diff --git a/src/lib/services/eoi-context.ts b/src/lib/services/eoi-context.ts
new file mode 100644
index 0000000..650c977
--- /dev/null
+++ b/src/lib/services/eoi-context.ts
@@ -0,0 +1,264 @@
+import { and, desc, eq } from 'drizzle-orm';
+
+import { db } from '@/lib/db';
+import { berths } from '@/lib/db/schema/berths';
+import { clients, clientAddresses, clientContacts } from '@/lib/db/schema/clients';
+import { companies, companyAddresses } from '@/lib/db/schema/companies';
+import { interests } from '@/lib/db/schema/interests';
+import { ports } from '@/lib/db/schema/ports';
+import { yachts } from '@/lib/db/schema/yachts';
+import { NotFoundError, ValidationError } from '@/lib/errors';
+
+// ─── Types ────────────────────────────────────────────────────────────────────
+
+export type EoiContext = {
+  client: {
+    fullName: string;
+    nationality: string | null;
+    primaryEmail: string | null;
+    primaryPhone: string | null;
+    address: { street: string; city: string; country: string } | null;
+  };
+  yacht: {
+    name: string;
+    lengthFt: string | null;
+    widthFt: string | null;
+    draftFt: string | null;
+    lengthM: string | null;
+    widthM: string | null;
+    draftM: string | null;
+    hullNumber: string | null;
+    flag: string | null;
+    yearBuilt: number | null;
+  };
+  company: {
+    name: string;
+    legalName: string | null;
+    taxId: string | null;
+    billingAddress: string | null;
+  } | null;
+  owner: {
+    type: 'client' | 'company';
+    name: string;
+    legalName?: string;
+  };
+  berth: {
+    mooringNumber: string;
+    area: string | null;
+    lengthFt: string | null;
+    price: string | null;
+    priceCurrency: string;
+    tenureType: string;
+  };
+  interest: {
+    stage: string;
+    leadCategory: string | null;
+    dateFirstContact: Date | null;
+    notes: string | null;
+  };
+  port: {
+    name: string;
+    defaultCurrency: string;
+  };
+  date: {
+    today: string;
+    year: string;
+  };
+};
+
+// ─── buildEoiContext ──────────────────────────────────────────────────────────
+
+/**
+ * Assembles the shared context object used by EOI generation, templates, and
+ * any other flow that needs a denormalised snapshot of an interest + its
+ * surrounding entities (client, yacht, berth, owner, port, etc.).
+ *
+ * Pure read-only: no audit logs, no socket emits, no mutations.
+ *
+ * Tenant-scoped: every fetch is gated by `portId`, and missing rows surface
+ * as NotFoundError. Missing yacht/berth references on the interest surface as
+ * ValidationError, because EOI flows cannot proceed without them.
+ */
+export async function buildEoiContext(interestId: string, portId: string): Promise<EoiContext> {
+  // 1. Interest (tenant-scoped)
+  const interest = await db.query.interests.findFirst({
+    where: and(eq(interests.id, interestId), eq(interests.portId, portId)),
+  });
+  if (!interest) {
+    throw new NotFoundError('Interest');
+  }
+
+  // 2. Yacht reference must exist on the interest
+  if (!interest.yachtId) {
+    throw new ValidationError('interest has no yacht');
+  }
+
+  // 3. Berth reference must exist on the interest
+  if (!interest.berthId) {
+    throw new ValidationError('interest has no berth');
+  }
+
+  // 2 + 3 + 4 + 9: parallelise independent reads.
+  const [yacht, berth, client, port] = await Promise.all([
+    db.query.yachts.findFirst({
+      where: and(eq(yachts.id, interest.yachtId), eq(yachts.portId, portId)),
+    }),
+    db.query.berths.findFirst({
+      where: and(eq(berths.id, interest.berthId), eq(berths.portId, portId)),
+    }),
+    db.query.clients.findFirst({
+      where: and(eq(clients.id, interest.clientId), eq(clients.portId, portId)),
+    }),
+    db.query.ports.findFirst({
+      where: eq(ports.id, portId),
+    }),
+  ]);
+
+  if (!yacht) throw new NotFoundError('Yacht');
+  if (!berth) throw new NotFoundError('Berth');
+  if (!client) throw new NotFoundError('Client');
+  if (!port) throw new NotFoundError('Port');
+
+  // 5. Primary contacts — email + phone for the interest's client.
+  const contactRows = await db
+    .select({
+      channel: clientContacts.channel,
+      value: clientContacts.value,
+      isPrimary: clientContacts.isPrimary,
+      updatedAt: clientContacts.updatedAt,
+    })
+    .from(clientContacts)
+    .where(eq(clientContacts.clientId, client.id))
+    .orderBy(desc(clientContacts.isPrimary), desc(clientContacts.updatedAt));
+
+  const firstEmail = contactRows.find((c) => c.channel === 'email');
+  const firstPhone =
+    contactRows.find((c) => c.channel === 'phone') ??
+    contactRows.find((c) => c.channel === 'whatsapp');
+
+  // 6. Primary address.
+  const [primaryAddress] = await db
+    .select({
+      streetAddress: clientAddresses.streetAddress,
+      city: clientAddresses.city,
+      country: clientAddresses.country,
+    })
+    .from(clientAddresses)
+    .where(and(eq(clientAddresses.clientId, client.id), eq(clientAddresses.isPrimary, true)))
+    .limit(1);
+
+  const clientAddress = primaryAddress
+    ? {
+        street: primaryAddress.streetAddress ?? '',
+        city: primaryAddress.city ?? '',
+        country: primaryAddress.country ?? '',
+      }
+    : null;
+
+  // 7 + 8. Yacht owner (polymorphic) + optional company billing address.
+  let ownerBlock: EoiContext['owner'];
+  let companyBlock: EoiContext['company'] = null;
+
+  if (yacht.currentOwnerType === 'client') {
+    // The yacht-owning client may or may not be the same as the interest's client.
+    const ownerClient =
+      yacht.currentOwnerId === client.id
+        ? client
+        : await db.query.clients.findFirst({
+            where: and(eq(clients.id, yacht.currentOwnerId), eq(clients.portId, portId)),
+          });
+    if (!ownerClient) throw new NotFoundError('Client');
+    ownerBlock = { type: 'client', name: ownerClient.fullName };
+  } else if (yacht.currentOwnerType === 'company') {
+    const company = await db.query.companies.findFirst({
+      where: and(eq(companies.id, yacht.currentOwnerId), eq(companies.portId, portId)),
+    });
+    if (!company) throw new NotFoundError('Company');
+
+    ownerBlock = {
+      type: 'company',
+      name: company.name,
+      ...(company.legalName ? { legalName: company.legalName } : {}),
+    };
+
+    const [companyPrimaryAddress] = await db
+      .select({
+        streetAddress: companyAddresses.streetAddress,
+        city: companyAddresses.city,
+        country: companyAddresses.country,
+      })
+      .from(companyAddresses)
+      .where(and(eq(companyAddresses.companyId, company.id), eq(companyAddresses.isPrimary, true)))
+      .limit(1);
+
+    const billingAddress = companyPrimaryAddress
+      ? [
+          companyPrimaryAddress.streetAddress,
+          companyPrimaryAddress.city,
+          companyPrimaryAddress.country,
+        ]
+          .filter((s): s is string => Boolean(s))
+          .join(', ') || null
+      : null;
+
+    companyBlock = {
+      name: company.name,
+      legalName: company.legalName,
+      taxId: company.taxId,
+      billingAddress,
+    };
+  } else {
+    throw new ValidationError(`unknown yacht owner type: ${String(yacht.currentOwnerType)}`);
+  }
+
+  // 10. Date.
+  const now = new Date();
+  const today = now.toISOString().slice(0, 10);
+  const year = String(now.getFullYear());
+
+  return {
+    client: {
+      fullName: client.fullName,
+      nationality: client.nationality,
+      primaryEmail: firstEmail?.value ?? null,
+      primaryPhone: firstPhone?.value ?? null,
+      address: clientAddress,
+    },
+    yacht: {
+      name: yacht.name,
+      lengthFt: yacht.lengthFt,
+      widthFt: yacht.widthFt,
+      draftFt: yacht.draftFt,
+      lengthM: yacht.lengthM,
+      widthM: yacht.widthM,
+      draftM: yacht.draftM,
+      hullNumber: yacht.hullNumber,
+      flag: yacht.flag,
+      yearBuilt: yacht.yearBuilt,
+    },
+    company: companyBlock,
+    owner: ownerBlock,
+    berth: {
+      mooringNumber: berth.mooringNumber,
+      area: berth.area,
+      lengthFt: berth.lengthFt,
+      price: berth.price,
+      priceCurrency: berth.priceCurrency,
+      tenureType: berth.tenureType,
+    },
+    interest: {
+      stage: interest.pipelineStage,
+      leadCategory: interest.leadCategory,
+      dateFirstContact: interest.dateFirstContact,
+      notes: interest.notes,
+    },
+    port: {
+      name: port.name,
+      defaultCurrency: port.defaultCurrency,
+    },
+    date: {
+      today,
+      year,
+    },
+  };
+}
diff --git a/tests/unit/services/eoi-context.test.ts b/tests/unit/services/eoi-context.test.ts
new file mode 100644
index 0000000..a1d1d27
--- /dev/null
+++ b/tests/unit/services/eoi-context.test.ts
@@ -0,0 +1,273 @@
+import { describe, it, expect } from 'vitest';
+
+import { buildEoiContext } from '@/lib/services/eoi-context';
+import { makePort, makeClient, makeCompany, makeBerth, makeYacht } from '../../helpers/factories';
+import { db } from '@/lib/db';
+import { interests, clientContacts, clientAddresses, companyAddresses } from '@/lib/db/schema';
+import { ValidationError, NotFoundError } from '@/lib/errors';
+
+// ─── Helpers ──────────────────────────────────────────────────────────────────
+
+async function insertInterest(args: {
+  portId: string;
+  clientId: string;
+  yachtId?: string | null;
+  berthId?: string | null;
+  pipelineStage?: string;
+}) {
+  const [row] = await db
+    .insert(interests)
+    .values({
+      portId: args.portId,
+      clientId: args.clientId,
+      yachtId: args.yachtId ?? null,
+      berthId: args.berthId ?? null,
+      pipelineStage: args.pipelineStage ?? 'open',
+    })
+    .returning();
+  return row!;
+}
+
+// ─── Tests ────────────────────────────────────────────────────────────────────
+
+describe('buildEoiContext', () => {
+  it('returns a fully-populated context for a client-owned yacht', async () => {
+    const port = await makePort();
+    const client = await makeClient({
+      portId: port.id,
+      overrides: { fullName: 'Alice Test', nationality: 'US' },
+    });
+
+    // Insert contacts.
+    await db.insert(clientContacts).values([
+      {
+        clientId: client.id,
+        channel: 'email',
+        value: 'alice@example.com',
+        isPrimary: true,
+      },
+      {
+        clientId: client.id,
+        channel: 'phone',
+        value: '+1-555-1234',
+        isPrimary: true,
+      },
+    ]);
+
+    // Insert primary address.
+    await db.insert(clientAddresses).values({
+      clientId: client.id,
+      portId: port.id,
+      streetAddress: '1 Harbour Way',
+      city: 'Anguilla',
+      country: 'AI',
+      isPrimary: true,
+    });
+
+    const yacht = await makeYacht({
+      portId: port.id,
+      ownerType: 'client',
+      ownerId: client.id,
+      name: 'Sea Breeze',
+      overrides: {
+        lengthFt: '60',
+        widthFt: '20',
+        draftFt: '8',
+        hullNumber: 'HN-1',
+        flag: 'US',
+        yearBuilt: 2020,
+      },
+    });
+
+    const berth = await makeBerth({
+      portId: port.id,
+      overrides: { mooringNumber: 'M-42', area: 'North', lengthFt: '70' },
+    });
+
+    const interest = await insertInterest({
+      portId: port.id,
+      clientId: client.id,
+      yachtId: yacht.id,
+      berthId: berth.id,
+      pipelineStage: 'in_communication',
+    });
+
+    const ctx = await buildEoiContext(interest.id, port.id);
+
+    // Client assertions.
+    expect(ctx.client.fullName).toBe('Alice Test');
+    expect(ctx.client.nationality).toBe('US');
+    expect(ctx.client.primaryEmail).toBe('alice@example.com');
+    expect(ctx.client.primaryPhone).toBe('+1-555-1234');
+    expect(ctx.client.address).toEqual({
+      street: '1 Harbour Way',
+      city: 'Anguilla',
+      country: 'AI',
+    });
+
+    // Yacht assertions.
+    expect(ctx.yacht.name).toBe('Sea Breeze');
+    expect(ctx.yacht.hullNumber).toBe('HN-1');
+    expect(ctx.yacht.yearBuilt).toBe(2020);
+
+    // Berth assertions.
+    expect(ctx.berth.mooringNumber).toBe('M-42');
+    expect(ctx.berth.area).toBe('North');
+
+    // Interest assertions.
+    expect(ctx.interest.stage).toBe('in_communication');
+
+    // Port assertions.
+    expect(ctx.port.name).toBe(port.name);
+    expect(ctx.port.defaultCurrency).toBe(port.defaultCurrency);
+
+    // Date assertions.
+    expect(ctx.date.today).toMatch(/^\d{4}-\d{2}-\d{2}$/);
+    expect(ctx.date.year).toMatch(/^\d{4}$/);
+
+    // Owner assertions.
+    expect(ctx.owner.type).toBe('client');
+    expect(ctx.owner.name).toBe('Alice Test');
+
+    // Company field.
+    expect(ctx.company).toBeNull();
+  });
+
+  it('returns a fully-populated context for a company-owned yacht', async () => {
+    const port = await makePort();
+    const company = await makeCompany({
+      portId: port.id,
+      overrides: { name: 'Acme Shipping', legalName: 'Acme Shipping Ltd.' },
+    });
+    const client = await makeClient({
+      portId: port.id,
+      overrides: { fullName: 'Bob Contact' },
+    });
+
+    const yacht = await makeYacht({
+      portId: port.id,
+      ownerType: 'company',
+      ownerId: company.id,
+      name: 'Acme Runner',
+    });
+
+    const berth = await makeBerth({ portId: port.id });
+
+    const interest = await insertInterest({
+      portId: port.id,
+      clientId: client.id,
+      yachtId: yacht.id,
+      berthId: berth.id,
+    });
+
+    const ctx = await buildEoiContext(interest.id, port.id);
+
+    expect(ctx.owner.type).toBe('company');
+    expect(ctx.owner.name).toBe('Acme Shipping');
+    expect(ctx.owner.legalName).toBe('Acme Shipping Ltd.');
+    expect(ctx.company).not.toBeNull();
+    expect(ctx.company!.name).toBe('Acme Shipping');
+    expect(ctx.company!.legalName).toBe('Acme Shipping Ltd.');
+  });
+
+  it('includes company billingAddress when company has a primary address', async () => {
+    const port = await makePort();
+    const company = await makeCompany({
+      portId: port.id,
+      overrides: { name: 'Billing Co' },
+    });
+    await db.insert(companyAddresses).values({
+      companyId: company.id,
+      portId: port.id,
+      streetAddress: '99 Commerce St',
+      city: 'Valley',
+      country: 'AI',
+      isPrimary: true,
+    });
+
+    const client = await makeClient({ portId: port.id });
+    const yacht = await makeYacht({
+      portId: port.id,
+      ownerType: 'company',
+      ownerId: company.id,
+    });
+    const berth = await makeBerth({ portId: port.id });
+
+    const interest = await insertInterest({
+      portId: port.id,
+      clientId: client.id,
+      yachtId: yacht.id,
+      berthId: berth.id,
+    });
+
+    const ctx = await buildEoiContext(interest.id, port.id);
+
+    expect(ctx.company).not.toBeNull();
+    expect(ctx.company!.billingAddress).not.toBeNull();
+    expect(ctx.company!.billingAddress).toContain('99 Commerce St');
+    expect(ctx.company!.billingAddress).toContain('Valley');
+    expect(ctx.company!.billingAddress).toContain('AI');
+  });
+
+  it('throws ValidationError when interest has no yacht', async () => {
+    const port = await makePort();
+    const client = await makeClient({ portId: port.id });
+    const berth = await makeBerth({ portId: port.id });
+
+    const interest = await insertInterest({
+      portId: port.id,
+      clientId: client.id,
+      yachtId: null,
+      berthId: berth.id,
+    });
+
+    await expect(buildEoiContext(interest.id, port.id)).rejects.toThrow(ValidationError);
+    await expect(buildEoiContext(interest.id, port.id)).rejects.toThrow(/interest has no yacht/i);
+  });
+
+  it('throws ValidationError when interest has no berth', async () => {
+    const port = await makePort();
+    const client = await makeClient({ portId: port.id });
+    const yacht = await makeYacht({
+      portId: port.id,
+      ownerType: 'client',
+      ownerId: client.id,
+    });
+
+    const interest = await insertInterest({
+      portId: port.id,
+      clientId: client.id,
+      yachtId: yacht.id,
+      berthId: null,
+    });
+
+    await expect(buildEoiContext(interest.id, port.id)).rejects.toThrow(ValidationError);
+    await expect(buildEoiContext(interest.id, port.id)).rejects.toThrow(/interest has no berth/i);
+  });
+
+  it('throws NotFoundError for non-existent interest', async () => {
+    const port = await makePort();
+    await expect(buildEoiContext('fake-id', port.id)).rejects.toThrow(NotFoundError);
+  });
+
+  it('is tenant-scoped (interest from different port throws NotFoundError)', async () => {
+    const portA = await makePort();
+    const portB = await makePort();
+    const client = await makeClient({ portId: portA.id });
+    const yacht = await makeYacht({
+      portId: portA.id,
+      ownerType: 'client',
+      ownerId: client.id,
+    });
+    const berth = await makeBerth({ portId: portA.id });
+
+    const interest = await insertInterest({
+      portId: portA.id,
+      clientId: client.id,
+      yachtId: yacht.id,
+      berthId: berth.id,
+    });
+
+    await expect(buildEoiContext(interest.id, portB.id)).rejects.toThrow(NotFoundError);
+  });
+});