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/WebTermTests/EventFanOutTests.swift

@@ -0,0 +1,79 @@
+import Testing
+@testable import WebTerm
+
+/// T-iOS-15 · Fan-out adapter tests. `SessionEngine.events` is a
+/// single-consumer `AsyncStream`, but TerminalViewModel, GateViewModel AND the
+/// session-activity bridge must all observe it — `EventFanOut` is the wiring
+/// layer's broadcast seam. These tests pin its contract: every branch receives
+/// every element, in order, and source termination / cancel() propagate.
+@Suite("EventFanOut")
+struct EventFanOutTests {
+    private static let branchCount = 3
+
+    @Test("每个分支都按序收到全部元素")
+    func allBranchesReceiveAllElementsInOrder() async {
+        // Arrange
+        let (source, continuation) = AsyncStream<Int>.makeStream()
+        let fanOut = EventFanOut(source: source, branchCount: Self.branchCount)
+
+        // Act
+        for value in 1...5 {
+            continuation.yield(value)
+        }
+        continuation.finish()
+
+        // Assert: unbounded buffering — late consumption still sees everything.
+        for branch in fanOut.branches {
+            var received: [Int] = []
+            for await value in branch {
+                received.append(value)
+            }
+            #expect(received == [1, 2, 3, 4, 5])
+        }
+    }
+
+    @Test("分支数量与请求一致")
+    func branchCountMatchesRequest() {
+        let (source, _) = AsyncStream<Int>.makeStream()
+        let fanOut = EventFanOut(source: source, branchCount: Self.branchCount)
+        #expect(fanOut.branches.count == Self.branchCount)
+    }
+
+    @Test("源结束 → 所有分支结束（消费循环退出，不悬挂）")
+    func sourceFinishFinishesEveryBranch() async {
+        // Arrange
+        let (source, continuation) = AsyncStream<String>.makeStream()
+        let fanOut = EventFanOut(source: source, branchCount: Self.branchCount)
+
+        // Act
+        continuation.yield("only")
+        continuation.finish()
+
+        // Assert: every branch loop terminates after draining.
+        for branch in fanOut.branches {
+            var count = 0
+            for await _ in branch {
+                count += 1
+            }
+            #expect(count == 1)
+        }
+    }
+
+    @Test("cancel() → 分支立即终止（teardown 不泄漏消费任务）")
+    func cancelTerminatesBranches() async {
+        // Arrange
+        let (source, continuation) = AsyncStream<Int>.makeStream()
+        let fanOut = EventFanOut(source: source, branchCount: Self.branchCount)
+
+        // Act: cancel without ever finishing the source.
+        fanOut.cancel()
+        continuation.yield(42) // post-cancel input must not hang consumers
+
+        // Assert: iteration completes (content is unspecified mid-flight —
+        // termination is the contract under test).
+        for branch in fanOut.branches {
+            for await _ in branch {}
+        }
+        #expect(Bool(true)) // reaching here = no hang
+    }
+}