perf(docs): resolve repository-reference candidates with one object listing

verify-repository-references asked git cat-file for each of about 26,000
abbreviated hexadecimal candidates, which took 135 s on a network
filesystem. One --batch-all-objects listing (about 1.2 million objects,
0.6 s) now feeds an in-memory prefix search; a candidate still counts
only when its prefix names exactly one available object and that object
is a commit. The gate drops from 166.8 s to 15.7 s, and both
implementations classify 27,050 real and synthetic candidates
identically.

Refs #5852

scripts/verify-repository-references.ts

@@ -14,6 +14,8 @@ const kitRepositoryUrl = new RegExp(`\\bgithub\\.com/${organization}/libreoffice
 const commitCandidate = /(?<![a-z0-9])[\da-f]{7,40}(?![a-z0-9])/gi
 const excludedPrefixes = ['vendor/', '.agents/notes/archived/']
 const gitOutputLimit = 64 * 1024 * 1024
+// One 41-byte line per object; 1.2 million objects produce about 49 MiB.
+const objectListingLimit = 1024 * 1024 * 1024
 
 /** One prohibited reference in a maintained source file. */
 export interface RepositoryReference {
@@ -70,24 +72,63 @@ function readMaintainedFiles(repoRoot: string): Map<string, string> {
   return sources
 }
 
-function repositoryCommits(repoRoot: string, sources: Iterable<string>): Set<string> {
-  const candidates = [...new Set([...sources].flatMap(source =>
-    [...source.matchAll(commitCandidate)].map(match => match[0].toLowerCase())))]
-  if (candidates.length === 0) return new Set()
-  const results = execFileSync('git', ['cat-file', '--batch-check=%(objectname) %(objecttype)'], {
+function gitLines(repoRoot: string, args: readonly string[], maxBuffer: number, input?: string): string[] {
+  const output = execFileSync('git', args, {
     cwd: repoRoot,
     env: { ...process.env, GIT_NO_LAZY_FETCH: '1' },
     encoding: 'utf8',
-    input: `${candidates.join('\n')}\n`,
-    maxBuffer: gitOutputLimit,
+    input,
+    maxBuffer,
     stdio: ['pipe', 'pipe', 'pipe'],
-  }).trimEnd().split('\n')
-  // Git resolves prefixes across all available objects, including unreachable ones.
+  }).trimEnd()
+  return output === '' ? [] : output.split('\n')
+}
+
+/**
+ * Find the one object whose name starts with a prefix.
+ * @param objects - Every object name in the local object database, sorted.
+ * @param prefix - Lowercase hexadecimal prefix.
+ * @returns The matching object name, or `undefined` when none or several match.
+ */
+function uniquePrefixMatch(objects: readonly string[], prefix: string): string | undefined {
+  let low = 0
+  let high = objects.length
+  while (low < high) {
+    const middle = (low + high) >>> 1
+    if ((objects[middle] ?? prefix) < prefix) low = middle + 1
+    else high = middle
+  }
+  const match = objects[low]
+  if (match?.startsWith(prefix) !== true || objects[low + 1]?.startsWith(prefix) === true) return undefined
+  return match
+}
+
+/**
+ * Resolve commit-identifier candidates in maintained sources against the local object database.
+ * @param repoRoot - Working tree whose Git objects are inspected.
+ * @param sources - File texts or symlink targets to extract candidates from.
+ * @returns Lowercase candidates that name exactly one available object, which is a commit.
+ */
+export function repositoryCommits(repoRoot: string, sources: Iterable<string>): Set<string> {
+  const candidates = [...new Set([...sources].flatMap(source =>
+    [...source.matchAll(commitCandidate)].map(match => match[0].toLowerCase())))]
+  if (candidates.length === 0) return new Set()
+  // Git resolves prefixes across all available objects, including unreachable and alternate ones;
+  // one listing of those objects replaces one Git prefix lookup per candidate.
   // Ambiguous prefixes do not identify one object and cannot establish a commit reference.
-  return new Set(candidates.filter((candidate, index) => {
-    const [object, type] = results[index]?.split(' ') ?? []
-    return type === 'commit' && object?.startsWith(candidate) === true
-  }))
+  const objects = gitLines(repoRoot, ['cat-file', '--batch-all-objects', '--batch-check=%(objectname)'], objectListingLimit).sort()
+  const matches = new Map<string, string>()
+  for (const candidate of candidates) {
+    const object = uniquePrefixMatch(objects, candidate)
+    if (object !== undefined) matches.set(candidate, object)
+  }
+  if (matches.size === 0) return new Set()
+  const matched = [...new Set(matches.values())]
+  const commits = new Set(gitLines(repoRoot, ['cat-file', '--batch-check=%(objectname) %(objecttype)'], gitOutputLimit, `${matched.join('\n')}\n`)
+    .map(line => line.split(' '))
+    .filter(([, type]) => type === 'commit')
+    .map(([object]) => object))
+  return new Set([...matches].filter(([, object]) => commits.has(object)).map(([candidate]) => candidate))
 }
 
 /**