audit matrix (Q2 sequence, Q3 context drift, Q4 envelope version) are
addressed in this release.

**Added:**

- **`envelopeVersion: 1`** on the batch envelope (POST body). Integer
  schema version required by the server's reject-unversioned rule
  (spec §6.1). Distinct from `sdk.version` — answers the ingest
  parsing question, not Version Health.
- **`seq` on every event** (spec §3). Per-session monotonic integer,
  reset to 0 at `setSessionId()` (session boundary), incremented
  synchronously at `track()` alongside `timestamp`. Persists across
  app background/foreground within the same session per the spec's
  non-negotiable §3 clauses.
- **`context` object on every event** (spec §4). Standardised
  device/platform fields promoted out of `properties`: `os`,
  `osVersion`, `appVersion`, `sdkName`, `sdkVersion`, `locale`,
  `timezone`, `deviceModel` (RN-specific; uses `Platform.constants.Model`
  falling back to `Brand`).

**Changed (breaking wire format):**

- Device info fields (`os`, `osVersion`, `model`, `brand`, etc.)
  are no longer spread into event `properties`. They live exclusively
  in the top-level `context` object. App-supplied caller properties
  remain in `properties` as before.