diff --git a/apps/server/src/common/decorators/auth-provenance.decorator.ts b/apps/server/src/common/decorators/auth-provenance.decorator.ts
index 3e49b6d4..8baa592b 100644
--- a/apps/server/src/common/decorators/auth-provenance.decorator.ts
+++ b/apps/server/src/common/decorators/auth-provenance.decorator.ts
@@ -13,6 +13,34 @@ export interface AuthProvenanceData {
   aiChatId: string | null;
 }
 
+/**
+ * Agent-edit write-stamp fields for a repository insert/update (#143 review).
+ * Spread into the row being written: for an agent it stamps the `*Source`
+ * column 'agent' and the AI-chat id; for a normal user it returns `{}` so the
+ * column keeps its default ('user'). The only per-table variation is the column
+ * names, passed as `sourceKey`/`chatKey`, so the agent-stamp idiom lives in ONE
+ * place instead of being hand-reimplemented at every write site (where a wrong
+ * literal or a forgotten `aiChatId` could drift).
+ *
+ *   insertComment({ ..., ...agentSourceFields(p, 'createdSource', 'aiChatId') })
+ *   updatePage({ ..., ...agentSourceFields(p, 'lastUpdatedSource', 'lastUpdatedAiChatId') })
+ *
+ * Does NOT cover sites that must CLEAR the source on a non-agent action (e.g.
+ * comment un-resolve, which writes an explicit null) — those keep their own
+ * conditional; nor the collab persistence path (its own sticky-window logic).
+ */
+export function agentSourceFields<S extends string, C extends string>(
+  provenance: AuthProvenanceData | undefined,
+  sourceKey: S,
+  chatKey: C,
+): Partial<Record<S, ProvenanceSource> & Record<C, string | null>> {
+  if (provenance?.actor !== 'agent') return {};
+  return {
+    [sourceKey]: 'agent',
+    [chatKey]: provenance.aiChatId,
+  } as Partial<Record<S, ProvenanceSource> & Record<C, string | null>>;
+}
+
 /**
  * Resolve the request's provenance. Defaults to a 'user' actor when the claim
  * is absent (e.g. an endpoint reached without going through the access-token
diff --git a/apps/server/src/core/comment/comment.service.ts b/apps/server/src/core/comment/comment.service.ts
index d88c5ffd..579438ef 100644
--- a/apps/server/src/core/comment/comment.service.ts
+++ b/apps/server/src/core/comment/comment.service.ts
@@ -22,7 +22,10 @@ import {
   ICommentResolvedNotificationJob,
 } from '../../integrations/queue/constants/queue.interface';
 import { WsService } from '../../ws/ws.service';
-import { AuthProvenanceData } from '../../common/decorators/auth-provenance.decorator';
+import {
+  AuthProvenanceData,
+  agentSourceFields,
+} from '../../common/decorators/auth-provenance.decorator';
 
 @Injectable()
 export class CommentService {
@@ -60,7 +63,6 @@ export class CommentService {
   ) {
     const { page, workspaceId, user } = opts;
     const commentContent = JSON.parse(createCommentDto.content);
-    const isAgent = provenance?.actor === 'agent';
 
     if (createCommentDto.parentCommentId) {
       const parentComment = await this.commentRepo.findById(
@@ -87,9 +89,7 @@ export class CommentService {
       spaceId: page.spaceId,
       // Agent-edit provenance: the user stays creatorId; this only annotates the
       // source. Normal user requests leave the column default ('user').
-      ...(isAgent
-        ? { createdSource: 'agent', aiChatId: provenance.aiChatId }
-        : {}),
+      ...agentSourceFields(provenance, 'createdSource', 'aiChatId'),
     });
 
     if (createCommentDto.yjsSelection) {
diff --git a/apps/server/src/core/page/services/page.service.ts b/apps/server/src/core/page/services/page.service.ts
index 6ea00188..88ef01c8 100644
--- a/apps/server/src/core/page/services/page.service.ts
+++ b/apps/server/src/core/page/services/page.service.ts
@@ -57,7 +57,10 @@ import { WatcherService } from '../../watcher/watcher.service';
 import { sql } from 'kysely';
 import { TransclusionService } from '../transclusion/transclusion.service';
 import { remapPageEmbedSourceId } from '../transclusion/utils/transclusion-prosemirror.util';
-import { AuthProvenanceData } from '../../../common/decorators/auth-provenance.decorator';
+import {
+  AuthProvenanceData,
+  agentSourceFields,
+} from '../../../common/decorators/auth-provenance.decorator';
 
 @Injectable()
 export class PageService {
@@ -135,7 +138,6 @@ export class PageService {
       ydoc = createYdocFromJson(prosemirrorJson);
     }
 
-    const isAgent = provenance?.actor === 'agent';
 
     const page = await this.pageRepo.insertPage({
       slugId: generateSlugId(),
@@ -153,12 +155,7 @@ export class PageService {
       // Agent-edit provenance. The human stays the responsible author
       // (creatorId/lastUpdatedById); these only annotate the source. A normal
       // user request leaves the column default ('user').
-      ...(isAgent
-        ? {
-            lastUpdatedSource: 'agent',
-            lastUpdatedAiChatId: provenance.aiChatId,
-          }
-        : {}),
+      ...agentSourceFields(provenance, 'lastUpdatedSource', 'lastUpdatedAiChatId'),
       content,
       textContent,
       ydoc,
@@ -231,7 +228,6 @@ export class PageService {
     contributors.add(user.id);
     const contributorIds = Array.from(contributors);
 
-    const isAgent = provenance?.actor === 'agent';
 
     // Detect a real title/icon change so the WS tree listener can broadcast an
     // `updateOne` to the space (rename / icon swap) WITHOUT re-broadcasting on a
@@ -251,12 +247,7 @@ export class PageService {
         lastUpdatedById: user.id,
         // Agent-edit provenance: annotate the source without changing the
         // responsible author. A normal user request leaves the column default.
-        ...(isAgent
-          ? {
-              lastUpdatedSource: 'agent',
-              lastUpdatedAiChatId: provenance.aiChatId,
-            }
-          : {}),
+        ...agentSourceFields(provenance, 'lastUpdatedSource', 'lastUpdatedAiChatId'),
         updatedAt: new Date(),
         contributorIds: contributorIds,
       },
@@ -443,7 +434,6 @@ export class PageService {
     provenance?: AuthProvenanceData,
   ) {
     let childPageIds: string[] = [];
-    const isAgent = provenance?.actor === 'agent';
 
     const allPages = await this.pageRepo.getPageAndDescendants(rootPage.id, {
       includeContent: false,
@@ -490,12 +480,7 @@ export class PageService {
           // Agent-edit provenance on the moved root page. Child pages are bulk
           // re-parented to the new space (no content change), so the marker is
           // stamped on the root the agent acted on. Normal user: no change.
-          ...(isAgent
-            ? {
-                lastUpdatedSource: 'agent',
-                lastUpdatedAiChatId: provenance.aiChatId,
-              }
-            : {}),
+          ...agentSourceFields(provenance, 'lastUpdatedSource', 'lastUpdatedAiChatId'),
         },
         rootPage.id,
         trx,
@@ -949,7 +934,6 @@ export class PageService {
       }
     }
 
-    const isAgent = provenance?.actor === 'agent';
 
     const updateResult = await this.pageRepo.updatePage(
       {
@@ -957,12 +941,7 @@ export class PageService {
         parentPageId: parentPageId,
         // Agent-edit provenance: annotate the source on an agent move. A normal
         // user request leaves the column default ('user').
-        ...(isAgent
-          ? {
-              lastUpdatedSource: 'agent',
-              lastUpdatedAiChatId: provenance.aiChatId,
-            }
-          : {}),
+        ...agentSourceFields(provenance, 'lastUpdatedSource', 'lastUpdatedAiChatId'),
       },
       dto.pageId,
     );