feat(i18n): briefing generator and pair-scoped pairing gate

gen-translation-brief assembles the minimal-update working set for an
out-of-sync pair from its consistency record: the authored side's diff
since last confirmation, the counterpart sections that diff lands in
(heading-mapped only where the last-confirmed structures align), the
terminology rows the diff touches, and a per-direction rules digest.

verify-translation-pairing now accepts pair paths to check just the
named pairs during update iteration; --write requires naming the
confirmed pairs (--write --all is the explicit corpus form) so a bulk
re-record can no longer silently bless drifted pairs the caller never
reviewed. Each record's comment names its own scoped command.

scripts/verify-translation-pairing.ts

@@ -2,8 +2,10 @@
  * Enforce complete English/Chinese pairs, matching structure, and recorded git
  * blob hashes for every in-scope document. The manifest contains only explicit
  * exclusions, which may have neither a counterpart nor a sidecar.
- * `--list` reports state and `--write` records both sides after human review.
- * Translation quality remains a review responsibility.
+ * `--list` reports state; `--write <pairs...>` records the named confirmed
+ * pairs (`--write --all` records every complete pair); a check or write named
+ * with pair paths touches only those pairs, so update iteration does not pay
+ * for a corpus scan. Translation quality remains a review responsibility.
  * See `docs/i18n/README.md` for the owning contract.
  */
 
@@ -13,6 +15,7 @@ import { basename, join, resolve, sep } from 'node:path'
 import {
   linksTo,
   parseTranslationMarkdown,
+  parseTranslationPairingCliArgs,
   parseTranslationPairingManifest,
   isTranslationScopeFile,
   TRANSLATION_SCOPE_GLOB_EXCLUDES,
@@ -21,8 +24,15 @@ import {
 } from './translation-pairing.ts'
 
 const root = resolve(import.meta.dirname, '..')
-const listMode = process.argv.includes('--list')
-const writeMode = process.argv.includes('--write')
+let request: ReturnType<typeof parseTranslationPairingCliArgs>
+try {
+  request = parseTranslationPairingCliArgs(process.argv.slice(2))
+} catch (error) {
+  console.error(`verify-translation-pairing: ${error instanceof Error ? error.message : String(error)}`)
+  process.exit(2)
+}
+const listMode = request.mode === 'list'
+const writeMode = request.mode === 'write'
 
 /** Discover source Markdown and pairing sidecars before applying the corpus predicate. */
 const SCOPE_PATTERNS = [
@@ -77,32 +87,67 @@ function renderMeta(source: string, sourceHash: string, zh: string, zhHash: stri
     '# Bilingual-pair consistency record (docs/i18n/README.md): the git blob hash of each',
     '# side as of the last confirmed-consistent state. Both languages carry equal authority;',
     '# after editing either side, bring the other along and re-record with:',
-    '#   pnpm run verify-translation-pairing --write',
+    `#   pnpm run verify-translation-pairing --write ${source}`,
     `${basename(source)}: ${sourceHash}`,
     `${basename(zh)}: ${zhHash}`,
     '',
   ].join('\n')
 }
 
-// Enumerate the scope once.
+// Enumerate the scope once: the whole corpus, or exactly the named pairs'
+// three files (a named pair whose files are absent is caught by the same
+// completeness rules that cover discovered remnants).
 const files = new Set<string>()
-for (const pattern of SCOPE_PATTERNS) {
-  for (const match of globSync(pattern, { cwd: root, exclude: TRANSLATION_SCOPE_GLOB_EXCLUDES })) {
-    const normalized = match.split(sep).join('/')
-    if (isTranslationScopeFile(normalized)) files.add(normalized)
+if (request.scope === 'pairs') {
+  for (const anchor of request.anchors) {
+    for (const file of [anchor, ...Object.values(pairPaths(anchor))]) {
+      if (existsSync(join(root, file))) files.add(file)
+    }
+    // A named anchor with no files on disk still enters the source list so
+    // the check reports it instead of silently passing an empty scope.
+    if (!existsSync(join(root, anchor))) files.add(anchor)
+  }
+} else {
+  for (const pattern of SCOPE_PATTERNS) {
+    for (const match of globSync(pattern, { cwd: root, exclude: TRANSLATION_SCOPE_GLOB_EXCLUDES })) {
+      const normalized = match.split(sep).join('/')
+      if (isTranslationScopeFile(normalized)) files.add(normalized)
+    }
   }
 }
 const translations = [...files].filter(f => f.endsWith('.zh.md')).sort()
 const metas = [...files].filter(f => f.endsWith('.i18n.yaml')).sort()
 const sources = [...files].filter(f => f.endsWith('.md') && !f.endsWith('.zh.md')).sort()
 
-// --write: (re)record both hashes for every complete pair, creating missing records.
+if (request.scope === 'pairs') {
+  const rejected = request.anchors.filter(anchor => !isTranslationScopeFile(anchor) || isExcluded(anchor))
+  const absent = request.anchors.filter(anchor => ![anchor, ...Object.values(pairPaths(anchor))].some(file => existsSync(join(root, file))))
+  if (rejected.length > 0 || absent.length > 0) {
+    for (const anchor of rejected) {
+      console.error(`verify-translation-pairing: ${anchor} is not an in-scope pair (excluded or outside the documentation corpus; see docs/i18n/README.md)`)
+    }
+    for (const anchor of absent) {
+      console.error(`verify-translation-pairing: ${anchor} names no pair on disk (none of its three files exist)`)
+    }
+    process.exit(2)
+  }
+}
+
+// --write: (re)record both hashes for the requested complete pairs, creating
+// missing records. A named pair that cannot be recorded (missing counterpart)
+// fails loud; corpus scope (--all) skips pairless sources as before.
 if (writeMode) {
   let written = 0
   for (const source of sources) {
     if (isExcluded(source)) continue
     const { zh, meta } = pairPaths(source)
-    if (!existsSync(join(root, zh))) continue
+    if (!existsSync(join(root, source)) || !existsSync(join(root, zh))) {
+      if (request.scope === 'pairs') {
+        console.error(`verify-translation-pairing: cannot record ${source}: missing ${existsSync(join(root, source)) ? zh : source}`)
+        process.exit(2)
+      }
+      continue
+    }
     const record = renderMeta(source, blobHash(readFileSync(join(root, source))), zh, blobHash(readFileSync(join(root, zh))))
     if (existsSync(join(root, meta)) && readFileSync(join(root, meta), 'utf8') === record) continue
     writeFileSync(join(root, meta), record)
@@ -204,7 +249,9 @@ if (listMode) {
 }
 
 if (errors.length === 0) {
-  console.log(`verify-translation-pairing: ${pairAnchors.size} pair(s) checked across all in-scope documentation, all consistent.`)
+  console.log(request.scope === 'pairs'
+    ? `verify-translation-pairing: ${pairAnchors.size} named pair(s) consistent; the corpus-wide check still runs in doc-sync.`
+    : `verify-translation-pairing: ${pairAnchors.size} pair(s) checked across all in-scope documentation, all consistent.`)
   process.exit(0)
 }