feat: show cache hit rate in web session info

pi-web/components/AppShell.tsx

@@ -1256,11 +1256,16 @@ export function AppShell() {
                        [translate("session.toolResults"), sessionStats.toolResults.toLocaleString(locale)],
                        [translate("session.total"), sessionStats.totalMessages.toLocaleString(locale)],
                     ];
+                    const promptTokens = sessionStats.tokens.input + sessionStats.tokens.cacheRead + sessionStats.tokens.cacheWrite;
+                    const cacheHitRate = promptTokens > 0 && (sessionStats.tokens.cacheRead > 0 || sessionStats.tokens.cacheWrite > 0)
+                      ? `${((sessionStats.tokens.cacheRead / promptTokens) * 100).toFixed(1)}%`
+                      : null;
                     const tokenRows = [
                        [translate("session.input"), sessionStats.tokens.input.toLocaleString(locale)],
                        [translate("session.output"), sessionStats.tokens.output.toLocaleString(locale)],
                        ...(sessionStats.tokens.cacheRead > 0 ? [[translate("session.cacheRead"), sessionStats.tokens.cacheRead.toLocaleString(locale)]] : []),
                        ...(sessionStats.tokens.cacheWrite > 0 ? [[translate("session.cacheWrite"), sessionStats.tokens.cacheWrite.toLocaleString(locale)]] : []),
+                       ...(cacheHitRate ? [[translate("session.cacheHitRate"), cacheHitRate]] : []),
                        [translate("session.total"), sessionStats.tokens.total.toLocaleString(locale)],
                     ];
                     const ctx = contextUsage ?? sessionStats.contextUsage;

pi-web/lib/i18n/messages/en.ts

@@ -43,6 +43,7 @@ export const enLocale: LocalePlugin = {
     "session.output": "Output",
     "session.cacheRead": "Cache Read",
     "session.cacheWrite": "Cache Write",
+    "session.cacheHitRate": "Cache Hit Rate",
     "session.cost": "Cost",
     "session.context": "Context",
     "session.copy": "Copy {value}",

pi-web/lib/i18n/messages/zh-CN.ts

@@ -43,6 +43,7 @@ export const zhCNLocale: LocalePlugin = {
     "session.output": "输出",
     "session.cacheRead": "缓存读取",
     "session.cacheWrite": "缓存写入",
+    "session.cacheHitRate": "缓存命中率",
     "session.cost": "费用",
     "session.context": "上下文",
     "session.copy": "复制{value}",