初始提交：terminalX 可运行态（M0/M1/M1.5 已真机验证）

- M0: libghostty SSH 终端（渲染/输入/连接）+ 白屏修复(OutputGate) + 会话状态机/自动重连
- M1: tsnet 用户态组网 + SSH-over-tsnet(fd 桥)，shell 级真机验证；R5(Go+gvisor+C+++Swift 同进程) retire
- M1.5: tmux -CC 原生 tab（MVP）
- 结构: packages/(TXCore·TXTransport), apps/TerminalX, vendor/(libghostty-spm/libssh2/mbedtls/tsnet-bridge), artifacts/
- 文档: CLAUDE.md + docs/HANDOFF.md（新会话入口）
- 环境: 认证代理→依赖 vendor 本地化；Go 在 ~/.local/go；仅模拟器/未签名
- 待续: M2 mosh, tmux 多 pane, M4 安全(host key/SE)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

vendor/libghostty-spm/Tests/GhosttyKitTest/InMemoryTerminalSessionViewportTests.swift

@@ -0,0 +1,25 @@
+@testable import GhosttyTerminal
+import Testing
+
+@MainActor
+struct InMemoryTerminalSessionViewportTests {
+    /// `readViewportText()` MUST return `nil` (not crash) when no surface is
+    /// attached. This is the canonical pre-surface / post-surface-teardown
+    /// state — consumers may call `readViewportText` from any thread that
+    /// holds a reference, and the contract is "nil means no surface."
+    @Test
+    func `read viewport text returns nil before surface attached`() {
+        let session = InMemoryTerminalSession(write: { _ in }, resize: { _ in })
+        #expect(session.readViewportText() == nil)
+    }
+
+    /// After clearing the surface, the read MUST go back to returning `nil`.
+    /// Together with the test above this pins the surface-presence semantics
+    /// of the public API.
+    @Test
+    func `read viewport text returns nil after surface cleared`() {
+        let session = InMemoryTerminalSession(write: { _ in }, resize: { _ in })
+        session.clearSurface(ifMatches: nil)
+        #expect(session.readViewportText() == nil)
+    }
+}