fix(dashboard-agent): report the line read_file actually reached when the cap cuts a range

Author: kathiekiwi

internal-packages/dashboard-agent/src/repo-tools.test.ts

@@ -139,6 +139,19 @@ describe("repo-tools", () => {
     expect(res.startLine).toBe(3000);
   });
 
+  it("read_file reports the last line it actually served when the cap cuts a range short", async () => {
+    const res: any = await call(tools.read_file, {
+      path: "src/trigger/narrow.ts",
+      startLine: 1,
+      endLine: 4000,
+    });
+    expect(res.truncated).toBe(true);
+    const served = res.content.split("\n");
+    expect(served).toHaveLength(MAX_READ_LINES);
+    expect(res.startLine).toBe(1);
+    expect(res.endLine).toBe(MAX_READ_LINES);
+  });
+
   it("read_file leaves a small file untruncated", async () => {
     const res: any = await call(tools.read_file, { path: "src/trigger/order.ts" });
     expect(res.truncated).toBe(false);

internal-packages/dashboard-agent/src/repo-tools.ts

@@ -268,11 +268,14 @@ export function buildRepoTools(
           const from = Math.max(1, startLine ?? 1);
           const to = Math.min(lines.length, endLine ?? lines.length);
           const range = capRead(lines.slice(from - 1, to).join("\n"));
+          // The cap can cut the range short, and a line number that outruns the
+          // content is a citation anchored to a line the model never saw.
+          const served = Math.min(to, from + range.content.split("\n").length - 1);
           return {
             path,
             content: range.content,
             startLine: from,
-            endLine: to,
+            endLine: served,
             ...(range.truncated ? { truncated: true, notice: READ_TRUNCATION_NOTICE } : {}),
           };
         }