refactor(coding-agent): changed file headers to display only filenames

- Updated `formatReadHashlineHeader` to use `path.basename` instead of the full path.
- Applied the new formatter across record and display functions in the read tool.
- Added and updated tests to verify that hashline headers now contain only the filename for nested files.

packages/coding-agent/test/read-multi-range.test.ts

@@ -48,13 +48,29 @@ describe("read tool multi-range selector", () => {
 		await fs.rm(tmpDir, { recursive: true, force: true });
 	});
 
+	it("uses only the filename in hashline headers for nested files", async () => {
+		const filePath = path.join(tmpDir, "src", "nested", "numbered.txt");
+		await fs.mkdir(path.dirname(filePath), { recursive: true });
+		await fs.writeFile(filePath, "alpha\nbeta\n");
+
+		const tool = new ReadTool(createSession(tmpDir));
+		const text = textOutput(await tool.execute("call-filename-header", { path: filePath }));
+		const firstLine = text.split("\n")[0];
+
+		expect(firstLine).toMatch(/^\[numbered\.txt#[0-9A-F]{4}\]$/);
+		expect(firstLine).not.toContain("src");
+	});
+
 	it("returns both ranges separated by an elision marker", async () => {
-		const filePath = path.join(tmpDir, "numbered.txt");
+		const filePath = path.join(tmpDir, "src", "numbered.txt");
+		await fs.mkdir(path.dirname(filePath), { recursive: true });
 		await fs.writeFile(filePath, makeNumberedContent(50));
 
 		const tool = new ReadTool(createSession(tmpDir));
 		const result = await tool.execute("call-multi", { path: `${filePath}:3-5,20-22` });
 		const text = textOutput(result);
+		const firstLine = text.split("\n")[0];
+		expect(firstLine).toMatch(/^\[numbered\.txt#[0-9A-F]{4}\]$/);
 
 		expect(text).toContain("line 3");
 		expect(text).toContain("line 4");