diff --git a/apps/hq-web/src/api.ts b/apps/hq-web/src/api.ts
index f74a632..7dd9030 100644
--- a/apps/hq-web/src/api.ts
+++ b/apps/hq-web/src/api.ts
@@ -559,6 +559,25 @@ export async function downloadModuleClientsCsv(moduleId: string, moduleCode: str
   URL.revokeObjectURL(url)
 }
 
+// ---------- APEX import (D18 WS-B; owner-only) ----------
+export interface ImportReport {
+  clients: { staged: number; problems: number }
+  invoices: { staged: number; problems: number; totalPaise: number }
+  samples: { firstClients: string[]; lastInvoices: string[] }
+}
+export interface ImportStatus {
+  report: ImportReport
+  problemClients: { row_no: number; code: string | null; name: string | null; problems: string }[]
+  problemInvoices: { row_no: number; client_code: string | null; doc_no: string | null; problems: string }[]
+}
+export const getImportStatus = (): Promise<ImportStatus> => apiFetch<ImportStatus>('/import/status')
+export const stageApexCsv = (body: { clientsCsv?: string; invoicesCsv?: string }): Promise<ImportReport> =>
+  apiFetch<{ report: ImportReport }>('/import/stage', { method: 'POST', body: JSON.stringify(body) }).then((r) => r.report)
+export const commitApexImport = (): Promise<{ clients: number; invoices: number; seeded: { fy: string; lastSeq: number } | null }> =>
+  apiFetch<{ result: { clients: number; invoices: number; seeded: { fy: string; lastSeq: number } | null } }>(
+    '/import/commit', { method: 'POST', body: '{}' },
+  ).then((r) => r.result)
+
 /** The PDF route needs the bearer header, which an <iframe src> can't carry — fetch a blob instead. */
 export async function fetchPdfBlob(documentId: string): Promise<Blob> {
   const token = localStorage.getItem(TOKEN_KEY) ?? ''
diff --git a/apps/hq-web/src/main.tsx b/apps/hq-web/src/main.tsx
index e87f034..163af04 100644
--- a/apps/hq-web/src/main.tsx
+++ b/apps/hq-web/src/main.tsx
@@ -17,6 +17,7 @@ import { NewDocument } from './pages/NewDocument'
 import { DocumentView } from './pages/DocumentView'
 import { Employees } from './pages/Employees'
 import { Profile } from './pages/Profile'
+import { ImportApex } from './pages/ImportApex'
 import { Pipeline } from './pages/Pipeline'
 import { Documents } from './pages/Documents'
 import { Reminders } from './pages/Reminders'
@@ -38,6 +39,7 @@ function App() {
           <Route path="/settings/template" element={<Navigate to="/settings?s=template" replace />} />
           <Route path="/employees" element={<Employees />} />
           <Route path="/profile" element={<Profile />} />
+          <Route path="/import" element={<ImportApex />} />
           <Route path="/documents" element={<Documents />} />
           <Route path="/documents/new" element={<NewDocument />} />
           <Route path="/documents/:id" element={<DocumentView />} />
diff --git a/apps/hq-web/src/nav.ts b/apps/hq-web/src/nav.ts
index 22cef8f..8b4660a 100644
--- a/apps/hq-web/src/nav.ts
+++ b/apps/hq-web/src/nav.ts
@@ -1,5 +1,6 @@
 import {
-  BarChart3, BellRing, Boxes, FilePlus2, Files, Filter, LayoutDashboard, Settings as SettingsIcon, UserCog, Users,
+  BarChart3, BellRing, Boxes, FilePlus2, Files, Filter, LayoutDashboard, Settings as SettingsIcon,
+  Upload, UserCog, Users,
   type LucideIcon,
 } from 'lucide-react'
 
@@ -29,6 +30,7 @@ export const NAV_GROUPS: NavGroup[] = [
     label: 'Admin',
     items: [
       { to: '/employees', label: 'Employees', icon: UserCog, ownerOnly: true },
+      { to: '/import', label: 'APEX Import', icon: Upload, ownerOnly: true },
       { to: '/settings', label: 'Settings', icon: SettingsIcon },
     ],
   },
diff --git a/apps/hq-web/src/pages/ImportApex.tsx b/apps/hq-web/src/pages/ImportApex.tsx
new file mode 100644
index 0000000..6d24904
--- /dev/null
+++ b/apps/hq-web/src/pages/ImportApex.tsx
@@ -0,0 +1,157 @@
+import { useState } from 'react'
+import { formatINR } from '@sims/domain'
+import {
+  Badge, Button, ConfirmDialog, DataTable, EmptyState, ErrorState, Notice, PageHeader,
+  Skeleton, StatCard, Stats, Toolbar, useToast,
+} from '@sims/ui'
+import { commitApexImport, getImportStatus, stageApexCsv } from '../api'
+import { useData } from './Clients'
+
+/**
+ * APEX cutover importer (D18 WS-B; owner-only). Stage the two CSV exports →
+ * every row carries its own problem list → verify the totals → Commit, which the
+ * server refuses while ANY problem remains. Re-stage as many times as needed;
+ * after the final commit APEX goes read-only (no double entry, spec §4).
+ */
+export function ImportApex() {
+  const toast = useToast()
+  const status = useData(getImportStatus, [])
+  const [clientsCsv, setClientsCsv] = useState<string | undefined>()
+  const [invoicesCsv, setInvoicesCsv] = useState<string | undefined>()
+  const [busy, setBusy] = useState(false)
+  const [confirming, setConfirming] = useState(false)
+  const [done, setDone] = useState<string | undefined>()
+
+  const readFile = (set: (t: string) => void) => (e: React.ChangeEvent<HTMLInputElement>) => {
+    const file = e.target.files?.[0]
+    if (file === undefined) return
+    const reader = new FileReader()
+    reader.onload = () => set(String(reader.result ?? ''))
+    reader.onerror = () => toast.err(`Could not read ${file.name}`)
+    reader.readAsText(file)
+  }
+
+  const stage = () => {
+    if (busy) return
+    if (clientsCsv === undefined && invoicesCsv === undefined) { toast.err('Pick at least one CSV first'); return }
+    setBusy(true); setDone(undefined)
+    stageApexCsv({
+      ...(clientsCsv !== undefined ? { clientsCsv } : {}),
+      ...(invoicesCsv !== undefined ? { invoicesCsv } : {}),
+    })
+      .then(() => { toast.ok('Staged — review the report below'); status.reload() })
+      .catch((e: Error) => toast.err(e.message))
+      .finally(() => setBusy(false))
+  }
+
+  const commit = () => {
+    setBusy(true)
+    commitApexImport()
+      .then((r) => {
+        setDone(`Committed: ${r.clients} clients, ${r.invoices} invoices`
+          + (r.seeded !== null ? ` · INVOICE series seeded past ${r.seeded.fy} #${r.seeded.lastSeq}` : ''))
+        toast.ok('Import committed — APEX is now read-only reference')
+        status.reload()
+      })
+      .catch((e: Error) => toast.err(e.message))
+      .finally(() => { setBusy(false); setConfirming(false) })
+  }
+
+  const s = status.data
+  const problems = (s?.report.clients.problems ?? 0) + (s?.report.invoices.problems ?? 0)
+  const staged = (s?.report.clients.staged ?? 0) + (s?.report.invoices.staged ?? 0)
+
+  return (
+    <div className="wf-page">
+      <PageHeader
+        title="APEX import"
+        desc="The one-time 300-client cutover: stage the CSVs, clear every problem, verify, commit. Trial-run freely — only Commit writes real data."
+      />
+
+      <section>
+        <h2>1 · Stage the CSV exports</h2>
+        <Toolbar>
+          <label className="wf" style={{ display: 'inline-flex', gap: 8, alignItems: 'center' }}>
+            clients.csv
+            <input type="file" accept=".csv,text/csv" onChange={readFile(setClientsCsv)} />
+            {clientsCsv !== undefined && <Badge tone="ok">loaded</Badge>}
+          </label>
+          <label className="wf" style={{ display: 'inline-flex', gap: 8, alignItems: 'center' }}>
+            invoices.csv
+            <input type="file" accept=".csv,text/csv" onChange={readFile(setInvoicesCsv)} />
+            {invoicesCsv !== undefined && <Badge tone="ok">loaded</Badge>}
+          </label>
+          <Button tone="primary" onClick={stage}>{busy ? 'Staging…' : 'Stage'}</Button>
+        </Toolbar>
+      </section>
+
+      <section>
+        <h2>2 · Verification report</h2>
+        {status.error !== undefined ? <ErrorState message={status.error} onRetry={status.reload} />
+          : s === undefined ? <Skeleton rows={3} />
+          : staged === 0 ? <EmptyState>Nothing staged yet.</EmptyState> : (
+          <>
+            <Stats>
+              <StatCard label="Clients staged" value={String(s.report.clients.staged)}
+                {...(s.report.clients.problems > 0 ? { hint: `${s.report.clients.problems} with problems`, hintTone: 'err' as const } : { hint: 'clean' })} />
+              <StatCard label="Invoices staged" value={String(s.report.invoices.staged)}
+                {...(s.report.invoices.problems > 0 ? { hint: `${s.report.invoices.problems} with problems`, hintTone: 'err' as const } : { hint: 'clean' })} />
+              <StatCard label="Invoice value" value={formatINR(s.report.invoices.totalPaise)} hint="cross-check vs APEX" />
+            </Stats>
+            <p style={{ fontSize: 12, opacity: 0.75 }}>
+              First clients: {s.report.samples.firstClients.join(' · ') || '—'}<br />
+              Last invoices: {s.report.samples.lastInvoices.join(' · ') || '—'}
+            </p>
+            {s.problemClients.length > 0 && (
+              <>
+                <h3>Client rows with problems (first 50 of {s.report.clients.problems})</h3>
+                <DataTable
+                  columns={[{ key: 'row', label: 'Row' }, { key: 'code', label: 'Code', mono: true }, { key: 'name', label: 'Name' }, { key: 'problems', label: 'Problems' }]}
+                  rows={s.problemClients.map((p) => ({
+                    row: String(p.row_no), code: p.code ?? '—', name: p.name ?? '—',
+                    problems: (JSON.parse(p.problems) as string[]).join('; '),
+                  }))}
+                />
+              </>
+            )}
+            {s.problemInvoices.length > 0 && (
+              <>
+                <h3>Invoice rows with problems (first 50 of {s.report.invoices.problems})</h3>
+                <DataTable
+                  columns={[{ key: 'row', label: 'Row' }, { key: 'client', label: 'Client code', mono: true }, { key: 'docNo', label: 'Doc no', mono: true }, { key: 'problems', label: 'Problems' }]}
+                  rows={s.problemInvoices.map((p) => ({
+                    row: String(p.row_no), client: p.client_code ?? '—', docNo: p.doc_no ?? '—',
+                    problems: (JSON.parse(p.problems) as string[]).join('; '),
+                  }))}
+                />
+              </>
+            )}
+          </>
+        )}
+      </section>
+
+      <section>
+        <h2>3 · Commit</h2>
+        {problems > 0 && <Notice tone="err">{problems} staged row(s) still carry problems — fix the CSVs and re-stage. Commit stays locked.</Notice>}
+        {done !== undefined && <Notice tone="ok">{done}</Notice>}
+        <Button
+          tone="primary"
+          onClick={() => { if (staged > 0 && problems === 0 && !busy) setConfirming(true) }}
+        >
+          {busy ? 'Working…' : `Commit import${staged > 0 ? ` (${staged} rows)` : ''}`}
+        </Button>
+        {confirming && (
+          <ConfirmDialog
+            open
+            onClose={() => setConfirming(false)}
+            onConfirm={commit}
+            title="Commit the APEX import"
+            body="This writes the staged clients and invoices for real and seeds the INVOICE series past the legacy numbers. After the final cutover, APEX goes read-only — no double entry. Commit?"
+            confirmLabel="Commit import"
+            tone="danger"
+          />
+        )}
+      </section>
+    </div>
+  )
+}
diff --git a/apps/hq/src/api.ts b/apps/hq/src/api.ts
index 99b729f..2c28638 100644
--- a/apps/hq/src/api.ts
+++ b/apps/hq/src/api.ts
@@ -52,6 +52,7 @@ import {
 } from './repos-aws'
 import { pullMonthlyCosts } from './aws-costs'
 import { clientProfitability, duesAging, moduleRevenue, type DateRange } from './repos-reports'
+import { commitImport, stageCsv, verificationReport } from './import-apex'
 import { documentHtml, documentHtmlSample } from './templates'
 import { renderPdf } from './pdf'
 import { emailStatus } from './repos-email'
@@ -938,6 +939,47 @@ export function apiRouter(
     }
   })
 
+  // ---------- APEX import (D18 WS-B; owner-only — the cutover is one-shot) ----------
+  r.post('/import/stage', requireAuth, requireOwner, (req, res) => {
+    try {
+      const body = req.body as { clientsCsv?: unknown; invoicesCsv?: unknown }
+      const out: { clientsStaged?: number; invoicesStaged?: number } = {}
+      if (typeof body.clientsCsv === 'string' && body.clientsCsv !== '') {
+        out.clientsStaged = stageCsv(db, 'clients', body.clientsCsv).staged
+      }
+      if (typeof body.invoicesCsv === 'string' && body.invoicesCsv !== '') {
+        out.invoicesStaged = stageCsv(db, 'invoices', body.invoicesCsv).staged
+      }
+      if (out.clientsStaged === undefined && out.invoicesStaged === undefined) {
+        res.status(400).json({ ok: false, error: 'Provide clientsCsv and/or invoicesCsv as CSV text' })
+        return
+      }
+      writeAudit(db, staffId(res), 'import_stage', 'import', 'apex', undefined, out)
+      res.json({ ok: true, ...out, report: verificationReport(db) })
+    } catch (err) {
+      res.status(400).json({ ok: false, error: err instanceof Error ? err.message : String(err) })
+    }
+  })
+  r.get('/import/status', requireAuth, requireOwner, (_req, res) => {
+    // Per-row problem lists (first 50 each, with honest totals — rule 8).
+    const problemClients = db.prepare(
+      `SELECT row_no, code, name, problems FROM stg_client WHERE problems <> '[]' ORDER BY row_no LIMIT 50`,
+    ).all()
+    const problemInvoices = db.prepare(
+      `SELECT row_no, client_code, doc_no, problems FROM stg_invoice WHERE problems <> '[]' ORDER BY row_no LIMIT 50`,
+    ).all()
+    res.json({ ok: true, report: verificationReport(db), problemClients, problemInvoices })
+  })
+  r.post('/import/commit', requireAuth, requireOwner, (_req, res) => {
+    try {
+      const result = commitImport(db, staffId(res)) // refuses while ANY staged row has problems
+      writeAudit(db, staffId(res), 'import_commit', 'import', 'apex', undefined, result)
+      res.json({ ok: true, result })
+    } catch (err) {
+      res.status(400).json({ ok: false, error: err instanceof Error ? err.message : String(err) })
+    }
+  })
+
   // ---------- dashboard ----------
   // ?mine=1 = My Day (D18 WS-E): owner/manager narrow to their own book; staff
   // are always scoped server-side regardless of the param.
diff --git a/apps/hq/test/import-routes.test.ts b/apps/hq/test/import-routes.test.ts
new file mode 100644
index 0000000..3b556cb
--- /dev/null
+++ b/apps/hq/test/import-routes.test.ts
@@ -0,0 +1,78 @@
+// apps/hq/test/import-routes.test.ts — go-live cluster WS-B: APEX import over HTTP (D18)
+import express from 'express'
+import { describe, it, expect, afterAll } from 'vitest'
+import { openDb } from '../src/db'
+import { seedIfEmpty } from '../src/seed'
+import { createStaff } from '../src/auth'
+import { apiRouter } from '../src/api'
+
+const CLIENTS_CSV = 'code,name,gstin,state_code,address,phone,email,status\nAPX001,Acme Bank,,32,Kochi,,r@acme.in,active\n'
+const BAD_CLIENTS_CSV = 'code,name,gstin,state_code,address,phone,email,status\n,No Code Bank,,32,,,,active\n'
+// Amounts are RUPEES in the APEX export; staging converts via fromRupees.
+// Current-FY doc date so the INVOICE series seeds past the legacy number.
+const INVOICES_CSV = 'client_code,doc_no,doc_date,taxable,tax,total,paid\nAPX001,INV/26-27-0042,2026-07-01,1000,180,1180,1\n'
+
+function appWith() {
+  const db = openDb(':memory:'); seedIfEmpty(db)
+  createStaff(db, { email: 'owner@test.in', displayName: 'O', role: 'owner', password: 'owner-password' })
+  createStaff(db, { email: 'staff@test.in', displayName: 'S', role: 'staff', password: 'staff-password' })
+  const app = express(); app.use(express.json({ limit: '5mb' })); app.locals['db'] = db
+  app.use('/api', apiRouter(db))
+  const server = app.listen(0)
+  const baseUrl = `http://localhost:${(server.address() as { port: number }).port}/api`
+  return { db, server, baseUrl }
+}
+const login = async (baseUrl: string, email: string, password: string) =>
+  ((await (await fetch(`${baseUrl}/auth/login`, {
+    method: 'POST', headers: { 'content-type': 'application/json' },
+    body: JSON.stringify({ email, password }),
+  })).json()) as { token: string }).token
+const H = (t: string) => ({ 'content-type': 'application/json', authorization: `Bearer ${t}` })
+
+describe('APEX import routes (owner-only)', () => {
+  const servers: { close: () => void }[] = []
+  afterAll(() => { for (const s of servers) s.close() })
+
+  it('staff get 403 on every import route', async () => {
+    const ctx = appWith(); servers.push(ctx.server)
+    const t = await login(ctx.baseUrl, 'staff@test.in', 'staff-password')
+    for (const [method, path] of [['POST', '/import/stage'], ['GET', '/import/status'], ['POST', '/import/commit']] as const) {
+      const res = await fetch(`${ctx.baseUrl}${path}`, { method, headers: H(t), ...(method === 'POST' ? { body: '{}' } : {}) })
+      expect(res.status).toBe(403)
+    }
+  })
+
+  it('stage → status → commit round-trip; problems lock the commit until re-staged clean', async () => {
+    const ctx = appWith(); servers.push(ctx.server)
+    const t = await login(ctx.baseUrl, 'owner@test.in', 'owner-password')
+    // Stage a BAD clients file → problems reported, commit refused.
+    const bad = await fetch(`${ctx.baseUrl}/import/stage`, {
+      method: 'POST', headers: H(t), body: JSON.stringify({ clientsCsv: BAD_CLIENTS_CSV }),
+    })
+    const badJson = await bad.json() as { report: { clients: { problems: number } } }
+    expect(bad.status).toBe(200)
+    expect(badJson.report.clients.problems).toBeGreaterThan(0)
+    const refused = await fetch(`${ctx.baseUrl}/import/commit`, { method: 'POST', headers: H(t), body: '{}' })
+    expect(refused.status).toBe(400)
+    // Re-stage clean + invoices → status shows zero problems → commit succeeds.
+    const ok = await fetch(`${ctx.baseUrl}/import/stage`, {
+      method: 'POST', headers: H(t), body: JSON.stringify({ clientsCsv: CLIENTS_CSV, invoicesCsv: INVOICES_CSV }),
+    })
+    expect(ok.status).toBe(200)
+    const status = await (await fetch(`${ctx.baseUrl}/import/status`, { headers: H(t) })).json() as {
+      report: { clients: { problems: number }; invoices: { problems: number } }
+      problemClients: unknown[]
+    }
+    expect(status.report.clients.problems).toBe(0)
+    expect(status.report.invoices.problems).toBe(0)
+    const commit = await fetch(`${ctx.baseUrl}/import/commit`, { method: 'POST', headers: H(t), body: '{}' })
+    const cj = await commit.json() as { result: { clients: number; invoices: number; seeded: { fy: string; lastSeq: number } | null } }
+    expect(commit.status).toBe(200)
+    expect(cj.result.clients).toBe(1)
+    expect(cj.result.invoices).toBe(1)
+    expect(cj.result.seeded).not.toBeNull() // INVOICE series seeded past the legacy number
+    // The imported rows are real now.
+    const imported = ctx.db.prepare(`SELECT source, status FROM document WHERE doc_no='INV/26-27-0042'`).get()
+    expect(imported).toMatchObject({ source: 'apex' })
+  })
+})