diff --git a/server/src/__tests__/issue-agent-mutation-ownership-routes.test.ts b/server/src/__tests__/issue-agent-mutation-ownership-routes.test.ts
index 821a5c37f0a..43ff1745882 100644
--- a/server/src/__tests__/issue-agent-mutation-ownership-routes.test.ts
+++ b/server/src/__tests__/issue-agent-mutation-ownership-routes.test.ts
@@ -9,6 +9,9 @@ const ownerAgentId = "33333333-3333-4333-8333-333333333333";
 const peerAgentId = "44444444-4444-4444-8444-444444444444";
 const ownerRunId = "55555555-5555-4555-8555-555555555555";
 const recoveryActionId = "77777777-7777-4777-8777-777777777777";
+const issueBoundaryError = "Issue is outside this actor's authorization boundary";
+const issueBoundaryHint =
+  "Do not retry. Route instead: create a child issue assigned to the owner, comment on your own issue naming the ask, or open an issue-thread interaction for board escalation.";
 
 const mockIssueService = vi.hoisted(() => ({
   addComment: vi.fn(),
@@ -356,6 +359,14 @@ function boardActor() {
   };
 }
 
+function expectIssueBoundaryDenied(body: Record<string, unknown>, reason: string) {
+  expect(body).toEqual({
+    error: issueBoundaryError,
+    reason,
+    hint: issueBoundaryHint,
+  });
+}
+
 describe("agent issue mutation checkout ownership", () => {
   beforeEach(() => {
     vi.resetModules();
@@ -805,7 +816,26 @@ describe("agent issue mutation checkout ownership", () => {
       .send({ body: "I was not mentioned." });
 
     expect(res.status, JSON.stringify(res.body)).toBe(403);
-    expect(res.body.error).toBe("Issue is outside this actor's authorization boundary");
+    expectIssueBoundaryDenied(res.body, "deny_missing_grant");
+    expect(mockIssueService.addComment).not.toHaveBeenCalled();
+  });
+
+  it("passes through the issue mutate denial reason for peer agents", async () => {
+    mockIssueService.getById.mockResolvedValue(makeIssue({ status: "todo", assigneeAgentId: ownerAgentId }));
+    mockAccessService.decide.mockImplementation(async (input: { action: string }) => ({
+      allowed: input.action !== "issue:mutate",
+      action: input.action,
+      reason: input.action === "issue:mutate" ? "deny_scope" : "allow_explicit_grant",
+      explanation: input.action === "issue:mutate" ? "Issue is outside scope." : "Allowed by test default.",
+    }));
+
+    const res = await request(await createApp(peerActor()))
+      .patch(`/api/issues/${issueId}`)
+      .send({ status: "done" });
+
+    expect(res.status, JSON.stringify(res.body)).toBe(403);
+    expectIssueBoundaryDenied(res.body, "deny_scope");
+    expect(mockIssueService.update).not.toHaveBeenCalled();
     expect(mockIssueService.addComment).not.toHaveBeenCalled();
   });
 
@@ -821,7 +851,7 @@ describe("agent issue mutation checkout ownership", () => {
       .get(`/api/issues/${issueId}/comments`);
 
     expect(res.status, JSON.stringify(res.body)).toBe(403);
-    expect(res.body.error).toBe("Issue is outside this actor's authorization boundary");
+    expectIssueBoundaryDenied(res.body, "deny_low_trust_boundary");
     expect(mockAccessService.decide).toHaveBeenCalledWith(expect.objectContaining({ action: "issue:read" }));
   });
 
@@ -837,7 +867,7 @@ describe("agent issue mutation checkout ownership", () => {
       .get(`/api/issues/${issueId}/interactions`);
 
     expect(res.status, JSON.stringify(res.body)).toBe(403);
-    expect(res.body.error).toBe("Issue is outside this actor's authorization boundary");
+    expectIssueBoundaryDenied(res.body, "deny_low_trust_boundary");
     expect(mockAccessService.decide).toHaveBeenCalledWith(expect.objectContaining({ action: "issue:read" }));
     expect(mockIssueThreadInteractionService.listForIssue).not.toHaveBeenCalled();
   });
@@ -883,7 +913,7 @@ describe("agent issue mutation checkout ownership", () => {
       .get(`/api/issues/${issueId}/comments/comment-1`);
 
     expect(res.status, JSON.stringify(res.body)).toBe(403);
-    expect(res.body.error).toBe("Issue is outside this actor's authorization boundary");
+    expectIssueBoundaryDenied(res.body, "deny_low_trust_boundary");
     expect(mockAccessService.decide).toHaveBeenCalledWith(expect.objectContaining({ action: "issue:read" }));
     expect(mockIssueService.getComment).not.toHaveBeenCalled();
   });
diff --git a/server/src/__tests__/issue-comment-reopen-routes.test.ts b/server/src/__tests__/issue-comment-reopen-routes.test.ts
index 3a0b0907480..2b6b05fbdb4 100644
--- a/server/src/__tests__/issue-comment-reopen-routes.test.ts
+++ b/server/src/__tests__/issue-comment-reopen-routes.test.ts
@@ -635,7 +635,11 @@ describe.sequential("issue comment reopen routes", () => {
         .send({ body: "Please continue this closed issue.", ...intent });
 
       expect(res.status, JSON.stringify(res.body)).toBe(403);
-      expect(res.body).toEqual({ error: "Issue is outside this actor's authorization boundary" });
+      expect(res.body).toEqual({
+        error: "Issue is outside this actor's authorization boundary",
+        reason: "deny_missing_grant",
+        hint: "Do not retry. Route instead: create a child issue assigned to the owner, comment on your own issue naming the ask, or open an issue-thread interaction for board escalation.",
+      });
       expect(mockAccessService.decide).toHaveBeenCalledWith(expect.objectContaining({ action: "issue:comment" }));
       expect(mockAccessService.decide).toHaveBeenCalledWith(expect.objectContaining({ action: "issue:mutate" }));
       expect(mockIssueService.update).not.toHaveBeenCalled();
diff --git a/server/src/routes/issues.ts b/server/src/routes/issues.ts
index 7d67db47344..9dff56bbe26 100644
--- a/server/src/routes/issues.ts
+++ b/server/src/routes/issues.ts
@@ -153,7 +153,7 @@ import {
   ISSUE_WAKE_DIAGNOSTICS_MAX_WAKE_REQUESTS,
   readAcceptedPlanConfirmationTarget,
 } from "../services/issues.js";
-import { authorizationDeniedDetails } from "../services/authorization.js";
+import { authorizationDeniedDetails, type AuthorizationDecision } from "../services/authorization.js";
 import { environmentService } from "../services/environments.js";
 import { environmentRuntimeService } from "../services/environment-runtime.js";
 import { redactSensitiveText } from "../redaction.js";
@@ -185,6 +185,9 @@ import {
 import { externalObjectService } from "../services/external-objects.js";
 
 const MAX_ISSUE_COMMENT_LIMIT = 500;
+const ISSUE_AUTHORIZATION_BOUNDARY_ERROR = "Issue is outside this actor's authorization boundary";
+const ISSUE_AUTHORIZATION_BOUNDARY_HINT =
+  "Do not retry. Route instead: create a child issue assigned to the owner, comment on your own issue naming the ask, or open an issue-thread interaction for board escalation.";
 const updateIssueRouteSchema = updateIssueSchema.extend({
   interrupt: z.boolean().optional(),
 });
@@ -3282,10 +3285,18 @@ export function issueRoutes(
   async function assertIssueReadAllowed(req: Request, res: Response, issue: Parameters<typeof decideIssueAccess>[1]) {
     const decision = await decideIssueAccess(req, issue, "issue:read");
     if (decision.allowed) return true;
-    res.status(403).json({ error: "Issue is outside this actor's authorization boundary" });
+    sendIssueAuthorizationBoundaryDenied(res, decision);
     return false;
   }
 
+  function sendIssueAuthorizationBoundaryDenied(res: Response, decision: AuthorizationDecision) {
+    res.status(403).json({
+      error: ISSUE_AUTHORIZATION_BOUNDARY_ERROR,
+      reason: decision.reason,
+      hint: ISSUE_AUTHORIZATION_BOUNDARY_HINT,
+    });
+  }
+
   async function assertAgentIssueCommentAllowed(
     req: Request,
     res: Response,
@@ -3322,7 +3333,7 @@ export function issueRoutes(
     }
     const boundaryDecision = await decideIssueAccess(req, issue, "issue:comment");
     if (!boundaryDecision.allowed) {
-      res.status(403).json({ error: "Issue is outside this actor's authorization boundary" });
+      sendIssueAuthorizationBoundaryDenied(res, boundaryDecision);
       return false;
     }
     return boundaryDecision;
@@ -3411,7 +3422,7 @@ export function issueRoutes(
     }
     const boundaryDecision = await decideIssueAccess(req, issue, "issue:mutate");
     if (!boundaryDecision.allowed) {
-      res.status(403).json({ error: "Issue is outside this actor's authorization boundary" });
+      sendIssueAuthorizationBoundaryDenied(res, boundaryDecision);
       return false;
     }
     if (issue.assigneeAgentId === null) {
diff --git a/skills/paperclip/SKILL.md b/skills/paperclip/SKILL.md
index 3c9b66555cd..3cad8aad915 100644
--- a/skills/paperclip/SKILL.md
+++ b/skills/paperclip/SKILL.md
@@ -301,6 +301,7 @@ For commands, response fields, and MCP tools, read:
 ## Critical Rules
 
 - **Never retry a 409.** The task belongs to someone else.
+- **403 boundary -> never retry; follow the hint in the error body.**
 - **Never look for unassigned work.** No assignments = exit.
 - **Self-assign only for explicit @-mention handoff.** Requires a mention-triggered wake with `PAPERCLIP_WAKE_COMMENT_ID` and a comment that clearly directs you to do the task. Use checkout (never direct assignee patch).
 - **Honor "send it back to me" requests from board users.** If a board/user asks for review handoff (e.g. "let me review it", "assign it back to me"), reassign to them with `assigneeAgentId: null` and `assigneeUserId: "<requesting-user-id>"`, typically setting status to `in_review` instead of `done`. Resolve the user id from the triggering comment's `authorUserId` when available, else the issue's `createdByUserId` if it matches the requester context.