refactor(tui): split createTuiChat into chat/ sub-controllers

Extract model-command, questions, and resume sub-machines from the
~1600-line createTuiChat closure into src/chat/ factories that take
explicit dependency bundles (shared ChatChannelDeps/ChannelNotice).
Reorganize src/ so chat/ holds all chat-channel concerns (former input
and session/ files move under it); xml-tool-output moves to components/;
TuiRuntime/TuiResumeHost move to runtime.ts. index.ts drops 2067->~1530
lines. Behavior identical: 167 tests and all TUI snapshots pass unchanged.

packages/ui/tui/src/runtime.ts

@@ -0,0 +1,45 @@
+/**
+ * Host and process boundary the interactive TUI runs against: the resume-handoff
+ * host and the {@link TuiRuntime} the shipped CLI supplies (terminal, process
+ * exit, clock, and optional prompt/git overrides). These are plain interfaces so
+ * tests can drive the channel with a fake terminal.
+ * @module @deepseek-ai/dsh-tui/runtime
+ */
+
+import type { Terminal } from '@earendil-works/pi-tui'
+import type { SessionId } from '@deepseek-ai/dsh-session'
+
+/** Process-lifecycle owner used by the shipped CLI for an atomic resume handoff. */
+export interface TuiResumeHost {
+  /**
+   * Dispose the current app and replace it with a runtime for `sessionId`.
+   * Success does not return. A host may reject before it commits teardown;
+   * after commit it owns fatal reporting and process exit.
+   * @param sessionId - validated persisted session selected by the user.
+   */
+  handoff(sessionId: SessionId): Promise<never>
+}
+
+/** Runtime boundary used by the interactive TUI. */
+export interface TuiRuntime {
+  /** Terminal implementation; production uses pi-tui's `ProcessTerminal`. */
+  terminal: Terminal
+  /** Exit hook used by terminal shutdown or a target-agent startup failure. */
+  exit(code: number): void
+  /**
+   * Override the prompt's logical working-directory label without changing the session directory used by tools.
+   * @param cwd - Operational working directory from the session header.
+   * @returns Unescaped label; the TUI makes terminal controls visible.
+   */
+  formatCwd?: (cwd: string | undefined) => string
+  /**
+   * Override the Git branch shown in the prompt context line; production resolves it once at mount.
+   * @param cwd - Operational working directory from the session header.
+   * @returns Unescaped branch name, or `undefined` outside a Git worktree.
+   */
+  gitBranch?: (cwd: string) => string | undefined
+  /** Monotonic-enough wall clock for elapsed status rendering. Defaults to `Date.now`. */
+  now?(): number
+  /** Host-owned process handoff; absent leaves `resumeCommand` as the fallback. */
+  handoffResume?: TuiResumeHost['handoff']
+}