diff --git a/packages/api/src/__tests__/rate-card-write-support.test.ts b/packages/api/src/__tests__/rate-card-write-support.test.ts
index c23416e..0e62806 100644
--- a/packages/api/src/__tests__/rate-card-write-support.test.ts
+++ b/packages/api/src/__tests__/rate-card-write-support.test.ts
@@ -1,13 +1,61 @@
 import { describe, expect, it } from "vitest";
 import {
+  buildRateCardCreateAuditAfter,
   buildRateCardCreateData,
+  buildRateCardLineCreateAuditAfter,
   buildRateCardLineCreateData,
   buildRateCardLineUpdateData,
   buildRateCardListWhere,
+  buildRateCardReplaceLinesAuditAfter,
   buildRateCardUpdateData,
+  rateCardCreateInclude,
+  rateCardDetailInclude,
+  rateCardLineOrderBy,
+  rateCardSummaryInclude,
 } from "../router/rate-card-write-support.js";
 
 describe("rate card write support", () => {
+  it("exposes shared include definitions", () => {
+    expect(rateCardSummaryInclude).toEqual({
+      _count: { select: { lines: true } },
+      client: { select: { id: true, name: true, code: true } },
+    });
+
+    expect(rateCardLineOrderBy).toEqual([
+      { chapter: "asc" },
+      { seniority: "asc" },
+      { createdAt: "asc" },
+    ]);
+
+    expect(rateCardDetailInclude).toEqual({
+      client: { select: { id: true, name: true, code: true } },
+      lines: {
+        select: {
+          id: true,
+          rateCardId: true,
+          roleId: true,
+          chapter: true,
+          seniority: true,
+          location: true,
+          workType: true,
+          serviceGroup: true,
+          costRateCents: true,
+          billRateCents: true,
+          machineRateCents: true,
+          attributes: true,
+          role: { select: { id: true, name: true } },
+        },
+        orderBy: rateCardLineOrderBy,
+      },
+    });
+
+    expect(rateCardCreateInclude).toEqual({
+      lines: {
+        select: rateCardDetailInclude.lines.select,
+      },
+    });
+  });
+
   it("builds rate card list filters including effective date windows", () => {
     expect(buildRateCardListWhere({
       isActive: true,
@@ -97,4 +145,37 @@ describe("rate card write support", () => {
       attributes: { region: "de" },
     });
   });
+
+  it("builds compact audit payloads", () => {
+    expect(buildRateCardCreateAuditAfter({
+      name: "Q1 2026",
+      currency: "EUR",
+      lines: [
+        { costRateCents: 9500, attributes: {} },
+        { costRateCents: 8000, attributes: {} },
+      ],
+    })).toEqual({
+      name: "Q1 2026",
+      currency: "EUR",
+      lineCount: 2,
+    });
+
+    expect(buildRateCardLineCreateAuditAfter({
+      rateCardId: "rc_1",
+      line: {
+        chapter: "Delivery",
+        costRateCents: 9500,
+        billRateCents: 14000,
+      },
+    })).toEqual({
+      rateCardId: "rc_1",
+      chapter: "Delivery",
+      costRateCents: 9500,
+      billRateCents: 14000,
+    });
+
+    expect(buildRateCardReplaceLinesAuditAfter(3)).toEqual({
+      replacedLineCount: 3,
+    });
+  });
 });
diff --git a/packages/api/src/router/rate-card-write-support.ts b/packages/api/src/router/rate-card-write-support.ts
index 026f372..42f27c9 100644
--- a/packages/api/src/router/rate-card-write-support.ts
+++ b/packages/api/src/router/rate-card-write-support.ts
@@ -19,6 +19,45 @@ type CreateRateCardLineInput = z.infer<typeof CreateRateCardLineSchema>;
 type UpdateRateCardInput = z.infer<typeof UpdateRateCardSchema>;
 type UpdateRateCardLineInput = z.infer<typeof UpdateRateCardLineSchema>;
 
+export const rateCardSummaryInclude = {
+  _count: { select: { lines: true } },
+  client: { select: { id: true, name: true, code: true } },
+} as const;
+
+export const rateCardLineOrderBy: Prisma.RateCardLineOrderByWithRelationInput[] = [
+  { chapter: "asc" },
+  { seniority: "asc" },
+  { createdAt: "asc" },
+];
+
+export const rateCardDetailInclude = {
+  client: { select: { id: true, name: true, code: true } },
+  lines: {
+    select: {
+      id: true,
+      rateCardId: true,
+      roleId: true,
+      chapter: true,
+      seniority: true,
+      location: true,
+      workType: true,
+      serviceGroup: true,
+      costRateCents: true,
+      billRateCents: true,
+      machineRateCents: true,
+      attributes: true,
+      role: { select: { id: true, name: true } },
+    },
+    orderBy: rateCardLineOrderBy,
+  },
+} as const;
+
+export const rateCardCreateInclude = {
+  lines: {
+    select: rateCardDetailInclude.lines.select,
+  },
+} as const;
+
 function buildRateCardLineCoreData(
   line: CreateRateCardLineInput,
 ) {
@@ -134,3 +173,33 @@ export function buildRateCardLineUpdateData(
 
   return updateData;
 }
+
+export function buildRateCardCreateAuditAfter(
+  input: Pick<CreateRateCardInput, "name" | "currency" | "lines">,
+) {
+  return {
+    name: input.name,
+    currency: input.currency,
+    lineCount: input.lines.length,
+  };
+}
+
+export function buildRateCardLineCreateAuditAfter(
+  input: {
+    rateCardId: string;
+    line: Pick<CreateRateCardLineInput, "costRateCents" | "billRateCents" | "chapter">;
+  },
+) {
+  return {
+    rateCardId: input.rateCardId,
+    costRateCents: input.line.costRateCents,
+    billRateCents: input.line.billRateCents,
+    chapter: input.line.chapter ?? null,
+  };
+}
+
+export function buildRateCardReplaceLinesAuditAfter(
+  replacedLineCount: number,
+) {
+  return { replacedLineCount };
+}
diff --git a/packages/api/src/router/rate-card.ts b/packages/api/src/router/rate-card.ts
index 6853bdb..326d9e8 100644
--- a/packages/api/src/router/rate-card.ts
+++ b/packages/api/src/router/rate-card.ts
@@ -15,12 +15,18 @@ import {
   resolveBestRateLineMatch,
 } from "./rate-card-read.js";
 import {
+  buildRateCardCreateAuditAfter,
   buildRateCardCreateData,
+  buildRateCardLineCreateAuditAfter,
   buildRateCardLineCreateData,
   buildRateCardLineUpdateData,
   buildRateCardListWhere,
+  buildRateCardReplaceLinesAuditAfter,
   buildRateCardUpdateData,
+  rateCardCreateInclude,
+  rateCardDetailInclude,
   buildRateCardNestedLineCreateData,
+  rateCardSummaryInclude,
 } from "./rate-card-write-support.js";
 
 export const rateCardRouter = createTRPCRouter({
@@ -36,10 +42,7 @@ export const rateCardRouter = createTRPCRouter({
     .query(async ({ ctx, input }) => {
       return ctx.db.rateCard.findMany({
         where: buildRateCardListWhere(input),
-        include: {
-          _count: { select: { lines: true } },
-          client: { select: { id: true, name: true, code: true } },
-        },
+        include: rateCardSummaryInclude,
         orderBy: [{ isActive: "desc" }, { effectiveFrom: "desc" }, { name: "asc" }],
       });
     }),
@@ -50,13 +53,7 @@ export const rateCardRouter = createTRPCRouter({
       const rateCard = await findUniqueOrThrow(
         ctx.db.rateCard.findUnique({
           where: { id: input.id },
-          include: {
-            client: { select: { id: true, name: true, code: true } },
-            lines: {
-              select: rateCardLineSelect,
-              orderBy: [{ chapter: "asc" }, { seniority: "asc" }, { createdAt: "asc" }],
-            },
-          },
+          include: rateCardDetailInclude,
         }),
         "Rate card",
       );
@@ -88,9 +85,7 @@ export const rateCardRouter = createTRPCRouter({
 
       const rateCard = await ctx.db.rateCard.create({
         data: buildRateCardCreateData(input),
-        include: {
-          lines: { select: rateCardLineSelect },
-        },
+        include: rateCardCreateInclude,
       });
 
       void createAuditEntry({
@@ -100,7 +95,7 @@ export const rateCardRouter = createTRPCRouter({
         entityName: rateCard.name,
         action: "CREATE",
         userId: ctx.dbUser?.id,
-        after: { name, currency, lineCount: lines.length },
+        after: buildRateCardCreateAuditAfter({ name, currency, lines }),
         source: "ui",
       });
 
@@ -118,10 +113,7 @@ export const rateCardRouter = createTRPCRouter({
       const updated = await ctx.db.rateCard.update({
         where: { id: input.id },
         data: buildRateCardUpdateData(input.data),
-        include: {
-          _count: { select: { lines: true } },
-          client: { select: { id: true, name: true, code: true } },
-        },
+        include: rateCardSummaryInclude,
       });
 
       void createAuditEntry({
@@ -183,7 +175,10 @@ export const rateCardRouter = createTRPCRouter({
         entityName: `${rateCard.name} — ${input.line.chapter ?? "line"}`,
         action: "CREATE",
         userId: ctx.dbUser?.id,
-        after: { rateCardId: input.rateCardId, costRateCents: input.line.costRateCents, billRateCents: input.line.billRateCents },
+        after: buildRateCardLineCreateAuditAfter({
+          rateCardId: input.rateCardId,
+          line: input.line,
+        }),
         source: "ui",
       });
 
@@ -279,7 +274,7 @@ export const rateCardRouter = createTRPCRouter({
         entityName: rateCard.name,
         action: "UPDATE",
         userId: ctx.dbUser?.id,
-        after: { replacedLineCount: result.length },
+        after: buildRateCardReplaceLinesAuditAfter(result.length),
         source: "ui",
         summary: `Replaced all lines with ${result.length} new lines`,
       });