server: cache workspace shortstat and warm in background

packages/server/src/server/session.ts

@@ -130,7 +130,7 @@ import { runAsyncWorktreeBootstrap } from "./worktree-bootstrap.js";
 import type { ServiceRouteStore } from "./service-proxy.js";
 import {
   getCheckoutDiff,
-  getCheckoutShortstat,
+  getCachedCheckoutShortstat,
   getCheckoutStatus,
   getCheckoutStatusLite,
   listBranchSuggestions,
@@ -140,6 +140,7 @@ import {
   pushCurrentBranch,
   createPullRequest,
   getPullRequestStatus,
+  warmCheckoutShortstatInBackground,
 } from "../utils/checkout-git.js";
 import { getProjectIcon } from "../utils/project-icon.js";
 import { expandTilde } from "../utils/path.js";
@@ -5176,10 +5177,11 @@ export class Session {
       projectRecord ?? (await this.projectRegistry.get(workspace.projectId));
 
     let diffStat: { additions: number; deletions: number } | null = null;
-    try {
-      diffStat = await getCheckoutShortstat(workspace.directory);
-    } catch {
-      // Non-critical — leave null on failure.
+    const cachedShortstat = getCachedCheckoutShortstat(workspace.directory);
+    if (cachedShortstat !== undefined) {
+      diffStat = cachedShortstat;
+    } else {
+      warmCheckoutShortstatInBackground(workspace.directory);
     }
 
     return {

packages/server/src/utils/checkout-git.test.ts

@@ -13,10 +13,12 @@ import { join } from "path";
 import { tmpdir } from "os";
 import {
   __resetGhPathCacheForTests,
+  __resetCheckoutShortstatCacheForTests,
   __resetPullRequestStatusCacheForTests,
   __setGhPathForTests,
   __setPullRequestStatusCacheTtlForTests,
   commitAll,
+  getCachedCheckoutShortstat,
   getCheckoutDiff,
   getCheckoutShortstat,
   getPullRequestStatus,
@@ -33,6 +35,7 @@ import {
   parseWorktreeList,
   isPaseoWorktreePath,
   isDescendantPath,
+  warmCheckoutShortstatInBackground,
 } from "./checkout-git.js";
 import { createWorktree } from "./worktree.js";
 import { getPaseoWorktreeMetadataPath } from "./worktree-metadata.js";
@@ -65,11 +68,13 @@ describe("checkout git utilities", () => {
     repoDir = setup.repoDir;
     paseoHome = join(tempDir, "paseo-home");
     __resetGhPathCacheForTests();
+    __resetCheckoutShortstatCacheForTests();
     __resetPullRequestStatusCacheForTests();
   });
 
   afterEach(() => {
     __resetGhPathCacheForTests();
+    __resetCheckoutShortstatCacheForTests();
     __resetPullRequestStatusCacheForTests();
     rmSync(tempDir, { recursive: true, force: true });
   });
@@ -238,6 +243,24 @@ const x = 1;
     expect(shortstat).toEqual({ additions: 1, deletions: 0 });
   });
 
+  it("warms shortstat cache in the background without blocking listing callers", async () => {
+    expect(getCachedCheckoutShortstat(repoDir)).toBeUndefined();
+
+    warmCheckoutShortstatInBackground(repoDir);
+
+    // A repo with no origin/main computes to null, but null should still be cached.
+    for (let attempts = 0; attempts < 20; attempts += 1) {
+      const cached = getCachedCheckoutShortstat(repoDir);
+      if (cached !== undefined) {
+        expect(cached).toBeNull();
+        return;
+      }
+      await sleep(25);
+    }
+
+    throw new Error("shortstat background warm did not populate cache in time");
+  });
+
   it("commits messages with quotes safely", async () => {
     const message = `He said "hello" and it's fine`;
     writeFileSync(join(repoDir, "file.txt"), "quoted\n");

packages/server/src/utils/checkout-git.ts

@@ -20,11 +20,16 @@ const READ_ONLY_GIT_ENV: NodeJS.ProcessEnv = {
 const SMALL_OUTPUT_MAX_BUFFER = 20 * 1024 * 1024; // 20MB
 const DEFAULT_PULL_REQUEST_STATUS_CACHE_TTL_MS = 30_000;
 const PULL_REQUEST_STATUS_CACHE_MAX = 1_000;
+const DEFAULT_SHORTSTAT_CACHE_TTL_MS = 15_000;
+const SHORTSTAT_CACHE_MAX = 1_000;
 
 let pullRequestStatusCacheTtlMs = DEFAULT_PULL_REQUEST_STATUS_CACHE_TTL_MS;
 let pullRequestStatusCache = createPullRequestStatusCache(pullRequestStatusCacheTtlMs);
 const pullRequestStatusInFlight = new Map<string, Promise<PullRequestStatusResult>>();
 let cachedGhPath: string | null | undefined = undefined;
+let shortstatCacheTtlMs = DEFAULT_SHORTSTAT_CACHE_TTL_MS;
+let shortstatCache = createShortstatCache(shortstatCacheTtlMs);
+const shortstatInFlight = new Map<string, Promise<CheckoutShortstat | null>>();
 
 function createPullRequestStatusCache(ttlMs: number) {
   return new TTLCache<string, PullRequestStatusResult>({
@@ -34,10 +39,22 @@ function createPullRequestStatusCache(ttlMs: number) {
   });
 }
 
+function createShortstatCache(ttlMs: number) {
+  return new TTLCache<string, CheckoutShortstat | null>({
+    ttl: ttlMs,
+    max: SHORTSTAT_CACHE_MAX,
+    checkAgeOnGet: true,
+  });
+}
+
 function getPullRequestStatusCacheKey(cwd: string): string {
   return resolve(cwd);
 }
 
+function getShortstatCacheKey(cwd: string): string {
+  return resolve(cwd);
+}
+
 export function __resetPullRequestStatusCacheForTests(): void {
   pullRequestStatusCache.clear();
   pullRequestStatusCache.cancelTimer();
@@ -62,6 +79,22 @@ export function __setGhPathForTests(path: string | null): void {
   cachedGhPath = path;
 }
 
+export function __resetCheckoutShortstatCacheForTests(): void {
+  shortstatCache.clear();
+  shortstatCache.cancelTimer();
+  shortstatCacheTtlMs = DEFAULT_SHORTSTAT_CACHE_TTL_MS;
+  shortstatCache = createShortstatCache(shortstatCacheTtlMs);
+  shortstatInFlight.clear();
+}
+
+export function __setCheckoutShortstatCacheTtlForTests(ttlMs: number): void {
+  shortstatCache.clear();
+  shortstatCache.cancelTimer();
+  shortstatCacheTtlMs = ttlMs;
+  shortstatCache = createShortstatCache(ttlMs);
+  shortstatInFlight.clear();
+}
+
 async function execGit(
   command: string,
   options: { cwd: string; env?: NodeJS.ProcessEnv },
@@ -1194,7 +1227,7 @@ export interface CheckoutShortstat {
   deletions: number;
 }
 
-export async function getCheckoutShortstat(
+async function getCheckoutShortstatUncached(
   cwd: string,
   context?: CheckoutContext,
 ): Promise<CheckoutShortstat | null> {
@@ -1273,6 +1306,56 @@ export async function getCheckoutShortstat(
   }
 }
 
+function getOrLoadCheckoutShortstat(
+  cwd: string,
+  context?: CheckoutContext,
+): Promise<CheckoutShortstat | null> {
+  const cacheKey = getShortstatCacheKey(cwd);
+  const cached = shortstatCache.get(cacheKey);
+  if (cached !== undefined) {
+    return Promise.resolve(cached);
+  }
+
+  const existing = shortstatInFlight.get(cacheKey);
+  if (existing) {
+    return existing;
+  }
+
+  const load = getCheckoutShortstatUncached(cwd, context)
+    .then((shortstat) => {
+      shortstatCache.set(cacheKey, shortstat);
+      return shortstat;
+    })
+    .finally(() => {
+      shortstatInFlight.delete(cacheKey);
+    });
+
+  shortstatInFlight.set(cacheKey, load);
+  return load;
+}
+
+export async function getCheckoutShortstat(
+  cwd: string,
+  context?: CheckoutContext,
+): Promise<CheckoutShortstat | null> {
+  return getOrLoadCheckoutShortstat(cwd, context);
+}
+
+export function getCachedCheckoutShortstat(cwd: string): CheckoutShortstat | null | undefined {
+  return shortstatCache.get(getShortstatCacheKey(cwd));
+}
+
+export function warmCheckoutShortstatInBackground(cwd: string, context?: CheckoutContext): void {
+  const cacheKey = getShortstatCacheKey(cwd);
+  if (shortstatCache.get(cacheKey) !== undefined || shortstatInFlight.has(cacheKey)) {
+    return;
+  }
+
+  void getOrLoadCheckoutShortstat(cwd, context).catch(() => {
+    // Non-critical: keep listing path resilient even if git commands fail.
+  });
+}
+
 export async function getCheckoutDiff(
   cwd: string,
   compare: CheckoutDiffCompare,