diff --git a/apps/opencase/src/application/case/endpoints/CreateFramework.ts b/apps/opencase/src/application/case/endpoints/CreateFramework.ts
index d042f77..2a78526 100644
--- a/apps/opencase/src/application/case/endpoints/CreateFramework.ts
+++ b/apps/opencase/src/application/case/endpoints/CreateFramework.ts
@@ -160,7 +160,7 @@ export class CreateFramework {
     // compare like-for-like against the existing persisted entities' own
     // .toJSON() output — comparing the raw POST payload directly against a
     // .toJSON()'d bundle would false-positive on every save, since GET-only
-    // fields (CFDocumentURI, CFPackageURI) are legitimately absent from POST
+    // fields (CFDocumentURI) are legitimately absent from POST
     // payloads by CASE spec convention but always present after fromRaw/toJSON.
     const buildEntities = (docPayload: any, itemsPayload: any[], assocPayload: any[], rubricsPayload: any[], uriOptions?: { preserveUris: boolean }) => {
       const doc = CFDocument.fromRaw(tenantId, caseVersion, docPayload, uriOptions)
@@ -321,7 +321,7 @@ export class CreateFramework {
           CFItems: sortById(items.map(i => i.toJSON())),
           CFAssociations: sortById(associations.map(a => a.toJSON())),
           CFRubrics: sortById(rubrics.map(r => r.toJSON())),
-          CFDefinitions: definitions
+          CFDefinitions: pkg.definitions
         }
 
         if (stableStringify(existingBundle) === stableStringify(newBundle)) {
diff --git a/apps/opencase/src/application/case/endpoints/GetAllCFDocuments.ts b/apps/opencase/src/application/case/endpoints/GetAllCFDocuments.ts
index 0304623..0708097 100644
--- a/apps/opencase/src/application/case/endpoints/GetAllCFDocuments.ts
+++ b/apps/opencase/src/application/case/endpoints/GetAllCFDocuments.ts
@@ -1,7 +1,7 @@
 import { type CaseVersion, type TenantId } from '../../../domain/case/value-objects/Identifiers'
 import { logger } from '../../../infrastructure/logging/Logger'
 import { type FileFrameworkStore } from '../../../infrastructure/persistence/file/FileFrameworkStore'
-import { type LinkData } from '../../../domain/case/value-objects/LinkData'
+import { buildCFPackageURI } from '../services/packageUri'
 
 export interface GetAllCFDocumentsQuery {
   tenantId?: TenantId  // Optional — when omitted, lists across ALL tenants (global catalog)
@@ -103,18 +103,12 @@ export class GetAllCFDocuments {
     const isV1p0 = query.caseVersion === '1.0'
 
     const cfDocuments = paginatedDocs.map(({ meta: docMeta, caseVersion }) => {
-      const packageURI: LinkData = {
-        title: 'CFPackage',
-        identifier: docMeta.sourcedId,
-        uri: `${requestedBasePath}/CFPackages/${docMeta.sourcedId}`
-      }
-
       const doc: any = {
         identifier: docMeta.sourcedId,
         uri: `${requestedBasePath}/CFDocuments/${docMeta.sourcedId}`,
         title: docMeta.title,
         lastChangeDateTime: docMeta.lastChangeDateTime.toISOString(),
-        CFPackageURI: packageURI
+        CFPackageURI: buildCFPackageURI(docMeta.sourcedId, query.caseVersion, docMeta.openCaseExtensions)
       }
 
       // Add optional fields if present
diff --git a/apps/opencase/src/application/case/endpoints/GetCFDocument.ts b/apps/opencase/src/application/case/endpoints/GetCFDocument.ts
index 021d3fd..704e9e3 100644
--- a/apps/opencase/src/application/case/endpoints/GetCFDocument.ts
+++ b/apps/opencase/src/application/case/endpoints/GetCFDocument.ts
@@ -1,8 +1,8 @@
 import { type CFPackageRepository } from '../ports/CFPackageRepository'
 import { type CaseVersion, type SourcedId, type TenantId } from '../../../domain/case/value-objects/Identifiers'
 import { logger } from '../../../infrastructure/logging/Logger'
-import { type LinkData } from '../../../domain/case/value-objects/LinkData'
 import { type FileFrameworkStore } from '../../../infrastructure/persistence/file/FileFrameworkStore'
+import { buildCFPackageURI, getOpenCaseExtension } from '../services/packageUri'
 
 export interface GetCFDocumentQuery {
   tenantId: TenantId
@@ -30,21 +30,14 @@ export class GetCFDocument {
 
     // Note: Get by ID returns archived documents regardless - filtering only applies to list endpoints
 
-    // Generate CFPackageURI — uses caseVersion for URI generation
-    const basePath = query.caseVersion === '1.1' ? '/ims/case/v1p1' : '/ims/case/v1p0'
-    const packageURI: LinkData = {
-      title: 'CFPackage',
-      identifier: query.sourcedId,
-      uri: `${basePath}/CFPackages/${query.sourcedId}`
-    }
-
     // Pass caseVersion to toJSON for correct field stripping when downconverting
     const serializeAs = query.loadVersion ? query.caseVersion : undefined
     const documentJSON = pkg.document.toJSON(serializeAs)
-    // Add CFPackageURI if not already present
-    if (!documentJSON.CFPackageURI) {
-      documentJSON.CFPackageURI = packageURI
-    }
+    documentJSON.CFPackageURI = buildCFPackageURI(
+      query.sourcedId,
+      query.caseVersion,
+      getOpenCaseExtension(pkg.document.extensions)
+    )
 
     return documentJSON
   }
diff --git a/apps/opencase/src/application/case/endpoints/GetCFPackage.ts b/apps/opencase/src/application/case/endpoints/GetCFPackage.ts
index b89ffaf..7790f99 100644
--- a/apps/opencase/src/application/case/endpoints/GetCFPackage.ts
+++ b/apps/opencase/src/application/case/endpoints/GetCFPackage.ts
@@ -1,7 +1,6 @@
 import type { CFPackageRepository } from '../ports/CFPackageRepository'
 import type { CaseVersion, SourcedId, TenantId } from '../../../domain/case/value-objects/Identifiers'
 import { logger } from '../../../infrastructure/logging/Logger'
-import { LinkData } from '../../../domain/case/value-objects/LinkData'
 import type { FileFrameworkStore } from '../../../infrastructure/persistence/file/FileFrameworkStore'
 
 export interface GetCFPackageQuery {
@@ -29,25 +28,22 @@ export class GetCFPackage {
 
     // Note: Get by ID returns archived packages regardless - filtering only applies to list endpoints
 
-    // Generate CFPackageURI for the document — uses caseVersion for URI generation
-    const basePath = query.caseVersion === '1.1' ? '/ims/case/v1p1' : '/ims/case/v1p0'
-    const packageURI: LinkData = {
-      title: 'CFPackage',
-      identifier: query.docId,
-      uri: `${basePath}/CFPackages/${query.docId}`
-    }
-
     // Pass caseVersion to toJSON for correct field stripping (e.g. v1.0 omits v1.1-only fields)
     const serializeAs = query.loadVersion ? query.caseVersion : undefined
+    // No CFPackageURI here: a CFPackage's CFDocument is a CFPckgDocument, which
+    // doesn't carry one (only getCFDocument(s) responses do).
     const documentJSON = pkg.document.toJSON(serializeAs)
-    // Add CFPackageURI if not already present
-    if (!documentJSON.CFPackageURI) {
-      documentJSON.CFPackageURI = packageURI
+
+    // Likewise CFPckgItem has no CFDocumentURI — the package itself establishes
+    // the document; only getCFItem responses carry the back-reference.
+    const toPckgItem = (item: typeof pkg.items[number]) => {
+      const { CFDocumentURI: _documentUri, ...rest } = item.toJSON(serializeAs)
+      return rest
     }
 
     const result: any = {
       CFDocument: documentJSON,
-      CFItems: pkg.items.map(i => i.toJSON(serializeAs)),
+      CFItems: pkg.items.map(toPckgItem),
       CFAssociations: pkg.associations.map(a => a.toJSON(serializeAs))
     }
 
diff --git a/apps/opencase/src/application/case/endpoints/__tests__/GetAllCFDocuments.test.ts b/apps/opencase/src/application/case/endpoints/__tests__/GetAllCFDocuments.test.ts
index 4bc37c4..cc1f4a1 100644
--- a/apps/opencase/src/application/case/endpoints/__tests__/GetAllCFDocuments.test.ts
+++ b/apps/opencase/src/application/case/endpoints/__tests__/GetAllCFDocuments.test.ts
@@ -295,6 +295,23 @@ describe('GetAllCFDocuments', () => {
       expect(result.CFDocuments[0].extensions).toEqual({ 'ext:opencase': openCaseExtensions })
     })
 
+    it('should derive CFPackageURI from mirror/fork state (CGE-59)', async () => {
+      const source = 'https://standards.example.org/ims/case/v1p1/CFPackages/mirror'
+      const documents = [
+        { sourcedId: 'mirror', title: 'Mirror', lastChangeDateTime: new Date('2024-01-01T00:00:00Z'), currentFile: 'a.json',
+          openCaseExtensions: { isModifiedFromSource: false, sourcePackageURI: source } },
+        { sourcedId: 'fork', title: 'Fork', lastChangeDateTime: new Date('2024-01-01T00:00:00Z'), currentFile: 'b.json',
+          openCaseExtensions: { isModifiedFromSource: true, sourcePackageURI: source } }
+      ]
+      mockStore.getAllDocuments.mockImplementation((_: any, v: any) => (v === '1.1' ? documents as any : []))
+
+      const result = await getAllCFDocuments.execute({ tenantId, caseVersion })
+      const byId = Object.fromEntries(result.CFDocuments.map((d: any) => [d.identifier, d]))
+
+      expect(byId.mirror.CFPackageURI.uri).toBe(source)
+      expect(byId.fork.CFPackageURI.uri).toBe('/ims/case/v1p1/CFPackages/fork')
+    })
+
     it('should omit the extensions block entirely for CASE 1.0', async () => {
       const documents = [
         {
diff --git a/apps/opencase/src/application/case/endpoints/__tests__/GetCFDocument.test.ts b/apps/opencase/src/application/case/endpoints/__tests__/GetCFDocument.test.ts
index 877c22c..f5fcb5d 100644
--- a/apps/opencase/src/application/case/endpoints/__tests__/GetCFDocument.test.ts
+++ b/apps/opencase/src/application/case/endpoints/__tests__/GetCFDocument.test.ts
@@ -68,6 +68,42 @@ describe('GetCFDocument', () => {
       }))
     })
 
+    it('should point a pristine mirror\'s CFPackageURI at its import source, ignoring any stored value (CGE-59)', async () => {
+      const source = 'https://standards.example.org/ims/case/v1p1/CFPackages/doc-123'
+      const document = CFDocument.fromRaw(tenantId, caseVersion, {
+        identifier: docId,
+        uri: 'https://standards.example.org/doc-123',
+        creator: 'Source',
+        title: 'Mirrored',
+        lastChangeDateTime: '2024-01-01T00:00:00Z',
+        CFPackageURI: { title: 'Stale', identifier: 'other', uri: 'https://elsewhere.example.org/x' },
+        extensions: { 'ext:opencase': { isModifiedFromSource: false, sourcePackageURI: source } }
+      }, { preserveUris: true })
+      mockRepository.load.mockResolvedValue(new CFPackage({ document, items: [], associations: [] }))
+
+      const result = await getCFDocument.execute({ tenantId, caseVersion, sourcedId: docId })
+
+      expect(result.CFPackageURI).toEqual({ title: 'CFPackage', identifier: docId, uri: source })
+    })
+
+    it('should point a forked framework\'s CFPackageURI at this server (CGE-59)', async () => {
+      const document = CFDocument.create({
+        tenantId,
+        caseVersion,
+        sourcedId: docId,
+        uri: `/ims/case/v1p1/CFDocuments/${docId}`,
+        creator: 'Test Creator',
+        title: 'Forked',
+        lastChangeDateTime: new Date('2024-01-01T00:00:00Z'),
+        extensions: { 'ext:opencase': { isModifiedFromSource: true, sourcePackageURI: 'https://standards.example.org/x' } }
+      })
+      mockRepository.load.mockResolvedValue(new CFPackage({ document, items: [], associations: [] }))
+
+      const result = await getCFDocument.execute({ tenantId, caseVersion, sourcedId: docId })
+
+      expect(result.CFPackageURI.uri).toBe(`/ims/case/v1p1/CFPackages/${docId}`)
+    })
+
     it('should include caseVersion for a CASE 1.1 document', async () => {
       const document = CFDocument.create({
         tenantId,
diff --git a/apps/opencase/src/application/case/endpoints/__tests__/GetCFPackage.test.ts b/apps/opencase/src/application/case/endpoints/__tests__/GetCFPackage.test.ts
index def0718..f80ed23 100644
--- a/apps/opencase/src/application/case/endpoints/__tests__/GetCFPackage.test.ts
+++ b/apps/opencase/src/application/case/endpoints/__tests__/GetCFPackage.test.ts
@@ -128,10 +128,7 @@ describe('GetCFPackage', () => {
       expect(result).toEqual({
         CFDocument: expect.objectContaining({
           identifier: docId,
-          title: 'Test Document',
-          CFPackageURI: expect.objectContaining({
-            identifier: docId
-          })
+          title: 'Test Document'
         }),
         CFItems: expect.arrayContaining([
           expect.objectContaining({ identifier: 'item-1' }),
@@ -149,6 +146,11 @@ describe('GetCFPackage', () => {
           })
         ])
       });
+      // CFPckgDocument has no CFPackageURI; CFPckgItem has no CFDocumentURI (CGE-59)
+      expect(result!.CFDocument).not.toHaveProperty('CFPackageURI');
+      for (const item of result!.CFItems) {
+        expect(item).not.toHaveProperty('CFDocumentURI');
+      }
     });
 
     it('should handle empty items and associations', async () => {
@@ -176,14 +178,13 @@ describe('GetCFPackage', () => {
       expect(result).toEqual({
         CFDocument: expect.objectContaining({
           identifier: docId,
-          title: 'Test Document',
-          CFPackageURI: expect.objectContaining({
-            identifier: docId
-          })
+          title: 'Test Document'
         }),
         CFItems: [],
         CFAssociations: []
       });
+      // CFPckgDocument has no CFPackageURI (CGE-59)
+      expect(result!.CFDocument).not.toHaveProperty('CFPackageURI');
     });
 
     it('should return archived document when getting by ID (archived documents always returned)', async () => {
diff --git a/apps/opencase/src/application/case/endpoints/__tests__/ImportFramework.test.ts b/apps/opencase/src/application/case/endpoints/__tests__/ImportFramework.test.ts
index cb8acc5..864d1c1 100644
--- a/apps/opencase/src/application/case/endpoints/__tests__/ImportFramework.test.ts
+++ b/apps/opencase/src/application/case/endpoints/__tests__/ImportFramework.test.ts
@@ -154,6 +154,51 @@ describe('ImportFramework', () => {
       expect(savedPkg.document.toJSON().uri).toBe('https://source.example.org/ims/case/v1p1/CFDocuments/doc-123')
     })
 
+    it('accepts a package with extra/unknown fields and does not save them (CGE-59)', async () => {
+      await importFramework.execute({
+        tenantId,
+        caseVersion,
+        cfPackage: {
+          CFPackage: {
+            CFDocument: {
+              ...cfDocument,
+              CFPackageURI: { title: 'Pkg', identifier: 'doc-123', uri: 'https://source.example.org/ims/case/v1p1/CFPackages/doc-123' },
+              somethingBogus: 'x'
+            },
+            CFItems: [{
+              identifier: 'item-1',
+              uri: '/ims/case/v1p1/CFItems/item-1',
+              fullStatement: 'Item',
+              lastChangeDateTime: '2024-01-01T00:00:00Z',
+              notInSpec: 42
+            }],
+            CFAssociations: [],
+            CFDefinitions: {
+              CFSubjects: [{ identifier: 's-1', uri: 'u', title: 'Math', hierarchyCode: '1', lastChangeDateTime: 'd', vendorJunk: true }],
+              CFMadeUp: []
+            },
+            totallyUnknownRoot: { a: 1 }
+          }
+        }
+      })
+
+      const savedPkg = mockRepository.saveNewVersion.mock.calls[0][2]
+      const doc = savedPkg.document.toJSON()
+      expect(doc).not.toHaveProperty('CFPackageURI')
+      expect(doc).not.toHaveProperty('somethingBogus')
+      expect(savedPkg.items[0].toJSON()).not.toHaveProperty('notInSpec')
+      expect(savedPkg.definitions).toEqual({
+        CFSubjects: [{ identifier: 's-1', uri: 'u', title: 'Math', hierarchyCode: '1', lastChangeDateTime: 'd' }]
+      })
+    })
+
+    it('does not add a CFPackageURI when the source has none (CGE-59)', async () => {
+      await importFramework.execute({ tenantId, caseVersion, cfPackage: { CFDocument: cfDocument } })
+
+      const savedPkg = mockRepository.saveNewVersion.mock.calls[0][2]
+      expect(savedPkg.document.toJSON()).not.toHaveProperty('CFPackageURI')
+    })
+
     it('throws when neither endpointUrl nor cfPackage is provided', async () => {
       await expect(
         importFramework.execute({ tenantId, caseVersion })
diff --git a/apps/opencase/src/application/case/services/__tests__/packageUri.test.ts b/apps/opencase/src/application/case/services/__tests__/packageUri.test.ts
new file mode 100644
index 0000000..934aa08
--- /dev/null
+++ b/apps/opencase/src/application/case/services/__tests__/packageUri.test.ts
@@ -0,0 +1,35 @@
+import { buildCFPackageURI, getOpenCaseExtension } from '../packageUri'
+
+describe('buildCFPackageURI (CGE-59)', () => {
+  const source = 'https://standards.example.org/ims/case/v1p1/CFPackages/doc-1'
+
+  it('points a pristine mirror imported by URL at its source', () => {
+    expect(buildCFPackageURI('doc-1', '1.1', { isModifiedFromSource: false, sourcePackageURI: source }))
+      .toEqual({ title: 'CFPackage', identifier: 'doc-1', uri: source })
+  })
+
+  it('points a forked framework at this server', () => {
+    expect(buildCFPackageURI('doc-2', '1.1', { isModifiedFromSource: true, sourcePackageURI: source }).uri)
+      .toBe('/ims/case/v1p1/CFPackages/doc-2')
+  })
+
+  it('points a mirror pasted as JSON (no known source) at this server', () => {
+    expect(buildCFPackageURI('doc-1', '1.1', { isModifiedFromSource: false }).uri)
+      .toBe('/ims/case/v1p1/CFPackages/doc-1')
+  })
+
+  it('points a locally authored framework at this server, using the requested CASE version', () => {
+    expect(buildCFPackageURI('doc-1', '1.0', undefined).uri).toBe('/ims/case/v1p0/CFPackages/doc-1')
+  })
+})
+
+describe('getOpenCaseExtension', () => {
+  it('returns the ext:opencase object when present', () => {
+    expect(getOpenCaseExtension({ 'ext:opencase': { a: 1 } })).toEqual({ a: 1 })
+  })
+
+  it('returns undefined when missing or not an object', () => {
+    expect(getOpenCaseExtension(undefined)).toBeUndefined()
+    expect(getOpenCaseExtension({ 'ext:opencase': 'x' })).toBeUndefined()
+  })
+})
diff --git a/apps/opencase/src/application/case/services/packageUri.ts b/apps/opencase/src/application/case/services/packageUri.ts
new file mode 100644
index 0000000..1baf9cf
--- /dev/null
+++ b/apps/opencase/src/application/case/services/packageUri.ts
@@ -0,0 +1,30 @@
+import type { CaseVersion, SourcedId } from '../../../domain/case/value-objects/Identifiers'
+import type { LinkData } from '../../../domain/case/value-objects/LinkData'
+
+/**
+ * Derive the CFPackageURI returned on a CFDocument by getCFDocument/getCFDocuments.
+ * It is never stored — a CFPackage's CFDocument (CFPckgDocument) has no
+ * CFPackageURI, so it only exists in these responses.
+ *
+ * - Pristine mirror imported by URL: points at the source it was imported from.
+ * - Everything else (forks, locally authored, mirrors pasted as JSON with no
+ *   known source): points at this server's CFPackages endpoint.
+ */
+export function buildCFPackageURI (
+  docId: SourcedId,
+  caseVersion: CaseVersion,
+  openCaseExtensions: Record<string, unknown> | undefined
+): LinkData {
+  const sourcePackageURI = openCaseExtensions?.sourcePackageURI
+  const isPristineMirror = openCaseExtensions?.isModifiedFromSource === false
+  const uri = isPristineMirror && typeof sourcePackageURI === 'string' && sourcePackageURI.trim() !== ''
+    ? sourcePackageURI.trim()
+    : `${caseVersion === '1.1' ? '/ims/case/v1p1' : '/ims/case/v1p0'}/CFPackages/${docId}`
+  return { title: 'CFPackage', identifier: docId, uri }
+}
+
+/** Read the `ext:opencase` object off a CFDocument's extensions, if present. */
+export function getOpenCaseExtension (extensions: Record<string, unknown> | undefined): Record<string, unknown> | undefined {
+  const ext = extensions?.['ext:opencase']
+  return ext && typeof ext === 'object' ? ext as Record<string, unknown> : undefined
+}
diff --git a/apps/opencase/src/domain/case/entities/CFDocument.ts b/apps/opencase/src/domain/case/entities/CFDocument.ts
index e7ca5b9..bbdc1b9 100644
--- a/apps/opencase/src/domain/case/entities/CFDocument.ts
+++ b/apps/opencase/src/domain/case/entities/CFDocument.ts
@@ -23,7 +23,6 @@ export interface CFDocumentProps {
   notes?: string;
   statusStartDate?: string;
   statusEndDate?: string;
-  CFPackageURI?: LinkData;
   extensions?: Record<string, unknown>;
 }
 
@@ -62,11 +61,13 @@ export class CFDocument {
     }
 
     // Rebase reference URIs onto the local host — these point at per-tenant
-    // definition entities (licenses, packages, subjects) that OpenCASE serves
+    // definition entities (licenses, subjects) that OpenCASE serves
     // itself, so they must resolve locally rather than to the source host.
     // Mirrored frameworks skip this and keep the source's reference URIs as-is.
     const licenseURI = options?.preserveUris ? raw.licenseURI : LinkDataHelper.rebaseLinkData(raw.licenseURI, caseVersion, 'CFLicenses')
-    const CFPackageURI = options?.preserveUris ? raw.CFPackageURI : LinkDataHelper.rebaseLinkData(raw.CFPackageURI, caseVersion, 'CFPackages')
+    // CFPackageURI is intentionally not read: it isn't part of a CFPackage's
+    // CFDocument (CFPckgDocument), so an incoming one is ignored rather than
+    // stored. getCFDocument(s) derive it at response time (see packageUri.ts).
     // subjectURI must use LinkURI format (UUID identifier required)
     const subjectURI = options?.preserveUris
       ? raw.subjectURI
@@ -102,7 +103,6 @@ export class CFDocument {
       notes: raw.notes,
       statusStartDate: raw.statusStartDate,
       statusEndDate: raw.statusEndDate,
-      CFPackageURI,
       extensions: raw.extensions
     });
   }
@@ -116,6 +116,7 @@ export class CFDocument {
   get tenantId(): TenantId { return this.props.tenantId; }
   get caseVersion(): CaseVersion { return this.props.caseVersion; }
   get sourcedId(): SourcedId { return this.props.sourcedId; }
+  get extensions(): Record<string, unknown> | undefined { return this.props.extensions; }
 
   toJSON(serializeAs?: CaseVersion) {
     const { tenantId, caseVersion, sourcedId, licenceUri, ...rest } = this.props;
diff --git a/apps/opencase/src/domain/case/entities/CFPackage.ts b/apps/opencase/src/domain/case/entities/CFPackage.ts
index 3ea5db4..1a01039 100644
--- a/apps/opencase/src/domain/case/entities/CFPackage.ts
+++ b/apps/opencase/src/domain/case/entities/CFPackage.ts
@@ -12,6 +12,46 @@ export interface CFDefinitions {
   extensions?: Record<string, unknown>
 }
 
+/**
+ * Fields each CFDefinitions entry may carry, per the CASE v1.1 CFPackage schema
+ * (CFConcept, CFSubject, CFLicense, CFItemType, CFAssociationGrouping).
+ * Anything else on an incoming entry is dropped rather than persisted.
+ */
+const DEFINITION_FIELDS: Record<string, readonly string[]> = {
+  CFConcepts: ['identifier', 'uri', 'title', 'keywords', 'hierarchyCode', 'description', 'lastChangeDateTime', 'extensions'],
+  CFSubjects: ['identifier', 'uri', 'title', 'hierarchyCode', 'description', 'lastChangeDateTime', 'extensions'],
+  CFLicenses: ['identifier', 'uri', 'title', 'description', 'licenseText', 'lastChangeDateTime', 'extensions'],
+  CFItemTypes: ['identifier', 'uri', 'title', 'description', 'hierarchyCode', 'typeCode', 'lastChangeDateTime', 'extensions'],
+  CFAssociationGroupings: ['identifier', 'uri', 'title', 'description', 'lastChangeDateTime', 'extensions']
+}
+
+function pickFields (entry: any, fields: readonly string[]): Record<string, unknown> {
+  const out: Record<string, unknown> = {}
+  for (const f of fields) {
+    if (entry[f] !== undefined) out[f] = entry[f]
+  }
+  return out
+}
+
+/**
+ * Keep only the spec-defined categories and entry fields of a CFDefinitions
+ * block — the same whitelisting CFDocument/CFItem/CFAssociation.fromRaw apply
+ * to their own fields — so unknown data from an import is ignored, not saved.
+ */
+export function sanitizeCFDefinitions (raw: any): CFDefinitions | null {
+  if (!raw || typeof raw !== 'object') return null
+  const result: CFDefinitions = {}
+  for (const [category, fields] of Object.entries(DEFINITION_FIELDS)) {
+    const entries = raw[category]
+    if (!Array.isArray(entries)) continue
+    (result as any)[category] = entries
+      .filter((e: unknown) => e && typeof e === 'object')
+      .map((e: any) => pickFields(e, fields))
+  }
+  if (raw.extensions && typeof raw.extensions === 'object') result.extensions = raw.extensions
+  return result
+}
+
 export interface CFPackageProps {
   document: CFDocument
   items: CFItem[]
@@ -22,7 +62,11 @@ export interface CFPackageProps {
 }
 
 export class CFPackage {
-  constructor (private readonly props: CFPackageProps) {}
+  private readonly props: CFPackageProps
+
+  constructor (props: CFPackageProps) {
+    this.props = { ...props, definitions: sanitizeCFDefinitions(props.definitions) }
+  }
 
   get document (): CFDocument { return this.props.document }
   get items (): CFItem[] { return this.props.items }
diff --git a/apps/opencase/src/domain/case/entities/__tests__/CFDocument.test.ts b/apps/opencase/src/domain/case/entities/__tests__/CFDocument.test.ts
index ccb49cd..3e16601 100644
--- a/apps/opencase/src/domain/case/entities/__tests__/CFDocument.test.ts
+++ b/apps/opencase/src/domain/case/entities/__tests__/CFDocument.test.ts
@@ -109,7 +109,7 @@ describe('CFDocument', () => {
       expect(json.lastChangeDateTime).toBe('2024-01-01T12:30:45.000Z');
     });
 
-    it('should rewrite licenseURI/CFPackageURI/subjectURI to the local host on import (POR-730)', () => {
+    it('should rewrite licenseURI/subjectURI to the local host and drop CFPackageURI on import (POR-730, CGE-59)', () => {
       const raw = {
         sourcedId: 'doc-123',
         title: 'Test Document',
@@ -135,9 +135,29 @@ describe('CFDocument', () => {
       const json = doc.toJSON();
 
       expect(json.licenseURI.uri).toBe('/ims/case/v1p1/CFLicenses/c0c0c0c0-0000-4000-a000-000000000002');
-      expect(json.CFPackageURI.uri).toBe('/ims/case/v1p1/CFPackages/doc-123');
+      expect(json.CFPackageURI).toBeUndefined();
       expect(json.subjectURI[0].uri).toBe('/ims/case/v1p1/CFSubjects/c0c0c0c0-0000-4000-a000-000000000012');
     });
+
+    it('should ignore an incoming CFPackageURI on a mirrored import (CGE-59)', () => {
+      const raw = {
+        identifier: 'doc-123',
+        uri: 'https://standards.example.org/doc-123',
+        title: 'Test Document',
+        creator: 'Source',
+        lastChangeDateTime: '2024-01-01T00:00:00Z',
+        CFPackageURI: {
+          title: 'Package',
+          identifier: 'doc-123',
+          uri: 'https://standards.example.org/ims/case/v1p1/CFPackages/doc-123'
+        }
+      };
+
+      const json = CFDocument.fromRaw(tenantId, caseVersion, raw, { preserveUris: true }).toJSON();
+
+      expect(json.CFPackageURI).toBeUndefined();
+      expect(json.uri).toBe('https://standards.example.org/doc-123');
+    });
   });
 
   describe('toJSON', () => {
diff --git a/apps/opencase/src/domain/case/entities/__tests__/CFPackage.test.ts b/apps/opencase/src/domain/case/entities/__tests__/CFPackage.test.ts
index 16a99bc..f773fbe 100644
--- a/apps/opencase/src/domain/case/entities/__tests__/CFPackage.test.ts
+++ b/apps/opencase/src/domain/case/entities/__tests__/CFPackage.test.ts
@@ -102,5 +102,49 @@ describe('CFPackage', () => {
     expect(pkg.rubrics.length).toBe(1);
     expect(pkg.rubrics[0].identifier).toBe('rubric-1');
   });
-});
 
+  describe('definitions (CGE-59)', () => {
+    it('drops unknown categories and unknown fields on definition entries, keeping extensions', () => {
+      const pkg = new CFPackage({
+        document: createDocument(),
+        items: [],
+        associations: [],
+        definitions: {
+          CFItemTypes: [{
+            identifier: 'type-1',
+            uri: '/ims/case/v1p1/CFItemTypes/type-1',
+            title: 'Standard',
+            description: 'A standard',
+            hierarchyCode: '1',
+            typeCode: 'std',
+            lastChangeDateTime: '2024-01-01T00:00:00Z',
+            extensions: { 'ext:vendor': { keep: true } },
+            bogusField: 'drop me'
+          }],
+          CFLicenses: [{ identifier: 'lic-1', uri: 'u', title: 'L', licenseText: 'T', lastChangeDateTime: 'd', junk: 1 }],
+          CFNotARealCategory: [{ identifier: 'x' }],
+          extensions: { 'ext:vendor': {} }
+        } as any
+      });
+
+      expect(pkg.definitions).toEqual({
+        CFItemTypes: [{
+          identifier: 'type-1',
+          uri: '/ims/case/v1p1/CFItemTypes/type-1',
+          title: 'Standard',
+          description: 'A standard',
+          hierarchyCode: '1',
+          typeCode: 'std',
+          lastChangeDateTime: '2024-01-01T00:00:00Z',
+          extensions: { 'ext:vendor': { keep: true } }
+        }],
+        CFLicenses: [{ identifier: 'lic-1', uri: 'u', title: 'L', licenseText: 'T', lastChangeDateTime: 'd' }],
+        extensions: { 'ext:vendor': {} }
+      });
+    });
+
+    it('returns null when no definitions are given', () => {
+      expect(new CFPackage({ document: createDocument(), items: [], associations: [] }).definitions).toBeNull();
+    });
+  });
+});
diff --git a/apps/opencase/src/infrastructure/http/OpenAPISpecGenerator.ts b/apps/opencase/src/infrastructure/http/OpenAPISpecGenerator.ts
index e7d775b..63f535a 100644
--- a/apps/opencase/src/infrastructure/http/OpenAPISpecGenerator.ts
+++ b/apps/opencase/src/infrastructure/http/OpenAPISpecGenerator.ts
@@ -1626,12 +1626,12 @@ export class OpenAPISpecGenerator {
             required: ['CFDocument', 'CFItems', 'CFAssociations'],
             properties: {
               CFDocument: {
-                $ref: '#/components/schemas/CFDocumentDType'
+                $ref: '#/components/schemas/CFPckgDocumentDType'
               },
               CFItems: {
                 type: 'array',
                 items: {
-                  $ref: '#/components/schemas/CFItemDType'
+                  $ref: '#/components/schemas/CFPckgItemDType'
                 }
               },
               CFAssociations: {
@@ -2086,6 +2086,22 @@ export class OpenAPISpecGenerator {
     spec.paths['/management/tenants/{tenantId}/ims/case/v1p0/CFPackages/{id}'] = deleteByVersion('1.0')
     spec.paths['/management/tenants/{tenantId}/ims/case/v1p1/CFPackages/{id}'] = deleteByVersion('1.1')
 
+    // A CFPackage's CFDocument is a CFPckgDocument: the same as CFDocument but
+    // without CFPackageURI, which only appears in getCFDocument(s) responses.
+    const { CFPackageURI: _packageUri, ...pckgDocumentProperties } = spec.components.schemas.CFDocumentDType.properties
+    spec.components.schemas.CFPckgDocumentDType = {
+      ...spec.components.schemas.CFDocumentDType,
+      properties: pckgDocumentProperties
+    }
+
+    // Likewise a CFPackage's items are CFPckgItems, which have no CFDocumentURI.
+    const { CFDocumentURI: _documentUri, ...pckgItemProperties } = spec.components.schemas.CFItemDType.properties
+    spec.components.schemas.CFPckgItemDType = {
+      ...spec.components.schemas.CFItemDType,
+      required: spec.components.schemas.CFItemDType.required.filter((r: string) => r !== 'CFDocumentURI'),
+      properties: pckgItemProperties
+    }
+
     return spec
   }
 
diff --git a/apps/opencase/src/infrastructure/http/__tests__/OpenAPISpecGenerator.test.ts b/apps/opencase/src/infrastructure/http/__tests__/OpenAPISpecGenerator.test.ts
index 5c24a69..b79fa54 100644
--- a/apps/opencase/src/infrastructure/http/__tests__/OpenAPISpecGenerator.test.ts
+++ b/apps/opencase/src/infrastructure/http/__tests__/OpenAPISpecGenerator.test.ts
@@ -29,5 +29,20 @@ describe('OpenAPISpecGenerator (discovery)', () => {
     expect(spec.paths['/management/tenants/{tenantId}/ims/case/v1p0/CFPackages/{id}']).toBeDefined()
     expect(spec.paths['/management/tenants/{tenantId}/ims/case/v1p1/CFPackages/{id}']).toBeDefined()
   })
-})
 
+  it('describes CFPackage contents as CFPckgDocument/CFPckgItem without CFPackageURI/CFDocumentURI (CGE-59)', () => {
+    const { schemas } = OpenAPISpecGenerator.generateV1p1({ baseUrl: 'https://example.com', version: '1.0.0' }).components
+
+    expect(schemas.CFPackageDType.properties.CFDocument.$ref).toBe('#/components/schemas/CFPckgDocumentDType')
+    expect(schemas.CFPckgDocumentDType.properties.CFPackageURI).toBeUndefined()
+    expect(schemas.CFPckgDocumentDType.properties.title).toBeDefined()
+    // getCFDocument(s) still carry it
+    expect(schemas.CFDocumentDType.properties.CFPackageURI).toBeDefined()
+
+    expect(schemas.CFPackageDType.properties.CFItems.items.$ref).toBe('#/components/schemas/CFPckgItemDType')
+    expect(schemas.CFPckgItemDType.properties.CFDocumentURI).toBeUndefined()
+    expect(schemas.CFPckgItemDType.required).not.toContain('CFDocumentURI')
+    // getCFItem still carries it
+    expect(schemas.CFItemDType.required).toContain('CFDocumentURI')
+  })
+})