v0.13.0

Security

• Bound every task-subscription event to the task ID and context returned by the preceding turn.
  A stream that crosses task or context boundaries now fails before its content reaches assertions,
  reports, or evidence.
• Kept file-content verification local and bounded. SHA-256 is computed only for inline raw parts;
  remote URLs are never fetched, and computed digests and bytes are excluded from reports and
  evidence.

Features

• Added action: subscribe for black-box SubscribeToTask contracts. A scenario can accept an
  active task, resume its stream, and apply existing state-trajectory, text, data, file, AP2,
  timing, and invariant checks to the completed subscription result.
• Required the subscription to start with the current task snapshot and finish in a terminal or
  interrupted state, matching the A2A 1.0 lifecycle contract across JSON-RPC, HTTP+JSON, and gRPC.
• Added exact size_bytes, inclusive min_size_bytes and max_size_bytes, and sha256 assertions
  for inline raw file parts. Exact size and range predicates are mutually exclusive, and content
  checks explicitly require kind: raw.

Documentation

• Added a focused stream-resumption contract to the lifecycle guide and documented file-integrity
  syntax, validation rules, and the passive treatment of remote URL parts.
• Updated the README capability map to surface stream resumption and file integrity without
  expanding the onboarding path.

Maintenance

• Added real JSON-RPC, HTTP+JSON, and gRPC subscription exchanges through the official A2A Python
  SDK, including task continuity, artifact collection, terminal state, timing, and digest checks.
• Extended runner, configuration, generated schema, protocol rejection, serialization, and
  assertion coverage while retaining the 99% coverage gate.
• Established a clean mutation baseline: 4,406 of 4,579 mutants are killed (96.22%), with no
  survivors in the v0.13 subscription or file-integrity paths. The three timeouts remain in the
  bounded push receiver's listener and socket-read mutations.