coach: reopen an interrupted conversation with a visible retry

An aborted stream now leaves a trace on both ends. The unmount cleanup
records the interrupted conversation (sessionStorage, one-shot) before
the abort fires, and invalidates the cached thread + rail so the return
visit refetches the advanced server state. The /coach page consumes the
record on its next mount: a known id reopens that thread, a first-turn
abort resolves via most-recent; every explicit entry intent (?c=, ?doc=,
?workout=, ?scope=, ?ask=) wins over the resume. The persisted cancelled
marker renders as a muted interrupted note with an Ask-again action that
resubmits the question through the normal send path and its gates.
Localised in all six languages. Refs #781

messages/de.json

@@ -2934,6 +2934,10 @@
         "railBadge": "Dokument-Chat (abgeschottet)",
         "uploadError": "Upload fehlgeschlagen. Bitte versuche es erneut.",
         "notFoundError": "Dieser Dokumentlink ist nicht mehr gültig – es wird ein normaler Chat gestartet."
+      },
+      "interrupted": {
+        "note": "Diese Antwort wurde unterbrochen, bevor sie fertig war.",
+        "retry": "Erneut fragen"
       }
     },
     "relativeJustNow": "gerade eben",

messages/en.json

@@ -2934,6 +2934,10 @@
         "railBadge": "Fenced document chat",
         "uploadError": "Upload failed. Please try again.",
         "notFoundError": "That document link is no longer valid — starting a normal chat instead."
+      },
+      "interrupted": {
+        "note": "This answer was interrupted before it finished.",
+        "retry": "Ask again"
       }
     },
     "relativeJustNow": "just now",

messages/es.json

@@ -2934,6 +2934,10 @@
         "railBadge": "Chat de documento aislado",
         "uploadError": "Error al subir. Inténtalo de nuevo.",
         "notFoundError": "Ese enlace de documento ya no es válido: se iniciará un chat normal."
+      },
+      "interrupted": {
+        "note": "Esta respuesta se interrumpió antes de terminar.",
+        "retry": "Preguntar de nuevo"
       }
     },
     "relativeJustNow": "ahora mismo",

messages/fr.json

@@ -2934,6 +2934,10 @@
         "railBadge": "Chat de document cloisonné",
         "uploadError": "Échec du téléversement. Veuillez réessayer.",
         "notFoundError": "Ce lien de document n'est plus valide : une conversation normale démarre à la place."
+      },
+      "interrupted": {
+        "note": "Cette réponse a été interrompue avant la fin.",
+        "retry": "Reposer la question"
       }
     },
     "relativeJustNow": "à l’instant",

messages/it.json

@@ -2934,6 +2934,10 @@
         "railBadge": "Chat documento isolata",
         "uploadError": "Caricamento non riuscito. Riprova.",
         "notFoundError": "Quel link al documento non è più valido: verrà avviata una chat normale."
+      },
+      "interrupted": {
+        "note": "Questa risposta è stata interrotta prima di essere completata.",
+        "retry": "Chiedi di nuovo"
       }
     },
     "relativeJustNow": "proprio ora",

messages/pl.json

@@ -2934,6 +2934,10 @@
         "railBadge": "Odizolowany czat dokumentu",
         "uploadError": "Przesyłanie nie powiodło się. Spróbuj ponownie.",
         "notFoundError": "Ten link do dokumentu jest już nieprawidłowy – zamiast tego rozpoczynamy zwykły czat."
+      },
+      "interrupted": {
+        "note": "Ta odpowiedź została przerwana przed ukończeniem.",
+        "retry": "Zapytaj ponownie"
       }
     },
     "relativeJustNow": "przed chwilą",

src/__tests__/coach-stream-lifecycle-guard.test.ts

@@ -77,6 +77,35 @@ describe("Coach streaming lifecycle", () => {
     ).toBe(true);
   });
 
+  it("the unmount cleanup records the interrupted conversation before the abort (#781)", () => {
+    const source = read("components/insights/coach-panel/use-coach.ts");
+
+    // A cleanup that writes the resume value under the storage key. Without
+    // it the unmount abort is silent again: the user returns to a blank new
+    // chat with no route back to the interrupted thread.
+    const recordsInterruption =
+      /return\s*\(\)\s*=>\s*\{[\s\S]*?interruptedResumeValue\(\s*active\s*\)[\s\S]*?sessionStorage\.setItem\(\s*COACH_INTERRUPTED_STORAGE_KEY/.test(
+        source,
+      );
+    expect(
+      recordsInterruption,
+      "use-coach.ts must record the interrupted conversation " +
+        "(COACH_INTERRUPTED_STORAGE_KEY) in an unmount cleanup",
+    ).toBe(true);
+
+    // And the recording effect must be defined BEFORE the abort effect so
+    // the flag is written while the send is still marked in flight.
+    const recordIndex = source.indexOf("COACH_INTERRUPTED_STORAGE_KEY,\n");
+    const abortIndex = source.indexOf("abortRef.current?.abort();\n    };");
+    expect(recordIndex).toBeGreaterThan(-1);
+    expect(abortIndex).toBeGreaterThan(-1);
+    expect(
+      recordIndex < abortIndex,
+      "the interruption-recording cleanup must be defined before the " +
+        "mount-scoped abort cleanup",
+    ).toBe(true);
+  });
+
   it("handleNewChat still resets too — the two paths must not diverge again", () => {
     const source = read(
       "components/insights/coach-panel/coach-conversation.tsx",

src/app/coach/__tests__/page-interrupted-resume.test.tsx

@@ -0,0 +1,129 @@
+import { describe, expect, it, vi, beforeEach } from "vitest";
+import { renderToStaticMarkup } from "react-dom/server";
+
+/**
+ * #781 — returning to `/coach` after a navigation aborted a streaming reply
+ * must land the user back IN the interrupted conversation, not on a blank
+ * new chat. The unmount cleanup in `use-coach.ts` records the interrupted
+ * conversation under `COACH_INTERRUPTED_STORAGE_KEY`; this pins the page's
+ * consumption side:
+ *
+ *  - a stored conversation id seeds `initialConversationId` (same prop the
+ *    `?c=` deep-link drives);
+ *  - the `"latest"` sentinel (a first-turn abort whose id never reached the
+ *    client) flips `autoOpenMostRecent` instead;
+ *  - every EXPLICIT entry intent (`?c=`, `?c=new`, `?doc=`, `?ask=`) wins
+ *    over the resume.
+ *
+ * Same probe pattern as `page-launch-params.test.tsx`: the conversation
+ * surface is stubbed and the resolved props are asserted.
+ */
+
+const conversationProps = vi.fn();
+
+vi.mock("@/components/insights/coach-panel/coach-conversation", () => ({
+  CoachConversation: (props: Record<string, unknown>) => {
+    conversationProps(props);
+    return <div data-slot="coach-conversation-probe" />;
+  },
+}));
+
+const searchParams = { current: new URLSearchParams() };
+vi.mock("next/navigation", () => ({
+  useSearchParams: () => searchParams.current,
+  useRouter: () => ({ replace: vi.fn(), push: vi.fn() }),
+}));
+
+vi.mock("@/lib/insights/coach-launch-context", () => ({
+  useCoachLaunch: () => ({ askCoach: vi.fn() }),
+}));
+vi.mock("@/hooks/use-feature-flags", () => ({
+  useFeatureFlags: () => ({ coach: true }),
+}));
+vi.mock("@/hooks/use-disable-coach", () => ({
+  useDisableCoach: () => false,
+}));
+vi.mock("@/hooks/use-auth", () => ({
+  useAuth: () => ({ user: {}, isLoading: false }),
+}));
+vi.mock("@/hooks/use-record-capabilities", () => ({
+  useRecordCapabilities: () => ({ inSharedRecord: false }),
+}));
+vi.mock("@tanstack/react-query", () => ({
+  useQuery: () => ({ data: undefined }),
+}));
+vi.mock("@/lib/api/api-fetch", () => ({ apiGet: vi.fn() }));
+
+import CoachPageClient from "../page-client";
+import { COACH_INTERRUPTED_STORAGE_KEY } from "@/components/insights/coach-panel/use-coach";
+
+// The vitest environment is `node` (SSR-only tests) — there is no `window`.
+// The page reads the flag through `window.sessionStorage` behind a
+// `typeof window` guard, so stub the minimal surface it touches.
+const store = new Map<string, string>();
+vi.stubGlobal("window", {
+  sessionStorage: {
+    getItem: (k: string) => store.get(k) ?? null,
+    setItem: (k: string, v: string) => void store.set(k, v),
+    removeItem: (k: string) => void store.delete(k),
+  },
+});
+
+function renderWith(query: string): Record<string, unknown> {
+  searchParams.current = new URLSearchParams(query);
+  renderToStaticMarkup(<CoachPageClient />);
+  const calls = conversationProps.mock.calls;
+  return calls[calls.length - 1][0] as Record<string, unknown>;
+}
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  store.clear();
+});
+
+describe("/coach — interrupted-conversation resume (#781)", () => {
+  it("reopens the interrupted conversation recorded by the aborted stream", () => {
+    store.set(COACH_INTERRUPTED_STORAGE_KEY, "conv-42");
+    const props = renderWith("");
+    expect(props.initialConversationId).toBe("conv-42");
+  });
+
+  it("resolves a first-turn abort (sentinel 'latest') via most-recent", () => {
+    store.set(COACH_INTERRUPTED_STORAGE_KEY, "latest");
+    const props = renderWith("");
+    expect(props.initialConversationId).toBe(null);
+    expect(props.autoOpenMostRecent).toBe(true);
+  });
+
+  it("without a recorded interruption the default new-chat hero stands", () => {
+    const props = renderWith("");
+    expect(props.initialConversationId).toBe(null);
+    expect(props.autoOpenMostRecent).toBe(false);
+  });
+
+  it("an explicit ?c= deep-link wins over the resume", () => {
+    store.set(COACH_INTERRUPTED_STORAGE_KEY, "conv-42");
+    const props = renderWith("c=conv-7");
+    expect(props.initialConversationId).toBe("conv-7");
+  });
+
+  it("an explicit ?c=new (fresh chat) wins over the resume", () => {
+    store.set(COACH_INTERRUPTED_STORAGE_KEY, "conv-42");
+    const props = renderWith("c=new");
+    expect(props.initialConversationId).toBe(null);
+    expect(props.autoOpenMostRecent).toBe(false);
+  });
+
+  it("an explicit ?ask= hand-off wins over the resume", () => {
+    store.set(COACH_INTERRUPTED_STORAGE_KEY, "conv-42");
+    const props = renderWith("ask=How%20did%20I%20sleep");
+    expect(props.initialConversationId).toBe(null);
+  });
+
+  it("a ?doc= scoped chat wins over the resume", () => {
+    store.set(COACH_INTERRUPTED_STORAGE_KEY, "conv-42");
+    const props = renderWith("doc=doc-1");
+    expect(props.initialConversationId).toBe(null);
+    expect(props.initialDocumentId).toBe("doc-1");
+  });
+});

src/app/coach/page-client.tsx

@@ -1,10 +1,11 @@
 "use client";
 
-import { Suspense, useEffect } from "react";
+import { Suspense, useEffect, useState } from "react";
 import { useRouter, useSearchParams } from "next/navigation";
 import { useQuery } from "@tanstack/react-query";
 
 import { CoachConversation } from "@/components/insights/coach-panel/coach-conversation";
+import { COACH_INTERRUPTED_STORAGE_KEY } from "@/components/insights/coach-panel/use-coach";
 import type { CoachNudgeStatus } from "@/components/insights/layout-coach-fab";
 import type { CoachLaunchScope } from "@/lib/insights/coach-launch-context";
 import { useCoachLaunch } from "@/lib/insights/coach-launch-context";
@@ -118,6 +119,47 @@ function CoachPageBody() {
     : null;
   const seedPrefill = freshChat ? searchParams.get("ask") : null;
 
+  // #781 — a navigation away mid-reply recorded the interrupted conversation
+  // (see `COACH_INTERRUPTED_STORAGE_KEY` in `use-coach.ts`). Returning to the
+  // Coach reopens that thread — where the persisted `cancelled` marker shows
+  // the turn as interrupted and offers the retry — instead of landing on a
+  // blank new chat. Read once per mount (lazy state, SSR-guarded), cleared in
+  // an effect so it is consumed exactly once. Every EXPLICIT entry intent
+  // wins over the resume: a `?c=` thread or `?c=new`, a `?doc=`/`?workout=`
+  // scoped chat, and a `?scope=`/`?ask=` hand-off all carry their own
+  // destination.
+  const [interruptedResume] = useState<string | null>(() => {
+    if (typeof window === "undefined") return null;
+    try {
+      return window.sessionStorage.getItem(COACH_INTERRUPTED_STORAGE_KEY);
+    } catch {
+      return null;
+    }
+  });
+  useEffect(() => {
+    if (interruptedResume === null) return;
+    try {
+      window.sessionStorage.removeItem(COACH_INTERRUPTED_STORAGE_KEY);
+    } catch {
+      // Best-effort clear; a stale flag only re-opens a conversation once.
+    }
+  }, [interruptedResume]);
+  const interruptedEligible =
+    rawC === null &&
+    rawDoc === null &&
+    rawWorkout === null &&
+    launchScope === null &&
+    !seedPrefill;
+  const interruptedId =
+    interruptedEligible && interruptedResume && interruptedResume !== "latest"
+      ? interruptedResume
+      : null;
+  // A first-turn abort never learned its conversation id (it rides the SSE
+  // `done` frame) — resolve via the server-authoritative most-recent thread,
+  // which the aborted turn's server-side persistence has just bumped to the top.
+  const resumeInterruptedLatest =
+    interruptedEligible && interruptedResume === "latest";
+
   // C1 exception — an unread coach-initiated message opens the most-recent
   // conversation (which holds that proactive turn). Only consulted when the
   // entry did not pin a specific thread or ask for a fresh chat.
@@ -144,7 +186,9 @@ function CoachPageBody() {
     <CoachConversation
       surface="page"
       autoFocusComposer
-      initialConversationId={deepLinkedId}
+      // #781 — the interrupted-conversation resume seeds the same prop the
+      // `?c=` deep-link drives; the explicit deep-link always wins.
+      initialConversationId={deepLinkedId ?? interruptedId}
       // v1.28.51 — seed the document scope for a `?doc=<id>` open so the first
       // turn is created + sent through the hardened fenced document endpoint.
       initialDocumentId={seedDocumentId}
@@ -153,9 +197,10 @@ function CoachPageBody() {
       // cross-surface hand-off carried in the URL.
       launchScope={launchScope}
       prefill={seedPrefill}
-      // Default is the new-chat hero; only resume most-recent for the
-      // unread coach-initiated exception.
-      autoOpenMostRecent={hasUnreadCoachMessage}
+      // Default is the new-chat hero; resume most-recent only for the
+      // unread coach-initiated exception and the interrupted first-turn
+      // resume (#781, whose conversation id never reached the client).
+      autoOpenMostRecent={hasUnreadCoachMessage || resumeInterruptedLatest}
     />
   );
 }

src/components/insights/coach-panel/__tests__/chat-bubble-cancelled.test.tsx

@@ -0,0 +1,96 @@
+import { describe, it, expect, vi } from "vitest";
+import { renderToStaticMarkup } from "react-dom/server";
+
+import { I18nProvider } from "@/lib/i18n/context";
+
+/**
+ * #781 — the persisted cancelled-turn marker (an EMPTY assistant row with
+ * `providerType: "cancelled"`) renders as a quiet interrupted note with a
+ * retry, never as an empty assistant bubble. SSR harness mirrors
+ * `chat-bubble-unverified-notice.test.tsx`.
+ */
+vi.mock("@/hooks/use-auth", () => ({
+  useAuth: () => ({
+    user: { id: "u1", username: "tester", role: "USER", avatarUrl: null },
+    isAuthenticated: true,
+    isLoading: false,
+  }),
+}));
+vi.mock("@tanstack/react-query", () => ({
+  useQuery: () => ({ data: undefined }),
+  useMutation: () => ({ mutate: vi.fn(), isPending: false, isError: false }),
+}));
+
+import { MessageThread } from "../message-thread";
+import type {
+  CoachConversationDetailDTO,
+  CoachMessageDTO,
+} from "@/lib/ai/coach/types";
+
+function render(node: React.ReactNode) {
+  return renderToStaticMarkup(
+    <I18nProvider initialLocale="en">{node}</I18nProvider>,
+  );
+}
+
+function conversationWith(
+  messages: Array<Partial<CoachMessageDTO>>,
+): CoachConversationDetailDTO {
+  return {
+    id: "c1",
+    title: "Test",
+    createdAt: "2026-08-13T10:00:00.000Z",
+    updatedAt: "2026-08-13T10:00:00.000Z",
+    messageCount: messages.length,
+    fenced: false,
+    attachments: [],
+    attachmentCount: 0,
+    documentTitle: null,
+    messages: messages.map((m, i) => ({
+      id: `m${i}`,
+      role: "user",
+      content: "",
+      createdAt: "2026-08-13T10:00:00.000Z",
+      metricSource: null,
+      providerType: null,
+      promptVersion: null,
+      tokensUsed: null,
+      model: null,
+      ...m,
+    })),
+  };
+}
+
+const interruptedThread = conversationWith([
+  { role: "user", content: "How is my blood pressure trending?" },
+  { role: "assistant", content: "", providerType: "cancelled" },
+]);
+
+describe("chat bubble — cancelled-turn marker (#781)", () => {
+  it("renders the interrupted note with a retry action, muted, no alarm colour", () => {
+    const html = render(
+      <MessageThread
+        conversation={interruptedThread}
+        onRegenerate={() => undefined}
+      />,
+    );
+    expect(html).toContain('data-slot="coach-bubble-cancelled"');
+    expect(html).toContain("This answer was interrupted before it finished.");
+    // The retry resubmits the preceding user question — the thread resolved
+    // one, so the affordance is present.
+    expect(html).toContain('data-slot="coach-interrupted-retry"');
+    expect(html).toContain("Ask again");
+    // Muted meta, not an alarm: the marker must not paint destructive/warning.
+    const markerHtml = html.slice(html.indexOf("coach-bubble-cancelled"));
+    expect(markerHtml).not.toContain("text-destructive");
+    expect(markerHtml).not.toContain("text-warning");
+    // No empty assistant prose bubble alongside the marker.
+    expect(html).not.toContain('data-slot="coach-bubble-assistant"');
+  });
+
+  it("omits the retry when the surface supplies no regenerate handler", () => {
+    const html = render(<MessageThread conversation={interruptedThread} />);
+    expect(html).toContain('data-slot="coach-bubble-cancelled"');
+    expect(html).not.toContain('data-slot="coach-interrupted-retry"');
+  });
+});

src/components/insights/coach-panel/__tests__/use-coach-interrupted.test.ts

@@ -0,0 +1,33 @@
+import { describe, it, expect } from "vitest";
+
+import { interruptedResumeValue } from "../use-coach";
+
+/**
+ * #781 — the write side of the interrupted-conversation resume. The unmount
+ * cleanup records `interruptedResumeValue(...)` under
+ * `COACH_INTERRUPTED_STORAGE_KEY` before aborting an in-flight stream; the
+ * `/coach` page's consumption side is pinned in
+ * `src/app/coach/__tests__/page-interrupted-resume.test.tsx`.
+ */
+describe("interruptedResumeValue (#781)", () => {
+  it("records the conversation id for an in-flight turn on an existing thread", () => {
+    expect(
+      interruptedResumeValue({ conversationId: "conv-42", inProgress: true }),
+    ).toBe("conv-42");
+  });
+
+  it("records the 'latest' sentinel for an in-flight FIRST turn (id unknown)", () => {
+    expect(
+      interruptedResumeValue({ conversationId: null, inProgress: true }),
+    ).toBe("latest");
+  });
+
+  it("records nothing for a settled turn — unmount after completion is not an interruption", () => {
+    expect(
+      interruptedResumeValue({ conversationId: "conv-42", inProgress: false }),
+    ).toBe(null);
+    expect(
+      interruptedResumeValue({ conversationId: null, inProgress: false }),
+    ).toBe(null);
+  });
+});

src/components/insights/coach-panel/chat-bubble.tsx

@@ -21,6 +21,7 @@ import {
 } from "lucide-react";
 
 import { cn } from "@/lib/utils";
+import { Button } from "@/components/ui/button";
 import { useTranslations, useFormatters } from "@/lib/i18n/context";
 import { ApiError, apiPost } from "@/lib/api/api-fetch";
 import { useAuth } from "@/hooks/use-auth";
@@ -567,6 +568,48 @@ function ChatBubbleImpl({
     );
   }
 
+  // #781 — the persisted cancelled-turn marker (an EMPTY assistant row the
+  // server writes when the client aborts mid-generation, e.g. navigating
+  // away). Rendered as a quiet interrupted note — muted meta text per
+  // UI-STANDARDS §3, never an alarm colour: nothing failed, the user left —
+  // plus a retry that resubmits the question that produced the turn (the
+  // regenerate closure, so the resend runs through the normal send path and
+  // every budget/rate gate). No provenance, feedback, copy, or token footer:
+  // there is no reply to act on.
+  if (providerType === "cancelled") {
+    return (
+      <div
+        data-slot="coach-bubble-cancelled"
+        className="flex items-start gap-2.5"
+      >
+        <div
+          aria-hidden="true"
+          className="from-primary to-brand-pink mt-0.5 flex size-8 shrink-0 items-center justify-center rounded-full bg-gradient-to-br"
+        >
+          <Sparkles className="text-background size-3.5" />
+        </div>
+        <div className="flex max-w-[calc(80%-2.625rem)] flex-col items-start gap-2">
+          <p className="text-muted-foreground text-xs leading-relaxed">
+            {t("insights.coach.interrupted.note")}
+          </p>
+          {onRegenerate && (
+            <Button
+              type="button"
+              variant="outline"
+              size="sm"
+              data-slot="coach-interrupted-retry"
+              className="min-h-11 sm:min-h-9"
+              onClick={onRegenerate}
+            >
+              <RotateCcw className="size-3.5" aria-hidden="true" />
+              {t("insights.coach.interrupted.retry")}
+            </Button>
+          )}
+        </div>
+      </div>
+    );
+  }
+
   // v1.4.25 W5 — map server-emitted error codes to specific Coach
   // i18n keys. Distinct user-quota and provider-rate-limit copy so the
   // user understands daily-cap (resets at UTC midnight) vs. transient

src/components/insights/coach-panel/use-coach.ts

@@ -586,6 +586,33 @@ export interface CoachOptimisticUserMessage {
   conversationId: string | null;
 }
 
+/**
+ * #781 — sessionStorage key recording a turn interrupted by navigation.
+ * Written by the unmount cleanup in `useSendCoachMessage` when a stream is
+ * still in flight; consumed (and cleared) by the `/coach` page on its next
+ * mount so the user lands back IN the interrupted conversation instead of a
+ * blank new chat. The value is the conversation id, or the sentinel
+ * `"latest"` when the aborted turn was creating a brand-new conversation —
+ * its id only travels on the SSE `done` frame, which never arrived, so the
+ * page resolves it via the server-authoritative most-recent thread instead.
+ */
+export const COACH_INTERRUPTED_STORAGE_KEY = "coach-interrupted-conversation";
+
+/**
+ * #781 — the resume value the unmount cleanup records, or null when nothing
+ * should be recorded. Pure so the decision is unit-testable without mounting
+ * the hook (this repo's tests are SSR-only): a settled turn records nothing,
+ * an in-flight turn records its conversation id, and an in-flight FIRST turn
+ * (id not yet known) records the `"latest"` sentinel.
+ */
+export function interruptedResumeValue(active: {
+  conversationId: string | null;
+  inProgress: boolean;
+}): string | null {
+  if (!active.inProgress) return null;
+  return active.conversationId ?? "latest";
+}
+
 const EMPTY_STREAMING: CoachStreamingMessage = {
   content: "",
   metricSource: null,
@@ -742,6 +769,48 @@ export function useSendCoachMessage(opts: UseSendCoachMessageOptions = {}) {
     optsRef.current = opts;
   }, [opts]);
 
+  // #781 — the send in flight at this moment, for the unmount cleanup below.
+  // A ref (not state): the cleanup closure must read the live value, and the
+  // bookkeeping must never re-render the surface.
+  const activeSendRef = useRef<{
+    conversationId: string | null;
+    inProgress: boolean;
+  }>({ conversationId: null, inProgress: false });
+
+  // #781 — the unmount abort below stays (it is the budget guard), but it
+  // must not be SILENT any more: record which conversation was interrupted so
+  // the next `/coach` mount reopens it (the server closes the turn with a
+  // persisted `cancelled` marker on its side), and drop the cached
+  // conversation + rail copies so the return visit refetches the
+  // just-advanced server state instead of serving a pre-abort cache entry.
+  // Its own effect, defined BEFORE the abort effect: within one component
+  // React runs unmount cleanups in definition order, and the bookkeeping
+  // must read `activeSendRef` while the send is still marked in flight
+  // (the abort's `finally` only clears the flag on a later microtask
+  // regardless, so either order is safe — this one is merely honest).
+  useEffect(() => {
+    return () => {
+      const active = activeSendRef.current;
+      const resumeValue = interruptedResumeValue(active);
+      if (resumeValue === null) return;
+      try {
+        window.sessionStorage.setItem(
+          COACH_INTERRUPTED_STORAGE_KEY,
+          resumeValue,
+        );
+      } catch {
+        // Storage can throw (private mode / quota) — the persisted
+        // cancelled marker still surfaces the interruption in history.
+      }
+      if (active.conversationId) {
+        queryClient.invalidateQueries({
+          queryKey: QUERY_KEYS.one(active.conversationId),
+        });
+      }
+      queryClient.invalidateQueries({ queryKey: QUERY_KEYS.list() });
+    };
+  }, [queryClient]);
+
   // Abort any in-flight stream when the hook unmounts. The drawer works around
   // this via `handleOpenChange`, but the full-page `/coach` surface passes no
   // `registerReset`, so navigating away mid-stream left the SSE reader loop
@@ -764,254 +833,269 @@ export function useSendCoachMessage(opts: UseSendCoachMessageOptions = {}) {
       abortRef.current?.abort();
       const controller = new AbortController();
       abortRef.current = controller;
-
-      // v1.4.25 W5 — surface the user's message in the thread BEFORE
-      // the "Thinking…" placeholder paints. Without this the send hook
-      // only exposed the streaming assistant bubble, so the first
-      // thing the user saw was the placeholder followed by their own
-      // message landing on the next refetch — the maintainer flagged the
-      // order as confusing on the suggested-prompt chips.
-      setOptimisticUser({
-        localId: `local-${Date.now()}-${Math.random().toString(36).slice(2, 7)}`,
-        content: params.message,
+      // #781 — mark the send in flight for the unmount cleanup. The whole
+      // body runs inside try/finally so EVERY exit (offline pre-check, fetch
+      // failure, error envelope, stream end, abort) clears the flag — an
+      // unmount after a settled turn must never record an interruption. The
+      // marker object is captured locally so a superseding send (which
+      // replaces `activeSendRef.current` with its own marker) is never
+      // cleared by the superseded send's finally.
+      const sendMarker = {
         conversationId: params.conversationId ?? null,
-      });
-      setStreaming({
-        content: "",
-        metricSource: null,
-        suggestion: null,
-        suggestedAction: null,
         inProgress: true,
-        messageId: null,
-        errorCode: null,
-        usage: null,
-      });
-
-      // v1.4.47 W8 — pre-check navigator.onLine so an airplane-mode
-      // user gets the offline-specific copy immediately rather than
-      // waiting for the fetch to fail with a generic network error.
-      if (typeof navigator !== "undefined" && navigator.onLine === false) {
-        setStreaming({
-          content: "",
-          metricSource: null,
-          suggestion: null,
-          suggestedAction: null,
-          inProgress: false,
-          messageId: null,
-          errorCode: "coach.network",
-          usage: null,
-        });
-        return null;
-      }
-
-      // v1.28.51 — resolve the target BEFORE the fetch. A doc-scoped turn
-      // resolves to the hardened fenced document endpoint; everything else to
-      // the Coach tool route. This is the prompt-injection fence's client edge.
-      const target = resolveCoachSendTarget(params);
-
-      // apiFetchRaw: the chat POST streams SSE — the envelope helpers
-      // would buffer and unwrap a body that never carries the envelope.
-      let response: Response;
+      };
+      activeSendRef.current = sendMarker;
       try {
-        response = await apiFetchRaw(target.url, {
-          method: "POST",
-          headers: {
-            "Content-Type": "application/json",
-            Accept: "text/event-stream",
-          },
-          body: target.body,
-          signal: controller.signal,
+        // v1.4.25 W5 — surface the user's message in the thread BEFORE
+        // the "Thinking…" placeholder paints. Without this the send hook
+        // only exposed the streaming assistant bubble, so the first
+        // thing the user saw was the placeholder followed by their own
+        // message landing on the next refetch — the maintainer flagged the
+        // order as confusing on the suggested-prompt chips.
+        setOptimisticUser({
+          localId: `local-${Date.now()}-${Math.random().toString(36).slice(2, 7)}`,
+          content: params.message,
+          conversationId: params.conversationId ?? null,
         });
-      } catch (err) {
-        if ((err as Error).name === "AbortError") return null;
         setStreaming({
           content: "",
           metricSource: null,
           suggestion: null,
           suggestedAction: null,
-          inProgress: false,
+          inProgress: true,
           messageId: null,
-          errorCode: "coach.network",
+          errorCode: null,
           usage: null,
         });
-        return null;
-      }
 
-      if (!response.body) {
-        setStreaming({
-          content: "",
-          metricSource: null,
-          suggestion: null,
-          suggestedAction: null,
-          inProgress: false,
-          messageId: null,
-          errorCode: `coach.http.${response.status}`,
-          usage: null,
-        });
-        return null;
-      }
-
-      // Even on `!response.ok`, the route may have emitted a structured
-      // `error` frame in an SSE body (e.g. 4xx/5xx + text/event-stream).
-      // Falling back to `coach.http.<status>` would discard the richer
-      // `errorCode`. Read the stream and let the parser route the frame
-      // through the same path as the success case.
-      const contentType = response.headers.get("Content-Type") ?? "";
-      const isEventStream = contentType
-        .toLowerCase()
-        .startsWith("text/event-stream");
-      if (!response.ok && !isEventStream) {
-        // v1.4.25 W5 — for JSON errors the apiHandler envelope carries
-        // a structured `error` code (e.g. `coach.budget.exceeded`).
-        // Surface the structured code directly so the drawer can show
-        // the right copy + toast variant; fall back to the generic
-        // `coach.http.<status>` only when parsing the envelope fails.
-        let structured: string | null = null;
-        try {
-          const envelope = (await response.clone().json()) as {
-            error?: unknown;
-          };
-          if (typeof envelope?.error === "string") {
-            structured = envelope.error;
-          }
-        } catch {
-          // body was not JSON; fall through to the http-status fallback
+        // v1.4.47 W8 — pre-check navigator.onLine so an airplane-mode
+        // user gets the offline-specific copy immediately rather than
+        // waiting for the fetch to fail with a generic network error.
+        if (typeof navigator !== "undefined" && navigator.onLine === false) {
+          setStreaming({
+            content: "",
+            metricSource: null,
+            suggestion: null,
+            suggestedAction: null,
+            inProgress: false,
+            messageId: null,
+            errorCode: "coach.network",
+            usage: null,
+          });
+          return null;
         }
-        setStreaming({
-          content: "",
-          metricSource: null,
-          suggestion: null,
-          suggestedAction: null,
-          inProgress: false,
-          messageId: null,
-          errorCode: structured ?? `coach.http.${response.status}`,
-          usage: null,
-        });
-        // v1.16.4 — KEEP the optimistic user bubble: a rejected turn
-        // (budget gate, 4xx) has no persisted twin coming, and dropping
-        // the bubble left the error standing next to an empty thread.
-        // The content-equality dedupe in <MessageThread> still
-        // suppresses the optimistic copy if a persisted twin lands.
-        return null;
-      }
 
-      const reader = response.body.getReader();
-      const decoder = new TextDecoder();
-      let buffer = "";
-      let resolvedConversationId: string | null = null;
-      let collectedContent = "";
-      let collectedProvenance: CoachProvenance | null = null;
-      let collectedSuggestion: CoachSuggestion | null = null;
-      let collectedSuggestedAction: CoachSuggestedAction | null = null;
-      let lastError: string | null = null;
-      let messageId: string | null = null;
-      let collectedUsage: CoachUsage | null = null;
+        // v1.28.51 — resolve the target BEFORE the fetch. A doc-scoped turn
+        // resolves to the hardened fenced document endpoint; everything else to
+        // the Coach tool route. This is the prompt-injection fence's client edge.
+        const target = resolveCoachSendTarget(params);
 
-      try {
-        while (true) {
-          const { done, value } = await reader.read();
-          if (done) break;
-          const text = decoder.decode(value, { stream: true });
-          const { events, rest } = parseSseChunk(buffer, text);
-          buffer = rest;
-          for (const evt of events) {
-            switch (evt.type) {
-              case "token":
-                collectedContent += evt.token;
-                setStreaming((prev) => ({
-                  ...prev,
-                  content: prev.content + evt.token,
-                }));
-                break;
-              case "provenance":
-                collectedProvenance = evt.metricSource;
-                setStreaming((prev) => ({
-                  ...prev,
-                  metricSource: evt.metricSource,
-                }));
-                break;
-              case "suggestion":
-                collectedSuggestion = evt.suggestion;
-                setStreaming((prev) => ({
-                  ...prev,
-                  suggestion: evt.suggestion,
-                }));
-                break;
-              case "suggestedAction":
-                collectedSuggestedAction = evt.suggestedAction;
-                setStreaming((prev) => ({
-                  ...prev,
-                  suggestedAction: evt.suggestedAction,
-                }));
-                break;
-              case "reasoning":
-                // v1.19.1 — the thinking disclosure was removed, so the
-                // additive `reasoning` frame is accepted off the wire and
-                // dropped. Kept as an explicit no-op case so the wire frame
-                // stays a recognised type rather than slipping to a default.
-                break;
-              case "done":
-                resolvedConversationId = evt.conversationId;
-                messageId = evt.messageId;
-                // v1.18.9 — additive per-turn usage envelope.
-                collectedUsage = evt.usage ?? null;
-                break;
-              case "error":
-                lastError = evt.code;
-                break;
+        // apiFetchRaw: the chat POST streams SSE — the envelope helpers
+        // would buffer and unwrap a body that never carries the envelope.
+        let response: Response;
+        try {
+          response = await apiFetchRaw(target.url, {
+            method: "POST",
+            headers: {
+              "Content-Type": "application/json",
+              Accept: "text/event-stream",
+            },
+            body: target.body,
+            signal: controller.signal,
+          });
+        } catch (err) {
+          if ((err as Error).name === "AbortError") return null;
+          setStreaming({
+            content: "",
+            metricSource: null,
+            suggestion: null,
+            suggestedAction: null,
+            inProgress: false,
+            messageId: null,
+            errorCode: "coach.network",
+            usage: null,
+          });
+          return null;
+        }
+
+        if (!response.body) {
+          setStreaming({
+            content: "",
+            metricSource: null,
+            suggestion: null,
+            suggestedAction: null,
+            inProgress: false,
+            messageId: null,
+            errorCode: `coach.http.${response.status}`,
+            usage: null,
+          });
+          return null;
+        }
+
+        // Even on `!response.ok`, the route may have emitted a structured
+        // `error` frame in an SSE body (e.g. 4xx/5xx + text/event-stream).
+        // Falling back to `coach.http.<status>` would discard the richer
+        // `errorCode`. Read the stream and let the parser route the frame
+        // through the same path as the success case.
+        const contentType = response.headers.get("Content-Type") ?? "";
+        const isEventStream = contentType
+          .toLowerCase()
+          .startsWith("text/event-stream");
+        if (!response.ok && !isEventStream) {
+          // v1.4.25 W5 — for JSON errors the apiHandler envelope carries
+          // a structured `error` code (e.g. `coach.budget.exceeded`).
+          // Surface the structured code directly so the drawer can show
+          // the right copy + toast variant; fall back to the generic
+          // `coach.http.<status>` only when parsing the envelope fails.
+          let structured: string | null = null;
+          try {
+            const envelope = (await response.clone().json()) as {
+              error?: unknown;
+            };
+            if (typeof envelope?.error === "string") {
+              structured = envelope.error;
+            }
+          } catch {
+            // body was not JSON; fall through to the http-status fallback
+          }
+          setStreaming({
+            content: "",
+            metricSource: null,
+            suggestion: null,
+            suggestedAction: null,
+            inProgress: false,
+            messageId: null,
+            errorCode: structured ?? `coach.http.${response.status}`,
+            usage: null,
+          });
+          // v1.16.4 — KEEP the optimistic user bubble: a rejected turn
+          // (budget gate, 4xx) has no persisted twin coming, and dropping
+          // the bubble left the error standing next to an empty thread.
+          // The content-equality dedupe in <MessageThread> still
+          // suppresses the optimistic copy if a persisted twin lands.
+          return null;
+        }
+
+        const reader = response.body.getReader();
+        const decoder = new TextDecoder();
+        let buffer = "";
+        let resolvedConversationId: string | null = null;
+        let collectedContent = "";
+        let collectedProvenance: CoachProvenance | null = null;
+        let collectedSuggestion: CoachSuggestion | null = null;
+        let collectedSuggestedAction: CoachSuggestedAction | null = null;
+        let lastError: string | null = null;
+        let messageId: string | null = null;
+        let collectedUsage: CoachUsage | null = null;
+
+        try {
+          while (true) {
+            const { done, value } = await reader.read();
+            if (done) break;
+            const text = decoder.decode(value, { stream: true });
+            const { events, rest } = parseSseChunk(buffer, text);
+            buffer = rest;
+            for (const evt of events) {
+              switch (evt.type) {
+                case "token":
+                  collectedContent += evt.token;
+                  setStreaming((prev) => ({
+                    ...prev,
+                    content: prev.content + evt.token,
+                  }));
+                  break;
+                case "provenance":
+                  collectedProvenance = evt.metricSource;
+                  setStreaming((prev) => ({
+                    ...prev,
+                    metricSource: evt.metricSource,
+                  }));
+                  break;
+                case "suggestion":
+                  collectedSuggestion = evt.suggestion;
+                  setStreaming((prev) => ({
+                    ...prev,
+                    suggestion: evt.suggestion,
+                  }));
+                  break;
+                case "suggestedAction":
+                  collectedSuggestedAction = evt.suggestedAction;
+                  setStreaming((prev) => ({
+                    ...prev,
+                    suggestedAction: evt.suggestedAction,
+                  }));
+                  break;
+                case "reasoning":
+                  // v1.19.1 — the thinking disclosure was removed, so the
+                  // additive `reasoning` frame is accepted off the wire and
+                  // dropped. Kept as an explicit no-op case so the wire frame
+                  // stays a recognised type rather than slipping to a default.
+                  break;
+                case "done":
+                  resolvedConversationId = evt.conversationId;
+                  messageId = evt.messageId;
+                  // v1.18.9 — additive per-turn usage envelope.
+                  collectedUsage = evt.usage ?? null;
+                  break;
+                case "error":
+                  lastError = evt.code;
+                  break;
+              }
             }
           }
-        }
-        // Final flush of any trailing frame in the residual buffer.
-        const tail = parseSseChunk(buffer, "\n\n");
-        for (const evt of tail.events) {
-          if (evt.type === "done") {
-            resolvedConversationId = evt.conversationId;
-            messageId = evt.messageId;
-            collectedUsage = evt.usage ?? null;
-          } else if (evt.type === "error") {
-            lastError = evt.code;
+          // Final flush of any trailing frame in the residual buffer.
+          const tail = parseSseChunk(buffer, "\n\n");
+          for (const evt of tail.events) {
+            if (evt.type === "done") {
+              resolvedConversationId = evt.conversationId;
+              messageId = evt.messageId;
+              collectedUsage = evt.usage ?? null;
+            } else if (evt.type === "error") {
+              lastError = evt.code;
+            }
+          }
+        } catch (err) {
+          if ((err as Error).name !== "AbortError") {
+            lastError = "coach.stream";
           }
         }
-      } catch (err) {
-        if ((err as Error).name !== "AbortError") {
-          lastError = "coach.stream";
-        }
-      }
 
-      setStreaming({
-        content: collectedContent,
-        metricSource: collectedProvenance,
-        suggestion: collectedSuggestion,
-        suggestedAction: collectedSuggestedAction,
-        inProgress: false,
-        messageId,
-        errorCode: lastError,
-        usage: collectedUsage,
-      });
-
-      if (resolvedConversationId) {
-        // Invalidate the freshly-persisted conversation + the rail so
-        // the drawer's next mount picks up the encrypted-on-disk shape
-        // and the rail orders the thread to the top.
-        queryClient.invalidateQueries({
-          queryKey: QUERY_KEYS.one(resolvedConversationId),
+        setStreaming({
+          content: collectedContent,
+          metricSource: collectedProvenance,
+          suggestion: collectedSuggestion,
+          suggestedAction: collectedSuggestedAction,
+          inProgress: false,
+          messageId,
+          errorCode: lastError,
+          usage: collectedUsage,
         });
-        queryClient.invalidateQueries({ queryKey: QUERY_KEYS.list() });
-        optsRef.current.onDone?.(resolvedConversationId);
+
+        if (resolvedConversationId) {
+          // Invalidate the freshly-persisted conversation + the rail so
+          // the drawer's next mount picks up the encrypted-on-disk shape
+          // and the rail orders the thread to the top.
+          queryClient.invalidateQueries({
+            queryKey: QUERY_KEYS.one(resolvedConversationId),
+          });
+          queryClient.invalidateQueries({ queryKey: QUERY_KEYS.list() });
+          optsRef.current.onDone?.(resolvedConversationId);
+        }
+        // v1.4.25 W5 — drop the optimistic user bubble; the persisted
+        // twin is on its way via the invalidate-refetch above.
+        // v1.16.4 — but only when a twin IS coming (the turn resolved a
+        // conversation) or the turn succeeded outright. An errored turn
+        // without a conversation id persisted nothing; dropping the
+        // bubble then erased the user's message next to the error bubble.
+        // The content-equality dedupe in <MessageThread> still suppresses
+        // the optimistic copy if a persisted twin does land later.
+        if (resolvedConversationId || !lastError) {
+          setOptimisticUser(null);
+        }
+        return resolvedConversationId;
+      } finally {
+        sendMarker.inProgress = false;
       }
-      // v1.4.25 W5 — drop the optimistic user bubble; the persisted
-      // twin is on its way via the invalidate-refetch above.
-      // v1.16.4 — but only when a twin IS coming (the turn resolved a
-      // conversation) or the turn succeeded outright. An errored turn
-      // without a conversation id persisted nothing; dropping the
-      // bubble then erased the user's message next to the error bubble.
-      // The content-equality dedupe in <MessageThread> still suppresses
-      // the optimistic copy if a persisted twin does land later.
-      if (resolvedConversationId || !lastError) {
-        setOptimisticUser(null);
-      }
-      return resolvedConversationId;
     },
     [queryClient],
   );