feat: add premium paywall conversion telemetry - #28425

TLDR: When someone using free Coder taps a "Start trial for free" button, we now write down which page they tapped it on, and whether they went on to actually start the trial. That tells us which locked features make people want Premium.

Brief summary

• Records two things: the button being clicked, and a trial actually being started.
• Each click gets a random ID that travels with the person to the trial form, so we can tell who finished from who walked away.
• Records a short label for the page (like appearance or audit_log), never the web address, so no customer names are collected.

#28226 added the trial form and has since merged, so this now targets main.

Description

Today the "Start trial for free" button just moves you to the Premium page and nothing is recorded, so there is no way to know which feature convinced someone.

This adds two events:

The click generates a random ID. It rides along to the trial form and gets saved on the signup, so a click and a signup can be matched up later. Clicks with no matching signup are the people who gave up. Trials started without a paywall (for example straight from the sidebar) are labelled direct, so "no label" never gets confused with "broken".

A few small choices worth knowing:

• The ID is kept in browser session storage, not in the web address, so the URL stays clean. It expires after 30 minutes.
• The trial signup event is recorded by the server, not the browser, so nobody can fake a signup.
• The browser cannot say which kind of event it is sending. It can only report a click; the server labels it.
• Only people allowed to start a trial are counted. The server rejects the rest, which matters because a few paywalls show their button to everyone.
• Nothing is recorded at all when telemetry is turned off.

There is deliberately no "paywall was shown" event. Every admin page visit would report one, which is a lot of noise for little insight.

Every paywall in the Premium Copy Updates table has a label. The rows that do not are badges and alerts with no button to click.

Proof

Ran a local Coder with no licence and clicked the paywall button on the Appearance page.

What the browser sent, and the reply:

POST /api/v2/deployment/premium-funnel-events  ->  204 No Content
{"id":"92d96afa-f975-4789-b8a7-b1fd19d4df85","source":"appearance","variant":"premium"}

What the browser saved for the trial form, same ID:

{"id":"92d96afa-f975-4789-b8a7-b1fd19d4df85","source":"appearance","createdAt":1787268520857}

The click then landed on the Premium page with the trial form. Screenshots of the network panel, the saved value, and the Premium page are attached below. The form itself was not submitted, since that would contact the real licence server.

Testing

• Backend tests: a click is recorded with the server's own label, an unknown page label is refused, and a normal member is refused.
• Storybook tests: button clicked and ID saved on all three paywall styles, plus the case where the viewer only sees guidance text and has nothing to click.
• Unit tests for the saved ID: expiry, bad data, unknown page label, and the direct fallback.
• make gen is clean, and lint, types, and formatting pass.

Two stories fail on main today and fail the same way here: ExternalAuthSettingsPageView > Page and PremiumPageView > No License. Neither file is touched by this branch; both were verified failing on main with this branch checked out elsewhere.

Follow-up

coder/coder-telemetry-server#45 saves these events for reporting. It merges after this one.

type PremiumFunnelEvent struct {
	ID            uuid.UUID // event ID; for a click this is also the matching ID
	EventType     string    // cta_click | trial_signup, set by the server
	Source        string    // appearance, audit_log, ..., direct
	Variant       string    // which paywall design was shown
	AttributionID uuid.UUID // the click this signup came from
	UserID        uuid.UUID
	CreatedAt     time.Time
}

Generated with Coder Agents on behalf of @david-fraley