diff --git a/server/src/__tests__/issue-comment-redaction.test.ts b/server/src/__tests__/issue-comment-redaction.test.ts
index d53392056c..423f1ab345 100644
--- a/server/src/__tests__/issue-comment-redaction.test.ts
+++ b/server/src/__tests__/issue-comment-redaction.test.ts
@@ -187,6 +187,27 @@ describeEmbeddedPostgres("deleted issue comment redaction", () => {
     expect(JSON.stringify(wakePayload)).not.toContain("secret metadata");
   });
 
+  it("serializes comment timestamps as ISO strings through the redacted comments route (PAP-16607)", async () => {
+    const { companyId, issueId } = await seedIssue();
+    const commentId = randomUUID();
+    await db.insert(issueComments).values({
+      id: commentId,
+      companyId,
+      issueId,
+      authorUserId: "board-user-1",
+      body: "ordinary comment",
+    });
+
+    const response = await request(createApp(companyId)).get(`/api/issues/${issueId}/comments`);
+    expect(response.status, JSON.stringify(response.body)).toBe(200);
+    expect(response.body).toHaveLength(1);
+    // Secret redaction must not collapse Date instances to `{}` — the chat
+    // renderer needs parseable timestamps.
+    expect(typeof response.body[0].createdAt).toBe("string");
+    expect(Number.isNaN(new Date(response.body[0].createdAt).getTime())).toBe(false);
+    expect(typeof response.body[0].updatedAt).toBe("string");
+  });
+
   it("excludes deleted comment bodies from company search", async () => {
     const { companyId, issueId } = await seedIssue();
     await db.insert(issueComments).values({
diff --git a/server/src/__tests__/run-secret-redaction.test.ts b/server/src/__tests__/run-secret-redaction.test.ts
index 5bff578f14..fa2dd60a06 100644
--- a/server/src/__tests__/run-secret-redaction.test.ts
+++ b/server/src/__tests__/run-secret-redaction.test.ts
@@ -54,4 +54,25 @@ describe("registered run secret redaction", () => {
     expect(redactRegisteredSecretValues("token-extended token", ["token-extended", "token"]))
       .toBe(`${REDACTED_EVENT_VALUE} ${REDACTED_EVENT_VALUE}`);
   });
+
+  it("preserves Date instances instead of collapsing them to empty objects (PAP-16607)", () => {
+    const createdAt = new Date("2026-08-06T12:00:00.000Z");
+    const result = redactRegisteredSecretValues({
+      comment: { body: `agent pasted ${secret}`, createdAt, updatedAt: createdAt },
+      nested: [{ finishedAt: createdAt }],
+    }, [secret]);
+
+    expect(result.comment.createdAt).toBeInstanceOf(Date);
+    expect(result.comment.createdAt.toISOString()).toBe("2026-08-06T12:00:00.000Z");
+    expect(result.comment.updatedAt).toBeInstanceOf(Date);
+    expect(result.nested[0]?.finishedAt).toBeInstanceOf(Date);
+    expect(result.comment.body).toBe(`agent pasted ${REDACTED_EVENT_VALUE}`);
+  });
+
+  it("preserves Date instances when no secret values are registered", () => {
+    const createdAt = new Date("2026-08-06T12:00:00.000Z");
+    const result = redactRegisteredSecretValues({ createdAt }, []);
+    expect(result.createdAt).toBeInstanceOf(Date);
+    expect(result.createdAt.toISOString()).toBe("2026-08-06T12:00:00.000Z");
+  });
 });
diff --git a/server/src/services/run-secret-redaction.ts b/server/src/services/run-secret-redaction.ts
index 4604d54ada..4ca7963e95 100644
--- a/server/src/services/run-secret-redaction.ts
+++ b/server/src/services/run-secret-redaction.ts
@@ -42,6 +42,9 @@ function redactText(input: string, values: string[]) {
 export function redactRegisteredSecretValues<T>(input: T, values: string[]): T {
   if (typeof input === "string") return redactText(input, values) as T;
   if (Array.isArray(input)) return input.map((value) => redactRegisteredSecretValues(value, values)) as T;
+  // Dates carry no redactable text; rebuilding them via Object.entries would
+  // collapse them to `{}` and break every timestamp in redacted responses.
+  if (input instanceof Date) return input;
   const record = asRecord(input);
   if (!record) return input;
   return Object.fromEntries(
diff --git a/ui/src/components/IssueChatThread.tsx b/ui/src/components/IssueChatThread.tsx
index c540cab21a..c6af475e50 100644
--- a/ui/src/components/IssueChatThread.tsx
+++ b/ui/src/components/IssueChatThread.tsx
@@ -773,6 +773,18 @@ function toIsoString(value: string | Date | null | undefined): string | null {
   return typeof value === "string" ? value : value.toISOString();
 }
 
+/**
+ * ISO timestamp for display, or undefined when the value does not parse as a
+ * real date. Comment timestamps can arrive malformed (e.g. a server
+ * serialization bug turning Dates into `{}`); formatting must degrade to "no
+ * timestamp" instead of throwing mid-render (PAP-16607).
+ */
+function toValidIsoString(value: Date | string | number | undefined): string | undefined {
+  if (value === undefined || value === null) return undefined;
+  const date = new Date(value);
+  return Number.isNaN(date.getTime()) ? undefined : date.toISOString();
+}
+
 function loadDraft(draftKey: string): string {
   try {
     return localStorage.getItem(draftKey) ?? "";
@@ -2737,7 +2749,7 @@ function SystemNoticeCommentRow({
         {bodyText}
       </MarkdownBody>
     ),
-    timestamp: message.createdAt ? new Date(message.createdAt).toISOString() : undefined,
+    timestamp: toValidIsoString(message.createdAt),
     source,
     runAgentId,
   });
diff --git a/ui/src/components/IssueChatThreadSystemNotice.test.tsx b/ui/src/components/IssueChatThreadSystemNotice.test.tsx
index 410d6b3068..8419c54ebe 100644
--- a/ui/src/components/IssueChatThreadSystemNotice.test.tsx
+++ b/ui/src/components/IssueChatThreadSystemNotice.test.tsx
@@ -150,6 +150,34 @@ describe("IssueChatThread system notice routing", () => {
     expect(container.querySelectorAll('[data-message-role="user"]').length).toBe(0);
   });
 
+  it("renders a system notice with a malformed createdAt without tripping the error boundary (PAP-16607)", () => {
+    const comment: IssueChatComment = {
+      id: "comment-system-bad-date",
+      companyId: "company-1",
+      issueId: "issue-1",
+      authorType: "system",
+      authorAgentId: null,
+      authorUserId: null,
+      body: "Workspace ready.",
+      presentation: {
+        kind: "system_notice",
+        tone: "info",
+        title: "Workspace ready",
+        detailsDefaultOpen: false,
+      },
+      metadata: { version: 1, sections: [] },
+      // A server serialization bug (Dates collapsed to `{}` by secret
+      // redaction) shipped comments whose timestamps parse to Invalid Date.
+      createdAt: {} as unknown as Date,
+      updatedAt: {} as unknown as Date,
+    };
+
+    renderThread([comment]);
+
+    expect(container.textContent).not.toContain("Chat renderer hit an internal state error.");
+    expect(container.textContent).toContain("Workspace ready");
+  });
+
   it("expands metadata when detailsDefaultOpen is true", () => {
     const comment: IssueChatComment = {
       id: "comment-system-open",