v1.15.0

Added

• SPEC_COMPLIANCE.md tracks PMCP against the current stable MCP revision
  (2025-11-25) with a per-requirement compliance table, a draft-revision
  migration assessment (stateless transport, the io.modelcontextprotocol/tasks
  extension, server/discover, CacheableResult, DCR→Client ID Metadata
  Documents, SSE resumability), and a next-stable tracking checklist. PMCP is
  confirmed compliant with the folded-in current-stable items (403 on invalid
  Origin per PR #1439, insufficient_scope 403 step-up per SEP-835,
  input-validation as tool-execution errors per SEP-1303, JSON Schema 2020-12
  default dialect per SEP-1613, tool/resource/prompt icon passthrough per
  SEP-973).
• MCP Registry incremental sync. The registry client persists last_synced_at
  and accepts updated_since to fetch only changed servers
  (?version=latest&updated_since=… with cursor pagination), merging deltas into
  the cache via merge_registry_delta. A failed incremental attempt degrades to
  a full fetch, and a failed full fetch degrades to the prior cache. Default
  full-fetch callers are unchanged.
• Opt-in private-registry support (PMCP_REGISTRY_ALLOW_PRIVATE, default off).
  When enabled with PMCP_REGISTRY_PRIVATE_ENDPOINT, PMCP discovers from a
  private/custom registry and tolerates draft/non-GA server.json schema fields,
  surfacing all versions — a debugging aid for developers building their own
  private MCP servers, not for production discovery. With the flag off,
  discovery behavior is unchanged.