diff --git a/e2e/work-orders/wizard-vendor-company-notes.spec.ts b/e2e/work-orders/wizard-vendor-company-notes.spec.ts
new file mode 100644
index 00000000..df507616
--- /dev/null
+++ b/e2e/work-orders/wizard-vendor-company-notes.spec.ts
@@ -0,0 +1,168 @@
+import { expect, test, type Page, type Route } from "@playwright/test";
+
+const FROZEN_NOW = "2026-08-19T15:00:00.000Z";
+
+const TEST_USER = {
+  token: "wizard-vendor-notes-e2e-token",
+  expiration: "2030-01-01T00:00:00.000Z",
+  email: "admin@seahavenind.com",
+  userRoles: "Admin",
+  phoneNumber: "5551234567",
+  fullname: "Work Order E2E Admin",
+  id: "1",
+};
+
+const LOCATIONS = [
+  {
+    id: 10,
+    name: "STL-01 · St. Louis, MO",
+    siteCode: "STL-01",
+    city: "St. Louis",
+    state: "MO",
+    code: "STL-01",
+  },
+];
+
+const VENDORS = [
+  {
+    id: 101,
+    companyName: "Gateway Plumbing",
+    contactName: "Adam Whyte",
+    tradeSpecialties: "Plumbing",
+    address: "1 Market St",
+  },
+];
+
+type Captured = { method: string; path: string; body: unknown };
+
+async function fulfillJson(route: Route, body: unknown, status = 200) {
+  await route.fulfill({ status, contentType: "application/json", body: JSON.stringify(body) });
+}
+
+async function mockApi(page: Page, captured: Captured[]) {
+  await page.route(
+    (url) => url.pathname.startsWith("/api/"),
+    async (route) => {
+      const request = route.request();
+      const { pathname } = new URL(request.url());
+      if (request.method() !== "GET") {
+        captured.push({ method: request.method(), path: pathname, body: request.postDataJSON() });
+      }
+      if (pathname.endsWith("/workorders/board") && request.method() === "POST") {
+        await fulfillJson(route, { data: { id: 900, woNumber: "SH00900" } });
+        return;
+      }
+      if (pathname.endsWith("/vendor-company-roster/55") && request.method() === "PATCH") {
+        await fulfillJson(route, {
+          companyId: 55,
+          rowVersion: "rv-2",
+          name: "Gateway Plumbing",
+          notes: "Gate code 4411",
+          technicians: [],
+        });
+        return;
+      }
+      if (pathname.endsWith("/vendor-company-roster") && request.method() === "GET") {
+        await fulfillJson(route, {
+          companyId: 55,
+          rowVersion: "rv-1",
+          name: "Gateway Plumbing",
+          notes: "Call before arrival",
+          technicians: [{ id: 101, contactName: "Adam Whyte", isActive: true }],
+        });
+        return;
+      }
+      if (pathname.includes("workorders/board")) {
+        await fulfillJson(route, {
+          weekStart: "2026-08-17",
+          weekEnd: "2026-08-21",
+          counts: { returned: 0, total: 0 },
+          unscheduled: [],
+          scheduled: [],
+          items: [],
+        });
+        return;
+      }
+      if (pathname.endsWith("/locations/10")) {
+        await fulfillJson(route, {
+          data: {
+            id: 10,
+            name: "STL-01 · St. Louis, MO",
+            contact: "Jamie Site",
+            phone: "3145550100",
+            zipCode: "63101",
+          },
+        });
+        return;
+      }
+      if (pathname.includes("/locations/sites") || pathname.includes("/Contact/GetLocations")) {
+        await fulfillJson(route, { data: LOCATIONS });
+        return;
+      }
+      if (pathname.toLowerCase().includes("/vendors/dropdown")) {
+        await fulfillJson(route, { data: VENDORS });
+        return;
+      }
+      await fulfillJson(route, { data: [], items: [] });
+    },
+  );
+}
+
+test.describe("wizard vendor company notes (SH-321)", () => {
+  test.setTimeout(60_000);
+
+  test("pre-fills the company notes and saves edits to the vendor company on create", async ({
+    page,
+  }) => {
+    const captured: Captured[] = [];
+    await page.clock.install({ time: new Date(FROZEN_NOW) });
+    await page.clock.resume();
+    await page.addInitScript((user) => {
+      localStorage.setItem("auth", JSON.stringify(user));
+      const style = document.createElement("style");
+      style.textContent = ".tsqd-parent-container { display: none !important; }";
+      document.documentElement.appendChild(style);
+    }, TEST_USER);
+    await mockApi(page, captured);
+
+    await page.goto("/workorders");
+    await page.getByRole("button", { name: "New WO" }).click();
+    await expect(page.getByRole("heading", { name: "Type & schedule" })).toBeVisible({
+      timeout: 20_000,
+    });
+    await page.getByRole("button", { name: "Continue" }).click();
+
+    await page.getByRole("button", { name: /Select site/ }).click();
+    await page.getByRole("button", { name: "STL-01 · St. Louis, MO" }).first().click();
+    await expect(page.getByRole("button", { name: "Continue" })).toBeEnabled();
+    await page.getByRole("button", { name: "Continue" }).click();
+
+    await page.getByRole("button", { name: /Select technician/ }).click();
+    await page
+      .getByRole("button", { name: /Adam Whyte/ })
+      .last()
+      .first()
+      .click();
+
+    const notes = page.getByPlaceholder("Contact preferences, availability, etc.");
+    await expect(notes).toHaveValue("Call before arrival");
+    await notes.fill("Gate code 4411");
+
+    await page.getByRole("button", { name: /Create/ }).click();
+
+    await expect
+      .poll(() => captured.find((c) => c.method === "PATCH"))
+      .toEqual({
+        method: "PATCH",
+        path: "/api/vendor-company-roster/55",
+        body: {
+          rowVersion: "rv-1",
+          addTechnicians: [],
+          companyFields: { notes: "Gate code 4411" },
+        },
+      });
+    expect(captured.some((c) => c.method === "POST" && c.path.endsWith("/workorders/board"))).toBe(
+      true,
+    );
+  });
+});
diff --git a/src/app/(protected)/workorders/_components/wizard/use-new-wo-wizard-controller.ts b/src/app/(protected)/workorders/_components/wizard/use-new-wo-wizard-controller.ts
index 0a5f394b..17069cc9 100644
--- a/src/app/(protected)/workorders/_components/wizard/use-new-wo-wizard-controller.ts
+++ b/src/app/(protected)/workorders/_components/wizard/use-new-wo-wizard-controller.ts
@@ -14,6 +14,7 @@ import { useCreateWorkOrderFromWizard } from "@/domain/work-orders/use-cases/use
 import { useNewWoWizardDraft } from "@/app/(protected)/workorders/_components/wizard/use-new-wo-wizard-draft";
 import { useWizardDuplicateActions } from "@/app/(protected)/workorders/_components/wizard/use-wizard-duplicate-actions";
 import { useWizardPocAutofill } from "@/app/(protected)/workorders/_components/wizard/use-wizard-poc-autofill";
+import { useWizardVendorCompanyNotes } from "@/app/(protected)/workorders/_components/wizard/use-wizard-vendor-company-notes";
 import { useServicesForWorkOrderType } from "@/domain/services/use-cases/use-services-for-work-order-type";
 
 type UseNewWoWizardControllerArgs = {
@@ -49,6 +50,12 @@ export function useNewWoWizardController({
     draftState.setDraft,
   );
 
+  const { saveCompanyNotes } = useWizardVendorCompanyNotes(
+    open,
+    draftState.draft.vendorId,
+    draftState.setDraft,
+  );
+
   const patchDraft = (patch: Partial<WorkOrderWizardDraft>) => {
     draftState.patchDraft(patch);
     if (patch.locationId !== undefined) {
@@ -56,7 +63,15 @@ export function useNewWoWizardController({
     }
   };
 
-  const createMutation = useCreateWorkOrderFromWizard(() => onOpenChange(false));
+  const createMutation = useCreateWorkOrderFromWizard((createdDraft) => {
+    // Close the dialog first: the work-order create's isPending has already dropped, so
+    // holding the dialog open through the notes save would re-enable Create and unlock
+    // pointer events, and a second click would create a second work order. The save runs
+    // independently of the dialog — fetchCurrentBaseline covers a missing baseline and the
+    // note-save failure toast is surfaced from the mutation itself, not the dialog.
+    onOpenChange(false);
+    void saveCompanyNotes(createdDraft);
+  });
   const { duplicateRow, setDuplicateRow, handleDuplicateFound, handleCreate, isCreating } =
     useWizardDuplicateActions({
       open,
diff --git a/src/app/(protected)/workorders/_components/wizard/use-wizard-vendor-company-notes.ts b/src/app/(protected)/workorders/_components/wizard/use-wizard-vendor-company-notes.ts
new file mode 100644
index 00000000..73625b6a
--- /dev/null
+++ b/src/app/(protected)/workorders/_components/wizard/use-wizard-vendor-company-notes.ts
@@ -0,0 +1,120 @@
+import { useEffect, useState } from "react";
+import { useQueryClient } from "@tanstack/react-query";
+import { toast } from "react-toastify";
+import type { WorkOrderWizardDraft } from "@/domain/work-orders/types/work-order-wizard";
+import { useVendorCompanyRoster } from "@/domain/vendors/use-cases/use-vendor-company-roster";
+import {
+  NOTES_SAVE_FAILED_MESSAGE,
+  useSaveVendorCompanyNotes,
+} from "@/domain/vendors/use-cases/use-save-vendor-company-notes";
+import { vendorCompanyRosterApi } from "@/domain/vendors/api/vendor-company-roster-api";
+import { queryKeys } from "@/infra/query-key/query-key";
+import {
+  buildCompanyNotesUpdate,
+  type VendorCompanyNotesBaseline,
+} from "@/domain/vendors/utils/build-company-notes-patch";
+
+type SetDraft = (updater: (current: WorkOrderWizardDraft) => WorkOrderWizardDraft) => void;
+
+type VendorNotesBaseline = VendorCompanyNotesBaseline & { vendorId: string };
+
+/**
+ * The wizard's Vendor Notes field is the vendor company's notes (same field as the Vendors
+ * page). Picking a technician pre-fills the company's current notes once per company, so
+ * switching technicians within the same company keeps the dispatcher's edits. Notes typed
+ * for the current selection always win over roster data that arrives late, and a save whose
+ * baseline is missing or belongs to another selection reads the current roster before
+ * building the PATCH.
+ */
+export function useWizardVendorCompanyNotes(open: boolean, vendorId: string, setDraft: SetDraft) {
+  const queryClient = useQueryClient();
+  const { data: roster } = useVendorCompanyRoster(vendorId || undefined);
+  const saveNotes = useSaveVendorCompanyNotes();
+  const [baseline, setBaseline] = useState<VendorNotesBaseline | null>(null);
+
+  useEffect(() => {
+    if (open) {
+      setBaseline(null);
+    }
+  }, [open]);
+
+  useEffect(() => {
+    if (!vendorId) {
+      // Cleared technician: the next pick re-seeds even for the same company.
+      if (baseline) setBaseline(null);
+      return;
+    }
+    if (!roster || roster.companyId === null) {
+      return;
+    }
+    if (
+      baseline &&
+      baseline.vendorId === vendorId &&
+      String(baseline.companyId) === String(roster.companyId)
+    ) {
+      return;
+    }
+    setBaseline({
+      vendorId,
+      companyId: roster.companyId,
+      rowVersion: roster.rowVersion,
+      notes: roster.notes,
+    });
+    setDraft((current) => {
+      if (current.vendorId !== vendorId) {
+        return current;
+      }
+      // Seed only empty content or content still holding the previous company's unedited
+      // notes; anything else is the dispatcher's typing and must never be overwritten.
+      if (current.vendorNotes !== "" && current.vendorNotes !== baseline?.notes) {
+        return current;
+      }
+      return { ...current, vendorNotes: roster.notes };
+    });
+  }, [vendorId, roster, baseline, setDraft]);
+
+  async function fetchCurrentBaseline(vendorId: string): Promise<VendorNotesBaseline | null> {
+    try {
+      const current = await queryClient.fetchQuery({
+        queryKey: queryKeys.vendors.roster("vendorId", vendorId),
+        queryFn: () => vendorCompanyRosterApi.get({ vendorId }),
+      });
+      if (!current || current.companyId === null) {
+        return null;
+      }
+      return {
+        vendorId,
+        companyId: current.companyId,
+        rowVersion: current.rowVersion,
+        notes: current.notes,
+      };
+    } catch {
+      toast.error(NOTES_SAVE_FAILED_MESSAGE);
+      return null;
+    }
+  }
+
+  async function saveCompanyNotes(draft: WorkOrderWizardDraft): Promise<void> {
+    if (!draft.vendorId) {
+      return;
+    }
+    const active =
+      baseline && baseline.vendorId === draft.vendorId
+        ? baseline
+        : await fetchCurrentBaseline(draft.vendorId);
+    if (!active) {
+      return;
+    }
+    const update = buildCompanyNotesUpdate(active, draft.vendorNotes);
+    if (!update) {
+      return;
+    }
+    try {
+      await saveNotes.mutateAsync(update);
+    } catch {
+      // The mutation already surfaces the note-save failure toast.
+    }
+  }
+
+  return { saveCompanyNotes };
+}
diff --git a/src/app/(protected)/workorders/_components/wizard/wizard-step-location-service-select.tsx b/src/app/(protected)/workorders/_components/wizard/wizard-step-location-service-select.tsx
index baadd66e..8b15610d 100644
--- a/src/app/(protected)/workorders/_components/wizard/wizard-step-location-service-select.tsx
+++ b/src/app/(protected)/workorders/_components/wizard/wizard-step-location-service-select.tsx
@@ -29,7 +29,7 @@ export function WizardStepLocationServiceSelect({
   onPatch,
 }: WizardStepLocationServiceSelectProps) {
   const clearVendorIfPrimaryChanged = (nextPm: string): Partial<WorkOrderWizardDraft> =>
-    nextPm !== draft.pm ? { vendorId: "", vendorName: "", techPhone: "" } : {};
+    nextPm !== draft.pm ? { vendorId: "", vendorName: "", techPhone: "", vendorNotes: "" } : {};
 
   const selectSvc = (p: string) => {
     const selected = services.find((service) => service.value === p);
diff --git a/src/app/(protected)/workorders/_components/wizard/wizard-step-vendor-time.tsx b/src/app/(protected)/workorders/_components/wizard/wizard-step-vendor-time.tsx
index 1fbd6142..1d052b45 100644
--- a/src/app/(protected)/workorders/_components/wizard/wizard-step-vendor-time.tsx
+++ b/src/app/(protected)/workorders/_components/wizard/wizard-step-vendor-time.tsx
@@ -206,7 +206,7 @@ export function WizardStepVendorTime({
           optional
           onClear={
             draft.vendorId !== ""
-              ? () => onPatch({ vendorId: "", vendorName: "", techPhone: "" })
+              ? () => onPatch({ vendorId: "", vendorName: "", techPhone: "", vendorNotes: "" })
               : undefined
           }
         >
diff --git a/src/domain/vendors/use-cases/use-save-vendor-company-notes.ts b/src/domain/vendors/use-cases/use-save-vendor-company-notes.ts
new file mode 100644
index 00000000..9e98976b
--- /dev/null
+++ b/src/domain/vendors/use-cases/use-save-vendor-company-notes.ts
@@ -0,0 +1,29 @@
+import { useMutation, useQueryClient, type UseMutationResult } from "@tanstack/react-query";
+import { toast } from "react-toastify";
+import { vendorCompanyRosterApi } from "@/domain/vendors/api/vendor-company-roster-api";
+import type { VendorCompanyRoster } from "@/domain/vendors/types/vendor";
+import type { VendorCompanyNotesUpdate } from "@/domain/vendors/utils/build-company-notes-patch";
+import { queryKeys } from "@/infra/query-key/query-key";
+
+export const NOTES_SAVE_FAILED_MESSAGE =
+  "Work order created, but the vendor notes could not be saved.";
+
+/** Writes company-level vendor notes and refreshes every vendor view that shows them. */
+export function useSaveVendorCompanyNotes(): UseMutationResult<
+  VendorCompanyRoster,
+  unknown,
+  VendorCompanyNotesUpdate
+> {
+  const queryClient = useQueryClient();
+
+  return useMutation({
+    mutationFn: ({ companyId, patch }: VendorCompanyNotesUpdate) =>
+      vendorCompanyRosterApi.addTechnicians(companyId, patch),
+    onSuccess: () => {
+      void queryClient.invalidateQueries({ queryKey: queryKeys.vendors.all });
+    },
+    onError: () => {
+      toast.error(NOTES_SAVE_FAILED_MESSAGE);
+    },
+  });
+}
diff --git a/src/domain/vendors/utils/build-company-notes-patch.ts b/src/domain/vendors/utils/build-company-notes-patch.ts
new file mode 100644
index 00000000..3546a3cc
--- /dev/null
+++ b/src/domain/vendors/utils/build-company-notes-patch.ts
@@ -0,0 +1,35 @@
+import type { VendorCompanyRoster } from "@/domain/vendors/types/vendor";
+import type { VendorRosterAdditivePatch } from "@/domain/vendors/mappers/vendor-roster-mapper";
+
+export type VendorCompanyNotesBaseline = Pick<
+  VendorCompanyRoster,
+  "companyId" | "rowVersion" | "notes"
+>;
+
+export interface VendorCompanyNotesUpdate {
+  companyId: string | number;
+  patch: VendorRosterAdditivePatch;
+}
+
+/**
+ * Company-level notes edited outside the Vendors page (e.g. the Create WO wizard)
+ * are written through the additive roster PATCH, which only touches the fields sent.
+ * Returns null when nothing changed. Clearing notes is not expressible on that PATCH
+ * (blank company fields mean "unchanged"), so an emptied field is not sent.
+ */
+export function buildCompanyNotesUpdate(
+  baseline: VendorCompanyNotesBaseline | null | undefined,
+  editedNotes: string,
+): VendorCompanyNotesUpdate | null {
+  if (!baseline || baseline.companyId === null || !baseline.rowVersion) {
+    return null;
+  }
+  const notes = editedNotes.trim();
+  if (!notes || notes === baseline.notes.trim()) {
+    return null;
+  }
+  return {
+    companyId: baseline.companyId,
+    patch: { rowVersion: baseline.rowVersion, addTechnicians: [], companyFields: { notes } },
+  };
+}
diff --git a/src/domain/work-orders/use-cases/use-create-work-order-from-wizard.ts b/src/domain/work-orders/use-cases/use-create-work-order-from-wizard.ts
index 4aa4c8b8..5e4ad7c9 100644
--- a/src/domain/work-orders/use-cases/use-create-work-order-from-wizard.ts
+++ b/src/domain/work-orders/use-cases/use-create-work-order-from-wizard.ts
@@ -13,19 +13,19 @@ import type { WorkOrderWizardDraft } from "@/domain/work-orders/types/work-order
 import { queryKeys } from "@/infra/query-key/query-key";
 
 export function useCreateWorkOrderFromWizard(
-  onSuccess?: () => void,
+  onSuccess?: (draft: WorkOrderWizardDraft) => void,
 ): UseMutationResult<WorkOrderDetail, Error, WorkOrderWizardDraft> {
   const queryClient = useQueryClient();
 
   return useMutation({
     mutationFn: (draft: WorkOrderWizardDraft) => workOrdersApi.createFromBoard(draft),
 
-    onSuccess: () => {
+    onSuccess: (_created, draft) => {
       void queryClient.invalidateQueries({ queryKey: queryKeys.workOrders.all });
 
       toast.success("Work Order created successfully!");
 
-      onSuccess?.();
+      onSuccess?.(draft);
     },
 
     onError: (error: Error) => {
diff --git a/src/test/app/(protected)/workorders/use-wizard-vendor-company-notes.test.tsx b/src/test/app/(protected)/workorders/use-wizard-vendor-company-notes.test.tsx
new file mode 100644
index 00000000..8801c765
--- /dev/null
+++ b/src/test/app/(protected)/workorders/use-wizard-vendor-company-notes.test.tsx
@@ -0,0 +1,222 @@
+import { act, renderHook, waitFor } from "@testing-library/react";
+import { QueryClientProvider } from "@tanstack/react-query";
+import { useState, type ReactNode } from "react";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { useWizardVendorCompanyNotes } from "@/app/(protected)/workorders/_components/wizard/use-wizard-vendor-company-notes";
+import { NOTES_SAVE_FAILED_MESSAGE } from "@/domain/vendors/use-cases/use-save-vendor-company-notes";
+import {
+  EMPTY_WIZARD_DRAFT,
+  type WorkOrderWizardDraft,
+} from "@/domain/work-orders/types/work-order-wizard";
+import { toast } from "react-toastify";
+import { createTestQueryClient } from "@/test/test-utils";
+
+const rosterGet = vi.fn();
+const addTechnicians = vi.fn();
+
+vi.mock("@/domain/vendors/api/vendor-company-roster-api", () => ({
+  vendorCompanyRosterApi: {
+    get: (...args: unknown[]) => rosterGet(...args),
+    addTechnicians: (...args: unknown[]) => addTechnicians(...args),
+  },
+}));
+
+vi.mock("react-toastify", () => ({ toast: { success: vi.fn(), error: vi.fn() } }));
+
+type Roster = ReturnType<typeof roster>;
+
+function roster(companyId: number, notes: string) {
+  return {
+    companyId,
+    rowVersion: `rv-${companyId}`,
+    name: `Company ${companyId}`,
+    companyPhone: "",
+    email: "",
+    address: "",
+    city: "",
+    state: "",
+    zip: "",
+    googleMapsUrl: "",
+    notes,
+    technicians: [],
+  };
+}
+
+function deferredRoster() {
+  let resolve!: (value: Roster) => void;
+  const pending = new Promise<Roster>((res) => {
+    resolve = res;
+  });
+  return {
+    promise: () => pending,
+    resolveAll: (value: Roster) => resolve(value),
+  };
+}
+
+function useHarness() {
+  const [draft, setDraft] = useState<WorkOrderWizardDraft>({ ...EMPTY_WIZARD_DRAFT });
+  const notes = useWizardVendorCompanyNotes(true, draft.vendorId, setDraft);
+  return { draft, setDraft, ...notes };
+}
+
+function renderHarness() {
+  const client = createTestQueryClient();
+  const wrapper = ({ children }: { children: ReactNode }) => (
+    <QueryClientProvider client={client}>{children}</QueryClientProvider>
+  );
+  return renderHook(() => useHarness(), { wrapper });
+}
+
+describe("useWizardVendorCompanyNotes", () => {
+  beforeEach(() => {
+    rosterGet.mockReset();
+    addTechnicians.mockReset();
+    vi.mocked(toast.error).mockClear();
+    rosterGet.mockImplementation(({ vendorId }: { vendorId: string }) =>
+      Promise.resolve(
+        vendorId === "31" ? roster(9, "Other company notes") : roster(7, "Call before arrival"),
+      ),
+    );
+    addTechnicians.mockResolvedValue(roster(7, "Gate code 4411"));
+  });
+
+  it("pre-fills the Notes field with the picked technician's company notes", async () => {
+    const { result } = renderHarness();
+
+    act(() => result.current.setDraft((d) => ({ ...d, vendorId: "21" })));
+
+    await waitFor(() => expect(result.current.draft.vendorNotes).toBe("Call before arrival"));
+    expect(rosterGet).toHaveBeenCalledWith({ vendorId: "21", companyId: undefined });
+  });
+
+  it("keeps edits when switching technicians within the same company", async () => {
+    rosterGet.mockResolvedValue(roster(7, "Call before arrival"));
+    const { result } = renderHarness();
+    act(() => result.current.setDraft((d) => ({ ...d, vendorId: "21" })));
+    await waitFor(() => expect(result.current.draft.vendorNotes).toBe("Call before arrival"));
+
+    act(() => result.current.setDraft((d) => ({ ...d, vendorNotes: "Gate code 4411" })));
+    act(() => result.current.setDraft((d) => ({ ...d, vendorId: "22" })));
+
+    await waitFor(() =>
+      expect(rosterGet).toHaveBeenCalledWith({ vendorId: "22", companyId: undefined }),
+    );
+    expect(result.current.draft.vendorNotes).toBe("Gate code 4411");
+  });
+
+  it("re-seeds notes when the technician belongs to a different company", async () => {
+    const { result } = renderHarness();
+    act(() => result.current.setDraft((d) => ({ ...d, vendorId: "21" })));
+    await waitFor(() => expect(result.current.draft.vendorNotes).toBe("Call before arrival"));
+
+    act(() => result.current.setDraft((d) => ({ ...d, vendorId: "31" })));
+
+    await waitFor(() => expect(result.current.draft.vendorNotes).toBe("Other company notes"));
+  });
+
+  it("keeps notes typed before the roster resolves and saves them for that company", async () => {
+    const lateRoster = deferredRoster();
+    rosterGet.mockImplementation(({ vendorId }: { vendorId: string }) =>
+      vendorId === "21" ? lateRoster.promise() : Promise.resolve(roster(7, "Call before arrival")),
+    );
+    const { result } = renderHarness();
+    act(() => result.current.setDraft((d) => ({ ...d, vendorId: "21" })));
+    act(() => result.current.setDraft((d) => ({ ...d, vendorNotes: "Gate code 4411" })));
+
+    await act(async () => lateRoster.resolveAll(roster(7, "Call before arrival")));
+    expect(result.current.draft.vendorNotes).toBe("Gate code 4411");
+
+    await act(async () => {
+      await result.current.saveCompanyNotes({
+        ...result.current.draft,
+        vendorNotes: "Gate code 4411",
+      });
+    });
+
+    expect(addTechnicians).toHaveBeenCalledWith(7, {
+      rowVersion: "rv-7",
+      addTechnicians: [],
+      companyFields: { notes: "Gate code 4411" },
+    });
+  });
+
+  it("targets the newly selected company at save time while its roster is still loading", async () => {
+    const companyB = deferredRoster();
+    rosterGet.mockImplementation(({ vendorId }: { vendorId: string }) =>
+      vendorId === "21" ? Promise.resolve(roster(7, "Call before arrival")) : companyB.promise(),
+    );
+    const { result } = renderHarness();
+    act(() => result.current.setDraft((d) => ({ ...d, vendorId: "21" })));
+    await waitFor(() => expect(result.current.draft.vendorNotes).toBe("Call before arrival"));
+
+    act(() => result.current.setDraft((d) => ({ ...d, vendorId: "31" })));
+    act(() => result.current.setDraft((d) => ({ ...d, vendorNotes: "Gate code 4411" })));
+
+    let savePromise!: Promise<void>;
+    act(() => {
+      savePromise = result.current
+        .saveCompanyNotes({ ...result.current.draft, vendorNotes: "Gate code 4411" })
+        .then(() => undefined);
+    });
+    await act(async () => companyB.resolveAll(roster(9, "Other company notes")));
+    await act(async () => {
+      await savePromise;
+    });
+
+    expect(addTechnicians).toHaveBeenCalledWith(9, {
+      rowVersion: "rv-9",
+      addTechnicians: [],
+      companyFields: { notes: "Gate code 4411" },
+    });
+    expect(addTechnicians).not.toHaveBeenCalledWith(7, expect.anything());
+    expect(result.current.draft.vendorNotes).toBe("Gate code 4411");
+  });
+
+  it("warns without writing when the save-time roster read fails", async () => {
+    rosterGet.mockRejectedValue(new Error("roster down"));
+    const { result } = renderHarness();
+    act(() => result.current.setDraft((d) => ({ ...d, vendorId: "21" })));
+    act(() => result.current.setDraft((d) => ({ ...d, vendorNotes: "Gate code 4411" })));
+
+    await act(async () => {
+      await result.current.saveCompanyNotes({
+        ...result.current.draft,
+        vendorNotes: "Gate code 4411",
+      });
+    });
+
+    expect(toast.error).toHaveBeenCalledWith(NOTES_SAVE_FAILED_MESSAGE);
+    expect(addTechnicians).not.toHaveBeenCalled();
+  });
+
+  it("writes edited notes to the vendor company when the work order is created", async () => {
+    const { result } = renderHarness();
+    act(() => result.current.setDraft((d) => ({ ...d, vendorId: "21" })));
+    await waitFor(() => expect(result.current.draft.vendorNotes).toBe("Call before arrival"));
+
+    await act(async () => {
+      await result.current.saveCompanyNotes({
+        ...result.current.draft,
+        vendorNotes: "Gate code 4411",
+      });
+    });
+
+    expect(addTechnicians).toHaveBeenCalledWith(7, {
+      rowVersion: "rv-7",
+      addTechnicians: [],
+      companyFields: { notes: "Gate code 4411" },
+    });
+  });
+
+  it("does not write when the notes were left as the company's existing notes", async () => {
+    const { result } = renderHarness();
+    act(() => result.current.setDraft((d) => ({ ...d, vendorId: "21" })));
+    await waitFor(() => expect(result.current.draft.vendorNotes).toBe("Call before arrival"));
+
+    await act(async () => {
+      await result.current.saveCompanyNotes(result.current.draft);
+    });
+
+    expect(addTechnicians).not.toHaveBeenCalled();
+  });
+});
diff --git a/src/test/app/(protected)/workorders/wizard-service-clears-vendor.test.tsx b/src/test/app/(protected)/workorders/wizard-service-clears-vendor.test.tsx
index c46f95df..30658510 100644
--- a/src/test/app/(protected)/workorders/wizard-service-clears-vendor.test.tsx
+++ b/src/test/app/(protected)/workorders/wizard-service-clears-vendor.test.tsx
@@ -15,6 +15,7 @@ describe("WizardStepLocationServiceSelect — vendor clear on service change", (
       vendorId: "9",
       vendorName: "Old Vendor",
       techPhone: "555-0100",
+      vendorNotes: "Old company notes",
     };
 
     render(
@@ -43,6 +44,7 @@ describe("WizardStepLocationServiceSelect — vendor clear on service change", (
         vendorId: "",
         vendorName: "",
         techPhone: "",
+        vendorNotes: "",
       }),
     );
   });
@@ -56,6 +58,7 @@ describe("WizardStepLocationServiceSelect — vendor clear on service change", (
       vendorId: "9",
       vendorName: "Old Vendor",
       techPhone: "555-0100",
+      vendorNotes: "Old company notes",
     };
 
     render(
@@ -84,6 +87,7 @@ describe("WizardStepLocationServiceSelect — vendor clear on service change", (
       vendorId: "",
       vendorName: "",
       techPhone: "",
+      vendorNotes: "",
     });
   });
 });
diff --git a/src/test/domain/vendors/utils/build-company-notes-patch.test.ts b/src/test/domain/vendors/utils/build-company-notes-patch.test.ts
new file mode 100644
index 00000000..824ad1c8
--- /dev/null
+++ b/src/test/domain/vendors/utils/build-company-notes-patch.test.ts
@@ -0,0 +1,31 @@
+import { describe, expect, it } from "vitest";
+import { buildCompanyNotesUpdate } from "@/domain/vendors/utils/build-company-notes-patch";
+
+const baseline = { companyId: 12, rowVersion: "AAAAAAAAB9E=", notes: "Call before arrival" };
+
+describe("buildCompanyNotesUpdate", () => {
+  it("builds a notes-only additive patch when the notes changed", () => {
+    expect(buildCompanyNotesUpdate(baseline, "  Gate code 4411  ")).toEqual({
+      companyId: 12,
+      patch: {
+        rowVersion: "AAAAAAAAB9E=",
+        addTechnicians: [],
+        companyFields: { notes: "Gate code 4411" },
+      },
+    });
+  });
+
+  it("skips the write when the notes are unchanged apart from whitespace", () => {
+    expect(buildCompanyNotesUpdate(baseline, "Call before arrival  ")).toBeNull();
+  });
+
+  it("skips the write without a loaded company baseline", () => {
+    expect(buildCompanyNotesUpdate(null, "New notes")).toBeNull();
+    expect(buildCompanyNotesUpdate({ ...baseline, companyId: null }, "New notes")).toBeNull();
+    expect(buildCompanyNotesUpdate({ ...baseline, rowVersion: "" }, "New notes")).toBeNull();
+  });
+
+  it("does not send an emptied field, which the additive patch treats as unchanged", () => {
+    expect(buildCompanyNotesUpdate(baseline, "   ")).toBeNull();
+  });
+});