v0.4.0

• The README now provides a runnable encrypted round trip and a current demo.
  The quickstart exercises two SDK clients through the in-memory relay. The new
  recording shows the same two-device and relay flow as the live desktop and
  mobile demo.

• Error-surface checks reject unresolved codes and cover media attachment
  codes. The analyser now reports forwarded code arguments in CI.
  It also checks every MediaAttachmentErrorCode value.
  This release removes RemoteObjectStoreNotConfigured because no media
  operation could produce it.

• The retry-request wire surface no longer includes
  RetryReason.INVALID_MESSAGE. No local failure produced it. The incoming
  retry handler did not support it. Malformed ciphertext failures use the supported
  DECRYPTION_FAILED recovery path.

• Generated API pages and shipped documentation examples now have source
  gates. CI regenerates docs/api with pinned tool versions. It rejects a
  diff. The snippet runner scans every packaged Markdown file and the internal
  lifecycle docs. It executes every complete example and matches its output.
  For an example that cannot run, it compiles every SDK name against the packed
  package. A renamed or deleted export therefore fails the build in every
  document that names it.

  An example that previews an unreleased API declares the import paths that do
  not exist yet. The build fails if one of them resolves. Only pseudocode is
  exempt, and the build names each exempt block on its own line.

• The error guide now documents all 33 EncryptionErrorCode values. Its
  session examples also use the current ProtocolAddress method signatures.