diff --git a/src/main/data/db/backup/contributor-types.ts b/src/main/data/db/backup/contributor-types.ts
index b6e47f246f..9e283df9a4 100644
--- a/src/main/data/db/backup/contributor-types.ts
+++ b/src/main/data/db/backup/contributor-types.ts
@@ -150,7 +150,7 @@ export interface UniqueMergeRule {
 export interface FieldMergePolicy {
   readonly table: DbTableName
   readonly column: DbColumnName
-  readonly strategy: 'remote-fills-local-null' | 'deep-merge' | 'local-priority'
+  readonly strategy: 'remote-fills-local-null' | 'remote-fills-local-empty' | 'deep-merge' | 'local-priority'
 }
 
 // ─── Contributor schema + policy + operations ──────────────────────────────────
diff --git a/src/main/data/services/__tests__/backupContributor-agents.test.ts b/src/main/data/services/__tests__/backupContributor-agents.test.ts
new file mode 100644
index 0000000000..8ce47bd803
--- /dev/null
+++ b/src/main/data/services/__tests__/backupContributor-agents.test.ts
@@ -0,0 +1,199 @@
+// Unit tests for the AGENTS contributor — pure declaration assertions (no DB).
+import { table } from '@main/data/db/backup/dbSchemaRefs'
+import { describe, expect, it } from 'vitest'
+
+import { AGENTS_CONTRIBUTOR } from '../backupContributor-agents'
+
+describe('AGENTS contributor', () => {
+  it('owns the 9 agent tables (8 graph tables + job_schedule row-scope)', () => {
+    expect(AGENTS_CONTRIBUTOR.schema.tables).toEqual([
+      table('agent'),
+      table('agent_session'),
+      table('agent_session_message'),
+      table('agent_workspace'),
+      table('agent_channel'),
+      table('agent_channel_task'),
+      table('agent_skill'),
+      table('agent_mcp_server'),
+      table('job_schedule')
+    ])
+  })
+
+  it('declares the job_schedule(type=agent.task) row-scope', () => {
+    expect(AGENTS_CONTRIBUTOR.schema.rowScopes).toEqual([
+      expect.objectContaining({
+        table: table('job_schedule'),
+        ownerDomain: 'AGENTS',
+        filter: expect.objectContaining({ column: 'type', op: 'eq', value: 'agent.task' })
+      })
+    ])
+  })
+
+  it('declares every FK as the correct ReferenceKind', () => {
+    const refs = AGENTS_CONTRIBUTOR.schema.references
+    const find = (t: string, c: string) => refs.find((r) => r.table === t && r.column === c)
+
+    // ── agent_session ──
+    // agentId → agent: optional (onDelete set null)
+    expect(find('agent_session', 'agentId')).toEqual(
+      expect.objectContaining({ referencedDomain: 'AGENTS', kind: 'optional' })
+    )
+    // workspaceId → agent_workspace: cross-aggregate OWNING (onDelete cascade), NOT a member
+    expect(find('agent_session', 'workspaceId')).toEqual(
+      expect.objectContaining({ referencedDomain: 'AGENTS', kind: 'owning' })
+    )
+
+    // ── agent_session_message ──
+    // sessionId → agent_session: owning (cascade) — drives aggregate membership
+    expect(find('agent_session_message', 'sessionId')).toEqual(
+      expect.objectContaining({ referencedDomain: 'AGENTS', kind: 'owning' })
+    )
+    // modelId → user_model: optional (set null)
+    expect(find('agent_session_message', 'modelId')).toEqual(
+      expect.objectContaining({ referencedDomain: 'PROVIDERS', kind: 'optional' })
+    )
+
+    // ── agent_channel ──
+    expect(find('agent_channel', 'agentId')).toEqual(
+      expect.objectContaining({ referencedDomain: 'AGENTS', kind: 'optional' })
+    )
+    expect(find('agent_channel', 'sessionId')).toEqual(
+      expect.objectContaining({ referencedDomain: 'AGENTS', kind: 'optional' })
+    )
+
+    // ── agent_channel_task (junction: dual cascade) ──
+    expect(find('agent_channel_task', 'channelId')).toEqual(
+      expect.objectContaining({ referencedDomain: 'AGENTS', kind: 'junction' })
+    )
+    expect(find('agent_channel_task', 'taskId')).toEqual(
+      expect.objectContaining({ referencedDomain: 'AGENTS', kind: 'junction' })
+    )
+
+    // ── agent_skill (junction: dual cascade) ──
+    expect(find('agent_skill', 'agentId')).toEqual(
+      expect.objectContaining({ referencedDomain: 'AGENTS', kind: 'junction' })
+    )
+    expect(find('agent_skill', 'skillId')).toEqual(
+      expect.objectContaining({ referencedDomain: 'SKILLS', kind: 'junction' })
+    )
+
+    // ── agent_mcp_server (junction: dual cascade) ──
+    expect(find('agent_mcp_server', 'agentId')).toEqual(
+      expect.objectContaining({ referencedDomain: 'AGENTS', kind: 'junction' })
+    )
+    expect(find('agent_mcp_server', 'mcpServerId')).toEqual(
+      expect.objectContaining({ referencedDomain: 'MCP_SERVERS', kind: 'junction' })
+    )
+
+    // ── agent (scalar model refs → PROVIDERS, optional) ──
+    expect(find('agent', 'model')).toEqual(
+      expect.objectContaining({ referencedDomain: 'PROVIDERS', kind: 'optional' })
+    )
+    expect(find('agent', 'planModel')).toEqual(
+      expect.objectContaining({ referencedDomain: 'PROVIDERS', kind: 'optional' })
+    )
+    expect(find('agent', 'smallModel')).toEqual(
+      expect.objectContaining({ referencedDomain: 'PROVIDERS', kind: 'optional' })
+    )
+  })
+
+  it('agent_session aggregate has agent_session_message as sessionId include member, non-renamable', () => {
+    const session = AGENTS_CONTRIBUTOR.schema.aggregates.find((a) => a.root === table('agent_session'))
+    expect(session).toBeDefined()
+    expect(session!.identityKey).toEqual(['id'])
+    expect(session!.renamable).toBe(false)
+    expect(session!.members).toEqual([
+      expect.objectContaining({ table: table('agent_session_message'), viaColumn: 'sessionId', cascade: 'include' })
+    ])
+  })
+
+  it('agent_session.members does NOT include agent_workspace (cross-aggregate owning ref, §5.4)', () => {
+    const session = AGENTS_CONTRIBUTOR.schema.aggregates.find((a) => a.root === table('agent_session'))
+    expect(session!.members?.some((m) => m.table === table('agent_workspace'))).toBe(false)
+  })
+
+  it('agent_workspace is a natural-key aggregate keyed by path UNIQUE, non-renamable', () => {
+    const workspace = AGENTS_CONTRIBUTOR.schema.aggregates.find((a) => a.root === table('agent_workspace'))
+    expect(workspace).toBeDefined()
+    expect(workspace!.identityKey).toEqual(['path'])
+    expect(workspace!.renamable).toBe(false)
+    expect(workspace!.members ?? []).toEqual([])
+  })
+
+  it('agent_channel and agent are single-table non-renamable aggregates', () => {
+    const channel = AGENTS_CONTRIBUTOR.schema.aggregates.find((a) => a.root === table('agent_channel'))
+    expect(channel!.identityKey).toEqual(['id'])
+    expect(channel!.renamable).toBe(false)
+    expect(channel!.members ?? []).toEqual([])
+
+    const agent = AGENTS_CONTRIBUTOR.schema.aggregates.find((a) => a.root === table('agent'))
+    expect(agent!.identityKey).toEqual(['id'])
+    expect(agent!.renamable).toBe(false)
+    expect(agent!.members ?? []).toEqual([])
+  })
+
+  it('job_schedule(agent.task) is a natural-key aggregate keyed by (type,name), non-renamable', () => {
+    const schedule = AGENTS_CONTRIBUTOR.schema.aggregates.find((a) => a.root === table('job_schedule'))
+    expect(schedule).toBeDefined()
+    expect(schedule!.identityKey).toEqual(['type', 'name'])
+    expect(schedule!.renamable).toBe(false)
+    expect(schedule!.members ?? []).toEqual([])
+  })
+
+  it('all aggregates are non-renamable (no cloneAggregate required, #16)', () => {
+    for (const aggregate of AGENTS_CONTRIBUTOR.schema.aggregates) {
+      expect(aggregate.renamable).toBe(false)
+    }
+    expect(AGENTS_CONTRIBUTOR.operations).toBeUndefined()
+  })
+
+  it('declares the required + tolerant JSON soft references', () => {
+    const jsonRefs = AGENTS_CONTRIBUTOR.schema.jsonSoftReferences
+    // agent_session_message.data: tolerant file-ref (attachments)
+    expect(jsonRefs).toContainEqual(
+      expect.objectContaining({
+        table: table('agent_session_message'),
+        column: 'data',
+        target: 'file-ref',
+        ownerDomain: 'AGENTS',
+        kind: 'tolerant'
+      })
+    )
+    // agent_channel.workspace: required entity-id (AgentSessionWorkspaceSource.workspaceId)
+    expect(jsonRefs).toContainEqual(
+      expect.objectContaining({
+        table: table('agent_channel'),
+        column: 'workspace',
+        target: 'entity-id',
+        ownerDomain: 'AGENTS',
+        kind: 'required'
+      })
+    )
+    // job_schedule.jobInputTemplate: required entity-id (same workspace source)
+    expect(jsonRefs).toContainEqual(
+      expect.objectContaining({
+        table: table('job_schedule'),
+        column: 'jobInputTemplate',
+        target: 'entity-id',
+        ownerDomain: 'AGENTS',
+        kind: 'required'
+      })
+    )
+  })
+
+  it('declares no fileRefSourcePolicies (no AGENTS-owned FileRefSourceType)', () => {
+    expect(AGENTS_CONTRIBUTOR.schema.fileRefSourcePolicies).toEqual([])
+  })
+
+  it('primary keys are non-ambiguous', () => {
+    for (const pk of AGENTS_CONTRIBUTOR.schema.primaryKeys) {
+      expect(pk.ambiguous).toBeFalsy()
+    }
+  })
+
+  it('schema is deep-frozen (mutation throws)', () => {
+    expect(() => {
+      ;(AGENTS_CONTRIBUTOR.schema.tables as unknown as string[]).push('x')
+    }).toThrow()
+  })
+})
diff --git a/src/main/data/services/__tests__/backupContributor-miniapps.test.ts b/src/main/data/services/__tests__/backupContributor-miniapps.test.ts
new file mode 100644
index 0000000000..d37254eb03
--- /dev/null
+++ b/src/main/data/services/__tests__/backupContributor-miniapps.test.ts
@@ -0,0 +1,43 @@
+// Unit tests for the MINIAPPS contributor — pure declaration assertions (no DB).
+import { table } from '@main/data/db/backup/dbSchemaRefs'
+import { describe, expect, it } from 'vitest'
+
+import { MINIAPPS_CONTRIBUTOR } from '../backupContributor-miniapps'
+
+describe('MINIAPPS contributor', () => {
+  it('owns mini_app', () => {
+    expect(MINIAPPS_CONTRIBUTOR.schema.tables).toEqual([table('mini_app')])
+  })
+
+  it('declares no references (presetMiniAppId points at a non-DB preset, not a DB row)', () => {
+    expect(MINIAPPS_CONTRIBUTOR.schema.references).toEqual([])
+  })
+
+  it('mini_app aggregate is a single-table natural-key root, non-renamable', () => {
+    const aggregate = MINIAPPS_CONTRIBUTOR.schema.aggregates[0]
+    expect(aggregate.root).toBe(table('mini_app'))
+    expect(aggregate.identityKey).toEqual(['appId'])
+    expect(aggregate.renamable).toBe(false)
+    expect(aggregate.members).toEqual([])
+  })
+
+  it('declares no fileRefSourcePolicies', () => {
+    expect(MINIAPPS_CONTRIBUTOR.schema.fileRefSourcePolicies).toEqual([])
+  })
+
+  it('declares no jsonSoftReferences', () => {
+    expect(MINIAPPS_CONTRIBUTOR.schema.jsonSoftReferences).toEqual([])
+  })
+
+  it('primary key is non-ambiguous (mini_app appId natural)', () => {
+    for (const pk of MINIAPPS_CONTRIBUTOR.schema.primaryKeys) {
+      expect(pk.ambiguous).toBeFalsy()
+    }
+  })
+
+  it('schema is deep-frozen (mutation throws)', () => {
+    expect(() => {
+      ;(MINIAPPS_CONTRIBUTOR.schema.tables as unknown as string[]).push('x')
+    }).toThrow()
+  })
+})
diff --git a/src/main/data/services/__tests__/backupContributor-paintings.test.ts b/src/main/data/services/__tests__/backupContributor-paintings.test.ts
new file mode 100644
index 0000000000..d70f09e532
--- /dev/null
+++ b/src/main/data/services/__tests__/backupContributor-paintings.test.ts
@@ -0,0 +1,80 @@
+// Unit tests for the PAINTINGS contributor — pure declaration assertions (no DB).
+import { table } from '@main/data/db/backup/dbSchemaRefs'
+import { describe, expect, it } from 'vitest'
+
+import { PAINTINGS_CONTRIBUTOR } from '../backupContributor-paintings'
+
+describe('PAINTINGS contributor', () => {
+  it('owns painting + painting_file_ref', () => {
+    expect(PAINTINGS_CONTRIBUTOR.schema.tables).toEqual([table('painting'), table('painting_file_ref')])
+  })
+
+  it('declares sourceId owning + fileEntryId cross-domain junction reference', () => {
+    const refs = PAINTINGS_CONTRIBUTOR.schema.references
+    expect(refs).toHaveLength(2)
+    // painting_file_ref.sourceId → painting: same-domain owning (aggregate membership).
+    expect(refs).toContainEqual(
+      expect.objectContaining({
+        table: table('painting_file_ref'),
+        column: 'sourceId',
+        referencedDomain: 'PAINTINGS',
+        kind: 'owning'
+      })
+    )
+    // painting_file_ref.fileEntryId → file_entry (FILE_STORAGE): junction (dual-cascade
+    // junction table, cross-domain endpoint — mirrors TOPICS chat_message_file_ref).
+    expect(refs).toContainEqual(
+      expect.objectContaining({
+        table: table('painting_file_ref'),
+        column: 'fileEntryId',
+        referencedDomain: 'FILE_STORAGE',
+        kind: 'junction'
+      })
+    )
+  })
+
+  it('painting aggregate has painting_file_ref as a sourceId include member, non-renamable', () => {
+    const aggregate = PAINTINGS_CONTRIBUTOR.schema.aggregates[0]
+    expect(aggregate.root).toBe(table('painting'))
+    expect(aggregate.identityKey).toEqual(['id'])
+    expect(aggregate.renamable).toBe(false)
+    expect(aggregate.members).toEqual([
+      expect.objectContaining({ table: table('painting_file_ref'), viaColumn: 'sourceId', cascade: 'include' })
+    ])
+  })
+
+  it('identityKey is the single-column root PK (uniqueness via uuid-v4)', () => {
+    const aggregate = PAINTINGS_CONTRIBUTOR.schema.aggregates[0]
+    expect(aggregate.identityKey).toEqual(['id'])
+    expect(aggregate.identityKey).toHaveLength(1)
+  })
+
+  it('classifies painting sourceType in fileRefSourcePolicies', () => {
+    const policies = PAINTINGS_CONTRIBUTOR.schema.fileRefSourcePolicies
+    expect(policies).toHaveLength(1)
+    expect(policies).toContainEqual(
+      expect.objectContaining({
+        sourceType: 'painting',
+        ownerDomain: 'PAINTINGS',
+        resourcePolicy: 'include-with-owner',
+        sourceTable: table('painting_file_ref')
+      })
+    )
+  })
+
+  it('declares no jsonSoftReferences', () => {
+    expect(PAINTINGS_CONTRIBUTOR.schema.jsonSoftReferences).toEqual([])
+  })
+
+  it('primary keys are non-ambiguous (painting uuid-v4; painting_file_ref uuid-v4)', () => {
+    for (const pk of PAINTINGS_CONTRIBUTOR.schema.primaryKeys) {
+      expect(pk.ambiguous).toBeFalsy()
+    }
+  })
+
+  it('schema is deep-frozen (mutation throws)', () => {
+    expect(() => {
+      ;(PAINTINGS_CONTRIBUTOR.schema.tables as unknown as string[]).push('x')
+    }).toThrow()
+  })
+})
diff --git a/src/main/data/services/__tests__/backupContributor-providers.test.ts b/src/main/data/services/__tests__/backupContributor-providers.test.ts
new file mode 100644
index 0000000000..83f7284b1b
--- /dev/null
+++ b/src/main/data/services/__tests__/backupContributor-providers.test.ts
@@ -0,0 +1,73 @@
+// Unit tests for the PROVIDERS contributor — pure declaration assertions (no DB).
+import { table } from '@main/data/db/backup/dbSchemaRefs'
+import { describe, expect, it } from 'vitest'
+
+import { PROVIDERS_CONTRIBUTOR } from '../backupContributor-providers'
+
+describe('PROVIDERS contributor', () => {
+  it('owns user_provider + user_model', () => {
+    expect(PROVIDERS_CONTRIBUTOR.schema.tables).toEqual([table('user_provider'), table('user_model')])
+  })
+
+  it('declares providerId owning reference (same-domain, aggregate membership)', () => {
+    const refs = PROVIDERS_CONTRIBUTOR.schema.references
+    expect(refs).toHaveLength(1)
+    // user_model.providerId → user_provider: same-domain owning (cascade).
+    expect(refs).toContainEqual(
+      expect.objectContaining({
+        table: table('user_model'),
+        column: 'providerId',
+        referencedDomain: 'PROVIDERS',
+        kind: 'owning'
+      })
+    )
+  })
+
+  it('user_provider aggregate has user_model as a providerId include member, non-renamable', () => {
+    const aggregate = PROVIDERS_CONTRIBUTOR.schema.aggregates[0]
+    expect(aggregate.root).toBe(table('user_provider'))
+    expect(aggregate.identityKey).toEqual(['providerId'])
+    expect(aggregate.renamable).toBe(false)
+    expect(aggregate.members).toEqual([
+      expect.objectContaining({ table: table('user_model'), viaColumn: 'providerId', cascade: 'include' })
+    ])
+  })
+
+  it('identity key is unique (user_provider.providerId is the business identity)', () => {
+    const aggregate = PROVIDERS_CONTRIBUTOR.schema.aggregates[0]
+    expect(aggregate.identityKey).toEqual(['providerId'])
+  })
+
+  it('declares no fileRefSourcePolicies and no jsonSoftReferences', () => {
+    expect(PROVIDERS_CONTRIBUTOR.schema.fileRefSourcePolicies).toEqual([])
+    expect(PROVIDERS_CONTRIBUTOR.schema.jsonSoftReferences).toEqual([])
+  })
+
+  it('primary keys are non-ambiguous (user_provider/user_model natural-key)', () => {
+    for (const pk of PROVIDERS_CONTRIBUTOR.schema.primaryKeys) {
+      expect(pk.ambiguous).toBeFalsy()
+    }
+  })
+
+  it('declares uniqueMergeRules for user_model by [providerId, modelId]', () => {
+    expect(PROVIDERS_CONTRIBUTOR.backupPolicy.uniqueMergeRules).toEqual([
+      expect.objectContaining({ table: table('user_model'), uniqueColumns: ['providerId', 'modelId'] })
+    ])
+  })
+
+  it('declares fieldMergePolicies for apiKeys + authConfig (remote-fills-local-empty)', () => {
+    // remote-fills-local-empty treats [], null, and empty/skeleton auth as missing —
+    // seeded providers ship apiKeys=[] / auth skeletons, so plain -local-null would
+    // drop backed-up credentials.
+    expect(PROVIDERS_CONTRIBUTOR.backupPolicy.fieldMergePolicies).toEqual([
+      expect.objectContaining({ table: table('user_provider'), column: 'apiKeys', strategy: 'remote-fills-local-empty' }),
+      expect.objectContaining({ table: table('user_provider'), column: 'authConfig', strategy: 'remote-fills-local-empty' })
+    ])
+  })
+
+  it('schema is deep-frozen (mutation throws)', () => {
+    expect(() => {
+      ;(PROVIDERS_CONTRIBUTOR.schema.tables as unknown as string[]).push('x')
+    }).toThrow()
+  })
+})
diff --git a/src/main/data/services/__tests__/backupContributor-topics.test.ts b/src/main/data/services/__tests__/backupContributor-topics.test.ts
new file mode 100644
index 0000000000..c54bf1d6bb
--- /dev/null
+++ b/src/main/data/services/__tests__/backupContributor-topics.test.ts
@@ -0,0 +1,185 @@
+// Unit tests for the TOPICS contributor — pure declaration assertions (no DB).
+import type { CloneAggregateContext } from '@main/data/db/backup/contexts'
+import { table } from '@main/data/db/backup/dbSchemaRefs'
+import { describe, expect, it } from 'vitest'
+
+import { TOPICS_CONTRIBUTOR } from '../backupContributor-topics'
+
+describe('TOPICS contributor', () => {
+  it('owns topic + message + chat_message_file_ref', () => {
+    expect(TOPICS_CONTRIBUTOR.schema.tables).toEqual([table('topic'), table('message'), table('chat_message_file_ref')])
+  })
+
+  it('declares 7 references: topicId/parentId owning + sourceId owning + modelId/assistantId/groupId optional + fileEntryId junction', () => {
+    const refs = TOPICS_CONTRIBUTOR.schema.references
+    expect(refs).toHaveLength(7)
+    // message.topicId → topic: same-domain owning, drives aggregate membership.
+    expect(refs).toContainEqual(
+      expect.objectContaining({
+        table: table('message'),
+        column: 'topicId',
+        referencedDomain: 'TOPICS',
+        kind: 'owning'
+      })
+    )
+    // message.parentId → message: self-FK owning (cascade), excluded from members.
+    expect(refs).toContainEqual(
+      expect.objectContaining({
+        table: table('message'),
+        column: 'parentId',
+        referencedDomain: 'TOPICS',
+        kind: 'owning'
+      })
+    )
+    // message.modelId → user_model (PROVIDERS): optional.
+    expect(refs).toContainEqual(
+      expect.objectContaining({
+        table: table('message'),
+        column: 'modelId',
+        referencedDomain: 'PROVIDERS',
+        kind: 'optional'
+      })
+    )
+    // chat_message_file_ref.sourceId → message: same-domain owning (nested member).
+    expect(refs).toContainEqual(
+      expect.objectContaining({
+        table: table('chat_message_file_ref'),
+        column: 'sourceId',
+        referencedDomain: 'TOPICS',
+        kind: 'owning'
+      })
+    )
+    // chat_message_file_ref.fileEntryId → file_entry: cross-domain junction.
+    expect(refs).toContainEqual(
+      expect.objectContaining({
+        table: table('chat_message_file_ref'),
+        column: 'fileEntryId',
+        referencedDomain: 'FILE_STORAGE',
+        kind: 'junction'
+      })
+    )
+    // topic.assistantId → assistant (ASSISTANTS): optional.
+    expect(refs).toContainEqual(
+      expect.objectContaining({
+        table: table('topic'),
+        column: 'assistantId',
+        referencedDomain: 'ASSISTANTS',
+        kind: 'optional'
+      })
+    )
+    // topic.groupId → group (TAGS_GROUPS): optional.
+    expect(refs).toContainEqual(
+      expect.objectContaining({
+        table: table('topic'),
+        column: 'groupId',
+        referencedDomain: 'TAGS_GROUPS',
+        kind: 'optional'
+      })
+    )
+  })
+
+  it('topic aggregate is renamable with message(topicId) + chat_message_file_ref(sourceId→message) include members', () => {
+    const aggregate = TOPICS_CONTRIBUTOR.schema.aggregates[0]
+    expect(aggregate.root).toBe(table('topic'))
+    expect(aggregate.identityKey).toEqual(['id'])
+    expect(aggregate.renamable).toBe(true)
+    expect(aggregate.members).toEqual([
+      expect.objectContaining({ table: table('message'), viaColumn: 'topicId', cascade: 'include' }),
+      // Nested member: parent=message disambiguates the sourceId→message leg.
+      expect.objectContaining({
+        table: table('chat_message_file_ref'),
+        viaColumn: 'sourceId',
+        parent: table('message'),
+        cascade: 'include'
+      })
+    ])
+  })
+
+  it('identity key is the single-column topic PK (uniqueness for cross-device match)', () => {
+    const aggregate = TOPICS_CONTRIBUTOR.schema.aggregates[0]
+    expect(aggregate.identityKey).toEqual(['id'])
+    // Single-column root PK satisfies finalize #26 (renamable root PK is single).
+    expect(aggregate.identityKey).toHaveLength(1)
+  })
+
+  it('declares chat_message FileRefSourceType owned by TOPICS (include-with-owner)', () => {
+    const policies = TOPICS_CONTRIBUTOR.schema.fileRefSourcePolicies
+    expect(policies).toHaveLength(1)
+    expect(policies[0]).toEqual(
+      expect.objectContaining({
+        sourceType: 'chat_message',
+        ownerDomain: 'TOPICS',
+        resourcePolicy: 'include-with-owner',
+        sourceTable: table('message')
+      })
+    )
+  })
+
+  it('declares message.data as a tolerant file-ref JSON soft reference', () => {
+    const softRefs = TOPICS_CONTRIBUTOR.schema.jsonSoftReferences
+    expect(softRefs).toHaveLength(1)
+    expect(softRefs[0]).toEqual(
+      expect.objectContaining({
+        table: table('message'),
+        column: 'data',
+        target: 'file-ref',
+        ownerDomain: 'TOPICS',
+        kind: 'tolerant'
+      })
+    )
+  })
+
+  it('renamable aggregate supplies cloneAggregate (finalize #16)', () => {
+    expect(TOPICS_CONTRIBUTOR.operations?.cloneAggregate).toBeDefined()
+  })
+
+  it('cloneAggregate replaces the root PK and rewrites activeNodeId to the cloned message id (§5.3)', async () => {
+    const cloneAggregate = TOPICS_CONTRIBUTOR.operations!.cloneAggregate!
+    // cloneAggregate is pure (no db on the context). The importer provides
+    // memberKeyMap; here we stub the message old→new id mapping.
+    const messageMap = new Map<string, string>([['msg-old', 'msg-new']])
+    const memberKeyMap = new Map([[table('message'), messageMap]] as const)
+    const ctx = {
+      aggregate: { root: table('topic') },
+      registry: { getPrimaryKey: () => ({ columns: ['id'] }) },
+      rootRow: { id: 'topic-old', name: 't', activeNodeId: 'msg-old' },
+      newRootKey: 'topic-new',
+      memberKeyMap
+    } as unknown as CloneAggregateContext
+    const result = await cloneAggregate(ctx)
+    expect(result.rootRow.id).toBe('topic-new')
+    expect(result.rootRow.name).toBe('t') // non-PK fields preserved by the spread
+    expect(result.rootRow.activeNodeId).toBe('msg-new') // rewritten to cloned message id
+  })
+
+  it('cloneAggregate clears activeNodeId when the referenced message is absent from backup', async () => {
+    const cloneAggregate = TOPICS_CONTRIBUTOR.operations!.cloneAggregate!
+    const messageMap = new Map<string, string>() // empty: message not cloned
+    const memberKeyMap = new Map([[table('message'), messageMap]] as const)
+    const ctx = {
+      aggregate: { root: table('topic') },
+      registry: { getPrimaryKey: () => ({ columns: ['id'] }) },
+      rootRow: { id: 'topic-old', activeNodeId: 'msg-gone' },
+      newRootKey: 'topic-new',
+      memberKeyMap
+    } as unknown as CloneAggregateContext
+    const result = await cloneAggregate(ctx)
+    expect(result.rootRow.activeNodeId).toBeNull() // cleared instead of dangling
+  })
+
+  it('primary keys are non-ambiguous (topic uuid-v4; message uuid-v7; chat_message_file_ref uuid-v4)', () => {
+    for (const pk of TOPICS_CONTRIBUTOR.schema.primaryKeys) {
+      expect(pk.ambiguous).toBeFalsy()
+    }
+    const topic = TOPICS_CONTRIBUTOR.schema.primaryKeys.find((p) => p.table === 'topic')!
+    expect(topic.kind).toBe('uuid-v4')
+    const message = TOPICS_CONTRIBUTOR.schema.primaryKeys.find((p) => p.table === 'message')!
+    expect(message.kind).toBe('uuid-v7')
+  })
+
+  it('schema is deep-frozen (mutation throws)', () => {
+    expect(() => {
+      ;(TOPICS_CONTRIBUTOR.schema.tables as unknown as string[]).push('x')
+    }).toThrow()
+  })
+})
diff --git a/src/main/data/services/backupContributor-agents.ts b/src/main/data/services/backupContributor-agents.ts
new file mode 100644
index 0000000000..3fff166b0d
--- /dev/null
+++ b/src/main/data/services/backupContributor-agents.ts
@@ -0,0 +1,255 @@
+// AGENTS backup contributor — owns the agent session/workspace/channel graph.
+//
+// Co-located in the agent owning module (the agent/session/channel tables are
+// authored from src/main/ai + this flat data-services dir) per backup-architecture
+// §7 placement. This is the most structurally complex domain (architecture §5):
+// four independent aggregate roots + two junction tables + a shared-table row-scope.
+//
+// Aggregate boundaries (§3.5 / §5):
+//  - agent_session (+ agent_session_message via sessionId): uuid-entity, SKIP.
+//    renamable:false — agent_session.workspaceId is a cross-aggregate owning FK to
+//    the independent agent_workspace aggregate (§5.4); RENAME would clone a session
+//    while its workspace target merges under a different id → owning FK dangles.
+//  - agent_workspace: natural-key (path UNIQUE), FIELD_MERGE. renamable:false.
+//    Independent aggregate root — NOT a member of agent_session (§5.4: workspaceId
+//    is a cross-aggregate owning ref, excluded from members by #14).
+//  - agent_channel: uuid-entity, SKIP. renamable:false (single-table).
+//  - agent: uuid-entity, SKIP. renamable:false (single-table).
+//
+// Junction tables (not aggregate members, §5.2 — cascade-prune, not clone-inherited):
+//  - agent_channel_task: composite PK, dual cascade FK (channelId→agent_channel +
+//    taskId→job_schedule). agent_channel_task.taskId points at job_schedule rows
+//    owned by the row-scope below; identity propagation rewrites taskId when the
+//    target schedule row merges under a new canonical id (§5.4).
+//  - agent_skill: composite PK, dual cascade FK (agentId→agent +
+//    skillId→agent_global_skill → SKILLS domain).
+//  - agent_mcp_server: composite PK, dual cascade FK (agentId→agent +
+//    mcpServerId→mcp_server → MCP_SERVERS domain).
+//
+// Shared-table row-scope (§5 / invariant #5/#23):
+//  - job_schedule.type='agent.task' → AGENTS. job_schedule is a SHARED table (other
+//    types belong to other domains / runtime); AGENTS owns only the
+//    type='agent.task' row partition via rowScopes. Those rows are a natural-key
+//    aggregate keyed by (type,name) UNIQUE → FIELD_MERGE (agent task definitions,
+//    otherwise design-loss of user tasks).
+//
+// JSON soft refs (§6.1):
+//  - agent_session_message.data: tolerant fileEntryId attachment refs (same shape as
+//    message.data in TOPICS).
+//  - agent_channel.workspace.workspaceId + job_schedule(type='agent.task')
+//    .jobInputTemplate.workspace.workspaceId (AgentSessionWorkspaceSource): REQUIRED
+//    — target merge (agent_workspace FIELD_MERGE) must rewrite the embedded
+//    workspaceId via identity propagation, or the channel/scheduled-task silently
+//    references a dangling workspace (§5.4).
+//
+// Preset: full + lite (agent history/config is a core migrate scenario).
+
+import type { BackupContributor } from '@main/data/db/backup/contributor-types'
+import { column, columns, mirrorPk, table } from '@main/data/db/backup/dbSchemaRefs'
+import { deepFreeze } from '@main/data/db/backup/freeze'
+
+/**
+ * AGENTS domain. Four independent aggregate roots + two junction tables + one
+ * shared-table row-scope. conflictDefault derives per root: uuid-entity roots →
+ * SKIP; agent_workspace + job_schedule(agent.task) → natural-key → FIELD_MERGE
+ * (§6.2). All aggregates are renamable:false.
+ */
+export const AGENTS_CONTRIBUTOR = deepFreeze<BackupContributor>({
+  domain: 'AGENTS',
+  schema: {
+    tables: [
+      table('agent'),
+      table('agent_session'),
+      table('agent_session_message'),
+      table('agent_workspace'),
+      table('agent_channel'),
+      table('agent_channel_task'),
+      table('agent_skill'),
+      table('agent_mcp_server'),
+      // job_schedule: AGENTS owns the type='agent.task' row partition. Listed as a
+      // table so #12/#13 recognize its jsonSoftRef + aggregate; rowScopes below filter
+      // export/restore to only agent.task rows (other job_schedule types are runtime).
+      table('job_schedule')
+    ],
+    references: [
+      // ── agent_session ──────────────────────────────────────────────────────
+      // agent_session.agentId → agent (AGENTS): optional (onDelete set null). #25-required.
+      { table: table('agent_session'), column: column('agentId'), referencedDomain: 'AGENTS', kind: 'optional' },
+      // agent_session.workspaceId → agent_workspace (AGENTS): cross-aggregate OWNING
+      // (onDelete cascade). Declared owning per #19/#25, but NOT a member of the
+      // session aggregate (#14: target is a different aggregate root, not session.root).
+      // See §5.4 — workspaceId is a cascade NOT NULL owning FK to an independent root.
+      {
+        table: table('agent_session'),
+        column: column('workspaceId'),
+        referencedDomain: 'AGENTS',
+        kind: 'owning'
+      },
+
+      // ── agent_session_message ──────────────────────────────────────────────
+      // agent_session_message.sessionId → agent_session: same-domain owning (cascade).
+      // Drives aggregate membership (#14/#15) — include member viaColumn.
+      {
+        table: table('agent_session_message'),
+        column: column('sessionId'),
+        referencedDomain: 'AGENTS',
+        kind: 'owning'
+      },
+      // agent_session_message.modelId → user_model (PROVIDERS): optional (onDelete set null). #25-required.
+      {
+        table: table('agent_session_message'),
+        column: column('modelId'),
+        referencedDomain: 'PROVIDERS',
+        kind: 'optional'
+      },
+
+      // ── agent_channel ──────────────────────────────────────────────────────
+      // agent_channel.agentId → agent (AGENTS): optional (onDelete set null). #25-required.
+      { table: table('agent_channel'), column: column('agentId'), referencedDomain: 'AGENTS', kind: 'optional' },
+      // agent_channel.sessionId → agent_session (AGENTS): optional (onDelete set null). #25-required.
+      { table: table('agent_channel'), column: column('sessionId'), referencedDomain: 'AGENTS', kind: 'optional' },
+
+      // ── agent_channel_task (junction: dual cascade) ────────────────────────
+      // channelId → agent_channel: same-domain junction (cascade). #25-required.
+      {
+        table: table('agent_channel_task'),
+        column: column('channelId'),
+        referencedDomain: 'AGENTS',
+        kind: 'junction'
+      },
+      // taskId → job_schedule (AGENTS row-scope): same-domain junction (cascade).
+      // Target is the job_schedule(type='agent.task') row partition owned below.
+      // #25-required; identity propagation rewrites taskId on target FIELD_MERGE (§5.4).
+      {
+        table: table('agent_channel_task'),
+        column: column('taskId'),
+        referencedDomain: 'AGENTS',
+        kind: 'junction'
+      },
+
+      // ── agent_skill (junction: dual cascade) ───────────────────────────────
+      // agentId → agent: same-domain junction (cascade). #25-required.
+      { table: table('agent_skill'), column: column('agentId'), referencedDomain: 'AGENTS', kind: 'junction' },
+      // skillId → agent_global_skill (SKILLS): cross-domain junction (cascade). #25-required.
+      { table: table('agent_skill'), column: column('skillId'), referencedDomain: 'SKILLS', kind: 'junction' },
+
+      // ── agent_mcp_server (junction: dual cascade) ──────────────────────────
+      // agentId → agent: same-domain junction (cascade). #25-required.
+      { table: table('agent_mcp_server'), column: column('agentId'), referencedDomain: 'AGENTS', kind: 'junction' },
+      // mcpServerId → mcp_server (MCP_SERVERS): cross-domain junction (cascade). #25-required.
+      {
+        table: table('agent_mcp_server'),
+        column: column('mcpServerId'),
+        referencedDomain: 'MCP_SERVERS',
+        kind: 'junction'
+      },
+
+      // ── agent (scalar model refs) ──────────────────────────────────────────
+      // agent.model / planModel / smallModel → user_model (PROVIDERS): optional
+      // (onDelete set null). Three #25-required FKs.
+      { table: table('agent'), column: column('model'), referencedDomain: 'PROVIDERS', kind: 'optional' },
+      { table: table('agent'), column: column('planModel'), referencedDomain: 'PROVIDERS', kind: 'optional' },
+      { table: table('agent'), column: column('smallModel'), referencedDomain: 'PROVIDERS', kind: 'optional' }
+    ],
+    primaryKeys: [
+      mirrorPk('agent'),
+      mirrorPk('agent_session'),
+      mirrorPk('agent_session_message'),
+      mirrorPk('agent_workspace'),
+      mirrorPk('agent_channel'),
+      mirrorPk('agent_channel_task'),
+      mirrorPk('agent_skill'),
+      mirrorPk('agent_mcp_server'),
+      mirrorPk('job_schedule')
+    ],
+    aggregates: [
+      // agent_session + agent_session_message: uuid-entity, SKIP, non-renamable.
+      {
+        root: table('agent_session'),
+        identityKey: columns(['id']),
+        members: [
+          { table: table('agent_session_message'), viaColumn: column('sessionId'), cascade: 'include' }
+        ],
+        renamable: false
+      },
+      // agent_workspace: natural-key (path UNIQUE), FIELD_MERGE, non-renamable.
+      // identityKey includes the UNIQUE non-PK column `path` (§6.2 unique-backing).
+      // identityClass explicit — root PK `id` is uuid, so the finalize default
+      // (uuid-entity→SKIP) would mis-derive; `path` is the business identity (§5.4).
+      {
+        root: table('agent_workspace'),
+        identityKey: columns(['path']),
+        identityClass: 'natural-key',
+        renamable: false
+      },
+      // agent_channel: single-table uuid-entity, SKIP, non-renamable.
+      {
+        root: table('agent_channel'),
+        identityKey: columns(['id']),
+        renamable: false
+      },
+      // agent: single-table uuid-entity, SKIP, non-renamable.
+      {
+        root: table('agent'),
+        identityKey: columns(['id']),
+        renamable: false
+      },
+      // job_schedule(type='agent.task') row-scope: natural-key ((type,name) UNIQUE),
+      // FIELD_MERGE. Root is the shared job_schedule table; ownership is row-scoped
+      // (only type='agent.task' rows belong to AGENTS). non-renamable.
+      // identityClass explicit — root PK `id` is uuid, finalize default would
+      // mis-derive uuid-entity→SKIP; (type,name) is the business identity (§5.4).
+      {
+        root: table('job_schedule'),
+        identityKey: columns(['type', 'name']),
+        identityClass: 'natural-key',
+        renamable: false
+      }
+    ],
+    // Shared-table row partition: job_schedule.type='agent.task' → AGENTS.
+    // Other job_schedule types are not owned here (invariant #5/#23 row-scope coverage).
+    rowScopes: [
+      { table: table('job_schedule'), ownerDomain: 'AGENTS', filter: { column: column('type'), op: 'eq', value: 'agent.task' } }
+    ],
+    fileRefSourcePolicies: [],
+    jsonSoftReferences: [
+      // agent_session_message.data embeds attachment fileEntryId soft refs (tolerant —
+      // missing blob degrades to a toast + orphan check, no identity propagation, §5.4).
+      {
+        table: table('agent_session_message'),
+        column: column('data'),
+        target: 'file-ref',
+        ownerDomain: 'AGENTS',
+        kind: 'tolerant'
+      },
+      // agent_channel.workspace embeds an AgentSessionWorkspaceSource whose workspaceId
+      // points at an agent_workspace (natural-key target). REQUIRED — target FIELD_MERGE
+      // must rewrite the embedded workspaceId via identity propagation (§5.4), or the
+      // channel silently references a dangling/merged-away workspace.
+      {
+        table: table('agent_channel'),
+        column: column('workspace'),
+        target: 'entity-id',
+        ownerDomain: 'AGENTS',
+        kind: 'required'
+      },
+      // job_schedule(type='agent.task').jobInputTemplate embeds the same
+      // AgentSessionWorkspaceSource.workspaceId. REQUIRED for the same reason — a
+      // scheduled agent task whose workspace id was merged away would fire against a
+      // dangling workspace. Covers the shared job_schedule table's agent.task rows.
+      {
+        table: table('job_schedule'),
+        column: column('jobInputTemplate'),
+        target: 'entity-id',
+        ownerDomain: 'AGENTS',
+        kind: 'required'
+      }
+    ]
+  },
+  backupPolicy: {},
+  // All aggregates are renamable:false → cloneAggregate is NOT required (#16).
+  // TODO(C/D track): afterImport must re-arm job_schedule(type='agent.task') timers
+  // (DB import does not call registerJobSchedule — agent tasks would not fire until
+  // restart, §5). Not a finalize concern; wired with the C/D restore track.
+  operations: undefined
+})
diff --git a/src/main/data/services/backupContributor-miniapps.ts b/src/main/data/services/backupContributor-miniapps.ts
new file mode 100644
index 0000000000..f10d549a22
--- /dev/null
+++ b/src/main/data/services/backupContributor-miniapps.ts
@@ -0,0 +1,42 @@
+// MINIAPPS backup contributor — owns the `mini_app` table.
+//
+// Co-located in the miniapps owning module (MiniAppService / MiniAppSeeder live in
+// this flat data-services dir) per backup-architecture §7 placement. Single-table
+// schema-only domain: no cross-domain FKs (presetMiniAppId points at an app-builtin
+// preset, NOT a DB row — §5.4 scalar-ID three-way rule: non-DB resource → not an
+// EntityReference candidate), no aggregate members, no file-ref / JSON soft refs,
+// no operations hooks (see openspec simple-domains.md "MINIAPPS").
+//
+// Preset: full + lite (lite includes miniapps — small config rows).
+
+import type { BackupContributor } from '@main/data/db/backup/contributor-types'
+import { columns, mirrorPk, table } from '@main/data/db/backup/dbSchemaRefs'
+import { deepFreeze } from '@main/data/db/backup/freeze'
+
+/**
+ * MINIAPPS domain: user miniapp configurations keyed by the natural `appId` PK.
+ * Per §6.2 identityClass derives to natural-key (PK kind natural), conflictDefault
+ * to FIELD_MERGE (aligns the same app across devices). renamable:false — a natural
+ * single-column PK clone would collide on the same appId, RENAME degrades to SKIP.
+ */
+export const MINIAPPS_CONTRIBUTOR = deepFreeze<BackupContributor>({
+  domain: 'MINIAPPS',
+  schema: {
+    tables: [table('mini_app')],
+    references: [],
+    primaryKeys: [mirrorPk('mini_app')],
+    aggregates: [
+      {
+        root: table('mini_app'),
+        identityKey: columns(['appId']),
+        members: [],
+        renamable: false
+      }
+    ],
+    fileRefSourcePolicies: [],
+    jsonSoftReferences: []
+  },
+  backupPolicy: {},
+  // Schema-only: no file resources, no row transform, no restoreResources.
+  operations: undefined
+})
diff --git a/src/main/data/services/backupContributor-paintings.ts b/src/main/data/services/backupContributor-paintings.ts
new file mode 100644
index 0000000000..5e44e9902d
--- /dev/null
+++ b/src/main/data/services/backupContributor-paintings.ts
@@ -0,0 +1,71 @@
+// PAINTINGS backup contributor — owns `painting` + `painting_file_ref`.
+//
+// Co-located in the paintings owning module (PaintingService lives in this flat
+// data-services dir) per backup-architecture §7 placement. painting is the
+// aggregate root; painting_file_ref is an include member via sourceId
+// (onDelete cascade). painting_file_ref is a junction with a second cascade FK
+// fileEntryId→file_entry (FILE_STORAGE) — a cross-domain owning reference, NOT a
+// member of the painting aggregate (§5.1: post-#16532 painting_file_ref belongs to
+// PAINTINGS by source domain; FILE_STORAGE owns file_entry only).
+//
+// painting has NO FKs (providerId/modelId are scalar soft refs pointing at DB rows
+// without a declared FK — per §5.4 three-way scalar-ID rule, these are NOT
+// EntityReferences; they stay tolerant: missing target degrades, no rewrite).
+//
+// renamable:false — paintings are uuid-entity with no business UNIQUE key; RENAME
+// is not applicable (architecture §3.5).
+//
+// Preset: full only (lite-excluded — painting images are large file blobs).
+
+import type { BackupContributor } from '@main/data/db/backup/contributor-types'
+import { column, columns, mirrorPk, table } from '@main/data/db/backup/dbSchemaRefs'
+import { deepFreeze } from '@main/data/db/backup/freeze'
+
+/**
+ * PAINTINGS domain. painting (uuid-v4) is the aggregate root; painting_file_ref
+ * (uuid-v4) is an include member via sourceId. painting_file_ref.fileEntryId→
+ * file_entry is a cross-domain owning reference (cascade). conflictDefault
+ * derives to SKIP (uuid-entity → SKIP, §6.2).
+ */
+export const PAINTINGS_CONTRIBUTOR = deepFreeze<BackupContributor>({
+  domain: 'PAINTINGS',
+  schema: {
+    tables: [table('painting'), table('painting_file_ref')],
+    references: [
+      // painting_file_ref.sourceId → painting: same-domain owning (cascade). Drives
+      // the aggregate membership (#14/#15) and is #25-required.
+      { table: table('painting_file_ref'), column: column('sourceId'), referencedDomain: 'PAINTINGS', kind: 'owning' },
+      // painting_file_ref.fileEntryId → file_entry (FILE_STORAGE): junction (dual-cascade
+      // junction table — sourceId & fileEntryId both onDelete cascade). Cross-domain
+      // endpoint, cascade-prune not DELETE_ROW; mirrors TOPICS chat_message_file_ref.fileEntryId
+      // per §5.2. #25-required (declare so the FK is covered; finalize #19 verifies cascade).
+      {
+        table: table('painting_file_ref'),
+        column: column('fileEntryId'),
+        referencedDomain: 'FILE_STORAGE',
+        kind: 'junction'
+      }
+    ],
+    primaryKeys: [mirrorPk('painting'), mirrorPk('painting_file_ref')],
+    aggregates: [
+      {
+        root: table('painting'),
+        identityKey: columns(['id']),
+        members: [{ table: table('painting_file_ref'), viaColumn: column('sourceId'), cascade: 'include' }],
+        renamable: false
+      }
+    ],
+    // file_ref.sourceType='painting' → ownerDomain=PAINTINGS (finalize #11). Drives
+    // export-time file blob collection via painting_file_ref (§5.1).
+    fileRefSourcePolicies: [
+      { sourceType: 'painting', ownerDomain: 'PAINTINGS', resourcePolicy: 'include-with-owner', sourceTable: table('painting_file_ref') }
+    ],
+    jsonSoftReferences: []
+  },
+  backupPolicy: {},
+  // TODO(C/D track) — collectFileResources (export painting file blobs via
+  // painting_file_ref.fileEntryId, filter deletedAt IS NULL) + restoreResources
+  // (blob restore runs before DB import, returns skippedFileEntryIds). Not a
+  // finalize concern; wired with the C/D restore track (like FILE_STORAGE / KNOWLEDGE).
+  operations: undefined
+})
diff --git a/src/main/data/services/backupContributor-providers.ts b/src/main/data/services/backupContributor-providers.ts
new file mode 100644
index 0000000000..745edba23b
--- /dev/null
+++ b/src/main/data/services/backupContributor-providers.ts
@@ -0,0 +1,81 @@
+// PROVIDERS backup contributor — owns `user_provider` + `user_model`.
+//
+// Co-located in the providers owning module (ProviderService / ModelService live
+// in this flat data-services dir) per backup-architecture §7 placement.
+// user_model is an include member of the user_provider aggregate via `providerId`
+// (onDelete cascade). The domain is self-contained: no cross-domain FKs.
+//
+// natural-key identity: user_provider.providerId is the business identity (a stable
+// provider key like 'openai'/'anthropic'), so cross-device merges line up without
+// UUID collisions. conflictDefault derives to FIELD_MERGE (natural-key →
+// FIELD_MERGE, §6.2) — column-level merge keeps the local API key and fills in
+// fields only present remotely, preventing API key loss on restore.
+//
+// renamable:false — user_model.id is a derived key (NOT a stable cross-device
+// identity; two devices generate different ids for the same provider+model pair).
+// The real model identity is the UNIQUE(providerId, modelId) pair. A RENAME clone
+// would have to re-derive model ids and rewrite every cross-domain FK that points
+// at them (message.modelId, assistant.modelId, knowledge_base.embeddingModelId,
+// etc.) — no safe clone path, so RENAME degrades to SKIP (architecture §3.5/§5).
+//
+// Preset: full + lite (configuration domain — users need their model service
+// config + API keys on a new machine).
+
+import type { BackupContributor } from '@main/data/db/backup/contributor-types'
+import { column, columns, mirrorPk, table } from '@main/data/db/backup/dbSchemaRefs'
+import { deepFreeze } from '@main/data/db/backup/freeze'
+
+/**
+ * PROVIDERS domain. user_provider (natural-key providerId) is the aggregate root;
+ * user_model (natural-key id, UNIQUE [providerId, modelId]) is an include member
+ * via providerId. conflictDefault derives to FIELD_MERGE (natural-key →
+ * FIELD_MERGE, §6.2). fieldMergePolicies keep local API keys and fill remote-only
+ * credential columns; uniqueMergeRules merge models by the business unique pair.
+ */
+export const PROVIDERS_CONTRIBUTOR = deepFreeze<BackupContributor>({
+  domain: 'PROVIDERS',
+  schema: {
+    tables: [table('user_provider'), table('user_model')],
+    references: [
+      // user_model.providerId → user_provider.providerId: same-domain owning
+      // (cascade). Drives aggregate membership (#14/#15) and is #25-required.
+      { table: table('user_model'), column: column('providerId'), referencedDomain: 'PROVIDERS', kind: 'owning' }
+    ],
+    primaryKeys: [mirrorPk('user_provider'), mirrorPk('user_model')],
+    aggregates: [
+      {
+        root: table('user_provider'),
+        identityKey: columns(['providerId']),
+        members: [{ table: table('user_model'), viaColumn: column('providerId'), cascade: 'include' }],
+        renamable: false
+      }
+    ],
+    fileRefSourcePolicies: [],
+    jsonSoftReferences: []
+  },
+  backupPolicy: {
+    // Merge user_model by its non-PK business UNIQUE pair so a provider's models
+    // line up across devices without colliding on the derived `id` PK.
+    uniqueMergeRules: [{ table: table('user_model'), uniqueColumns: columns(['providerId', 'modelId']) }],
+    // Credential columns: keep the local value and only fill from remote when local
+    // is null/empty/default-skeleton. Seeded providers ship apiKeys=[] and non-null
+    // authConfig skeletons, so a plain `remote-fills-local-null` would treat those as
+    // "present" and silently drop backed-up credentials. `remote-fills-local-empty`
+    // treats [], null, and empty/skeleton auth configs as missing — preserves a
+    // working local API key, brings in keys present only in the backup (§5 "防丢 API
+    // key"). Restore (C/D track) implements the empty/skeleton detection.
+    fieldMergePolicies: [
+      {
+        table: table('user_provider'),
+        column: column('apiKeys'),
+        strategy: 'remote-fills-local-empty'
+      },
+      {
+        table: table('user_provider'),
+        column: column('authConfig'),
+        strategy: 'remote-fills-local-empty'
+      }
+    ]
+  },
+  operations: undefined
+})
diff --git a/src/main/data/services/backupContributor-topics.ts b/src/main/data/services/backupContributor-topics.ts
new file mode 100644
index 0000000000..652b663ca2
--- /dev/null
+++ b/src/main/data/services/backupContributor-topics.ts
@@ -0,0 +1,145 @@
+// TOPICS backup contributor — owns `topic` + `message` + `chat_message_file_ref`.
+//
+// Co-located in the topics owning module (TopicService / MessageService, the table
+// CRUD owners, live in this flat data-services dir) per backup-architecture §7
+// placement. The topic aggregate is renamable: RENAME on id conflict clones the
+// topic AND its message tree (and chat_message_file_ref rows), and cloneAggregate
+// must additionally rewrite the `topic.activeNodeId` scalar soft ref to the cloned
+// message's new id (architecture §5.3 — required, not optional).
+//
+// Post-#16532 the old polymorphic `file_ref` was split; `chat_message_file_ref`
+// (FK sourceId→message cascade + fileEntryId→file_entry cascade) belongs to TOPICS
+// by source domain. It is an include member (via sourceId→message), not a junction
+// reference, because its TOPICS-side leg (sourceId) remaps with the message tree on
+// clone; the FILE_STORAGE leg (fileEntryId) is declared as a junction reference.
+//
+// message.data carries a tolerant fileEntryId JSON soft ref (attachments). The
+// `chat_message` FileRefSourceType is owned here (include-with-owner) so file blobs
+// follow chat messages in full backups.
+//
+// Preset: full + lite (chat history is a core migrate scenario).
+
+import type { BackupContributor } from '@main/data/db/backup/contributor-types'
+import { column, columns, mirrorPk, table } from '@main/data/db/backup/dbSchemaRefs'
+import { deepFreeze } from '@main/data/db/backup/freeze'
+
+/**
+ * TOPICS domain. topic (uuid-v4) is the aggregate root; message (uuid-v7) is an
+ * include member via topicId (onDelete cascade); chat_message_file_ref (uuid-v4) is
+ * a nested include member via sourceId→message (onDelete cascade). conflictDefault
+ * derives to SKIP (uuid-entity → SKIP, §6.2).
+ *
+ * message.parentId is a self-FK (message→message, cascade). It is declared owning
+ * to satisfy #19 (cascade→owning) and #25 (every FK declared), but does NOT enter
+ * the aggregate members: it targets `message` (the member table), not the root
+ * `topic`, so #14 excludes it from member derivation.
+ *
+ * topic.activeNodeId is a scalar text soft ref to a message id with NO FK. It is
+ * not an EntityReference (#24 requires a FK); instead cloneAggregate rewrites it to
+ * the cloned message's new id (§5.3) on RENAME.
+ */
+export const TOPICS_CONTRIBUTOR = deepFreeze<BackupContributor>({
+  domain: 'TOPICS',
+  schema: {
+    tables: [table('topic'), table('message'), table('chat_message_file_ref')],
+    references: [
+      // message.topicId → topic: same-domain owning (cascade). Drives aggregate
+      // membership (#14/#15) and is #25-required.
+      { table: table('message'), column: column('topicId'), referencedDomain: 'TOPICS', kind: 'owning' },
+      // message.parentId → message: self-FK (cascade). Declared owning per #19/#25,
+      // but excluded from members (#14: targets the member, not the root).
+      { table: table('message'), column: column('parentId'), referencedDomain: 'TOPICS', kind: 'owning' },
+      // message.modelId → user_model (PROVIDERS): optional (onDelete set null). #25-required.
+      { table: table('message'), column: column('modelId'), referencedDomain: 'PROVIDERS', kind: 'optional' },
+      // chat_message_file_ref.sourceId → message: same-domain owning (cascade), nested
+      // include member (file refs follow their owning message on clone/prune).
+      {
+        table: table('chat_message_file_ref'),
+        column: column('sourceId'),
+        referencedDomain: 'TOPICS',
+        kind: 'owning'
+      },
+      // chat_message_file_ref.fileEntryId → file_entry (FILE_STORAGE): cross-domain
+      // junction (cascade-prune with FILE_STORAGE).
+      {
+        table: table('chat_message_file_ref'),
+        column: column('fileEntryId'),
+        referencedDomain: 'FILE_STORAGE',
+        kind: 'junction'
+      },
+      // topic.assistantId → assistant (ASSISTANTS): optional (onDelete set null). #25-required.
+      { table: table('topic'), column: column('assistantId'), referencedDomain: 'ASSISTANTS', kind: 'optional' },
+      // topic.groupId → group (TAGS_GROUPS): optional (onDelete set null). #25-required.
+      { table: table('topic'), column: column('groupId'), referencedDomain: 'TAGS_GROUPS', kind: 'optional' }
+    ],
+    primaryKeys: [mirrorPk('topic'), mirrorPk('message'), mirrorPk('chat_message_file_ref')],
+    aggregates: [
+      {
+        root: table('topic'),
+        identityKey: columns(['id']),
+        members: [
+          { table: table('message'), viaColumn: column('topicId'), cascade: 'include' },
+          {
+            table: table('chat_message_file_ref'),
+            viaColumn: column('sourceId'),
+            // Nested member: chat_message_file_ref.sourceId points at message (the
+            // parent member), not the root topic — declare parent to disambiguate
+            // (#14/#15 multi-owning-ref rule).
+            parent: table('message'),
+            cascade: 'include'
+          }
+        ],
+        renamable: true
+      }
+    ],
+    fileRefSourcePolicies: [
+      // chat_message file refs are owned by TOPICS (source domain) and bundled with
+      // the topic/message tree in full backups (#11 coverage).
+      {
+        sourceType: 'chat_message',
+        ownerDomain: 'TOPICS',
+        resourcePolicy: 'include-with-owner',
+        sourceTable: table('message')
+      }
+    ],
+    jsonSoftReferences: [
+      // message.data embeds attachment fileEntryId soft refs (tolerant — missing blob
+      // degrades to a toast + orphan check, no identity propagation, §5.4).
+      {
+        table: table('message'),
+        column: column('data'),
+        target: 'file-ref',
+        ownerDomain: 'TOPICS',
+        kind: 'tolerant'
+      }
+    ]
+  },
+  backupPolicy: {},
+  operations: {
+    // Renamable aggregate (RENAME on conflict) → cloneAggregate is required (#16).
+    // Pure: no db on the context. The root PK column is read from the registry
+    // (#26 guarantees a single-column root PK). The importer remaps member rows
+    // (message.id, chat_message_file_ref.sourceId/fileEntryId) via memberKeyMap.
+    // Additionally, topic.activeNodeId is a scalar soft ref to a message id with no
+    // FK (§5.3): on RENAME it MUST be rewritten to the cloned message's new id, or
+    // the restored topic points at the old aggregate's node / dangles.
+    cloneAggregate: async (ctx) => {
+      const pkColumn = ctx.registry.getPrimaryKey(ctx.aggregate.root).columns[0]
+      // Map old message id → cloned message id from the importer's memberKeyMap, and
+      // rewrite activeNodeId so the renamed topic points inside its own clone.
+      const messageKeyMap = ctx.memberKeyMap.get(table('message'))
+      const oldActiveNodeId = ctx.rootRow.activeNodeId
+      const newActiveNodeId =
+        typeof oldActiveNodeId === 'string' && messageKeyMap ? messageKeyMap.get(oldActiveNodeId) : undefined
+      return {
+        rootRow: {
+          ...ctx.rootRow,
+          [pkColumn]: ctx.newRootKey,
+          // Rewrite the scalar soft ref; if activeNodeId is null or its message was
+          // not cloned (e.g. absent from backup), clear it rather than dangle.
+          activeNodeId: newActiveNodeId ?? null
+        }
+      }
+    }
+  }
+})