feat(web): add optional path filter to /api/diff and get_diff tool

Adds a `path` query/tool parameter to restrict diff output to changes
touching a single file via git's `-- <pathspec>` separator. Refactors
the route handler to use the shared `getDiffRequestSchema`.

Fixes SOU-1154 (#1154)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: brendan-kellam

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Added commit history viewer to code browser. [#1150](https://github.com/sourcebot-dev/sourcebot/pull/1150)
 - Added `/api/commits/authors` to the public API to allow fetching a list of authors for a given path and revision. [#1150](https://github.com/sourcebot-dev/sourcebot/pull/1150)
+- Added optional `path` query parameter to the `/api/diff` endpoint and `get_diff` MCP tool to restrict diffs to changes touching a specific file. [#1154](https://github.com/sourcebot-dev/sourcebot/pull/1154)
 
 ### Fixed
 - Bumped `postcss` to `8.5.10`. [#1155](https://github.com/sourcebot-dev/sourcebot/pull/1155)

docs/api-reference/sourcebot-public.openapi.json

@@ -1585,6 +1585,16 @@
             "description": "The head git ref (branch, tag, or commit SHA) to diff to.",
             "name": "head",
             "in": "query"
+          },
+          {
+            "schema": {
+              "type": "string",
+              "description": "Restrict the diff to changes touching this file path. Omit to diff all changes between the two refs."
+            },
+            "required": false,
+            "description": "Restrict the diff to changes touching this file path. Omit to diff all changes between the two refs.",
+            "name": "path",
+            "in": "query"
           }
         ],
         "responses": {

packages/web/src/app/api/(server)/diff/route.ts

@@ -1,24 +1,18 @@
 import { getDiff } from "@/features/git";
+import { getDiffRequestSchema } from "@/features/git/schemas";
 import { apiHandler } from "@/lib/apiHandler";
 import { queryParamsSchemaValidationError, serviceErrorResponse } from "@/lib/serviceError";
 import { isServiceError } from "@/lib/utils";
 import { NextRequest } from "next/server";
-import { z } from "zod";
-
-const getDiffQueryParamsSchema = z.object({
-    repo: z.string(),
-    base: z.string(),
-    head: z.string(),
-});
 
 export const GET = apiHandler(async (request: NextRequest): Promise<Response> => {
     const rawParams = Object.fromEntries(
-        Object.keys(getDiffQueryParamsSchema.shape).map(key => [
+        Object.keys(getDiffRequestSchema.shape).map(key => [
             key,
             request.nextUrl.searchParams.get(key) ?? undefined
         ])
     );
-    const parsed = getDiffQueryParamsSchema.safeParse(rawParams);
+    const parsed = getDiffRequestSchema.safeParse(rawParams);
 
     if (!parsed.success) {
         return serviceErrorResponse(

packages/web/src/features/git/getDiffApi.ts

@@ -32,12 +32,14 @@ type GetDiffRequest = {
     repo: string;
     base: string;
     head: string;
+    path?: string;
 }
 
 export const getDiff = async ({
     repo: repoName,
     base,
     head,
+    path,
 }: GetDiffRequest): Promise<GetDiffResult | ServiceError> => sew(() =>
     withOptionalAuth(async ({ org, prisma }) => {
         if (!isGitRefValid(base)) {
@@ -63,7 +65,15 @@ export const getDiff = async ({
         const git = simpleGit().cwd(repoPath);
 
         try {
-            const rawDiff = await git.raw(['diff', base, head]);
+            const diffArgs: string[] = ['diff', base, head];
+            // The `--` pathspec separator both restricts the diff to the path
+            // and prevents anything path-shaped from being interpreted as a
+            // flag or ref by git.
+            if (path) {
+                diffArgs.push('--', path);
+            }
+
+            const rawDiff = await git.raw(diffArgs);
             const files = parseDiff(rawDiff);
 
             const nodes: FileDiff[] = files.map((file) => ({

packages/web/src/features/git/schemas.ts

@@ -41,6 +41,7 @@ export const getDiffRequestSchema = z.object({
     repo: z.string().describe('The fully-qualified repository name.'),
     base: z.string().describe('The base git ref (branch, tag, or commit SHA) to diff from.'),
     head: z.string().describe('The head git ref (branch, tag, or commit SHA) to diff to.'),
+    path: z.string().optional().describe('Restrict the diff to changes touching this file path. Omit to diff all changes between the two refs.'),
 });
 
 const hunkRangeSchema = z.object({

packages/web/src/features/tools/getDiff.ts

@@ -28,10 +28,10 @@ export const getDiffDefinition: ToolDefinition<'get_diff', typeof getDiffRequest
     isIdempotent: true,
     description,
     inputSchema: getDiffRequestSchema,
-    execute: async ({ repo, base, head }, _context) => {
-        logger.debug('get_diff', { repo, base, head });
+    execute: async ({ repo, base, head, path }, _context) => {
+        logger.debug('get_diff', { repo, base, head, path });
 
-        const response = await getDiff({ repo, base, head });
+        const response = await getDiff({ repo, base, head, path });
 
         if (isServiceError(response)) {
             throw new Error(response.message);