docs(runner): document what the Loki browser tenant holds

[demtario]

Context

Two runner docs described the browser telemetry path incorrectly, and one operator-facing fact was missing. run-and-deploy.md said the only demo-runtime Loki line is the Tier-1 compile failure, but emitCollapsedDemoEvent in apps/authoring/src/sentry.ts files every collapsed report as a handled Faro exception, which lands in Loki. observability-contract.md §6 carried a "scope note, not yet fixed" saying lite vitals are still stored, but lite.ts already stores a record only for t:"err" and faro.ts already sets storeRecord = false for measurements and example.* events. This PR fixes both and adds a paragraph on what the Loki browser tenant actually holds, the consequence (a healthy demo produces no Loki lines until something throws, and drain timing means a new error can wait for the next wake), a safe way to force a probe line, and the Explore gotcha that the Analytics Engine ClickHouse datasource needs Format As = Table.

Types of changes

• New example
• Update to an existing example
• README / documentation change
• Demo runner (runner/) change
• CI / tooling change

How was this verified?

Docs only. Every statement was checked against the code: apps/authoring/src/sentry.ts (collapsed demo events call telemetry.error), workers/o11y/src/lite.ts (storeRecord = body.t === "err"), workers/o11y/src/normalise/faro.ts (measurement and example.* paths set storeRecord = false; logs and other events store a record), workers/o11y/src/box.ts (sleepAfter = "15m"), workers/o11y/src/index.ts (cron wake at oldest inbox key over 1 h or backlog over 64 MB), and packages/runtime/src/telemetry/inbox.ts (60 s pack interval). The forced-error path to Loki (browser) under {service_name="demos-authoring"} was also observed in production.

Checklist

• New/renamed example: added to runner/config/frameworks.json (see CONTRIBUTING.md); otherwise it won't appear on demos.handsontable.com
• New example: added a row to the tables in README.md
• Ran pnpm build (and pnpm dev) in the affected example/server-example locally

None of the checklist items apply: no example was added, renamed or changed, only two markdown files under runner/docs/.

Related issue(s):

None.

---

Note

Low Risk
Documentation-only changes under runner/docs/; no runtime, ingest, or deploy behavior is modified.

Overview
Updates runner observability docs so they match current ingest behavior and give operators clearer Grafana guidance.

In observability-contract.md, the stale “lite vitals still store a Loki record” note is replaced: POST /telemetry/lite now documents the same rule as Faro—only t:"err" gets a Loki record; t:"vital" is hash-only for Analytics Engine dedupe.

In run-and-deploy.md, demo-runtime logging is corrected: collapsed preview errors land in Loki via emitCollapsedDemoEvent (handled Faro exceptions with fingerprint-shaped messages), not only Tier-1 compile failures. New sections spell out what the Loki browser tenant contains (exceptions/logs/non-example.* events vs AE-only measurements/metrics/lite vitals), why a healthy demo may show no Loki lines, how to force a probe line, the AE Explore “Format As = Table” gotcha, and wake/drain latency plus cron backlog wake thresholds.

^{Reviewed by Cursor Bugbot for commit cbba141. Bugbot is set up for automated code reviews on this repo. Configure here.}