feat(coach): add a full-page conversation mode with a maximize control

Extract the Coach chat surface (header actions, message thread,
composer, provenance rails, settings, mobile trays) into a shared
<CoachConversation> component so the drawer and a new full-page route
render the exact same implementation — no forked chat logic. The drawer
keeps only its <Sheet> chrome (close button + maximize control); the
page supplies a minimize-back-to-drawer control.

The maximize control in the drawer header navigates to /insights/coach
and closes the drawer (aborting any in-flight stream); the page's
minimize control routes back to /insights and reopens the drawer through
the shared launch context. Both surfaces preserve incremental streaming,
collapsible history + provenance, the single composer disclaimer, the
auto-grow composer, refusal / budget handling, and the aiMode gating —
the full page redirects to /insights when the operator flag is off or
the user has opted out.

Lift useResettableValue / nextResettableValue into their own module so
the shared surface seeds its composer from the same controlled-prefill
contract without importing the drawer shell. Register the new route in
the coach feature-flag and per-user-disable gate-site invariants, and
add the maximize / minimize labels across all six locales.

messages/de.json

@@ -1736,6 +1736,8 @@
       "errorCredentialExpired": "Deine Verbindung zum KI-Anbieter ist abgelaufen. Stelle sie in den Einstellungen wieder her, damit der Coach weiterläuft.",
       "tagline": "Persönlicher Gesundheitscoach, auf deine Daten gestützt.",
       "newChat": "Neuer Chat",
+      "maximizeAriaLabel": "Im Vollbild öffnen",
+      "minimizeAriaLabel": "Zurück zum Seitenfenster",
       "send": "Senden",
       "stop": "Stopp",
       "thinking": "Denke nach…",

messages/en.json

@@ -1736,6 +1736,8 @@
       "errorCredentialExpired": "Your AI provider connection has expired. Reconnect it in Settings to keep the Coach running.",
       "tagline": "Personal health coach, grounded in your data.",
       "newChat": "New chat",
+      "maximizeAriaLabel": "Open in full page",
+      "minimizeAriaLabel": "Back to the drawer",
       "send": "Send",
       "stop": "Stop",
       "thinking": "Thinking…",

messages/es.json

@@ -1736,6 +1736,8 @@
       "errorCredentialExpired": "Tu conexión con el proveedor de IA ha caducado. Vuelve a conectarla en Ajustes para que el Coach siga funcionando.",
       "tagline": "Coach personal de salud, apoyado en tus datos.",
       "newChat": "Nueva conversación",
+      "maximizeAriaLabel": "Abrir en pantalla completa",
+      "minimizeAriaLabel": "Volver al panel",
       "send": "Enviar",
       "stop": "Detener",
       "thinking": "Pensando…",

messages/fr.json

@@ -1736,6 +1736,8 @@
       "errorCredentialExpired": "Ta connexion au fournisseur d'IA a expiré. Reconnecte-la dans les Réglages pour que le Coach continue de fonctionner.",
       "tagline": "Coach personnel de santé, ancré sur tes données.",
       "newChat": "Nouvelle conversation",
+      "maximizeAriaLabel": "Ouvrir en pleine page",
+      "minimizeAriaLabel": "Revenir au panneau",
       "send": "Envoyer",
       "stop": "Arrêter",
       "thinking": "Réflexion en cours…",

messages/it.json

@@ -1736,6 +1736,8 @@
       "errorCredentialExpired": "La connessione al provider di IA è scaduta. Riconnettila nelle Impostazioni per mantenere attivo il Coach.",
       "tagline": "Coach personale di salute, basato sui tuoi dati.",
       "newChat": "Nuova chat",
+      "maximizeAriaLabel": "Apri a pagina intera",
+      "minimizeAriaLabel": "Torna al pannello",
       "send": "Invia",
       "stop": "Interrompi",
       "thinking": "Sto pensando…",

messages/pl.json

@@ -1736,6 +1736,8 @@
       "errorCredentialExpired": "Połączenie z dostawcą AI wygasło. Połącz je ponownie w Ustawieniach, aby Coach działał dalej.",
       "tagline": "Osobisty coach zdrowia, oparty na twoich danych.",
       "newChat": "Nowa rozmowa",
+      "maximizeAriaLabel": "Otwórz na pełnej stronie",
+      "minimizeAriaLabel": "Powrót do panelu",
       "send": "Wyślij",
       "stop": "Zatrzymaj",
       "thinking": "Myślę…",

src/app/insights/coach/page.tsx

@@ -0,0 +1,88 @@
+"use client";
+
+import { useEffect } from "react";
+import { useRouter } from "next/navigation";
+import { Minimize2 } from "lucide-react";
+
+import { Button } from "@/components/ui/button";
+import { CoachConversation } from "@/components/insights/coach-panel/coach-conversation";
+import { useTranslations } from "@/lib/i18n/context";
+import { useCoachLaunch } from "@/lib/insights/coach-launch-context";
+import { useFeatureFlags } from "@/hooks/use-feature-flags";
+import { useDisableCoach } from "@/hooks/use-disable-coach";
+
+/**
+ * v1.12.0 (Coach v2 #6) — full-page Coach conversation.
+ *
+ * Renders the exact same `<CoachConversation>` surface the drawer uses
+ * (history + streaming thread + composer + provenance + settings) at
+ * full width and height. There is no forked chat logic — the page is a
+ * thin chrome wrapper that supplies a "minimize back to drawer"
+ * control where the drawer supplies "maximize" + "close".
+ *
+ * The route lives inside `app/insights/layout.tsx` (sticky tab strip +
+ * mobile FAB) and the authenticated `<AuthShell>` (which provides the
+ * `<CoachLaunchProvider>` the minimize control reopens the drawer
+ * through), so the page inherits the same Coach feature gating as every
+ * other Insights surface. When the operator's master flag is off or the
+ * user opted out, the page redirects back to `/insights` rather than
+ * painting a dead chat shell.
+ */
+export default function CoachPage() {
+  const { t } = useTranslations();
+  const router = useRouter();
+  const launch = useCoachLaunch();
+  const flags = useFeatureFlags();
+  const disableCoach = useDisableCoach();
+
+  const coachUnavailable = !flags.coach || disableCoach;
+
+  // Coach surface gating mirrors `<CoachLaunchButton>` / `<LayoutCoachFab>`:
+  // operator master flag OR per-user opt-out hides the Coach entirely.
+  // Send a direct navigator back to the Insights mother page so the
+  // route is never a dead-end.
+  useEffect(() => {
+    if (coachUnavailable) {
+      router.replace("/insights");
+    }
+  }, [coachUnavailable, router]);
+
+  if (coachUnavailable) return null;
+
+  const handleMinimize = () => {
+    // Hand the conversation back to the drawer overlay: route to the
+    // Insights mother page and reopen the drawer through the shared
+    // launch context.
+    router.push("/insights");
+    launch?.askCoach(null);
+  };
+
+  return (
+    <div
+      data-slot="coach-page"
+      className="flex h-[calc(100dvh-13rem)] min-h-[28rem] flex-col overflow-hidden rounded-2xl border"
+    >
+      <CoachConversation
+        surface="page"
+        autoFocusComposer
+        renderTitle={(title) => (
+          <h1 className="min-w-0 truncate text-sm font-semibold">{title}</h1>
+        )}
+        leadingHeaderActions={
+          <Button
+            type="button"
+            variant="ghost"
+            size="icon"
+            onClick={handleMinimize}
+            data-slot="coach-page-minimize"
+            aria-label={t("insights.coach.minimizeAriaLabel")}
+            title={t("insights.coach.minimizeAriaLabel")}
+            className="text-muted-foreground hover:text-foreground size-11 shrink-0"
+          >
+            <Minimize2 className="size-4" aria-hidden="true" />
+          </Button>
+        }
+      />
+    </div>
+  );
+}

src/components/insights/coach-panel/coach-conversation.tsx

@@ -0,0 +1,256 @@
+"use client";
+
+import { useEffect, useState } from "react";
+import { Plus, Settings, Sparkles } from "lucide-react";
+
+import { Button } from "@/components/ui/button";
+import { cn } from "@/lib/utils";
+import { useTranslations } from "@/lib/i18n/context";
+
+import { CoachDrawerBody } from "./coach-drawer-body";
+import { CoachInput } from "./coach-input";
+import { CoachSettingsSheet } from "./coach-settings-sheet";
+import { HistoryRail } from "./history-rail";
+import { MessageThread } from "./message-thread";
+import { MobileRailTray } from "./mobile-rail-tray";
+import { SourcesRail } from "./sources-rail";
+import { useResettableValue } from "./use-resettable-value";
+import { useCoachConversation, useSendCoachMessage } from "./use-coach";
+
+/**
+ * v1.12.0 (Coach v2 #6) — shared chat surface for both the Coach drawer
+ * (`<CoachDrawer>`, right/bottom `<Sheet>` overlay) and the full-page
+ * Coach route (`/insights/coach`).
+ *
+ * This component is the single source of truth for the Coach
+ * conversation: it owns the active-conversation id, the streaming send
+ * hook, the composer value, the settings sheet, and the mobile rail
+ * trays — every piece of Coach v2 behaviour (incremental streaming,
+ * collapsible history + provenance, the single composer disclaimer,
+ * the auto-grow composer, refusal / budget handling) lives here once.
+ * The drawer and the page differ ONLY in their chrome: the drawer wraps
+ * this surface in a `<Sheet>` and supplies a close button + a maximize
+ * control; the page renders it edge-to-edge and supplies a minimize
+ * control. Neither forks the chat logic.
+ *
+ * The title + description render through `renderTitle` / `renderDescription`
+ * render-props so the drawer can mount the Radix `<SheetTitle>` /
+ * `<SheetDescription>` (required for the dialog's accessible name) while
+ * the page mounts a plain `<h1>` / `<p>`.
+ */
+export interface CoachConversationProps {
+  /**
+   * Pre-fill for the composer (suggested-prompt chip click). Resets the
+   * composer on change via `useResettableValue`; the user can still type
+   * freely between prop changes.
+   */
+  prefill?: string | null;
+  /**
+   * Renders the conversation title. The surface passes the resolved
+   * title string; the drawer wraps it in `<SheetTitle>`, the page in an
+   * `<h1>`. Falls back to a plain element when omitted.
+   */
+  renderTitle?: (title: string) => React.ReactNode;
+  /** Renders the tagline line beneath the title (see `renderTitle`). */
+  renderDescription?: (tagline: string) => React.ReactNode;
+  /**
+   * Chrome-specific header action(s) — the maximize control (drawer) or
+   * the minimize control (page) — mounted before the avatar so the
+   * surface-toggle sits at the leading edge of the header.
+   */
+  leadingHeaderActions?: React.ReactNode;
+  /**
+   * Chrome-specific trailing control — the drawer's close button. The
+   * page leaves this empty (it has no close affordance of its own).
+   */
+  trailingHeaderActions?: React.ReactNode;
+  /**
+   * Focus the composer on mount. The drawer sets this so the composer
+   * takes focus when the sheet opens; the page sets it so a keyboard
+   * user lands in the composer after the route change.
+   */
+  autoFocusComposer?: boolean;
+  /**
+   * Hands the chrome an imperative reset (abort any in-flight SSE +
+   * clear the thread + composer). The drawer wires this to its close
+   * handler so closing the overlay does not leave a stream running. The
+   * page omits it — navigating away unmounts the whole subtree, which
+   * tears the stream down on its own.
+   */
+  registerReset?: (reset: () => void) => void;
+  /** className passthrough for the outer flex column. */
+  className?: string;
+  /** data-variant on the root, surfaced for e2e + styling hooks. */
+  surface: "drawer" | "page";
+}
+
+export function CoachConversation({
+  prefill,
+  renderTitle,
+  renderDescription,
+  leadingHeaderActions,
+  trailingHeaderActions,
+  autoFocusComposer,
+  registerReset,
+  className,
+  surface,
+}: CoachConversationProps) {
+  const { t } = useTranslations();
+
+  const [currentConversationId, setCurrentConversationId] = useState<
+    string | null
+  >(null);
+  const [historyTrayOpen, setHistoryTrayOpen] = useState(false);
+  const [sourcesTrayOpen, setSourcesTrayOpen] = useState(false);
+  const [settingsOpen, setSettingsOpen] = useState(false);
+  const [inputValue, setInputValue] = useResettableValue(prefill ?? "");
+
+  const { data: conversation } = useCoachConversation(currentConversationId);
+  const send = useSendCoachMessage({
+    onDone: (resolvedId) => {
+      setCurrentConversationId(resolvedId);
+    },
+  });
+
+  // Hand the chrome an imperative reset so the drawer can abort the
+  // in-flight SSE stream + clear the thread on close. Re-registered when
+  // the closed-over state setters / send hook change identity so the
+  // callback never captures a stale conversation id.
+  useEffect(() => {
+    if (!registerReset) return;
+    registerReset(() => {
+      send.cancel();
+      setCurrentConversationId(null);
+      setInputValue("");
+    });
+  }, [registerReset, send, setInputValue]);
+
+  async function handleSubmit(value: string) {
+    const trimmed = value.trim();
+    if (!trimmed || send.isStreaming) return;
+    setInputValue("");
+    await send.send({
+      conversationId: currentConversationId ?? undefined,
+      message: trimmed,
+    });
+  }
+
+  function handleNewChat() {
+    setCurrentConversationId(null);
+    setInputValue("");
+    send.reset();
+  }
+
+  const title = conversation?.title ?? t("insights.coach.newChat");
+  const tagline = t("insights.coach.tagline");
+
+  return (
+    <div
+      data-slot="coach-conversation"
+      data-variant={surface}
+      className={cn("flex min-h-0 flex-1 flex-col", className)}
+    >
+      <header
+        data-slot="coach-conversation-header"
+        className="border-border/70 flex flex-row items-center gap-2 border-b p-3 sm:gap-3 sm:p-4"
+      >
+        {leadingHeaderActions}
+        <div
+          aria-hidden="true"
+          className="from-dracula-purple to-dracula-pink flex size-8 shrink-0 items-center justify-center rounded-full bg-gradient-to-br"
+        >
+          <Sparkles className="text-background size-4" />
+        </div>
+        <div className="min-w-0 flex-1">
+          {renderTitle ? (
+            renderTitle(title)
+          ) : (
+            <p className="min-w-0 truncate text-sm font-semibold">{title}</p>
+          )}
+          {renderDescription ? (
+            renderDescription(tagline)
+          ) : (
+            <p className="text-muted-foreground truncate text-[11px]">
+              {tagline}
+            </p>
+          )}
+        </div>
+        <Button
+          type="button"
+          variant="ghost"
+          size="icon"
+          onClick={handleNewChat}
+          data-slot="coach-new-chat"
+          aria-label={t("insights.coach.newChat")}
+          title={t("insights.coach.newChat")}
+          className="text-muted-foreground hover:text-foreground size-11 shrink-0"
+        >
+          <Plus className="size-4" aria-hidden="true" />
+        </Button>
+        <Button
+          type="button"
+          variant="ghost"
+          size="icon"
+          onClick={() => setSettingsOpen(true)}
+          data-slot="coach-settings"
+          aria-label={t("insights.coach.settingsAriaLabel")}
+          title={t("insights.coach.settingsAriaLabel")}
+          className="text-muted-foreground hover:text-foreground size-11 shrink-0"
+        >
+          <Settings className="size-4" aria-hidden="true" />
+        </Button>
+        {trailingHeaderActions}
+      </header>
+
+      <CoachDrawerBody
+        sourcesRail={<SourcesRail />}
+        thread={
+          <MessageThread
+            conversation={conversation ?? null}
+            streaming={send.streaming}
+            optimisticUser={send.optimisticUser}
+          />
+        }
+        disclaimer={
+          <p
+            data-slot="coach-composer-disclaimer"
+            className="text-muted-foreground text-xs leading-relaxed"
+          >
+            {t("insights.coach.composerDisclaimer")}
+          </p>
+        }
+        composer={
+          <CoachInput
+            value={inputValue}
+            onChange={setInputValue}
+            onSubmit={() => handleSubmit(inputValue)}
+            onCancel={send.cancel}
+            disabled={send.isStreaming}
+            isStreaming={send.isStreaming}
+            autoFocusOnOpen={autoFocusComposer}
+          />
+        }
+        onOpenHistoryTray={() => setHistoryTrayOpen(true)}
+        onOpenSourcesTray={() => setSourcesTrayOpen(true)}
+      />
+
+      <CoachSettingsSheet open={settingsOpen} onOpenChange={setSettingsOpen} />
+      <MobileRailTray
+        historyOpen={historyTrayOpen}
+        onHistoryOpenChange={setHistoryTrayOpen}
+        historyRail={
+          <HistoryRail
+            activeId={currentConversationId}
+            onSelect={(id) => {
+              setCurrentConversationId(id);
+              setHistoryTrayOpen(false);
+            }}
+          />
+        }
+        sourcesOpen={sourcesTrayOpen}
+        onSourcesOpenChange={setSourcesTrayOpen}
+        sourcesRail={<SourcesRail />}
+      />
+    </div>
+  );
+}

src/components/insights/coach-panel/coach-drawer.tsx

@@ -1,8 +1,8 @@
 "use client";
 
-import { useCallback, useState } from "react";
-import type { Dispatch, SetStateAction } from "react";
-import { Plus, Settings, Sparkles, X } from "lucide-react";
+import { useCallback, useRef } from "react";
+import { useRouter } from "next/navigation";
+import { Maximize2, X } from "lucide-react";
 
 import { Button } from "@/components/ui/button";
 import {
@@ -10,117 +10,48 @@ import {
   SheetClose,
   SheetContent,
   SheetDescription,
-  SheetHeader,
   SheetTitle,
 } from "@/components/ui/sheet";
 import { cn } from "@/lib/utils";
 import { useTranslations } from "@/lib/i18n/context";
 import { useIsMobile } from "@/hooks/use-is-mobile";
 
-import { CoachDrawerBody } from "./coach-drawer-body";
-import { CoachInput } from "./coach-input";
-import { CoachSettingsSheet } from "./coach-settings-sheet";
-import { HistoryRail } from "./history-rail";
-import { MessageThread } from "./message-thread";
-import { MobileRailTray } from "./mobile-rail-tray";
-import { SourcesRail } from "./sources-rail";
-import { useCoachConversation, useSendCoachMessage } from "./use-coach";
+import { CoachConversation } from "./coach-conversation";
+
+// v1.12.0 — `useResettableValue` + `nextResettableValue` moved into
+// `./use-resettable-value` so the shared `<CoachConversation>` surface
+// can seed its composer without importing the drawer shell. Re-exported
+// here for the existing prefill-controller unit test import path.
+export {
+  useResettableValue,
+  nextResettableValue,
+} from "./use-resettable-value";
 
 /**
  * v1.4.20 phase B2b — AI Coach drawer (right-side `<Sheet>` overlay).
  *
  * Mounts above `/insights` so the user keeps the dashboard context
- * behind it. Single-column on `<lg`; on desktop the history rail and
- * sources rail mount alongside the message thread (delivered in
- * commit 3, this file lays out the slots).
- *
- * The drawer is fully-controlled by the parent (`open` /
+ * behind it. The drawer is fully-controlled by the parent (`open` /
  * `onOpenChange`). The `prefill` prop lets the hero strip's
  * suggested-prompt chips pre-populate the input on open.
  *
- * History rail + sources rail import-load asynchronously to keep the
- * drawer's first-paint cheap. Until commit 3 lands, those slots
- * render as visual placeholders that match the column widths.
+ * v1.12.0 (Coach v2 #6) — the chat surface itself (header actions,
+ * body, thread, composer, rails, settings, mobile trays) is now the
+ * shared `<CoachConversation>` component, reused verbatim by the
+ * full-page Coach route (`/insights/coach`). This file is the drawer
+ * CHROME only: the `<Sheet>` wrapper, the close button, and the
+ * maximize control that hands the conversation off to the full page.
  */
 export interface CoachDrawerProps {
   open: boolean;
   onOpenChange: (next: boolean) => void;
   /** Optional pre-fill for the input box (suggested-prompt chip click). */
   prefill?: string | null;
-  /**
-   * Optional rail slots — passed by the parent so commit-3 can mount
-   * the history + sources rails without coupling them to the drawer
-   * shell. Falls through to a no-op when omitted.
-   */
-  historyRail?: React.ReactNode;
-  sourcesRail?: React.ReactNode;
-  /**
-   * Composer slot — the parent wires `<CoachInput>` here in commit 3
-   * so this shell stays presentational. The shell renders its own
-   * minimal input fallback when no slot is supplied (used during the
-   * commit-2 boundary to keep the drawer functional in isolation).
-   */
-  composer?: React.ReactNode;
 }
 
-/**
- * v1.4.23 H3 — local state seeded from a controlled prop, reset on
- * prop change. Same render-phase pattern React's docs recommend in
- * place of `useEffect(() => setState(prop), [prop])` (which the
- * `react-hooks/set-state-in-effect` ESLint rule banned). The reset
- * runs during render: React detects the queued setState, restarts
- * the render with the new value, and commits a single coherent
- * snapshot — no double paint, no flash of stale state.
- *
- * Exported so the drawer's prefill-reset behaviour can be unit-
- * tested in isolation without standing up the whole Sheet portal.
- */
-export function useResettableValue<T>(
-  controlledValue: T,
-): [T, Dispatch<SetStateAction<T>>] {
-  const [value, setValue] = useState<T>(controlledValue);
-  // Mirror the last observed controlled value via a sibling useState
-  // pair (per React docs:
-  // https://react.dev/learn/you-might-not-need-an-effect#adjusting-some-state-when-a-prop-changes).
-  // useRef is the wrong tool here — ESLint rejects ref read+write
-  // during render, and useState already gives us identity tracking
-  // with no extra cost.
-  const [lastSeen, setLastSeen] = useState<T>(controlledValue);
-  if (!Object.is(controlledValue, lastSeen)) {
-    setLastSeen(controlledValue);
-    setValue(controlledValue);
-  }
-  return [value, setValue];
-}
-
-/**
- * v1.4.23 H3 — pure decision function behind `useResettableValue`.
- * Given the previous controlled value the hook recorded and the
- * incoming controlled value, returns either `{ reset: true, value }`
- * (the next render must seed local state with `value`) or
- * `{ reset: false }` (local state survives — the user's edits are
- * preserved). Pure + dependency-free so it tests cleanly without a
- * React renderer — pin the contract here and trust the hook
- * implementation to wire the same comparison.
- */
-export function nextResettableValue<T>(
-  previous: T,
-  incoming: T,
-): { reset: true; value: T } | { reset: false } {
-  return Object.is(previous, incoming)
-    ? { reset: false }
-    : { reset: true, value: incoming };
-}
-
-export function CoachDrawer({
-  open,
-  onOpenChange,
-  prefill,
-  historyRail,
-  sourcesRail,
-  composer,
-}: CoachDrawerProps) {
+export function CoachDrawer({ open, onOpenChange, prefill }: CoachDrawerProps) {
   const { t } = useTranslations();
+  const router = useRouter();
   // v1.4.27 R3d MB1 — below the `sm` breakpoint (640 px) the Coach
   // drawer slides up from the bottom edge of the viewport instead of
   // sliding in from the right. Right-side slide makes the back-arrow
@@ -129,86 +60,33 @@ export function CoachDrawer({
   // its existing right-side slide and `sm:max-w-[720px]` cap.
   const isPhoneViewport = useIsMobile("sm");
 
-  const [currentConversationId, setCurrentConversationId] = useState<
-    string | null
-  >(null);
-  // v1.4.20 phase B4 — mobile rail trays. The history + sources rails
-  // are hidden on `<lg` from B2b; the chevron buttons below toggle them
-  // as side-sheets so the user can browse conversations + see what
-  // data the Coach is using without losing the message thread context.
-  const [historyTrayOpen, setHistoryTrayOpen] = useState(false);
-  const [sourcesTrayOpen, setSourcesTrayOpen] = useState(false);
-  // v1.4.23 H4 — Coach prompt-tuning sheet. The v1.4.22 B5 audit had
-  // removed the placeholder cog from the drawer header; v1.4.23 H4
-  // returns it with a real surface backed by `/api/auth/me/coach-prefs`.
-  const [settingsOpen, setSettingsOpen] = useState(false);
-  // v1.4.23 H3 — `prefill` is now a fully-controlled prop. The
-  // v1.4.20 implementation used `key={prefill}` on the parent mount
-  // to force a fresh `useState()` initialiser run on every prefill
-  // transition (the "weaponise-React-keys" pattern senior-dev
-  // review flagged as Sr-HIGH-4). The replacement is a tiny
-  // `useResettableValue` hook below: tracks the last observed
-  // prefill in a ref and schedules a same-render state update when
-  // the prop changes — a textbook React render-phase update,
-  // ESLint-clean against `react-hooks/set-state-in-effect`. The
-  // user can still type freely; the drawer only resets the composer
-  // when the parent changes which suggested-prompt chip is active.
-  const [inputValue, setInputValue] = useResettableValue(prefill ?? "");
-
-  // v1.7.2 — the data-source scope is no longer ephemeral drawer state.
-  // Both the chat-side sources rail and the settings cog now drive the
-  // persisted `coachPrefsJson` row (clusters + default window) through
-  // `PUT /api/auth/me/coach-prefs`. The chat request carries no `scope`
-  // override at all, so the snapshot builder expands the saved clusters
-  // and folds the saved window server-side — "what the rail shows" and
-  // "what the model receives" cannot drift.
-
-  const { data: conversation } = useCoachConversation(currentConversationId);
-  const send = useSendCoachMessage({
-    onDone: (resolvedId) => {
-      setCurrentConversationId(resolvedId);
-    },
-  });
+  // The shared surface hands us an imperative reset so closing the
+  // drawer can abort an in-flight SSE stream + clear the thread.
+  const resetRef = useRef<(() => void) | null>(null);
+  const registerReset = useCallback((reset: () => void) => {
+    resetRef.current = reset;
+  }, []);
 
   const handleOpenChange = useCallback(
     (next: boolean) => {
       if (!next) {
-        // Abort any in-flight streamed reply so closing the drawer
-        // doesn't leave the SSE request running in the background.
-        send.cancel();
-        // Reset thread + composer on close so the next open starts on
-        // the rail's empty hint instead of re-rendering the previous
-        // conversation by accident.
-        setCurrentConversationId(null);
-        setInputValue("");
+        // Abort any in-flight streamed reply + reset the thread so the
+        // next open starts on the rail's empty hint.
+        resetRef.current?.();
       }
       onOpenChange(next);
     },
-    [onOpenChange, send, setInputValue],
+    [onOpenChange],
   );
 
-  async function handleSubmit(value: string) {
-    const trimmed = value.trim();
-    if (!trimmed || send.isStreaming) return;
-    setInputValue("");
-    // v1.7.2 — no `scope` override on the wire. The route resolves the
-    // source set and window from the user's persisted `coachPrefsJson`
-    // (the same row the sources rail + settings cog edit), so the chat
-    // request stays minimal and the prompt scope is guaranteed to match
-    // what the rail displays.
-    await send.send({
-      conversationId: currentConversationId ?? undefined,
-      message: trimmed,
-    });
-  }
-
-  function handleNewChat() {
-    setCurrentConversationId(null);
-    setInputValue("");
-    send.reset();
-  }
-
-  const drawerTitle = conversation?.title ?? t("insights.coach.newChat");
+  const handleMaximize = useCallback(() => {
+    // Hand the conversation off to the full-page surface. Close the
+    // drawer first (aborts any in-flight stream via `handleOpenChange`)
+    // then route to the dedicated page.
+    onOpenChange(false);
+    resetRef.current?.();
+    router.push("/insights/coach");
+  }, [onOpenChange, router]);
 
   return (
     <Sheet open={open} onOpenChange={handleOpenChange}>
@@ -218,189 +96,74 @@ export function CoachDrawer({
         // above `sm` it keeps its existing right-side slide.
         side={isPhoneViewport ? "bottom" : "right"}
         // v1.4.25 W5 — render our own Close button inside the header so
-        // X / cog / new-chat sit on the same baseline with identical
-        // size, color, and hit target. The Sheet's default close-X is
-        // absolutely positioned with `opacity-70` + tiny `rounded-xs`,
-        // which Marc flagged as misaligned with the rest of the header
-        // cluster.
+        // X / maximize sit on the same baseline with identical size,
+        // color, and hit target.
         showCloseButton={false}
         data-slot="coach-drawer"
         data-variant={isPhoneViewport ? "bottom-sheet" : "side-sheet"}
         className={cn(
-          // Drawer keeps the dashboard context behind it. On laptops
-          // (1280-1366px viewports) the previous lg:max-w-[1080px] cap
-          // left only ~200-286px of underlying /insights visible — a
-          // takeover, not a sheet. Drop the lg cap to min(960px,75vw)
-          // so /insights always retains a readable column; restore
-          // the wider three-column layout at xl+ (≥1280px sources rail
-          // is hidden below xl by the body's lg:hidden chevron rules).
+          // Drawer keeps the dashboard context behind it. Drop the lg
+          // cap to min(960px,75vw) so /insights always retains a
+          // readable column; restore the wider layout at xl+.
           "w-full p-0 sm:max-w-[720px]",
           "lg:!max-w-[min(960px,75vw)] xl:!max-w-[1080px]",
           isPhoneViewport
-            ? // Bottom-sheet caps at 90 dvh so a 10 % slice of the
-              // underlying /insights page stays visible — same
-              // convention as every other mobile sheet on the app via
-              // <ResponsiveSheet>'s phone branch (v1.4.28 R3c BK-M5
-              // alignment; previously 95 dvh, which left only a 5 %
-              // sliver and read as a takeover instead of a sheet).
-              // Rounded top corners match the iOS bottom-sheet feel.
-              "flex h-[90dvh] max-h-[90dvh] flex-col gap-0 rounded-t-2xl"
+            ? "flex h-[90dvh] max-h-[90dvh] flex-col gap-0 rounded-t-2xl"
             : "flex h-[100dvh] flex-col gap-0",
         )}
       >
-        {/* Header (full width). Avatar + title + new-chat button +
-            settings cog + close X. v1.4.25 W5 — the three header
-            actions (new chat, settings, close) all use the same
-            `ghost / size-icon / size-9` shape so they share a single
-            visual cluster instead of feeling like three different
-            controls. The close X used to be the Sheet's absolutely
-            positioned default; bringing it inline normalises the row
-            and frees the `pr-*` reservation. */}
-        <SheetHeader
-          data-slot="coach-drawer-header"
-          className="border-border/70 flex-row items-center gap-2 border-b p-3 sm:gap-3 sm:p-4"
-        >
-          <div
-            aria-hidden="true"
-            className="from-dracula-purple to-dracula-pink flex size-8 shrink-0 items-center justify-center rounded-full bg-gradient-to-br"
-          >
-            <Sparkles className="text-background size-4" />
-          </div>
-          <div className="min-w-0 flex-1">
-            {/* v1.4.27 R3d MB4 / CF-73 — pin `min-w-0` on the title
-                node itself in addition to the wrapper so the
-                truncate clipping survives any flex-shrink quirk
-                with very long conversation titles. */}
+        <CoachConversation
+          surface="drawer"
+          prefill={prefill}
+          autoFocusComposer
+          registerReset={registerReset}
+          // Radix requires an accessible name + description on the
+          // dialog content. Mount them through the title/description
+          // render-props so the page can swap in a plain heading.
+          renderTitle={(title) => (
             <SheetTitle className="min-w-0 truncate text-sm font-semibold">
-              {drawerTitle}
+              {title}
             </SheetTitle>
+          )}
+          renderDescription={(tagline) => (
             <SheetDescription className="text-muted-foreground truncate text-[11px]">
-              {t("insights.coach.tagline")}
+              {tagline}
             </SheetDescription>
-          </div>
-          {/* v1.7.2 — the per-conversation window override pill was
-              retired. The analysis window now persists alongside the
-              data-source clusters via the sources rail (and the
-              settings cog), so a single, sticky window control replaces
-              the ephemeral header override. */}
-          {/* v1.4.25 W5 — header action cluster. All three buttons
-              share the same `ghost / size-icon / size-9` shape so they
-              visually belong together. 36×36 px hit target meets the
-              WCAG 2.1 AA touch-target minimum on mobile; the icons
-              themselves stay 18 px to match the avatar's optical
-              weight. */}
-          <Button
-            type="button"
-            variant="ghost"
-            size="icon"
-            onClick={handleNewChat}
-            data-slot="coach-drawer-new-chat"
-            aria-label={t("insights.coach.newChat")}
-            title={t("insights.coach.newChat")}
-            className="text-muted-foreground hover:text-foreground size-11 shrink-0"
-          >
-            <Plus className="size-4" aria-hidden="true" />
-          </Button>
-          <Button
-            type="button"
-            variant="ghost"
-            size="icon"
-            onClick={() => setSettingsOpen(true)}
-            data-slot="coach-drawer-settings"
-            aria-label={t("insights.coach.settingsAriaLabel")}
-            title={t("insights.coach.settingsAriaLabel")}
-            className="text-muted-foreground hover:text-foreground size-11 shrink-0"
-          >
-            <Settings className="size-4" aria-hidden="true" />
-          </Button>
-          <SheetClose asChild>
+          )}
+          // Maximize control at the leading edge — hands the
+          // conversation off to the full-page Coach route.
+          leadingHeaderActions={
             <Button
               type="button"
               variant="ghost"
               size="icon"
-              data-slot="coach-drawer-close"
-              aria-label={t("common.close")}
-              title={t("common.close")}
+              onClick={handleMaximize}
+              data-slot="coach-drawer-maximize"
+              aria-label={t("insights.coach.maximizeAriaLabel")}
+              title={t("insights.coach.maximizeAriaLabel")}
               className="text-muted-foreground hover:text-foreground size-11 shrink-0"
             >
-              <X className="size-4" aria-hidden="true" />
+              <Maximize2 className="size-4" aria-hidden="true" />
             </Button>
-          </SheetClose>
-        </SheetHeader>
-
-        {/* Body — three columns on lg+, single column on smaller.
-            The body slot is a separate component so the SSR test
-            harness can pin the mobile rail-tray triggers without
-            rendering the Sheet portal. */}
-        <CoachDrawerBody
-          sourcesRail={sourcesRail ?? <SourcesRail />}
-          thread={
-            <MessageThread
-              conversation={conversation ?? null}
-              streaming={send.streaming}
-              optimisticUser={send.optimisticUser}
-            />
           }
-          disclaimer={
-            <p
-              data-slot="coach-composer-disclaimer"
-              className="text-muted-foreground text-xs leading-relaxed"
-            >
-              {t("insights.coach.composerDisclaimer")}
-            </p>
+          // Close button — the drawer's own, replacing the Sheet's
+          // absolutely-positioned default so the action cluster shares
+          // one baseline.
+          trailingHeaderActions={
+            <SheetClose asChild>
+              <Button
+                type="button"
+                variant="ghost"
+                size="icon"
+                data-slot="coach-drawer-close"
+                aria-label={t("common.close")}
+                title={t("common.close")}
+                className="text-muted-foreground hover:text-foreground size-11 shrink-0"
+              >
+                <X className="size-4" aria-hidden="true" />
+              </Button>
+            </SheetClose>
           }
-          composer={
-            composer ?? (
-              <CoachInput
-                value={inputValue}
-                onChange={setInputValue}
-                onSubmit={() => handleSubmit(inputValue)}
-                onCancel={send.cancel}
-                disabled={send.isStreaming}
-                isStreaming={send.isStreaming}
-                // v1.4.27 MB3 / CF-30 — the composer mounts on drawer
-                // open and unmounts on close (the body collapses with
-                // the sheet), so a one-shot mount focus matches the
-                // "drawer just opened" semantic without any re-render
-                // gymnastics.
-                autoFocusOnOpen
-              />
-            )
-          }
-          onOpenHistoryTray={() => setHistoryTrayOpen(true)}
-          onOpenSourcesTray={() => setSourcesTrayOpen(true)}
-        />
-
-        {/* v1.4.23 H4 — Coach prompt-tuning sheet. Right-edge sheet so
-            it doesn't conflict with the existing rail trays (those are
-            <lg / <xl only; the settings sheet works on every
-            viewport). */}
-        <CoachSettingsSheet
-          open={settingsOpen}
-          onOpenChange={setSettingsOpen}
-        />
-        {/* v1.4.28 R3c (BK-F-M6) — mobile-only rail trays carved out of
-            the drawer shell. Each tray surfaces the same HistoryRail /
-            SourcesRail instance the desktop layout uses; the parent
-            still owns the open/closed state + the rail callbacks so
-            the carve-out is pure render. */}
-        <MobileRailTray
-          historyOpen={historyTrayOpen}
-          onHistoryOpenChange={setHistoryTrayOpen}
-          historyRail={
-            historyRail ?? (
-              <HistoryRail
-                activeId={currentConversationId}
-                onSelect={(id) => {
-                  setCurrentConversationId(id);
-                  setHistoryTrayOpen(false);
-                }}
-              />
-            )
-          }
-          sourcesOpen={sourcesTrayOpen}
-          onSourcesOpenChange={setSourcesTrayOpen}
-          sourcesRail={sourcesRail ?? <SourcesRail />}
         />
       </SheetContent>
     </Sheet>

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

@@ -0,0 +1,58 @@
+"use client";
+
+import { useState } from "react";
+import type { Dispatch, SetStateAction } from "react";
+
+/**
+ * v1.4.23 H3 — local state seeded from a controlled prop, reset on
+ * prop change. Same render-phase pattern React's docs recommend in
+ * place of `useEffect(() => setState(prop), [prop])` (which the
+ * `react-hooks/set-state-in-effect` ESLint rule banned). The reset
+ * runs during render: React detects the queued setState, restarts
+ * the render with the new value, and commits a single coherent
+ * snapshot — no double paint, no flash of stale state.
+ *
+ * v1.12.0 — lifted out of `coach-drawer.tsx` into its own module so the
+ * shared `<CoachConversation>` surface (drawer + full-page) can seed its
+ * composer from the same controlled-prefill contract without importing
+ * the drawer shell.
+ *
+ * Exported so the drawer's prefill-reset behaviour can be unit-tested in
+ * isolation without standing up the whole Sheet portal.
+ */
+export function useResettableValue<T>(
+  controlledValue: T,
+): [T, Dispatch<SetStateAction<T>>] {
+  const [value, setValue] = useState<T>(controlledValue);
+  // Mirror the last observed controlled value via a sibling useState
+  // pair (per React docs:
+  // https://react.dev/learn/you-might-not-need-an-effect#adjusting-some-state-when-a-prop-changes).
+  // useRef is the wrong tool here — ESLint rejects ref read+write
+  // during render, and useState already gives us identity tracking
+  // with no extra cost.
+  const [lastSeen, setLastSeen] = useState<T>(controlledValue);
+  if (!Object.is(controlledValue, lastSeen)) {
+    setLastSeen(controlledValue);
+    setValue(controlledValue);
+  }
+  return [value, setValue];
+}
+
+/**
+ * v1.4.23 H3 — pure decision function behind `useResettableValue`.
+ * Given the previous controlled value the hook recorded and the
+ * incoming controlled value, returns either `{ reset: true, value }`
+ * (the next render must seed local state with `value`) or
+ * `{ reset: false }` (local state survives — the user's edits are
+ * preserved). Pure + dependency-free so it tests cleanly without a
+ * React renderer — pin the contract here and trust the hook
+ * implementation to wire the same comparison.
+ */
+export function nextResettableValue<T>(
+  previous: T,
+  incoming: T,
+): { reset: true; value: T } | { reset: false } {
+  return Object.is(previous, incoming)
+    ? { reset: false }
+    : { reset: true, value: incoming };
+}

src/lib/feature-flags/__tests__/coach-cascade.test.tsx

@@ -283,6 +283,9 @@ describe("Coach disable cascade invariant", () => {
     "src/components/insights/layout-coach-fab.tsx",
     "src/components/insights/layout-coach-mount.tsx",
     "src/components/insights/suggested-prompts.tsx",
+    // v1.12.0 — the full-page Coach route gates on `flags.coach` and
+    // redirects to `/insights` when the operator master flag is off.
+    "src/app/insights/coach/page.tsx",
   ];
 
   /**

src/lib/feature-flags/__tests__/coach-user-disable.test.tsx

@@ -280,6 +280,10 @@ describe("Coach per-user disableCoach invariant", () => {
     "src/components/insights/layout-coach-fab.tsx",
     "src/components/insights/layout-coach-mount.tsx",
     "src/components/insights/suggested-prompts.tsx",
+    // v1.12.0 — the full-page Coach route mirrors the launch-button /
+    // FAB gate: operator master flag OR per-user opt-out redirects the
+    // page back to `/insights` instead of painting a dead chat shell.
+    "src/app/insights/coach/page.tsx",
     // The hook itself + its `useAuth`-backed reader.
     "src/hooks/use-disable-coach.ts",
     // Cross-cut gates owned by sibling invariants / route tests.