diff --git a/server/src/__tests__/privacy-production-review.test.ts b/server/src/__tests__/privacy-production-review.test.ts
index 20e77b0fd32..1e0b37396ca 100644
--- a/server/src/__tests__/privacy-production-review.test.ts
+++ b/server/src/__tests__/privacy-production-review.test.ts
@@ -244,6 +244,42 @@ describe("private task production review", () => {
     expect(await canActorReadIssuePrivacy(db, f.actor(f.outsider), grandchild)).toBe(false);
   });
 
+  it("binds child-manager grant writes to the child and rejects ancestor or sibling grants", async () => {
+    const f = await fixture();
+    const { issueService } = await import("../services/issues.js");
+    const { issueRoutes } = await import("../routes/issues.js");
+    const { errorHandler } = await import("../middleware/index.js");
+    const svc = issueService(db);
+    const root = await svc.create(f.company.id, { title: "Ancestor", visibility: "private", createdByUserId: f.outsider });
+    const child = await svc.create(f.company.id, { title: "Managed child", parentId: root.id, createdByUserId: f.owner });
+    const grandchild = await svc.create(f.company.id, { title: "Descendant", parentId: child.id, createdByUserId: f.outsider });
+    const sibling = await svc.create(f.company.id, { title: "Sibling", parentId: root.id, createdByUserId: f.outsider });
+    const [rootGrant] = await db.insert(issueAccessGrants).values({ issueId: root.id, subjectType: "user", subjectId: f.owner, source: "explicit" }).returning();
+    const [siblingGrant] = await db.insert(issueAccessGrants).values({ issueId: sibling.id, subjectType: "user", subjectId: f.owner, source: "explicit" }).returning();
+    const app = express(); app.use(express.json());
+    app.use((req, _res, next) => { req.actor = f.actor(f.owner); next(); });
+    app.use("/api", issueRoutes(db, {} as any)); app.use(errorHandler);
+    const audience = await request(app).get(`/api/issues/${child.id}/access-grants`).expect(200);
+    expect(audience.body).toContainEqual(expect.objectContaining({ id: rootGrant.id, inherited: true }));
+    for (const grant of [rootGrant, siblingGrant]) {
+      await request(app).post(`/api/issues/${child.id}/access-grants/${grant.id}/revoke`).send({}).expect(404);
+      const [unchanged] = await db.select().from(issueAccessGrants).where(eq(issueAccessGrants.id, grant.id));
+      expect(unchanged.revokedAt).toBeNull();
+    }
+    for (const task of [root, sibling]) {
+      await request(app).post(`/api/issues/${task.id}/access-grants`).send({ subjectType: "agent", subjectId: f.agent.id }).expect(403);
+    }
+    const added = await request(app).post(`/api/issues/${child.id}/access-grants`).send({ subjectType: "agent", subjectId: f.agent.id }).expect(201);
+    expect(added.body.issueId).toBe(child.id);
+    const agent: AuthorizationActor = { type: "agent", companyId: f.company.id, agentId: f.agent.id };
+    for (const [task, expected] of [[root, false], [child, true], [grandchild, true], [sibling, false]] as const) {
+      expect(await canActorReadIssuePrivacy(db, agent, task)).toBe(expected);
+    }
+    await request(app).post(`/api/issues/${child.id}/access-grants/${added.body.id}/revoke`).send({}).expect(200);
+    expect(await canActorReadIssuePrivacy(db, agent, child)).toBe(false);
+    expect(await canActorReadIssuePrivacy(db, agent, grandchild)).toBe(false);
+  });
+
   it("retains a child assignment grant after unassignment without granting the root", async () => {
     const f = await fixture();
     const { issueService } = await import("../services/issues.js");
diff --git a/server/src/routes/issues.ts b/server/src/routes/issues.ts
index 465e6b52764..579756c9ce4 100644
--- a/server/src/routes/issues.ts
+++ b/server/src/routes/issues.ts
@@ -5214,7 +5214,7 @@ export function issueRoutes(
     return false;
   }
 
-  async function resolveIssuePrivacyManagementRoot(
+  async function resolveManagedIssueForPrivacy(
     req: Request,
     res: Response,
     issue: Parameters<typeof decideIssueAccess>[1] & {
@@ -5225,6 +5225,8 @@ export function issueRoutes(
   ) {
     if (!(await assertIssueReadAllowed(req, res, issue))) return null;
     if (!(await assertCanManageIssuePrivacy(req, res, issue))) return null;
+    // Management is scoped to this exact task; an ancestor privacy root is
+    // inheritance provenance, never authority to mutate its grants.
     return issue;
   }
 
@@ -13070,7 +13072,7 @@ export function issueRoutes(
 
   router.get("/issues/:id/privacy-constraints", async (req, res) => {
     const issue = await getAccessibleResource(req, res, svc.getById(req.params.id as string), "Issue not found");
-    if (!issue || !(await resolveIssuePrivacyManagementRoot(req, res, issue))) return;
+    if (!issue || !(await resolveManagedIssueForPrivacy(req, res, issue))) return;
     // A task owner need not be able to read its surrounding private scope.
     // Read policy internally and return only action hints, never scope identity.
     const [project] = issue.projectId ? await db.select({ visibility: projects.visibility, personalOwnerUserId: projects.personalOwnerUserId })
@@ -13090,8 +13092,8 @@ export function issueRoutes(
   router.get("/issues/:id/access-grants", async (req, res) => {
     const issue = await getAccessibleResource(req, res, svc.getById(req.params.id as string), "Issue not found");
     if (!issue || !(await assertIssueReadAllowed(req, res, issue))) return;
-    const privacyRoot = await resolveIssuePrivacyManagementRoot(req, res, issue);
-    if (!privacyRoot) return;
+    const managedIssue = await resolveManagedIssueForPrivacy(req, res, issue);
+    if (!managedIssue) return;
     const ancestry = await db.select().from(issueRows).where(inArray(issueRows.id, sql`(
       with recursive ancestry as (
         select id, company_id, privacy_parent_issue_id from issues where id = ${issue.id} and company_id = ${issue.companyId}
@@ -13128,9 +13130,9 @@ export function issueRoutes(
     async (req, res) => {
       const issue = await getAccessibleResource(req, res, svc.getById(req.params.id as string), "Issue not found");
       if (!issue || !(await assertIssueReadAllowed(req, res, issue))) return;
-      const privacyRoot = await resolveIssuePrivacyManagementRoot(req, res, issue);
-      if (!privacyRoot) return;
-      if (privacyRoot.privacyRootIssueId === null) {
+      const managedIssue = await resolveManagedIssueForPrivacy(req, res, issue);
+      if (!managedIssue) return;
+      if (managedIssue.privacyRootIssueId === null) {
         res.status(409).json({ error: "Open issues do not require access grants" });
         return;
       }
@@ -13139,7 +13141,7 @@ export function issueRoutes(
       await assertIssueGrantSubjectExists(issue.companyId, subjectType, subjectId);
       const actor = getActorInfo(req);
       const result = await db.transaction((tx) => ensureActiveIssueAccessGrant(tx, {
-        issueId: privacyRoot.id,
+        issueId: managedIssue.id,
         subjectType,
         subjectId,
         source: "explicit",
@@ -13176,15 +13178,14 @@ export function issueRoutes(
     async (req, res) => {
       const issue = await getAccessibleResource(req, res, svc.getById(req.params.id as string), "Issue not found");
       if (!issue || !(await assertIssueReadAllowed(req, res, issue))) return;
-      const privacyRoot = await resolveIssuePrivacyManagementRoot(req, res, issue);
-      if (!privacyRoot) return;
-      const grantIssueIds = [...new Set([issue.id, privacyRoot.id])];
+      const managedIssue = await resolveManagedIssueForPrivacy(req, res, issue);
+      if (!managedIssue) return;
       const [grant] = await db
         .update(issueAccessGrants)
         .set({ revokedAt: new Date() })
         .where(and(
           eq(issueAccessGrants.id, req.params.grantId as string),
-          inArray(issueAccessGrants.issueId, grantIssueIds),
+          eq(issueAccessGrants.issueId, managedIssue.id),
           isNull(issueAccessGrants.revokedAt),
         ))
         .returning();
@@ -13395,7 +13396,7 @@ export function issueRoutes(
       }
       // An authorized agent may restrict a task; widening access remains an owner/admin action.
       if (req.body.visibility !== undefined && !(req.actor.type === "agent" && req.body.visibility === "private")
-        && !(await resolveIssuePrivacyManagementRoot(req, res, existing))) return;
+        && !(await resolveManagedIssueForPrivacy(req, res, existing))) return;
       // MCP task changes cannot stop a run or implicitly decide a pending review.
       const mcpParticipationChange = req.actor.source === "mcp_oauth" &&
         ["status", "assigneeAgentId", "assigneeUserId", "blockedByIssueIds", "parentId", "projectId"].some(key => req.body[key] !== undefined);