feat(07-01): grow TelegramWebAppLike with 8.0-optional fullscreen members + capability wrapper

- TelegramWebAppLike gains requestFullscreen/exitFullscreen/isFullscreen/lockOrientation/unlockOrientation as OPTIONAL members only (no existing member reshaped)
- new web/src/telegram/fullscreen.ts: requestGuidanceFullscreen/exitGuidanceFullscreen/watchFullscreenEvents behind the BOTH-halves guard (method presence AND isVersionAtLeast("8.0"))
- every platform call in try/catch — a refused request is a supported degradation, never an error surface (T-07-06)
- no DOM Fullscreen API, no generic orientation lock, zero logging (T-07-10, T-07-09)

web/src/telegram/fullscreen.ts

@@ -0,0 +1,101 @@
+/*
+ * fullscreen.ts — PX-04 (D-03): the Telegram-native fullscreen capability
+ * layer, guarded by BOTH halves of the Bot API 8.0 capability check.
+ * -----------------------------------------------------------------------------
+ * The affordance is `Telegram.WebApp.requestFullscreen()` / `exitFullscreen()`
+ * ONLY — Bot API 8.0+ methods on the narrow `TelegramWebAppLike` contract
+ * (the same phase-scoped law as homescreen.ts: guard on the optional member,
+ * a total-function handler, no new UI furniture).
+ *
+ * The capability guard is BOTH halves: the method may be absent on older
+ * clients, AND the platform documents the API as Bot API 8.0+ — a no-op on
+ * an unsupported client either way (the homescreen.ts precedent).
+ *
+ * A refused request is a SUPPORTED DEGRADATION, never an error surface: every
+ * platform call rides inside a try/catch, and the boolean returns are
+ * best-effort signals the caller deliberately ignores. The orientation lock
+ * locks the CURRENT orientation only — never force landscape — and the DOM
+ * Fullscreen API plus the generic screen-level orientation lock are
+ * hard-banned: the Telegram-native path is the
+ * only primary path (T-07-10, pinned by the FS9 source-scan ban).
+ *
+ * D-14 category-only law: this path logs NOTHING — no coordinates, no user
+ * ids, no route payloads. A `fullscreenFailed` is a category event.
+ */
+import type { TelegramWebAppLike } from "./webapp.ts";
+
+/**
+ * Best-effort request for the Mini App's native fullscreen at the
+ * guidance-start edge. Returns true only when the platform call did not
+ * throw; false is the honest fallback on null WebApp, absent method, an
+ * old client, or a refusal — never an error surface.
+ */
+export function requestGuidanceFullscreen(wa: TelegramWebAppLike | null): boolean {
+  if (wa === null) return false;
+  if (typeof wa.requestFullscreen !== "function") return false;
+  if (typeof wa.isVersionAtLeast !== "function" || !wa.isVersionAtLeast("8.0")) return false;
+  try {
+    wa.requestFullscreen();
+    try {
+      // Telegram's lock pins the CURRENT orientation — never force landscape,
+      // and never the DOM's screen-level orientation lock (T-07-10).
+      wa.lockOrientation?.();
+    } catch {
+      /* best-effort: an orientation refusal is not a guidance failure */
+    }
+    return true;
+  } catch {
+    // the platform refused (FS4) — a supported degradation, never an error
+    return false;
+  }
+}
+
+/**
+ * The mirror of requestGuidanceFullscreen: releases fullscreen and the
+ * orientation lock at the trip-end / walk-back teardown edges, same
+ * both-halves guard, same try/catch law.
+ */
+export function exitGuidanceFullscreen(wa: TelegramWebAppLike | null): boolean {
+  if (wa === null) return false;
+  if (typeof wa.exitFullscreen !== "function") return false;
+  if (typeof wa.isVersionAtLeast !== "function" || !wa.isVersionAtLeast("8.0")) return false;
+  try {
+    wa.exitFullscreen?.();
+    try {
+      wa.unlockOrientation?.();
+    } catch {
+      /* best-effort: the lock release is not a guidance failure */
+    }
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * Register the fullscreen observability listeners (Bot API 8.0+ clients
+ * fire `fullscreenChanged` / `fullscreenFailed`). The onChange callback is
+ * wrapped in try/catch so a throwing client callback can never break the
+ * guidance pump; the events are observability, never correctness, and this
+ * path logs NOTHING (the D-14 category-only law, T-07-09).
+ */
+export function watchFullscreenEvents(
+  wa: TelegramWebAppLike | null,
+  onChange: (isFullscreen: boolean) => void,
+): void {
+  if (wa === null || typeof wa.onEvent !== "function") return;
+  wa.onEvent("fullscreenChanged", () => {
+    try {
+      onChange(true);
+    } catch {
+      /* a throwing observer must never break the guidance pump */
+    }
+  });
+  wa.onEvent("fullscreenFailed", () => {
+    try {
+      onChange(false);
+    } catch {
+      /* a throwing observer must never break the guidance pump */
+    }
+  });
+}

web/src/telegram/webapp.ts

@@ -23,8 +23,12 @@
  * `enableClosingConfirmation`/`disableClosingConfirmation` (6.2+) and
  * `isActive` (8.0+) — the contract stays the contract, no existing member
  * changes shape, every test fake and the harness mock satisfy exactly
- * these members. `@types/telegram-web-app` remains deliberately
+ * these members. Phase 7 (PX-04/D-03) adds the native-fullscreen members as
- * NOT a dependency.
+ * OPTIONAL only: requestFullscreen/exitFullscreen/isFullscreen/
+ * lockOrientation/unlockOrientation (8.0+) — the contract stays the contract,
+ * no existing member changes shape, every test fake and the harness mock
+ * satisfy exactly these members. `@types/telegram-web-app` remains
+ * deliberately NOT a dependency.
  */
 export type HomeScreenStatus =
   | "unsupported" // the feature is not supported here
@@ -71,6 +75,17 @@ export interface TelegramWebAppLike {
   enableClosingConfirmation?: () => void;
   /** Bot API 6.2+ — release the native close net (at trip end). */
   disableClosingConfirmation?: () => void;
+  /** Bot API 8.0+ — request the Mini App's native fullscreen. Optional:
+   *  absent on older clients; the 8.0 guard runs before every call. */
+  requestFullscreen?(): void;
+  /** Bot API 8.0+ — leave the Mini App's native fullscreen. Optional. */
+  exitFullscreen?(): void;
+  /** Bot API 8.0+ — whether the Mini App is currently fullscreen. Optional. */
+  isFullscreen?: boolean;
+  /** Bot API 8.0+ — lock the CURRENT orientation (never forces landscape). */
+  lockOrientation?(): void;
+  /** Bot API 8.0+ — release the orientation lock. */
+  unlockOrientation?: () => void;
   onEvent?(event: string, cb: () => void): void;
   offEvent?(event: string, cb: () => void): void;
   BackButton?: { show(): void; hide(): void; onClick(cb: () => void): void; offClick(cb: () => void): void };