Cohort membership now survives a config wipe. Canaries bucket on a
dedicated bucketSeed (fresh random UUID, distinct from anonymousId by
design) that is mirrored write-once into the install-state file and
inherited at mint: a wipe re-rolls the telemetry id but never the canary
assignment. This removes cumulative-exposure drift for the recoverable
churn bucket entirely — the residual drift comes only from fresh
machines, containers, and genuinely new users — and keeps before/after
comparisons valid across a reinstall.
The seed is never emitted in telemetry (only the resulting true/false
assignments are), so it does not link the old id to the new one
server-side. The residual linker is the flag vector itself (k bits for k
live canaries), documented as such. An explicit reset still works by
deleting the state file, and the no-identity test now also asserts the
seed differs from the anonymousId.
Cross-surface coherence: the CLI's studio server injects the seed as
window.__HF_CLI_BUCKET_SEED (same telemetry gate and script-escaping as
the distinct id, and on the /api/telemetry-identity fallback), and the
Studio binding buckets on it when present — without this the CLI would
bucket on the seed while Studio bucketed on the distinct id, splitting
one machine across cohorts (calibration check 4 would catch exactly
this). Standalone Studio still buckets on its localStorage id: the
browser has no second storage location, so that id doubles as the seed.
Legacy configs are backfilled once (lineage seed if the state file has
one, else minted) and persisted immediately — an unpersisted seed would
re-roll cohorts every process. Safe to ship in the same release as the
first canaries: no prior release emitted canary properties, so the
bucketing-unit change is unobservable.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Replaces the single `canaries: "a,b"` telemetry property with PostHog's own
flag shape, one property per registered canary:
$feature/canary-de-parallel-router: "true" | "false"
PostHog treats `$feature/<key>` as a first-class flag property, so breakdowns,
funnels split by cohort and the experiment surfaces work on a canary with
nothing configured server-side. The decision still happens locally: the render
path forbids render-time network calls, behaviour must not depend on analytics
being reachable, and neither the CLI nor Studio ships posthog-js (both
hand-roll a batch POST, so there is no SDK to evaluate a real flag with).
Decide locally, analyse natively.
Two decisions worth recording:
- BOTH ARMS ARE EMITTED. A non-enrolled install reports "false" rather than
omitting the property. Absent means "this build predates the canary", which
is a different fact from "this install is control" — collapsing them makes a
ramp unreadable, because you cannot separate a control group from an old
version.
- KEYS ARE NAMESPACED with a `canary-` infix. A real PostHog flag namespace
already exists in this project, owned by the web app (`enable-chat-tab`, set
by posthog-js from `$lib=web` events). Namespacing guarantees a canary key
can never alias a real flag key and have the two fight over one property.
Values are the strings "true"/"false" to match how PostHog records boolean
flag values, so the property is directly comparable to a real flag.
98 core / 1437, 166 cli / 2194, 269 studio / 2982 green; tsc clean across all
three packages.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Adds the Studio (browser) binding so a canary can span the CLI and the editor,
and fixes a bundling mistake the studio test suite caught.
## The binding
Same public API as the CLI — `isCanaryEnabled("name")` — so a call site reads
identically whether it runs in Node or the browser. Three inputs differ:
- UNIT ID: `resolveStudioDistinctId()`, which already adopts
`window.__HF_CLI_DISTINCT_ID` when the CLI launched Studio. A CLI-launched
Studio therefore lands in the SAME cohort as the CLI: a rollout spanning
render and editor is coherent for that user instead of enrolling their
terminal but not their editor. A test pins that the id is passed through
unmodified — prefixing or re-hashing it would silently break that parity.
- OVERRIDE: no `process.env` in a page, so `?hf_canary_<name>=on` mirrored
into sessionStorage. Session scope is deliberate. A URL is the right carrier
(shareable — "support: open this link"), but persisting a URL-borne override
to localStorage would let one click silently pin a browser into a cohort
forever, long after anyone remembers why. Closing the tab is the reset;
`=reset` clears it explicitly.
- EXCLUSION: `navigator.webdriver` stands in for the CLI's `is_ci`. Automated
browsers mint a fresh localStorage id per run, so they would hop cohorts
between runs — noise in the signal, nothing learned about real users. An
override still reaches them, which is how you test a canary under Playwright.
Studio's `trackEvent` now attaches `canaries` to every event, mirroring the CLI.
## The bundling fix
Importing the `@hyperframes/core` barrel into studio browser code broke two
unrelated hook test files with an esbuild TextEncoder invariant violation. The
barrel re-exports the whole core surface (parsers, lint, studio-server), so it
drags a Node-oriented dependency graph into a browser bundle — the test
failure was the symptom, the bundle bloat was the bug.
`@hyperframes/core` now exposes `./canary` and `./canary-registry`, declared in
packages/core/package-subpaths.json (the generated source of truth for exports —
hand-editing package.json is reverted by the sync script) and marked
`environments: [browser, bun, node]`. Both the studio AND cli bindings import
the leaf modules; the CLI gets the same benefit for a different reason, since
this resolves on the startup path — the reason the producer is lazily loaded.
Verified: the two hook files pass again; 269 studio files / 2982 tests, 98
core / 1433, 166 cli / 2194 green, `bun run lint` clean including the subpath
check. Fault-injection confirms both design decisions are pinned — swapping
session for local storage fails the scope test, prefixing the unit id fails the
CLI/Studio cohort-parity test.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
