feat(ios): W4 app wiring — DI graph, event fan-out, lifecycle, privacy shade

T-iOS-15: AppEnvironment production DI (real Keychain/probe/transports), EventFanOut
(engine.events → TerminalVM + GateVM + activity bridge), scenePhase lifecycle
(.background→close, suspend→rebuild+reopen reclaims size), privacy shade on != .active,
spike screen deleted, cold-start routing
Walkthrough proxies: hosted live-server smoke over the production DI graph (probe→store→
attach→echo→close) + real-Keychain kSecAttrAccessible assertion (closes T-iOS-7 deferral)
Deviation closed: TerminalViewModel.lastSentDims (valid-only) + alive-engine .active →
notifyForegrounded(dims:) (orchestrator fix on behalf of T-iOS-11 owner)
Env finding: repo under ~/Documents → TCC blocks sim-spawned node; SimServerHarness dual-mode
(self-bootstrap / WEBTERM_SERVER_URL via simctl launchctl setenv)
Verified: 214 pkg + 76 app + 10 integration tests green; verify agent 8/8 PASS

ios/App/WebTerm/Wiring/AppEnvironment.swift

@@ -0,0 +1,56 @@
+import APIClient
+import Foundation
+import HostRegistry
+import SessionCore
+import WireProtocol
+
+/// T-iOS-15 · Production dependency graph (composition root). One immutable
+/// value assembled at launch; every screen/VM receives its dependencies from
+/// here — no ad-hoc URLSession/keychain access anywhere else in the App layer.
+///
+/// Assembly security audit (task 安全注, verified at this single point):
+/// - All `G` (state-changing) HTTP goes through `APIClient` (kill via
+///   SessionListViewModel's client, probe's kill round-trip inside
+///   `runPairingProbe`); `URLSessionHTTPTransport` adds no headers of its own.
+/// - Origin is derived solely by `HostEndpoint` (WS: URLSessionTermTransport;
+///   HTTP: APIClient's route builder) — nothing here hand-assembles one.
+/// - Secrets: hosts in `KeychainHostStore`
+///   (AfterFirstUnlockThisDeviceOnly, hosted keychain test asserts it);
+///   UserDefaults carries only the non-secret per-host lastSessionId.
+/// - No debug ATS overrides exist (project.yml declares NO
+///   NSAllowsArbitraryLoads in any configuration — only the five §5.2 CIDR
+///   exceptions), and no isSecureTextEntry-style screenshot hacks are used;
+///   `UIScreen.isCaptured` detection is SKIPPED per plan (accepted residual
+///   risk, local trust model).
+struct AppEnvironment: Sendable {
+    let hostStore: any HostStore
+    let lastSessionStore: any LastSessionStore
+    let http: any HTTPTransport
+    let termTransport: any TermTransport
+    /// Injected into `PairingViewModel` — production is `runPairingProbe`
+    /// over the real transports (two-step: RO GET, then WS attach + guarded
+    /// kill; only runs after the user's explicit confirm, T-iOS-12).
+    let probe: PairingViewModel.Probe
+
+    static func production() -> AppEnvironment {
+        let http = URLSessionHTTPTransport()
+        let termTransport = URLSessionTermTransport()
+        return AppEnvironment(
+            hostStore: KeychainHostStore(),
+            lastSessionStore: UserDefaultsLastSessionStore(),
+            http: http,
+            termTransport: termTransport,
+            probe: { endpoint in
+                await runPairingProbe(endpoint: endpoint, http: http, ws: termTransport)
+            }
+        )
+    }
+
+    /// Away-digest source for a session engine: wraps `APIClient.events` per
+    /// host (the engine never holds an HTTP client — plan §3.2).
+    func makeEventsSource(endpoint: HostEndpoint)
+        -> @Sendable (UUID) async throws -> [TimelineEvent] {
+        let client = APIClient(endpoint: endpoint, http: http)
+        return { id in try await client.events(id: id) }
+    }
+}