Include desktop app logs in diagnostics (#1914)

* fix(diagnostics): include desktop app logs

Settings diagnostics now collect the Electron main-process log separately from daemon.log so desktop startup and environment-probe failures are included in app reports.

* refactor(desktop): share log tail reader

* fix(diagnostics): surface desktop app log read errors

* refactor(diagnostics): tighten desktop report API

packages/desktop/src/diagnostics/app-logs.ts

@@ -0,0 +1,17 @@
+import log from "electron-log/main";
+import { tailFile } from "./tail-file.js";
+
+const APP_LOG_TAIL_LINES = 100;
+
+export interface DesktopAppLogs {
+  logPath: string;
+  contents: string;
+}
+
+export function getDesktopAppLogs(): DesktopAppLogs {
+  const logPath = log.transports.file.getFile().path;
+  return {
+    logPath,
+    contents: tailFile(logPath, APP_LOG_TAIL_LINES, { throwOnReadError: true }),
+  };
+}

packages/desktop/src/diagnostics/tail-file.test.ts

@@ -0,0 +1,34 @@
+import { mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import path from "node:path";
+import { afterEach, beforeEach, describe, expect, it } from "vitest";
+import { tailFile } from "./tail-file";
+
+let testDir = "";
+
+describe("tailFile", () => {
+  beforeEach(() => {
+    testDir = mkdtempSync(path.join(tmpdir(), "paseo-tail-file-"));
+  });
+
+  afterEach(() => {
+    rmSync(testDir, { recursive: true, force: true });
+  });
+
+  it("returns the requested tail lines", () => {
+    const filePath = path.join(testDir, "main.log");
+    writeFileSync(filePath, "one\ntwo\nthree\n");
+
+    expect(tailFile(filePath, 2)).toBe("two\nthree");
+  });
+
+  it("keeps missing files empty", () => {
+    expect(tailFile(path.join(testDir, "missing.log"), 2)).toBe("");
+    expect(tailFile(path.join(testDir, "missing.log"), 2, { throwOnReadError: true })).toBe("");
+  });
+
+  it("can propagate read failures", () => {
+    expect(() => tailFile(testDir, 2, { throwOnReadError: true })).toThrow();
+    expect(tailFile(testDir, 2)).toBe("");
+  });
+});

packages/desktop/src/diagnostics/tail-file.ts

@@ -0,0 +1,21 @@
+import { readFileSync } from "node:fs";
+
+interface TailFileOptions {
+  throwOnReadError?: boolean;
+}
+
+export function tailFile(filePath: string, lines = 50, options: TailFileOptions = {}): string {
+  try {
+    const content = readFileSync(filePath, "utf-8");
+    return content.split("\n").filter(Boolean).slice(-lines).join("\n");
+  } catch (error) {
+    if (options.throwOnReadError && !isMissingFileError(error)) {
+      throw error;
+    }
+    return "";
+  }
+}
+
+function isMissingFileError(error: unknown): boolean {
+  return typeof error === "object" && error !== null && "code" in error && error.code === "ENOENT";
+}