feat(api): expose cache metrics in REPL + normalize across providers (#813)

* feat(api): expose cache metrics in REPL + /cache-stats command

* fix(api): normalize Kimi/DeepSeek/Gemini cache fields through shim layer

* test(api): cover /cache-stats rendering + fix CacheMetrics docstring drift

* fix(api): always reset cache turn counter + include date in /cache-stats rows

* refactor(api): unify shim usage builder + add cost-tracker wiring test

* fix(api): classify private-IP/self-hosted OpenAI endpoints as N/A instead of cold

* fix(api): require colon guard on IPv6 ULA prefix to avoid public-host over-match

* perf(api): ring buffer for cache history + hit rate clamp + .localhost TLD

* fix(api): null guards on formatters + document Codex Responses API shape

* fix(api): defensive start-of-turn reset + config gate fallback + env var docs

* fix(api): trust forwarded cache data on self-hosted URLs (data-driven)

* refactor(api): delegate streaming Responses usage to shared makeUsage helper

src/commands/cacheStats/cacheStats.ts

@@ -0,0 +1,74 @@
+import {
+  getCacheStatsHistory,
+  getCurrentTurnCacheMetrics,
+  getSessionCacheMetrics,
+  type CacheStatsEntry,
+} from '../../services/api/cacheStatsTracker.js'
+import {
+  formatCacheMetricsCompact,
+  formatCacheMetricsFull,
+  type CacheMetrics,
+} from '../../services/api/cacheMetrics.js'
+import type { LocalCommandCall } from '../../types/command.js'
+
+// Cap the per-request breakdown to keep output readable. Users wanting
+// the full history can rely on OPENCLAUDE_LOG_TOKEN_USAGE=verbose for
+// structured per-request stderr output.
+const MAX_RECENT_ROWS = 20
+
+function formatRow(entry: CacheStatsEntry, idx: number): string {
+  // `YYYY-MM-DD HH:MM:SS` — long-running sessions can span midnight and a
+  // bare time-of-day makes the wrong row look "most recent" when two
+  // entries on different days share the same HH:MM:SS.
+  const iso = new Date(entry.timestamp).toISOString()
+  const ts = `${iso.slice(0, 10)} ${iso.slice(11, 19)}`
+  const line = formatCacheMetricsCompact(entry.metrics)
+  return `  #${String(idx + 1).padStart(3)}  ${ts}  ${entry.label.padEnd(28).slice(0, 28)}  ${line}`
+}
+
+function summarize(label: string, m: CacheMetrics): string {
+  return `${label.padEnd(18)}${formatCacheMetricsFull(m)}`
+}
+
+export const call: LocalCommandCall = async () => {
+  const history = getCacheStatsHistory()
+  const session = getSessionCacheMetrics()
+  const turn = getCurrentTurnCacheMetrics()
+
+  if (history.length === 0) {
+    return {
+      type: 'text',
+      value:
+        'Cache stats\n  No API requests yet this session.\n  Start a turn and re-run /cache-stats to see results.',
+    }
+  }
+
+  const recent = history.slice(-MAX_RECENT_ROWS)
+  const omitted = history.length - recent.length
+
+  const lines: string[] = ['Cache stats', '']
+  lines.push(summarize('Current turn:', turn))
+  lines.push(summarize('Session total:', session))
+  lines.push('')
+  lines.push(`Recent requests (${recent.length}${omitted > 0 ? ` of ${history.length}, ${omitted} older omitted` : ''}):`)
+  lines.push(`  #     time      model                         cache`)
+  for (const [i, entry] of recent.entries()) {
+    lines.push(formatRow(entry, history.length - recent.length + i))
+  }
+
+  // Honesty footnote — providers without cache reporting (vanilla Copilot,
+  // Ollama) show [Cache: N/A] rather than a fake 0%. Tell the user so they
+  // don't read "N/A" as "broken".
+  const hasUnsupported = recent.some((e) => !e.metrics.supported)
+  if (hasUnsupported) {
+    lines.push('')
+    lines.push(
+      '  N/A rows: provider API does not expose cache usage (GitHub Copilot, Ollama).',
+    )
+    lines.push(
+      '  The request still ran normally — only the metric is unavailable.',
+    )
+  }
+
+  return { type: 'text', value: lines.join('\n') }
+}