chore: bump context window to match what zed uses

mcp/readFile.ts

@@ -3,6 +3,9 @@ import { type } from "arktype";
 import type { ToolContext } from "./server.ts";
 import { execute, tool } from "./shared.ts";
 
+/** Hard cap on returned content to avoid flooding the model's context window. */
+const MAX_CHARS = 6000;
+
 export const ReadFileParams = type({
   path: type.string.describe("absolute path to the file to read"),
   "start_line?": type.number.describe("start line, 1-based inclusive (default: 1)"),
@@ -14,6 +17,8 @@ export function ReadFileTool(_ctx: ToolContext) {
     name: "read_file",
     description:
       "Read lines from a file. Use this to read sections of the PR diff returned by checkout_pr. " +
+      `Returns at most ${MAX_CHARS} characters — use narrow line ranges to stay within budget. ` +
+      "Read selectively: only the files most relevant to the review, not the entire diff at once. " +
       "Example: `read_file({ path: diffPath, start_line: 5, end_line: 42 })`.",
     parameters: ReadFileParams,
     execute: execute(async ({ path, start_line, end_line }) => {
@@ -25,14 +30,23 @@ export function ReadFileTool(_ctx: ToolContext) {
         throw new Error(`failed to read ${path}: ${msg}`);
       }
 
-      if (start_line === undefined && end_line === undefined) {
-        return { content };
-      }
-
       const lines = content.split("\n");
       const start = Math.max(0, (start_line ?? 1) - 1);
       const end = Math.min(lines.length, end_line ?? lines.length);
-      return { content: lines.slice(start, end).join("\n") };
+      const slice = lines.slice(start, end).join("\n");
+
+      if (slice.length <= MAX_CHARS) {
+        return { content: slice };
+      }
+
+      const truncated = slice.slice(0, MAX_CHARS);
+      const linesShown = truncated.split("\n").length;
+      const linesTotal = end - start;
+      return {
+        content: truncated,
+        truncated: true,
+        note: `Output capped at ${MAX_CHARS} chars (showed ${linesShown}/${linesTotal} lines). Use a narrower line range to read the rest.`,
+      };
     }),
   });
 }