# telemetry

Plugin analytics as a plugin: one `engine.create` step adds `$.telemetry` to
the engine interface every plugin above it is handed, built over the
`$.session` and `$.http` nouns beneath. `$.telemetry.log({ event, props })`
sends one event as one first-party row, `tengu_plugin_<event>`;
`$.telemetry.mark({ feature, kind, reason?, props? })` marks one use of a
feature as the CLI's own feature events do, `tengu_feature_<kind>` with a
`feature_name` and the mark's properties beside it. Each call is one POST to
the event-logging ingest with the session's own credential
(`$.session.authorize()`, resolved at each call), one attempt, nothing
batched; a session with no first-party credential, or an ingest that
refuses, rejects the caller's promise.

It sends nothing wherever the CLI's own analytics are off: under
`DISABLE_TELEMETRY`, `CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC` or
`DO_NOT_TRACK`, on any third-party provider (Bedrock, Vertex, Foundry and
kin), and on a deployment with its own OAuth URL. Each is read through
`$.env` at every call, rows go one after another, and the credential is
authorized afresh right before each POST, so a session that has since moved
to a third-party provider or a cloud gateway sends nothing more. The row's
`user_type` is `ant` when `USER_TYPE` says so, else `external`.

Nothing free-form reaches a row. An event name and every property key is a
snake_case token; a value is a finite number, a boolean, or a Choice (a
string named together with the list it is chosen from), under `log` and
`mark` alike; `mark` takes `ok`, `sad` or `bad`, with a `reason` required on
the last two and refused on the first. An entry that breaks a rule is
refused before anything is sent.

`hooks/register.ts` is the module; `types/index.d.ts` is the noun's contract,
the one declaration of `$.telemetry` that this mod's hooks, a mod calling the
noun and a test answering it all read.

## What it hooks

`engine.create`: `{ ...await next(e), telemetry }`, so the noun is added and
nothing beneath is replaced.

## What it calls on `$`

`session.authorize`, `session.id`, `session.model`, `http.fetch`, `env.get`
(the switches above and `USER_TYPE`, by literal name), each on the
interface the fold handed it.

## Where it runs

This plugin is seated by the CLI itself, on internal builds whose own
analytics are on, and nowhere else: `session.authorize` exists only there,
and the rows it writes join tables only the CLI's own events reach. It is
not meant to be installed or loaded with `--plugin-dir`; the folder has a
manifest so it reads like every other plugin, not so it can stand alone. A
plugin that calls `$.telemetry` where this one is absent finds no such noun
and should treat that as "no analytics here".