fix(web-probe): stabilize browser transport sampling (#717)

Co-authored-by: Codex <codex@noreply.local>

scripts/src/hwlab-node-help.ts

@@ -74,8 +74,8 @@ export function hwlabNodeWebProbeHelp(): Record<string, unknown> {
     examples: [
       "bun scripts/cli.ts hwlab nodes web-probe run --node D601 --lane v03 --wait-messages-ms 1000",
       "bun scripts/cli.ts hwlab nodes web-probe run --node D601 --lane v03 --url https://hwlab.pikapython.com --fresh-session --message 'ping'",
-      "bun scripts/cli.ts hwlab nodes web-probe script --node D601 --lane v03 --script-file .state/probes/workbench.mjs",
-      "bun scripts/cli.ts hwlab nodes web-probe observe start --node D601 --lane v03 --target-path /workbench --sample-interval-ms 5000",
+      "bun scripts/cli.ts hwlab nodes web-probe script --node D601 --lane v03 --browser-proxy-mode direct --script-file .state/probes/workbench.mjs",
+      "bun scripts/cli.ts hwlab nodes web-probe observe start --node D601 --lane v03 --target-path /workbench --sample-interval-ms 5000 --browser-proxy-mode direct",
       "bun scripts/cli.ts hwlab nodes web-probe observe command webobs-xxxx --type newSession",
       "bun scripts/cli.ts hwlab nodes web-probe observe command webobs-xxxx --type selectProvider --provider codex-api",
       "bun scripts/cli.ts hwlab nodes web-probe observe command webobs-xxxx --type sendPrompt --text 'ping'",
@@ -97,6 +97,7 @@ export function hwlabNodeWebProbeHelp(): Record<string, unknown> {
       "observe analyze is offline-only: it reads artifact JSONL and writes analysis/report.md plus analysis/report.json without accessing Workbench APIs or driving the browser.",
       "observe analyze scans every sampled DOM point, extracts Workbench timing text such as 总耗时/total and 最近 N 秒/分前, and writes a sample point vs turn timing report: each Markdown table row starts with the timestamp, followed by each turn's 总耗时(s) and 最近更新(s). Timing series are reported for post-processing/manual analysis instead of auto-judged from status tail output.",
       "observe analyze also reports visible “加载中” count, owner attribution, concurrent loading owners, and continuous visible segments; fixes must reduce real loading latency, not reveal incomplete content early to make this metric disappear.",
+      "script/observe support --browser-proxy-mode auto|direct; use direct for A/B evidence when frontend RUM is slow but OTel server spans are absent or fast, instead of falling back to raw Playwright.",
       "Use recordStep(name, data) or fetchApiMatrix(paths) to keep structured partial evidence when a later step fails.",
       "Use reloadStable(), gotoCurrentStable(), or safeReload() for bounded retries around page reload/current-URL navigation jitter such as ERR_NETWORK_CHANGED.",
       "Playwright page.evaluate accepts one serializable argument; use page.evaluate(({ a, b }) => ..., { a, b }) or safeEvaluate(fn, { a, b }).",