chore(analytics): drop unused Amplitude events and sample the rest

[dylanjeffers]

The Amplitude proxy (gain2.audius.co, metrics-worker) caps us at 1.95M events a month, and it has been hitting that in about 4 days. This PR removes most of the events the clients send: anything that's a duplicate, automatic, from a bot, or not used by any recent chart. What's left, apart from the core events, goes out from 10% of devices.

Volume before (Amplitude stored totals, Aug 31 to Sep 4, 5 days, project 265616)

#	Event	Stored	Status after this PR
1	Session Start	118,654	removed, replaced by a client user property
2	Page View	44,992	kept (core; also used by sign-up charts)
3	Playback: Play	38,170	kept (core)
4	Search: Search	23,636	removed
5	Embed: Open Player	23,015	removed
6	Favorite	20,708	kept (core)
7	Buffering Time	18,473	removed
8	Repost	17,618	kept (core)
9	Explore: Section View	11,997	removed
10	Follow	9,718	kept (core)
11	Playback: Pause	8,047	kept (core)
12	Link Click	7,340	removed
13	session_end	7,279	removed (SDK automatic tracking off)
14	Share	5,821	kept (core)
15	Track Upload: Track Uploading	4,094	removed
16	Message Unfurl: Track	3,966	removed
17	[Amplitude] Form Started / Submitted	3,798	removed (SDK automatic tracking off)
18	Create Account: Select Genre	3,786	kept (core, sign-up)
19	Feed: Change view	3,298	sampled at 10% (Chronological Feed dashboard)
20	Comments: Load More Comments	3,222	removed

Web plus embed is 314k of that, iOS 66k and Android 64k. Some events are sent but never stored, so they don't show up above: [Amplitude] Page Viewed, session_start (both deleted in the project) and $identify.

What changed

1. SDK automatic events off, and bots skipped

• Web defaultTracking: it now names every option. Any option left out defaults to on (isTrackingEnabled in analytics-client-common), so { sessions: true } had also been sending page views, form events and file downloads. Attribution stays on.
• Bots: crawler and navigator.webdriver traffic gets no analytics on web or embed. On Aug 1-3, one Singapore "Chrome 145" crawler sent 371k Session Starts from 347k new devices.
• Identify dedupe: identify only goes out when the traits change, on web and mobile, and is resent weekly.

2. Session Start removed everywhere

The platform it carried (Android Web, iOS Web, MacOS, Windows, Linux, Desktop Web, iOS App, Android App, Embed) is now a client user property. It's set through identify only when it changes for a device. Amplitude already computes sessions from session ids.

3. Events removed (call site, enum entry and type)

The rule: an event is removed if it isn't core and isn't referenced by an Amplitude chart, dashboard or cohort that was viewed or edited in the last 12 months.

I listed all 642 charts, dashboards, cohorts and notebooks in project 265616, then read the definitions of the 33 charts and 7 dashboards used since 2025-09-24. None of the 11 cohorts or 3 notebooks had been used in that window.

• Session and diagnostics: Session Start, App Error, App Unexpected Error, Buffering Time, Not Found Page, Chat Websocket Error, Modal Opened/Closed
• Search and navigation: Search: Search, Tag Search, Result Select, Tag Click, Link Click, Explore: Section View, Section Click, Trending: Change view, Profile Page: Tab Click, Sort, the social and website link clicks, Shown Artist Recommendations, Track Page: Play More By This Artist, Visualizer: Open/Close
• Embed: Open Player, Player Error, Open modal
• Comments (all interaction events): create, update, delete, like, report, mute, pin, reply, mention, timestamp and link clicks, load more/new, sort, drawer open/close, overflow menus, notification toggles, Comments History, Recent Comments
• Chat: Create Chat, Chat Blast CTA/Create/Message Viewed, Send Message: Failure, Delete Chat, Set Chat Category, Block User, Change Inbox Settings, Send Message Reaction, Message Unfurl: Track/Playlist, Chat Entry Point (see note)
• Playlists and library: Playlist: Add To Playlist, Open/Start/Complete Create, Make Public, Open Edit From Sidebar, Play; Playlist Library: Reorder; Folder: Open/Submit/Cancel Edit
• Tracks: Track Download (all 6), Track Edit (all 3), Collection Edit (both), Track Replace (all 3), Track Upload: Track Uploading, View Track page, the follow and token gated upload variants; Follow/Token Gated unlocks; Stem: Complete Upload, Delete; Delete; Remix: New Remix, CoSign, CoSign Indicator, Hide; Artist Pick: Select Track
• Remix contests: Create, Update, Delete, Pick Winners Open, Finalize Winners, View, Enter, View Submissions
• Settings and account: Change Theme, Resend Account Recovery, Complete Change Password, Log Out, Deactivate Account (all 4), Developer Apps (all 8), Authorized Apps (both), Manager Mode (all 5), Export Private Key (all 5), Notifications: Toggle Setting, Browser Push Notification, Account Health: Upload Cover Photo, Upload Profile Picture, Download Desktop
• Wallet and rewards: Connect Wallet (all 5), Create User Bank (both), Rewards Claim: Opened/Request/Success, Rewards Claim All: Failure
• Banners and prompts: Banner Artist Coins/Yak Coin/Trading Volume/TOS clicks, Rate CTA (all 3)
• Mobile offline mode: everything except Offline Play (the migration and download lifecycle events)

The analytics-only source props on SearchTag, ExternalLink and UserGeneratedText (linkSource) are removed too.

4. Sampling

• Core allowlist: CORE_ANALYTICS_EVENTS in @audius/common (models/AnalyticsSampling.ts), plus the mobile share-channel events.
• What's core: Playback Play/Pause, Listen, Page View, and the sign-up, sign-in, create-account and OAuth flows. Also purchase, buy, withdraw, USDC, Stripe, coin swaps and Launchpad; the upload open/start/complete/success/failure funnel; Share and share channels (including the notification and first-upload Twitter shares); Favorite, Repost and Follow and their undos; notification opens and clicks (including push and comment notifications); chat sends (Send Message: Success, Chat Blast: Message Sent); Report User: Chat (the only record of an abuse report); Rewards Claim All request/success; Embed: Copy; and all Weekly Rotation events.
• Everything else: sent only from devices where an FNV-1a hash of the Amplitude device id falls in the bottom 10%. It carries sampleRate: 0.1, so counts scale back up by dividing by sampleRate. What's still sampled after step 3 is only chart-backed: Play Queue (all 7), Feed: Change view, Error Page, Account Health: Meter Full, Folder: Delete, the Playlist Library folder moves, Offline Play, and Chat Entry Point.
• Where it runs: once, in the shared track path: web services/analytics/amplitude.ts and mobile services/analytics.ts. Embed now only sends core events.

Why the proxy counts about 5.5x what Amplitude stores

• Confirmed: the proxy counted events that Amplitude drops without billing: session_start and [Amplitude] Page Viewed. It also counted $identify on every account load. Together that's roughly 50-70k a day.
• Inferred: the other ~330k a day. The proxy counts a batch before forwarding it, so every SDK resend counts again (after 400/413/429/5xx responses, network errors, and the localStorage queue being replayed on the next load). Amplitude removes duplicates by insert_id, so it bills only one copy. AudiusProject/metrics-worker#1 gives back events Amplitude doesn't accept, and now also drops the removed event types that older clients still send.

Estimate against the 1.95M cap

	Per day now	Per day after	Per month after
Amplitude stored (billed)	~100k	~35k (core 35.0k + sampled 0.1k)	~1.05M
Proxy count, if the gap is retries of rejected batches (fixed by worker#1)	~488k	~34k events + ≤8k identify	~1.3M
Proxy count, if the gap is duplicates Amplitude accepts with a 200	~488k	~34k × 4.8 + 8k	~5.2M

• Billed volume ends up under 1.95M either way, with about 45% headroom. Kept core events stored 175k over the 5 days. The sampled events stored 4.7k and will keep 10% of that.
• The proxy count ends up under 1.95M only if the unexplained gap is retries of rejected batches. After deploying metrics-worker#1, compare the counter against Amplitude's daily totals for a few days to find out.
• Rollout timing: web doesn't auto-deploy (Production gate), and mobile needs an OTA dispatch. Until those ship, metrics-worker#1's denylist is what stops old clients from spending the budget.

Kept even though it's low value

• Undo actions: Unfavorite, Undo Repost and Unfollow. They're the inverse of core actions and about 1k in 5 days.
• Upload USDC-gated variants and USDC unlock events: grouped with purchase. Tiny volume.
• Launchpad form-change events: part of the coin flow and nearly zero volume.
• Chat Entry Point: still fired from ShareModal and ShareDrawer, which feat(weekly-rotation): instrument plays, shares and notifications for usage analytics #14605 is changing. The enum and type stay so that merges cleanly. It's sampled on the client and dropped by the proxy. Remove it after feat(weekly-rotation): instrument plays, shares and notifications for usage analytics #14605 lands.
• A few enum entries and types stay next to lines feat(weekly-rotation): instrument plays, shares and notifications for usage analytics #14605 changes, even though nothing fires them anymore: Modal Opened/Closed, Explore: Section Click, Browser Push Notification, Chat Websocket Error, Message Unfurl, Playlist: Play, Stem: Complete Upload, Export Private Key link. They can be deleted after feat(weekly-rotation): instrument plays, shares and notifications for usage analytics #14605 merges.

Behavior changes to review

• Sign-out: Log Out used to run through the analytics callback. It's now called directly on desktop web and in the mobile web SignOutModal, still before the redirect.
• Modal sagas: store/ui/modals/sagas.ts now returns no sagas. trackModalOpened/trackModalClosed still get dispatched and now do nothing.
• Wallet-connect errors: the catch blocks in the mobile wallet-connect sagas only sent an error event, so they're now empty.
• Mobile Chat screen: the blast "viewed" AsyncStorage bookkeeping was only for the removed event, so it's gone.

Tests

• Typecheck: tsc passes for common, web and mobile. The local sdk and spl dist were rebuilt, because they were stale.
• Lint: eslint on all touched files has no errors. Two exhaustive-deps warnings in the remix-contest host were already there.
• Web vitest: 33 files and 177 tests pass. That includes services/analytics/amplitude.test.ts: automatic events off, client property set once per device, core events always sent, about 10% of devices kept for non-core events with sampleRate, identify dedupe, and bots skipped.
• Common vitest: 172 of 179 pass. The 7 failures are in store/upload/selectors.test.ts, which fails the same way on an untouched checkout.
• Embed jest: passes.
• Mobile jest: can't run in this worktree, because react-native can't be resolved from the copied node_modules.

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