feat(filter_protocol): FilterTransform SDK contract + pj.filter_registry.v1 service

Replaces the originally-proposed split where the host carried its own copy of
the FilterTransform catalogue. Now ONE FilterTransformFactory exists at runtime,
owned by the host, populated by the Filter Editor plugin via the new
pj.filter_registry.v1 service. Preview, layout-restore, and the streaming
read path all resolve through the same instances — no math drift possible.

Contents:
- Abstract contract: PJ::sdk::FilterTransform (filter_transform.hpp)
- The 12 builtin strategies vendored as header-only (builtin_transforms.hpp):
  NoneTransform / AbsoluteTransform / ScaleTransform / DerivativeTransform /
  IntegralTransform / MovingAverageTransform / MovingRMSTransform /
  MovingVarianceTransform / OutlierRemovalTransform / SamplesCounterTransform /
  BinaryFilterTransform / TimeSincePreviousTransform
- FilterTransformFactory: keeps (create_fn, delete_fn, library_owner) per entry.
  Cross-DSO destruction goes through the registered deleter; library_owner
  pins the registering DSO while any of its entries is live.
- New host service pj.filter_registry.v1: C ABI vtable + Traits + C++ View.
  Plugins receive the View at bind() and register their classes into the
  host's factory; host code resolves via factory.create(id).
- FilterRegistryHost: in-process adapter that wraps a FilterTransformFactory
  as the C-ABI service ctx, with paired thunks and a LibraryOwnerResolver.
- Lift Point2 from pj_base/builtin/image_annotations.hpp to pj_base/point2.hpp
  (unchanged ABI; same struct).
- Surface manifest 'tags' array on PluginDescriptor + RuntimeToolboxPlugin.

Versioning: additive — no existing header, struct layout, or ABI signature
changes; required release level when merged is MINOR.

Verified locally: build green, 44/44 tests pass.

Author: pabloinigoblasco

pj_base/include/pj_base/builtin/image_annotations.hpp

@@ -19,6 +19,7 @@
 #include <string>
 #include <vector>
 
+#include "pj_base/point2.hpp"
 #include "pj_base/types.hpp"
 
 namespace PJ {
@@ -32,12 +33,8 @@ enum class AnnotationTopology : uint8_t {
   kLineLoop,   ///< Like LineStrip but closes back to the first point. 4-point loop = rectangle.
 };
 
-/// 2D point in image-pixel coordinates (origin top-left).
-struct Point2 {
-  double x = 0.0;
-  double y = 0.0;
-  bool operator==(const Point2&) const = default;
-};
+// `Point2` lives in pj_base/point2.hpp (generic 2D vocab type). In this header
+// it's used in image-pixel coordinates (origin top-left).
 
 /// 8-bit per-channel RGBA color. a=0 means transparent / disabled.
 struct ColorRGBA {

pj_base/include/pj_base/point2.hpp

@@ -0,0 +1,18 @@
+// Copyright 2026 Davide Faconti
+// SPDX-License-Identifier: Apache-2.0
+#pragma once
+
+// Plain (x, y) 2D point. Generic double-precision vocab type — used by image
+// annotations (pixel coordinates), Filter Editor transforms (time/value
+// samples), and any other 2D context where a tagged shape would be overkill.
+// The semantic of x / y is owned by the caller.
+
+namespace PJ::sdk {
+
+struct Point2 {
+  double x = 0.0;
+  double y = 0.0;
+  bool operator==(const Point2&) const = default;
+};
+
+}  // namespace PJ::sdk

pj_plugins/CMakeLists.txt

@@ -17,6 +17,25 @@ target_link_libraries(pj_plugin_loader_detail PUBLIC pj_base)
 
 add_subdirectory(dialog_protocol)
 
+# Filter Editor transform contract (header-only) — plugins implement the 12
+# concrete strategies and self-register with the factory at load time. See
+# pj_plugins/filter_protocol/include/pj_plugins/sdk/filter_transform.hpp.
+add_library(pj_filter_sdk INTERFACE)
+target_compile_features(pj_filter_sdk INTERFACE cxx_std_20)
+target_include_directories(pj_filter_sdk INTERFACE
+  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/filter_protocol/include>
+  $<INSTALL_INTERFACE:include>
+)
+# Builtin strategies (in the plugin) use nlohmann/json for saveParams /
+# loadParams; propagate the dep so consumers get it transitively. Also pulls
+# pj_base for the C ABI primitives (PJ_string_view_t, PJ_error_t, PJ_NOEXCEPT)
+# referenced by the filter registry service.
+target_link_libraries(pj_filter_sdk INTERFACE pj_base nlohmann_json::nlohmann_json)
+set_target_properties(pj_filter_sdk PROPERTIES EXPORT_NAME filter_sdk)
+add_library(plotjuggler_sdk::filter_sdk ALIAS pj_filter_sdk)
+install(DIRECTORY filter_protocol/include/ DESTINATION include)
+install(TARGETS pj_filter_sdk EXPORT plotjuggler_sdkTargets ARCHIVE DESTINATION lib LIBRARY DESTINATION lib INCLUDES DESTINATION include)
+
 # ---------------------------------------------------------------------------
 # pj_plugin_sdk — umbrella INTERFACE library that exposes the full plugin-author
 # SDK surface: C++ SDK headers (MessageParserPluginBase, ObjectIngestPolicy,
@@ -29,7 +48,7 @@ target_include_directories(pj_plugin_sdk INTERFACE
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
   $<INSTALL_INTERFACE:include>
 )
-target_link_libraries(pj_plugin_sdk INTERFACE pj_base pj_dialog_sdk)
+target_link_libraries(pj_plugin_sdk INTERFACE pj_base pj_dialog_sdk pj_filter_sdk)
 set_target_properties(pj_plugin_sdk PROPERTIES EXPORT_NAME plugin_sdk)
 add_library(plotjuggler_sdk::plugin_sdk ALIAS pj_plugin_sdk)