diff --git a/ondeck/src/lib/tasks/__tests__/generate-and-assign-core.test.ts b/ondeck/src/lib/tasks/__tests__/generate-and-assign-core.test.ts
new file mode 100644
index 0000000..ed5dccb
--- /dev/null
+++ b/ondeck/src/lib/tasks/__tests__/generate-and-assign-core.test.ts
@@ -0,0 +1,47 @@
+import { parseGenerateAndAssignTarget, GenerateAndAssignError } from '../generate-and-assign-core'
+
+describe('parseGenerateAndAssignTarget', () => {
+  it('parses advocate+designation mode', () => {
+    const { target, dryRun } = parseGenerateAndAssignTarget({
+      advocateId: 'adv-1',
+      designationId: 'des-1',
+    })
+    expect(target).toEqual({ mode: 'advocate-designation', advocateId: 'adv-1', designationId: 'des-1' })
+    expect(dryRun).toBe(false)
+  })
+
+  it('parses client mode', () => {
+    const { target, dryRun } = parseGenerateAndAssignTarget({ clientId: 'client-1', dryRun: true })
+    expect(target).toEqual({ mode: 'client', clientId: 'client-1' })
+    expect(dryRun).toBe(true)
+  })
+
+  it('defaults dryRun to false when omitted', () => {
+    const { dryRun } = parseGenerateAndAssignTarget({ clientId: 'client-1' })
+    expect(dryRun).toBe(false)
+  })
+
+  it('throws when both modes are provided', () => {
+    expect(() =>
+      parseGenerateAndAssignTarget({ advocateId: 'a', designationId: 'd', clientId: 'c' })
+    ).toThrow(GenerateAndAssignError)
+  })
+
+  it('throws when neither mode is provided', () => {
+    expect(() => parseGenerateAndAssignTarget({})).toThrow(GenerateAndAssignError)
+  })
+
+  it('throws when advocateId is given without designationId', () => {
+    expect(() => parseGenerateAndAssignTarget({ advocateId: 'a' })).toThrow(GenerateAndAssignError)
+  })
+
+  it('sets a 400 status on validation errors', () => {
+    try {
+      parseGenerateAndAssignTarget({})
+      fail('expected throw')
+    } catch (err) {
+      expect(err).toBeInstanceOf(GenerateAndAssignError)
+      expect((err as GenerateAndAssignError).status).toBe(400)
+    }
+  })
+})
diff --git a/ondeck/src/lib/tasks/generate-and-assign-core.ts b/ondeck/src/lib/tasks/generate-and-assign-core.ts
new file mode 100644
index 0000000..da5d545
--- /dev/null
+++ b/ondeck/src/lib/tasks/generate-and-assign-core.ts
@@ -0,0 +1,38 @@
+export class GenerateAndAssignError extends Error {
+  status: number
+  constructor(message: string, status: number) {
+    super(message)
+    this.status = status
+  }
+}
+
+export type GenerateTarget =
+  | { mode: 'advocate-designation'; advocateId: string; designationId: string }
+  | { mode: 'client'; clientId: string }
+
+/**
+ * Parses and validates a generate-and-assign request body. Exactly one of
+ * (advocateId + designationId) or clientId must be present.
+ */
+export function parseGenerateAndAssignTarget(body: any): { target: GenerateTarget; dryRun: boolean } {
+  const dryRun = body?.dryRun === true
+  const hasAdvocateDesignation = !!body?.advocateId && !!body?.designationId
+  const hasClient = !!body?.clientId
+
+  if (hasAdvocateDesignation && hasClient) {
+    throw new GenerateAndAssignError(
+      'Provide either advocateId+designationId or clientId, not both',
+      400
+    )
+  }
+  if (hasClient) {
+    return { target: { mode: 'client', clientId: body.clientId }, dryRun }
+  }
+  if (hasAdvocateDesignation) {
+    return {
+      target: { mode: 'advocate-designation', advocateId: body.advocateId, designationId: body.designationId },
+      dryRun,
+    }
+  }
+  throw new GenerateAndAssignError('advocateId and designationId, or clientId, are required', 400)
+}