feat(canvas): live events + realtime stats for freeform canvases

[fuziontech]

Problem

Freeform canvases (agent-built React apps in the desktop app) could only fetch historical data via ph.query / ph.loadInsight — saved insights re-run against ClickHouse. Anything that should update as events arrive (a live event feed, a "users online" counter) had to re-poll an insight, which lags ingestion and hammers /query. PostHog's own Activity → Live events and Web Analytics Live surfaces already solve this with a dedicated livestream SSE service, but canvases had no way to reach it: the sandboxed iframe can't hold the project-scoped live_events_token JWT, and its CSP blocks the host.

This adds a host-brokered live events avenue so canvases can subscribe to the live stream and read realtime counters — keeping the token server-side, matching the existing ph.* security model.

Changes

New streaming capability on the ph.* canvas bridge (shim → postMessage → ui bridge → tRPC → core service, the documented extension path in the canvas-templates skill):

• ph.subscribeLiveEvents(params, onEvent, onEnd) — opens a live SSE subscription. The canvas posts a live-subscribe frame; the renderer fetches a brokered connection config (canvasData.liveConnectionConfig → CanvasDataService.liveConnectionConfig), opens the SSE to live.{region}.posthog.com/events itself, and fans each event into the iframe as a live-event frame. The scoped JWT lives only in the renderer — it never crosses into the sandbox. params.properties filters only support the livestream operator allowlist (LIVE_EVENTS_SUPPORTED_OPERATORS, mirroring the app's live feed) — validated by the schema and spelled out in the agent prompt.
• ph.liveStats() — a ONE-SHOT poll (rides the generic data-request frame, method: "liveStats") → canvasData.liveStats → GET <live host>/stats → { users_on_product, active_recordings }, the same "users online" pill the Activity page shows. For a live readout the prompt also documents the client-side 60s sliding-window count derived from the streamed distinct_ids — matching the Web-Analytics-Live tab without an extra host method.

Plumbing:

• core: live message frames + Zod schemas on the postMessage protocol (live-subscribe/live-unsubscribe/live-event/live-stream-status), getLiveEventsUrlFromRegion (shared), CanvasDataService.liveConnectionConfig/liveStats, ICanvasDataService surface, cached per-project live JWT.
• host-router: canvasData.liveConnectionConfig + canvasData.liveStats procedures.
• ui: openLiveEventsStream + exported buildLiveEventsUrl/parseSseChunk in the data bridge; FreeformCanvas routes the live frames and owns stream lifecycle (close on unmount/unsubscribe, replace on resubscribe); sandbox shim gets ph.subscribeLiveEvents/ph.liveStats + event dispatch.
• prompt/docs: FREEFORM_BASE documents the live APIs + users-online pattern; canvas-templates SKILL.md gains a "Live / realtime (SSE)" section. Companion MCP PR documents the same in the canvas-publish tool description (see PostHog/posthog).

How did you test this?

• Automated: new unit tests for the SSE chunk parser + /events URL builder (freeformDataBridge.live.test.ts), and schema round-trip cases for the new live frames + operator allowlist (freeformSchemas.test.ts). Full @posthog/core (2,844) and @posthog/ui (2,413) suites green; core/ui/host-router typecheck clean; biome check clean on all touched packages.
• Not run: end-to-end against a live project (requires the running desktop app + a signed-in PostHog project with ingesting traffic). The SSE parse + URL + schema layers are covered by the unit tests above; the actual stream rendering should be verified in the app before un-drafting.

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

Created with PostHog Code

[trunk-io]

Merging to main in this repository is managed by Trunk.

• To merge this pull request, check the box to the left or comment /trunk merge below.

After your PR is submitted to the merge queue, this comment will be automatically updated with its status. If the PR fails, failure details will also be posted here

[github-actions]

React Doctor found 1 issue in 1 file · 1 warning.

1 warning

src/features/canvas/freeform/FreeformCanvas.tsx

• ⚠️ src/features/canvas/freeform/FreeformCanvas.tsx:81 Ref initializer runs on every render rerender-lazy-ref-init

_{Reviewed by React Doctor for commit 53233cc.}

[charlesvien]

Hey @fuziontech, we've migrated this repo into the PostHog/posthog monorepo, so this PR needs to be recreated there.

Easiest path: check out the monorepo and run the /porting-code-prs skill with your agent pointed at this PR. It has the migration guide and path remappings baked in so the agent doesn't have to figure them out. You don't strictly need it though, just asking your agent to port the PR works fine too.

Shout if you get stuck.