v0.5.0

Closes #50.

A 0.x minor that changes the API list: EnvironmentSnapshot's initializer and stored properties
change, and beginSession() returns a value. The payload version moves to 2.1.0, which adds three
fields and a preset and fixes two values, each checked against TelemetryDeck's SwiftSDK at
58f43629, its docs at 2b9c2108 (the default-parameters reference, basics/acquisition.md, and
articles/decide-to-drop-ios-version.md), and its KotlinSDK at 10b87d4a.

Payload 2.1.0

• device.systemMajorVersion, sent as TelemetryDeck.Device.systemMajorVersion: the major OS
  version, 26. The vendor documents it among its default parameters, its SDK sends it, and its
  docs describe the prebuilt system-version chart offering a major-version breakdown beside the
  major.minor one.
  All three version strings stay bare (26.5.1, 26.5, 26). The default-parameters reference
  types each only as a String, and the vendor's own articles show both forms; its Swift SDK
  prefixes the platform where its Kotlin SDK sends the major and major.minor versions bare. A
  changed form would split every chart already grouped on the bare systemVersion and
  systemMajorMinorVersion, and the new field takes the same form as those two.
• runContext.language, sent as TelemetryDeck.RunContext.language: the language the app runs in,
  the locale's language code.
• calendar.dayOfWeek, sent as TelemetryDeck.Calendar.dayOfWeek: the local day numbered as ISO
  8601 numbers it, Monday 1 through Sunday 7, as the vendor documents it and its SDK sends it.
• userPreference.language is the language the user most prefers on the device, the language
  subtag of the first Locale.preferredLanguages entry, as the vendor defines it. It was the
  locale's language, which is the app's, so an app localized only in English reported en from a
  device set to German. The key and the form are unchanged.
• calendar.isWeekend is true on a Saturday or a Sunday, as the vendor defines it, and is
  derived from the day of week. It followed the locale's weekend, so under a Friday-Saturday weekend
  a Friday reported true and a Sunday false. The key and the form are unchanged.
• PresetSignal.newInstallDetected, acquisition.newInstallDetected, sent as the vendor's
  TelemetryDeck.Acquisition.newInstallDetected. The vendor's docs name that signal as how new
  users are detected, sent on first launch. Its SDK sends it whenever a session starts with no
  stored session behind it, which is also after 90 days without a session, or after sessions that
  each lasted under a second. This package reports it once per retention record, so only after an
  install or an erase.

API

• SignalRecorder.beginSession() returns true when the call created the retention record, which
  makes its session the first counted since install or since the last erase. It is
  @discardableResult, so an existing call compiles unchanged. It returns false on every later
  session, on a repeat in the same activation, and while collection is not permitted. The session
  resetClosingCollection(during:) reopens is counted by that reopen, so no later beginSession()
  reports it: a host that counts a data reset as a new install records the preset once that call
  returns. A RetentionStore whose load() returns nil, for a record it could not decode
  included, reads as no record, and the next session reports true.
• SignalRecorder.recordNewInstallDetected(parameters:) records the preset, unprefixed like the
  other presets. The recorder never records it on its own: a host calls it when beginSession()
  returns true, on the path every other signal takes, so whatever the host applies there covers
  it too.
• EnvironmentSnapshot holds the OS version once, as systemMajorVersion, systemMinorVersion,
  and systemPatchVersion, in place of systemVersion and systemMajorMinorVersion, and derives
  all three version fields from it. language becomes preferredLanguage and appLanguage. The
  initializer takes the new properties.
• EnvironmentSnapshot.current() takes preferredLanguages:, defaulting to
  Locale.preferredLanguages.

Upgrading

• A call to EnvironmentSnapshot's initializer passes the three version components and the two
  languages. Calls to current() and beginSession() change nothing.
• An install whose retention record predates the upgrade already has one, so beginSession()
  never reports it as new.
• A host swapping to this package from the vendor's SDK starts every existing install without a
  retention record (ADOPTING.md, Phase 6). Its first beginSession() after the swap returns
  true, and recording the preset on that answer counts every existing install as new on the
  migration day. After that, a user returning from 90 days away is not counted as new again, as
  the SDK would count them, and the three OS version fields arrive bare where the Swift SDK sent
  them with the platform.

Tooling

• A contract suite records a signal through the recorder, encodes it with the adapter, and holds it
  to TelemetryDeck's SwiftSDK at 58f43629 and its default-parameters reference at 2b9c2108, as
  read on 2026-09-29: the key set, the value forms, the deliberately absent keys and their reasons,
  and the install preset's name. The test floor rises to 224.
• The consumer fixture compiles a host's activation with the new preset.