Synth resource port integration (`kMethcla_ResourcePort`)

[kaoskorobase]

Summary

Integrates the resource system from #147 into the Synth layer: declares resource ports in Methcla_SynthDef, acquires/releases resource handles on synth construction/destruction, and extends /node/set to accept integer resource ids for resource ports.

Depends on

• Generic RT/NRT shared resource system (with MultiChannelBuffer as first class) #147 — generic resource system (engine pool, OSC verbs, C API types)

Scope

New port type

Add kMethcla_ResourcePort to the Methcla_PortType enum in include/methcla/plugin.h.

Port direction is informational metadata for resource ports; the engine does not enforce mutability against direction. Methcla_PortDescriptor stays unchanged.

Synth memory layout

Extend Synth::construct() static factory (src/Methcla/Audio/Synth.cpp) to count kMethcla_ResourcePort descriptors, then append a ResourcePortConnection[] array to the single synth allocation block:

[Synth C++ object]
[AudioInputConnection[]]
[AudioOutputConnection[]]
[ResourcePortConnection[]]   // ← new
[control buffers]
[audio buffers]

struct ResourcePortConnection {
    Methcla_PortCount  index;
    Methcla_ResourceId resourceId;
    void*              data;   // cached from resource_acquire
};

Acquire / release lifecycle

• During Synth::construct(): for each resource port, call methcla_world_resource_acquire(world, id, def), store the result in ResourcePortConnection.data, call synthDef.connect(synth, portIndex, data).
• If any acquire fails, construct() fails gracefully (releases already-acquired resources).
• During Synth::~Synth(): call methcla_world_resource_release(world, id) for each resource port with non-null data.

Dynamic re-assignment

Extend /node/set to accept i:value (integer) when the port at portIndex is kMethcla_ResourcePort. The engine:

1. Releases the old resource (if any).
2. Acquires the new resource.
3. Calls synthDef.connect(synth, portIndex, newData).

Using f:value against a resource port returns replyError unchanged.

C++ helper

ResourceRef<T> (defined in #147, include/methcla/plugin.hpp) works as the per-synth-lifetime RAII wrapper for plugins that prefer a C++ interface over explicit acquire/release in construct/destroy.

Files to modify

File	Change
include/methcla/plugin.h	Add kMethcla_ResourcePort to Methcla_PortType
src/Methcla/Audio/Synth.hpp	Add ResourcePortConnection, extend Synth members
src/Methcla/Audio/Synth.cpp	Count resource ports, adjust memory layout, acquire/release
src/Methcla/Audio/EngineImpl.cpp	Extend /node/set handler for resource ports
tests/resource_tests.cpp	Add synth integration test cases
CHANGELOG.md	Entry under [Unreleased]
docs/osc-api.md	Document i:value form for /node/set on resource ports