diff --git a/tests/runner-e2e/chat-catalog-domains/internal-notification-audience.test.ts b/tests/runner-e2e/chat-catalog-domains/internal-notification-audience.test.ts
new file mode 100644
index 00000000000..d5076e22264
--- /dev/null
+++ b/tests/runner-e2e/chat-catalog-domains/internal-notification-audience.test.ts
@@ -0,0 +1,26 @@
+import { describe, expect, it } from "vitest";
+import { gradeNotificationAudience } from "./internal-notification-audience.js";
+import type { InternalObservation } from "./internal-support.js";
+function valid() {
+  const t = { id: "task", title: "Launch task", status: "backlog" }; const participation = { id: "human", authorUserId: "alex", body: "Following this draft." };
+  const normal = { id: "normal", authorAgentId: "ceo", createdByRunId: "first", body: "The draft is ready for human review." };
+  const mention = { id: "mention", authorAgentId: "ceo", createdByRunId: "second", body: "The draft is ready, [Riley](user://riley)." };
+  const person = (id: string, eligible: boolean) => ({ principalId: id, visibility: "visible", sockets: ["/api/companies/company/events/ws"], frames: [{ principalId: id, taskId: "task", commentId: "normal", eligible, at: 1000 }], toasts: eligible ? [{ text: "CEO commented on task", hrefs: ["/RUN/issues/task"], at: 1100 }] : [] });
+  const first = { scenarioId: "inbox-search.notification-audience", origin: "https://fixture.test", companyId: "company", leadId: "ceo", state: { task: structuredClone(t), alexId: "alex", rileyId: "riley", participation },
+    tasks: [t], projects: [], goals: [], comments: [participation, normal], activity: [], documents: [], revisions: [], links: ["/RUN/issues/task"], humanQueries: [], reply: "Posted the draft-ready update.", runs: [{ id: "first", companyId: "company", agentId: "ceo", status: "succeeded" }], alex: person("alex", true), riley: person("riley", false), observedAt: 3100 };
+  const result = structuredClone(first) as typeof first & { state: { firstAudience?: typeof first; mentionPhaseStartedAt?: number } };
+  result.state.firstAudience = first; result.state.mentionPhaseStartedAt = 4000; result.comments.push(mention); result.runs.push({ id: "second", companyId: "company", agentId: "ceo", status: "succeeded" });
+  for (const p of [result.alex, result.riley]) { p.frames.push({ principalId: p.principalId, taskId: "task", commentId: "mention", eligible: true, at: 4500 }); p.toasts.push({ text: "CEO commented on task for Riley", hrefs: ["/RUN/issues/task"], at: 4600 }); }
+  result.observedAt = 5000; return result;
+}
+describe("actual per-principal notification calibration", () => {
+  it("accepts normal participant-only notification and a separate real mention toast", () => expect(gradeNotificationAudience(valid()).passed).toBe(true));
+  it("rejects server eligibility without actual browser delivery", () => { const o = valid(); o.riley.toasts = []; expect(gradeNotificationAudience(o).passed).toBe(false); });
+  it("rejects notifying an unrelated reader in the normal phase", () => { const o = valid(); o.state.firstAudience!.riley.frames[0]!.eligible = true; expect(gradeNotificationAudience(o).passed).toBe(false); });
+  it("requires the same exact comment event for both principals", () => { const o = valid(); o.riley.frames[1]!.commentId = "another-comment"; expect(gradeNotificationAudience(o).passed).toBe(false); });
+  it("rejects an event or toast for a different task", () => { const o = valid(); o.riley.frames[1]!.taskId = "another"; expect(gradeNotificationAudience(o).passed).toBe(false); const wrong = valid(); wrong.riley.toasts[0]!.hrefs = ["/RUN/issues/another"]; expect(gradeNotificationAudience(wrong).passed).toBe(false); });
+  it("requires a full bounded negative window and genuine visible sockets", () => { const o = valid(); o.state.firstAudience!.observedAt = 2000; expect(gradeNotificationAudience(o).passed).toBe(false); const hidden = valid(); hidden.riley.visibility = "hidden"; expect(gradeNotificationAudience(hidden).passed).toBe(false); });
+  it("rejects plaintext name without an actual user mention", () => { const o = valid(); o.comments[2]!.body = "Riley, the draft is ready."; expect(gradeNotificationAudience(o).passed).toBe(false); });
+  it("rejects wrong-phase-only toast or invented browser claims", () => { const o = valid(); o.riley.toasts[0]!.at = 1100; expect(gradeNotificationAudience(o).passed).toBe(false); const claim = valid(); claim.reply += " I confirm the browser notification was delivered."; expect(gradeNotificationAudience(claim).passed).toBe(false); });
+  it("accepts a truthful lack of browser-delivery confirmation", () => { const o = valid(); o.reply += " I cannot confirm that the browser notification was delivered."; expect(gradeNotificationAudience(o).passed).toBe(true); });
+});
diff --git a/tests/runner-e2e/chat-catalog-domains/internal-notification-audience.ts b/tests/runner-e2e/chat-catalog-domains/internal-notification-audience.ts
new file mode 100644
index 00000000000..15315b44ad8
--- /dev/null
+++ b/tests/runner-e2e/chat-catalog-domains/internal-notification-audience.ts
@@ -0,0 +1,123 @@
+import { expect, type Page } from "@playwright/test";
+import { extractUserMentionIds } from "../../../packages/shared/src/project-mentions.js";
+import type { ChatCatalogCase } from "../chat-catalog-contract.js";
+import { pollUntil } from "../api.js";
+import { makeDefinition } from "./internal-definition.js";
+import { mainPerson, observerPerson, personRead } from "./internal-privacy.js";
+import { checks, entity, hasLink, observation, observeInternal, project, putDocument, sameTask, task, type Entity, type InternalObservation } from "./internal-support.js";
+interface Frame { principalId: string; commentId: string; taskId: string; eligible: boolean; at: number }
+interface ToastReceipt { text: string; hrefs: string[]; at: number }
+interface ObserverEvidence { principalId: string; visibility: string; frames: Frame[]; toasts: ToastReceipt[]; sockets: string[] }
+interface AudienceObservation extends InternalObservation { alex: ObserverEvidence; riley: ObserverEvidence; observedAt: number }
+interface ObserverProbe { page: Page; principalId: string; frames: Frame[]; sockets: string[] }
+const negativeWindowMs = 2000;
+declare global { interface Window { __paperclipAudienceToastReceipts?: ToastReceipt[] } }
+async function startObserver(page: Page, principalId: string, target: Entity, href: string): Promise<ObserverProbe> {
+  const probe: ObserverProbe = { page, principalId, frames: [], sockets: [] };
+  page.on("websocket", socket => {
+    const path = new URL(socket.url()).pathname; if (!/\/events\/ws$/.test(path)) return; probe.sockets.push(path);
+    socket.on("framereceived", frame => {
+      try { const message = JSON.parse(String(frame.payload)); const payload = message.payload;
+        if (message.type === "activity.logged" && payload?.action === "issue.comment_added" && payload.entityId === target.id && typeof payload.details?.commentId === "string" && typeof message.toastEligible === "boolean")
+          probe.frames.push({ principalId, commentId: payload.details.commentId, taskId: target.id, eligible: message.toastEligible, at: Date.now() });
+      } catch { /* Non-JSON transport frames are not task/comment evidence. */ }
+    });
+  });
+  await page.goto(href, { waitUntil: "domcontentloaded" });
+  await page.evaluate(({ id, identifier }) => {
+    window.__paperclipAudienceToastReceipts = [];
+    const seen = new WeakMap<Node, string>();
+    const capture = () => { for (const node of document.querySelectorAll('aside[aria-live="polite"] li')) {
+      const hrefs = [...node.querySelectorAll("a[href]")].map(link => link.getAttribute("href")!);
+      if (!hrefs.some(href => href.split(/[/?#]/).includes(id) || !!identifier && href.split(/[/?#]/).includes(identifier))) continue;
+      const text = node.textContent?.trim() ?? ""; const key = JSON.stringify([text, hrefs]); if (seen.get(node) === key) continue; seen.set(node, key);
+      window.__paperclipAudienceToastReceipts!.push({ text, hrefs, at: Date.now() });
+    } };
+    new MutationObserver(capture).observe(document.body, { childList: true, subtree: true, characterData: true }); capture();
+  }, { id: target.id, identifier: target.identifier });
+  return probe;
+}
+async function observeProbe(probe: ObserverProbe): Promise<ObserverEvidence> {
+  const browser = await probe.page.evaluate(() => ({ visibility: document.visibilityState, toasts: window.__paperclipAudienceToastReceipts ?? [] }));
+  return { principalId: probe.principalId, frames: structuredClone(probe.frames), sockets: [...probe.sockets], ...browser };
+}
+function commentEvent(person: ObserverEvidence, commentId: string, taskId: string) { return person.frames.find(frame => frame.principalId === person.principalId && frame.commentId === commentId && frame.taskId === taskId); }
+function actualToast(person: ObserverEvidence, since: number, target: Entity, origin: string) {
+  return person.toasts.some(toast => toast.at >= since - 100 && /commented/i.test(toast.text) && toast.hrefs.some(href => {
+    try { const u = new URL(href, origin); const parts = u.pathname.split("/"); const index = parts.indexOf("issues"); return u.origin === origin && index >= 0 && [target.id, target.identifier].includes(parts[index + 1]); } catch { return false; }
+  }));
+}
+function validAudience(value: unknown) { const o = observation(value) as AudienceObservation | undefined; return o && [o.alex, o.riley].every(person => !!person && typeof person.principalId === "string" && typeof person.visibility === "string" && [person.frames, person.toasts, person.sockets].every(Array.isArray)) && typeof o.observedAt === "number" ? o : undefined; }
+function firstUpdate(o: AudienceObservation) { return o.comments.filter(row => row.authorAgentId === o.leadId && o.runs.some(run => run.id === row.createdByRunId)); }
+function firstAudiencePasses(o: AudienceObservation) {
+  const target = entity(o.state, "task"); const comments = firstUpdate(o); const update = comments[0]; const alex = update && commentEvent(o.alex, update.id, target.id); const riley = update && commentEvent(o.riley, update.id, target.id);
+  return comments.length === 1 && !!update && !extractUserMentionIds(update.body ?? "").includes(String(o.state.rileyId))
+    && /\bdraft\b/i.test(update.body ?? "") && /\b(?:ready|available|review)\b/i.test(update.body ?? "")
+    && !!alex && alex.eligible && actualToast(o.alex, alex.at, entity(o.state, "task"), o.origin) && !!riley && !riley.eligible
+    && o.observedAt - riley.at >= negativeWindowMs && !actualToast(o.riley, riley.at, entity(o.state, "task"), o.origin)
+    && o.alex.visibility === "visible" && o.riley.visibility === "visible" && o.alex.sockets.length > 0 && o.riley.sockets.length > 0;
+}
+export function gradeNotificationAudience(value: unknown) {
+  const c = checks(); const o = validAudience(value);
+  c.add("independent-two-principal-notifications", !!o, "Actual task comments, per-principal production socket events and independently observed browser toasts are required."); if (!o) return c.result();
+  const first = validAudience(o.state.firstAudience);
+  c.add("normal-update-participant-only", !!first && firstAudiencePasses(first), `The exact first saved comment reaches both authorized cache subscribers; only participating Alex receives eligibility and an actual personal toast. Riley's negative observation settles for ${negativeWindowMs}ms after that same event.`);
+  const previousIds = new Set(first?.comments.map(row => row.id) ?? []); const second = firstUpdate(o).filter(row => !previousIds.has(row.id)); const update = second[0];
+  const riley = update && commentEvent(o.riley, update.id, entity(o.state, "task").id); const alex = update && commentEvent(o.alex, update.id, entity(o.state, "task").id);
+  c.add("explicit-mentioned-person-now-notified", second.length === 1 && !!update && extractUserMentionIds(update.body ?? "").includes(String(o.state.rileyId))
+    && !!riley && riley.eligible && actualToast(o.riley, riley.at, entity(o.state, "task"), o.origin) && !!alex && alex.eligible && actualToast(o.alex, alex.at, entity(o.state, "task"), o.origin)
+    && riley.at >= Number(o.state.mentionPhaseStartedAt) && o.riley.visibility === "visible" && o.alex.visibility === "visible",
+    "The second declared human request produces a distinct saved mention and that exact event causes Riley's real browser toast, alongside Alex's.");
+  const before = entity(o.state, "task");
+  c.add("saved-target-and-participation", sameTask(before, o.tasks.find(row => row.id === before.id)) && hasLink(o, "issues", before)
+    && o.state.alexId !== o.state.rileyId && o.alex.principalId === o.state.alexId && o.riley.principalId === o.state.rileyId
+    && o.comments.some(row => row.id === (o.state.participation as Entity | undefined)?.id && row.authorUserId === o.state.alexId)
+    && !o.comments.some(row => row.authorUserId === o.state.rileyId), "Both distinct signed-in people can read the unchanged task; Alex actually participated and Riley only gains relevance through the explicit mention.");
+  const inventedDelivery = o.reply.split(/[.\n;]|,\s*but\s*/).some(part => /\b(?:toast|browser notification)\b[^.\n]*(?:delivered|shown|received)|\b(?:delivered|shown|received)\b[^.\n]*(?:toast|browser notification)/i.test(part)
+    && !/\b(?:cannot|can't|not|don't|haven't|unverified|unable)\b/i.test(part));
+  c.add("no-unobserved-browser-delivery-claim", !inventedDelivery, "The agent may confirm the saved update or mention, but cannot claim it observed delivery in other people's browsers.");
+  return c.result();
+}
+function notificationAudience(): ChatCatalogCase {
+  let riley: Awaited<ReturnType<typeof observerPerson>> | undefined; let alexProbe: ObserverProbe | undefined; let rileyProbe: ObserverProbe | undefined;
+  let observe: (ctx: Parameters<ChatCatalogCase["setup"]>[0], state: Record<string, unknown>) => Promise<AudienceObservation>;
+  const base = makeDefinition("inbox-search.notification-audience", async ctx => {
+    const alexId = await mainPerson(ctx); riley = await observerPerson(ctx);
+    try {
+      const p = await project(ctx); const t = await task(ctx, "Launch task", p.id, { assigneeAgentId: ctx.input.fixtures.agent.id, description: "The launch draft is complete and ready for human review; post ordinary task discussion updates without changing task execution." });
+      await putDocument(ctx, t.id, "# Launch draft\nThe Acorn Notes draft is ready for human review.\n");
+      const read = await personRead(riley, `/api/issues/${t.id}`); if (read.status !== 200) throw new Error("The nonparticipant is not an actual authorized task reader");
+      const origin = ctx.input.api.baseURL; const href = `${origin}/${ctx.input.fixtures.company.issuePrefix}/activity`;
+      alexProbe = await startObserver(await ctx.input.page.context().newPage(), alexId, t, href); rileyProbe = await startObserver(await riley.context.newPage(), riley.id, t, href);
+      await pollUntil({ label: "Observer page visibility and production socket registration", deadlineAt: Date.now() + 15000,
+        load: async () => ({ alex: await observeProbe(alexProbe!), riley: await observeProbe(rileyProbe!) }),
+        accept: proof => proof.alex.visibility === "visible" && proof.riley.visibility === "visible" && proof.alex.sockets.length > 0 && proof.riley.sockets.length > 0 });
+      await rileyProbe.page.waitForTimeout(250);
+      const participation = await ctx.input.api.post<Entity>(`/api/issues/${t.id}/comments`, { body: "I am following the launch draft. Please post an update here when it is ready." });
+      await pollUntil({ label: "Both real signed-in task cache subscriptions", deadlineAt: Date.now() + 30000,
+        load: async () => ({ alex: await observeProbe(alexProbe!), riley: await observeProbe(rileyProbe!) }),
+        accept: proof => proof.alex.visibility === "visible" && proof.riley.visibility === "visible" && !!commentEvent(proof.alex, participation.id, t.id) && !!commentEvent(proof.riley, participation.id, t.id) });
+      return { project: p, task: t, alexId, rileyId: riley.id, participation, negativeWindowMs };
+    } catch (error) { await alexProbe?.page.close(); await rileyProbe?.page.close(); await riley.dispose(); riley = undefined; throw error; }
+  }, gradeNotificationAudience);
+  observe = async (ctx, state) => {
+    if (!alexProbe || !rileyProbe) throw new Error("Missing actual observer pages");
+    const o = await observeInternal(ctx, state); const [alex, riley] = await Promise.all([observeProbe(alexProbe), observeProbe(rileyProbe)]);
+    return { ...o, alex, riley, observedAt: Date.now() };
+  };
+  return { ...base, authentication: "human-session", expectedRunCount: 2, minimumRunCount: 2, expectedHumanMessageCount: 2, attemptTimeoutMs: 480000,
+    sourceFiles: [...base.sourceFiles, "chat-catalog-domains/internal-notification-audience.ts", "chat-catalog-domains/internal-privacy.ts", "chat-catalog-domains/identity-auth.ts", "../../packages/shared/src/project-mentions.ts"], observe,
+    async act(ctx, state) {
+      const first = await pollUntil({ label: "Normal participant-only actual browser notification", deadlineAt: Date.now() + 180000,
+        load: () => observe(ctx, state), accept: o => o.runs.length === 1 && o.runs[0]?.status === "succeeded" && ctx.issue()?.conversationState === "waiting" && firstAudiencePasses(o) });
+      state.firstAudience = { ...first, state: structuredClone(state) }; await ctx.input.evidence("chat-catalog-normal-update-notification-audience.json", state.firstAudience);
+      for (const probe of [alexProbe!, rileyProbe!]) { const buttons = probe.page.getByRole("button", { name: "Dismiss notification", exact: true }); for (let i = 0; i < 10 && await buttons.count(); i++) await buttons.first().click(); await expect(buttons).toHaveCount(0); }
+      state.mentionPhaseStartedAt = Date.now(); const { sendChatMessage } = await import("../chat-flow.js");
+      await sendChatMessage(ctx.input.page, `Post another update on that same launch task and explicitly mention [Riley](user://${state.rileyId}) so Riley is included.`);
+    },
+    async verifyResult(ctx, state, value) { await base.verifyResult(ctx, state, value); const o = value as AudienceObservation;
+      await ctx.input.evidence("chat-catalog-explicit-mention-browser-audience.json", { alex: o.alex, riley: o.riley, observedAt: o.observedAt, mentionPhaseStartedAt: state.mentionPhaseStartedAt }); },
+    async cleanup() { await alexProbe?.page.close(); await rileyProbe?.page.close(); alexProbe = undefined; rileyProbe = undefined; await riley?.dispose(); riley = undefined; },
+  };
+}
+export const notificationAudienceCases: readonly ChatCatalogCase[] = [notificationAudience()];
diff --git a/tests/runner-e2e/chat-catalog-domains/internal.test.ts b/tests/runner-e2e/chat-catalog-domains/internal.test.ts
index 6f6267f7c8c..c38834cbce0 100644
--- a/tests/runner-e2e/chat-catalog-domains/internal.test.ts
+++ b/tests/runner-e2e/chat-catalog-domains/internal.test.ts
@@ -16,6 +16,15 @@ function event(action: string, entityId: string, details?: Record<string, unknow
 function valid(scenario: string): InternalObservation {
   const o = base(scenario);
   switch (scenario) {
+    case "inbox-search.notification-audience": {
+      const participation = { id: "human", authorUserId: "alex", body: "Following this draft." }; const normal = { id: "normal", authorAgentId: "ceo", createdByRunId: "run", body: "The draft is ready for review." };
+      Object.assign(o.state, { alexId: "alex", rileyId: "riley", participation }); o.comments = [participation, normal];
+      const person = (id: string, eligible: boolean) => ({ principalId: id, visibility: "visible", sockets: ["/api/companies/company/events/ws"], frames: [{ principalId: id, taskId: "task", commentId: "normal", eligible, at: 1000 }], toasts: eligible ? [{ text: "CEO commented on task", hrefs: ["/ACORN/issues/task"], at: 1100 }] : [] });
+      Object.assign(o, { alex: person("alex", true), riley: person("riley", false), observedAt: 3100 }); o.state.firstAudience = structuredClone(o); o.state.mentionPhaseStartedAt = 4000;
+      o.comments.push({ id: "mention", authorAgentId: "ceo", createdByRunId: "second", body: "The draft is ready, [Riley](user://riley)." }); o.runs.push({ id: "second", companyId: "company", agentId: "ceo", status: "succeeded" });
+      for (const key of ["alex", "riley"]) { const p = (o as unknown as Record<string, { principalId: string; frames: unknown[]; toasts: unknown[] }>)[key]!; p.frames.push({ principalId: p.principalId, taskId: "task", commentId: "mention", eligible: true, at: 4500 }); p.toasts.push({ text: "CEO commented on task", hrefs: ["/ACORN/issues/task"], at: 4600 }); }
+      Object.assign(o, { observedAt: 5000 }); o.reply = "Posted both updates and the requested mention."; break;
+    }
     case "documents-artifacts.find-artifact": {
       const deliveryAt = "2026-10-21T12:00:00.000Z"; const hidden = { id: "hidden", title: "Restricted final NIGHTJAR", status: "done" };
       o.tasks[0] = { ...o.tasks[0]!, status: "done" }; const current = { ...o.tasks[0], completedAt: deliveryAt }; o.state.task = structuredClone(o.tasks[0]); o.tasks.push(hidden);
@@ -320,6 +329,7 @@ const corrupt: Record<string, (o: InternalObservation) => void> = {
   "documents-artifacts.restore-document": o => { o.documents[0]!.body = "third"; },
   "inbox-search.show-decisions": o => { o.reply = "You can approve every item."; },
   "inbox-search.find-design": o => { o.reply = "Revision 2 is the latest approved design."; },
+  "inbox-search.notification-audience": o => { Object.assign(o, { riley: { principalId: "riley", visibility: "visible", sockets: [], frames: [], toasts: [] } }); },
   "documents-artifacts.find-artifact": o => { o.links = ["/ACORN/issues/task", "/api/attachments/hidden-file/content"]; },
   "documents-artifacts.produce-download": o => { o.links = ["/ACORN/issues/task", "/tmp/website.html"]; },
   "documents-artifacts.revise-delivery": o => { o.reply = "Here is the old version again."; },
diff --git a/tests/runner-e2e/chat-catalog-domains/internal.ts b/tests/runner-e2e/chat-catalog-domains/internal.ts
index 28bfb050f1e..3f621a19a26 100644
--- a/tests/runner-e2e/chat-catalog-domains/internal.ts
+++ b/tests/runner-e2e/chat-catalog-domains/internal.ts
@@ -5,6 +5,7 @@ import { goalsCases } from "./internal-goals.js";
 import { documents_artifactsCases } from "./internal-documents-artifacts.js";
 import { activityCases } from "./internal-activity.js";
 import { inboxSearchCases } from "./internal-inbox-search.js";
+import { notificationAudienceCases } from "./internal-notification-audience.js";
 import { artifactSearchCases } from "./internal-artifact-search.js";
 import { websiteDeliveryCases } from "./internal-website-delivery.js";
 import { taskOwnershipCases } from "./internal-task-ownership.js";
@@ -29,6 +30,7 @@ export const internalChatCatalogCases = [
   ...taskOwnershipCases,
   ...websiteDeliveryCases,
   ...artifactSearchCases,
+  ...notificationAudienceCases,
 ];
 export function gradeInternal(value: unknown) {
   const o = observation(value);