diff --git a/apps/desktop/electron/bundle-skew.test.ts b/apps/desktop/electron/bundle-skew.test.ts
index d08aa97018..252fdd02f6 100644
--- a/apps/desktop/electron/bundle-skew.test.ts
+++ b/apps/desktop/electron/bundle-skew.test.ts
@@ -5,7 +5,7 @@ import { dirname, join } from 'node:path'
 
 import { afterAll, describe, expect, it } from 'vitest'
 
-import { detectBundleSkew, isFallbackCommit, type RunGit, RUNTIME_PATHS } from './bundle-skew'
+import { createBundleSkewChecker, detectBundleSkew, isFallbackCommit, type RunGit, RUNTIME_PATHS } from './bundle-skew'
 
 const REPO = '/repo'
 const STAMP = { commit: 'a'.repeat(40), source: 'ci' }
@@ -44,6 +44,54 @@ function gitCounting(count: string): RunGit {
   return gitAnswering({ 'merge-base': { code: 0 }, 'rev-list': { stdout: count } }).git
 }
 
+it('coalesces polls, backs off failures, and skips checks while an update owns the checkout', async () => {
+  let updating = false
+  let now = 0
+  let finish: (value: { code: number; stderr: string; stdout: string }) => void
+  const calls: string[][] = []
+
+  const git: RunGit = (args, options) => {
+    calls.push(args)
+    expect(options.timeoutMs).toBeGreaterThan(0)
+    expect(options.timeoutMs).toBeLessThanOrEqual(5000)
+    expect(options.env?.GIT_NO_LAZY_FETCH).toBe('1')
+
+    return new Promise(resolve => {
+      finish = resolve
+    })
+  }
+
+  const check = createBundleSkewChecker(STAMP, git, { isUpdating: () => updating, now: () => now })
+  const quiet = { desktopCommitsBehind: null, outOfSync: false }
+
+  const polls = Array.from({ length: 40 }, () => check(REPO))
+  expect(calls).toHaveLength(1)
+  finish!({ code: 128, stderr: 'missing tree', stdout: '' })
+  expect(await Promise.all(polls)).toEqual(polls.map(() => quiet))
+  await check(REPO)
+  expect(calls).toHaveLength(1)
+
+  now += 60_000
+  const retry = check(REPO)
+  expect(calls).toHaveLength(2)
+  finish!({ code: 128, stderr: '', stdout: '' })
+  await retry
+
+  updating = true
+  expect(await check(REPO)).toEqual(quiet)
+  expect(calls).toHaveLength(2)
+  updating = false
+  const refreshed = check(REPO)
+  expect(calls).toHaveLength(3) // update invalidates the cached failure
+  finish!({ code: 128, stderr: '', stdout: '' })
+  await refreshed
+
+  const other = check('/another-checkout')
+  expect(calls).toHaveLength(4)
+  finish!({ code: 128, stderr: '', stdout: '' })
+  await other
+})
+
 describe('isFallbackCommit', () => {
   it('matches the all-zero placeholder at any stamp length', () => {
     expect(isFallbackCommit('0'.repeat(40))).toBe(true)
diff --git a/apps/desktop/electron/bundle-skew.ts b/apps/desktop/electron/bundle-skew.ts
index ecb4cae7a5..2a389e132a 100644
--- a/apps/desktop/electron/bundle-skew.ts
+++ b/apps/desktop/electron/bundle-skew.ts
@@ -56,8 +56,8 @@ export interface BundleSkewResult {
 
 export type RunGit = (
   args: string[],
-  options: { cwd: string }
-) => Promise<{ code: number; stderr: string; stdout: string }>
+  options: { cwd: string; env?: NodeJS.ProcessEnv; timeoutMs?: number }
+) => Promise<{ code: number | null; stderr: string; stdout: string }>
 
 /**
  * The paths that actually reach the user: renderer sources, main-process
@@ -82,6 +82,52 @@ export const RUNTIME_PATHS = [
 
 const NOT_STALE: BundleSkewResult = { desktopCommitsBehind: null, outOfSync: false }
 
+/** About/version polls share one check per checkout, including failed checks. */
+export function createBundleSkewChecker(
+  stamp: BundleSkewStamp | null,
+  runGit: RunGit,
+  { isUpdating, now = Date.now }: { isUpdating: () => boolean; now?: () => number }
+): (repoRoot: string) => Promise<BundleSkewResult> {
+  const pending = new Map<string, Promise<BundleSkewResult>>()
+  const cached = new Map<string, { result: BundleSkewResult; at: number }>()
+
+  return repoRoot => {
+    if (isUpdating()) {
+      cached.clear()
+
+      return Promise.resolve(NOT_STALE)
+    }
+
+    const running = pending.get(repoRoot)
+
+    if (running) {
+      return running
+    }
+
+    const previous = cached.get(repoRoot)
+
+    if (previous && now() - previous.at < 30_000) {
+      return Promise.resolve(previous.result)
+    }
+
+    const check = detectBundleSkew(stamp, runGit, repoRoot)
+      .then(result => {
+        if (isUpdating()) {
+          return NOT_STALE
+        }
+
+        cached.set(repoRoot, { result, at: now() })
+
+        return result
+      })
+      .finally(() => pending.delete(repoRoot))
+
+    pending.set(repoRoot, check)
+
+    return check
+  }
+}
+
 /** Matches write-build-stamp.mjs's all-zero placeholder for non-git builds. */
 export function isFallbackCommit(commit: string): boolean {
   return /^0{7,40}$/.test(commit)
@@ -97,6 +143,15 @@ export async function detectBundleSkew(
   }
 
   try {
+    // A path-filtered walk of a tree:0 clone can otherwise fetch its entire
+    // missing history. Older Git ignores NO_LAZY_FETCH, so also bound and reap
+    // the process tree in execGit, not just the promise waiting for it.
+    const options = {
+      cwd: repoRoot,
+      env: { ...process.env, GIT_NO_LAZY_FETCH: '1', GIT_TERMINAL_PROMPT: '0', GCM_INTERACTIVE: 'Never' },
+      timeoutMs: 5000
+    }
+
     // Exit 0 = ancestor, 1 = unrelated or diverged, anything else = git could
     // not answer (unknown object, shallow clone, not a repo). Only the first
     // makes the commit count below a statement about skew, and the other two
@@ -108,17 +163,13 @@ export async function detectBundleSkew(
     // would be told "app build out of date" backwards. Ancestry is what makes
     // this a proof that the renderer PREDATES the tree, which is the claim the
     // warning actually makes.
-    const ancestry = await runGit(['merge-base', '--is-ancestor', stamp.commit, 'HEAD'], {
-      cwd: repoRoot
-    })
+    const ancestry = await runGit(['merge-base', '--is-ancestor', stamp.commit, 'HEAD'], options)
 
     if (ancestry.code !== 0) {
       return NOT_STALE
     }
 
-    const result = await runGit(['rev-list', '--count', `${stamp.commit}..HEAD`, '--', ...RUNTIME_PATHS], {
-      cwd: repoRoot
-    })
+    const result = await runGit(['rev-list', '--count', `${stamp.commit}..HEAD`, '--', ...RUNTIME_PATHS], options)
 
     if (result.code !== 0) {
       return NOT_STALE
diff --git a/apps/desktop/electron/main.ts b/apps/desktop/electron/main.ts
index 749ccd0a52..6460d6613e 100644
--- a/apps/desktop/electron/main.ts
+++ b/apps/desktop/electron/main.ts
@@ -114,7 +114,7 @@ import {
   BROWSER_WINDOW_WIDTH,
   buildBrowserWindowUrl
 } from './browser-windows'
-import { detectBundleSkew } from './bundle-skew'
+import { createBundleSkewChecker } from './bundle-skew'
 import { detectBundleSwap, readBundleSwapStamp } from './bundle-swap'
 import { registerChatOnboardingWindow } from './chat-onboarding-window'
 import { provisionCliLinks } from './cli-provision'
@@ -368,7 +368,7 @@ import {
 } from './native-oauth'
 import { runNativeLogin } from './native-oauth-login'
 import { loadNativeTokenSet, type NativeTokenStoreIo, persistNativeTokenSet } from './native-token-store'
-import { planNoConsoleGitSpawn, setNoConsoleGitRoots, windowsGitHost } from './no-console-git'
+import { execGit, planNoConsoleGitSpawn, setNoConsoleGitRoots, windowsGitHost } from './no-console-git'
 import { registerNativeNotifications } from './notification-ipc'
 import { isExpectedOauthNavigationAbort } from './oauth-navigation'
 import { serializeJsonBody, setJsonRequestHeaders } from './oauth-net-request'
@@ -531,7 +531,7 @@ import {
   windowOpacityFor,
   windowOpacityOptions
 } from './translucency'
-import { waitForUpdateClearance } from './update-gate'
+import { updateGateReason, waitForUpdateClearance } from './update-gate'
 import { readLiveUpdateMarker, updateHandoffConflict, writeUpdateMarker } from './update-marker'
 import {
   resolveUpdaterMechanism,
@@ -18265,8 +18265,14 @@ function resolveHermesVersion(scope: { connectionId?: string; profile?: string }
 // apps/desktop/, and warn when the running renderer is provably behind.
 // Fail-quiet: dev runs (no stamp), non-git builds, and shallow-clone gaps all
 // report in-sync rather than risk a false "your install is torn" warning.
+const checkRendererSkew = createBundleSkewChecker(
+  INSTALL_STAMP,
+  (args, options) => execGit(resolveGitBinary(), args, options),
+  { isUpdating: () => updateGateReason(updateGateDeps()) !== null }
+)
+
 async function detectRendererSkew() {
-  return detectBundleSkew(INSTALL_STAMP, runGit, resolveUpdateRoot())
+  return checkRendererSkew(resolveUpdateRoot())
 }
 
 // Re-resolve the live Hermes version and push it into the native About panel
diff --git a/apps/desktop/electron/no-console-git.test.ts b/apps/desktop/electron/no-console-git.test.ts
index 11c21042ed..3c5cbd1b80 100644
--- a/apps/desktop/electron/no-console-git.test.ts
+++ b/apps/desktop/electron/no-console-git.test.ts
@@ -1,13 +1,15 @@
 import assert from 'node:assert/strict'
 import { execFileSync } from 'node:child_process'
 import fs from 'node:fs'
+import { connect } from 'node:net'
 import os from 'node:os'
 import path from 'node:path'
 
-import { test } from 'vitest'
+import { expect, test, vi } from 'vitest'
 
 import {
   CREATE_NO_WINDOW,
+  execGit,
   NO_CONSOLE_GIT_SCRIPT,
   planNoConsoleGitSpawn,
   resolveNoConsolePython,
@@ -17,6 +19,67 @@ import {
 const gitArgs = ['-c', 'windows.appendAtomically=false', 'merge-base', '--is-ancestor', 'origin/main', 'HEAD']
 const gitBin = 'C:\\Program Files\\Git\\cmd\\git.exe'
 
+test('a timed-out git command reaps descendants, including the Windows Python host', async () => {
+  const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'git-timeout-'))
+  const pids = path.join(dir, 'pids.json')
+  const fixture = path.join(dir, 'hang.cjs')
+
+  const listening = (port: number): Promise<boolean> =>
+    new Promise(resolve => {
+      const socket = connect(port, '127.0.0.1')
+
+      const done = (alive: boolean) => {
+        socket.destroy()
+        resolve(alive)
+      }
+
+      socket.once('connect', () => done(true))
+      socket.once('error', () => done(false))
+      socket.setTimeout(2000, () => done(true))
+    })
+
+  fs.writeFileSync(
+    fixture,
+    `
+    const { spawn } = require('node:child_process');
+    const worker = String.raw\`const fs = require('node:fs');
+      const server = require('node:net').createServer(socket => socket.end());
+      server.listen(0, '127.0.0.1', () => fs.writeFileSync(process.argv[1],
+        JSON.stringify({ pids: [Number(process.argv[2]), process.pid], port: server.address().port })));\`;
+    spawn(process.execPath, ['-e', worker, process.argv[2], String(process.pid)], { stdio: 'inherit' });
+    setInterval(() => {}, 1000);
+  `
+  )
+
+  try {
+    if (process.platform === 'win32') {
+      const python = execFileSync('python3', ['-c', 'import sys; print(sys.executable)'], { encoding: 'utf8' }).trim()
+      vi.stubEnv('HERMES_DESKTOP_PYTHON', python)
+    }
+
+    const success = await execGit(process.execPath, ['-e', 'process.stdout.write("ok")'], { timeoutMs: 5000 })
+    expect(success).toMatchObject({ code: 0, stdout: 'ok' })
+
+    const error = await execGit(process.execPath, [fixture, pids], { timeoutMs: 5000 }).catch(error => error)
+    const { port } = JSON.parse(fs.readFileSync(pids, 'utf8'))
+    await vi.waitFor(async () => expect(await listening(port)).toBe(false), { timeout: 3000 })
+    expect(error).toMatchObject({ code: 'ETIMEDOUT' })
+  } finally {
+    if (fs.existsSync(pids)) {
+      for (const pid of JSON.parse(fs.readFileSync(pids, 'utf8')).pids) {
+        try {
+          process.kill(pid, 'SIGKILL')
+        } catch {
+          /* already reaped */
+        }
+      }
+    }
+
+    vi.unstubAllEnvs()
+    fs.rmSync(dir, { recursive: true, force: true })
+  }
+}, 20_000)
+
 test('windows git spawn uses a CREATE_NO_WINDOW host and does not rewrite git argv', () => {
   const plan = planNoConsoleGitSpawn({
     gitBin,
diff --git a/apps/desktop/electron/no-console-git.ts b/apps/desktop/electron/no-console-git.ts
index e969556651..dfeffe0e75 100644
--- a/apps/desktop/electron/no-console-git.ts
+++ b/apps/desktop/electron/no-console-git.ts
@@ -8,7 +8,7 @@
 // unchanged. simple-git cannot take a creation flag, so its binary tuple is
 // [python, this host script].
 
-import { spawn, type SpawnOptions } from 'node:child_process'
+import { execFile, spawn, type SpawnOptions } from 'node:child_process'
 import fs from 'node:fs'
 import os from 'node:os'
 import path from 'node:path'
@@ -252,6 +252,9 @@ export function execGit(
   const spec = hiddenGitSpawnSpec(gitBin, args, {
     cwd: options.cwd,
     env: options.env,
+    // Timed commands own a POSIX group so a promisor fetch cannot outlive
+    // the git process. On Windows taskkill follows the Python host's tree.
+    detached: Boolean(options.timeoutMs) && process.platform !== 'win32',
     stdio: ['ignore', 'pipe', 'pipe']
   })
 
@@ -260,6 +263,7 @@ export function execGit(
     let stdout = ''
     let stderr = ''
     let settled = false
+    let timeoutError: (NodeJS.ErrnoException & { stderr?: string }) | undefined
 
     const finish = (error?: Error, code: number | null = child.exitCode) => {
       if (settled) {
@@ -268,6 +272,10 @@ export function execGit(
 
       settled = true
 
+      if (timer) {
+        clearTimeout(timer)
+      }
+
       if (error) {
         reject(error)
 
@@ -279,11 +287,40 @@ export function execGit(
 
     const timer = options.timeoutMs
       ? setTimeout(() => {
-          child.kill()
-          const error = new Error('git timed out') as NodeJS.ErrnoException & { stderr?: string }
+          timeoutError = Object.assign(new Error('git timed out'), { code: 'ETIMEDOUT', stderr })
 
-          error.stderr = stderr
-          finish(error)
+          const done = () => {
+            // Pipes held by descendants must not keep Electron alive after a
+            // failed tree kill. The timeout remains a failure, never exit 0.
+            child.stdout?.destroy()
+            child.stderr?.destroy()
+            finish(timeoutError)
+          }
+
+          if (process.platform === 'win32' && child.pid) {
+            execFile(
+              'taskkill',
+              ['/PID', String(child.pid), '/T', '/F'],
+              { windowsHide: true, timeout: 5000 },
+              error => {
+                if (error) {
+                  child.kill('SIGKILL')
+                }
+
+                done()
+              }
+            )
+          } else {
+            try {
+              if (child.pid) {
+                process.kill(-child.pid, 'SIGKILL')
+              }
+            } catch {
+              child.kill('SIGKILL')
+            }
+
+            done()
+          }
         }, options.timeoutMs)
       : null
 
@@ -305,7 +342,10 @@ export function execGit(
         clearTimeout(timer)
       }
 
-      finish(undefined, code)
+      // On Windows wait for taskkill's completion, not just the root's exit.
+      if (!timeoutError) {
+        finish(undefined, code)
+      }
     })
   })
 }