards to avoid rendering duplicate full-output truncation paths ([#4819](https://github.com/earendil-works/pi/issues/4819)).

packages/coding-agent/docs/sdk.md

@@ -473,6 +473,8 @@ Specify which built-in tools to enable:
 - `noTools: "all"` disables all tools
 - `noTools: "builtin"` disables default built-ins while keeping extension and custom tools enabled
 
+The `edit` tool returns `details.diff` for Pi's TUI display and `details.patch` as a standard unified patch for SDK consumers.
+
 ```typescript
 import { createAgentSession } from "@earendil-works/pi-coding-agent";
 

packages/coding-agent/src/core/tools/edit-diff.ts

@@ -259,8 +259,16 @@ export function applyEditsToNormalizedContent(
 	return { baseContent, newContent };
 }
 
+/** Generate a standard unified patch. */
+export function generateUnifiedPatch(path: string, oldContent: string, newContent: string, contextLines = 4): string {
+	return Diff.createTwoFilesPatch(path, path, oldContent, newContent, undefined, undefined, {
+		context: contextLines,
+		headerOptions: Diff.FILE_HEADERS_ONLY,
+	});
+}
+
 /**
- * Generate a unified diff string with line numbers and context.
+ * Generate a display-oriented diff string with line numbers and context.
  * Returns both the diff string and the first changed line number (in the new file).
  */
 export function generateDiffString(

packages/coding-agent/src/core/tools/edit.ts

@@ -13,6 +13,7 @@ import {
 	type EditDiffError,
 	type EditDiffResult,
 	generateDiffString,
+	generateUnifiedPatch,
 	normalizeToLF,
 	restoreLineEndings,
 	stripBom,
@@ -57,8 +58,10 @@ type LegacyEditToolInput = EditToolInput & {
 };
 
 export interface EditToolDetails {
-	/** Unified diff of the changes made */
+	/** Display-oriented diff of the changes made */
 	diff: string;
+	/** Standard unified patch of the changes made */
+	patch: string;
 	/** Line number of the first change in the new file (for editor navigation) */
 	firstChangedLine?: number;
 }
@@ -394,6 +397,7 @@ export function createEditToolDefinition(
 								}
 
 								const diffResult = generateDiffString(baseContent, newContent);
+								const patch = generateUnifiedPatch(path, baseContent, newContent);
 								resolve({
 									content: [
 										{
@@ -401,7 +405,7 @@ export function createEditToolDefinition(
 											text: `Successfully replaced ${edits.length} block(s) in ${path}.`,
 										},
 									],
-									details: { diff: diffResult.diff, firstChangedLine: diffResult.firstChangedLine },
+									details: { diff: diffResult.diff, patch, firstChangedLine: diffResult.firstChangedLine },
 								});
 							} catch (error: unknown) {
 								// Clean up abort handler.

packages/coding-agent/test/tools.test.ts

@@ -1,3 +1,4 @@
+import { applyPatch } from "diff";
 import { chmodSync, existsSync, mkdirSync, readFileSync, rmSync, writeFileSync } from "fs";
 import { tmpdir } from "os";
 import { join } from "path";
@@ -239,6 +240,12 @@ describe("Coding Agent Tools", () => {
 			expect(result.details.diff).toBeDefined();
 			expect(typeof result.details.diff).toBe("string");
 			expect(result.details.diff).toContain("testing");
+			expect(result.details.patch).toContain("--- ");
+			expect(result.details.patch).toContain("+++ ");
+			expect(result.details.patch).toContain("@@");
+			expect(result.details.patch).toContain("-Hello, world!");
+			expect(result.details.patch).toContain("+Hello, testing!");
+			expect(applyPatch(originalContent, result.details.patch)).toBe("Hello, testing!");
 		});
 
 		it("should fail if text not found", async () => {