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/chat/helpers.ts

@@ -0,0 +1,151 @@
+/**
+ * Zero-state helpers for the interactive chat channel: prompt-directory and
+ * Git-branch formatting, surface/tool-call derivations over the session log,
+ * session-reference context cards, the placeholder editor, and banner-reveal
+ * timing constants. None of these close over channel state.
+ * @module @deepseek-ai/dsh-tui/chat/helpers
+ */
+
+import { execFileSync } from 'node:child_process'
+import { homedir } from 'node:os'
+import { isAbsolute, relative, resolve, sep } from 'node:path'
+import {
+  CURSOR_MARKER,
+  Editor,
+  truncateToWidth,
+  visibleWidth,
+} from '@earendil-works/pi-tui'
+import type { Session, SessionEvent } from '@deepseek-ai/dsh-session'
+
+/** Editor that shows a placeholder without making it editable content. */
+export class HintEditor extends Editor {
+  /** Placeholder shown in the empty input row; `undefined` hides it. */
+  hint: string | undefined
+  /** Prompt text rendered before the placeholder, matching the live prompt width. */
+  hintPrefix = ''
+
+  override render(width: number): string[] {
+    const lines = super.render(width)
+    if (this.hint === undefined || this.getText() !== '') return lines
+    const content = lines[0]
+    /* v8 ignore next -- Editor always renders one content row. */
+    if (content === undefined) return lines
+    const padding = ' '.repeat(this.getPaddingX())
+    /* v8 ignore next -- the mounted editor is focused whenever its empty-input hint is rendered. */
+    const marker = this.focused ? CURSOR_MARKER : ''
+    const available = Math.max(0, width - visibleWidth(padding) - visibleWidth(this.hintPrefix))
+    const placeholder = truncateToWidth(this.hint, available, '')
+    const used = visibleWidth(padding) + visibleWidth(this.hintPrefix) + visibleWidth(placeholder)
+    lines[0] = `${padding}${this.hintPrefix}${marker}${placeholder}${' '.repeat(Math.max(0, width - used))}`
+    return lines
+  }
+}
+
+/**
+ * Format the session working directory as a prompt label: `~` for home,
+ * `~/rel` for a home-relative path, the raw path otherwise.
+ * @param cwd - operational working directory from the session header.
+ * @returns unescaped prompt label.
+ */
+export function formatCwd(cwd: string | undefined): string {
+  if (cwd === undefined) return 'cwd unset'
+  const home = homedir()
+  const rel = relative(resolve(home), resolve(cwd))
+  if (rel === '') return '~'
+  /* v8 ignore next -- Windows cross-drive coverage; POSIX relative() cannot return an absolute path. */
+  if (isAbsolute(rel)) return cwd
+  if (rel !== '..' && !rel.startsWith(`..${sep}`)) return `~${sep}${rel}`
+  return cwd
+}
+
+/**
+ * Resolve the current Git branch for the prompt context line.
+ * @param cwd - operational working directory to query.
+ * @returns branch name, or `undefined` outside a worktree or on any failure.
+ */
+export function gitBranch(cwd: string): string | undefined {
+  try {
+    const env = Object.fromEntries(
+      Object.entries(process.env).filter(([name]) => !/(?:KEY|SECRET|TOKEN)/iu.test(name)),
+    )
+    const branch = execFileSync('git', ['branch', '--show-current'], {
+      cwd,
+      encoding: 'utf8',
+      env,
+      stdio: ['ignore', 'pipe', 'ignore'],
+      timeout: 1_000,
+    }).trim()
+    /* v8 ignore next -- detached-HEAD behavior is exercised by the runtime smoke, not the unit checkout. */
+    return branch === '' ? undefined : branch
+  } catch (_gitUnavailableOrOutsideWorktree) {
+    return undefined
+  }
+}
+
+/**
+ * Sequence numbers currently visible on the session surface.
+ * @param session - session whose surface nodes to read.
+ * @returns the set of visible event sequence numbers.
+ */
+export function activeSurfaceSeqs(session: Session): Set<number> {
+  return new Set(session.surface.nodes)
+}
+
+/**
+ * Tool-call ids whose owning assistant message is on the active surface.
+ * @param session - session whose events to scan.
+ * @param active - sequence numbers currently on the surface.
+ * @returns the set of active tool-call ids.
+ */
+export function activeToolCallIds(session: Session, active: ReadonlySet<number>): Set<string> {
+  const ids = new Set<string>()
+  for (const event of session.events) {
+    if (event.type !== 'assistant/message' || !active.has(event.seq)) continue
+    for (const block of event.data.content) {
+      if (block.type === 'tool-call') ids.add(block.id)
+    }
+  }
+  return ids
+}
+
+/**
+ * Read a session-reference context card's display labels from event meta.
+ * @param meta - envelope-context meta to inspect.
+ * @returns per-reference labels, or `undefined` when meta is not a reference card.
+ */
+export function sessionReferenceCard(meta: unknown): string[] | undefined {
+  if (typeof meta !== 'object' || meta === null) return undefined
+  const record = meta as Record<string, unknown>
+  if (record['kind'] !== 'session-reference' || !Array.isArray(record['references'])) return undefined
+  const references = record['references'] as unknown[]
+  const labels: string[] = []
+  for (const reference of references) {
+    if (typeof reference !== 'object' || reference === null) return undefined
+    const entry = reference as Record<string, unknown>
+    const sessionId = entry['sessionId']
+    const label = entry['label']
+    if (typeof sessionId !== 'string' || typeof label !== 'string') return undefined
+    labels.push(label === sessionId ? sessionId : `${label} (${sessionId})`)
+  }
+  return labels
+}
+
+/**
+ * Session-reference cards attached to a prompt or steering message envelope.
+ * @param event - the user or steering message event to read.
+ * @returns per-envelope-context reference-label lists, empty when none.
+ */
+export function promptReferenceCards(
+  event: Extract<SessionEvent, { type: 'user/message' | 'steering/message' }>,
+): string[][] {
+  return event.data.envelope?.prefixContexts.flatMap((context) => {
+    const card = sessionReferenceCard(context.meta)
+    return card === undefined ? [] : [card]
+  }) ?? []
+}
+
+/** Milliseconds between banner sweep-reveal frames (~60 fps). */
+export const BANNER_REVEAL_INTERVAL_MS = 15
+
+/** Number of sweep frames the banner reveal spreads the terminal width over. */
+export const BANNER_REVEAL_STEPS = 24