Implement trigger control input reset in Synth::doProcess

[kaoskorobase]

Background

kMethcla_Trigger (0x1) is already defined in Methcla_PortFlags in include/methcla/plugin.h, and SynthDef::portDescriptor() already exposes Methcla_PortDescriptor (which carries the flags field). The engine never acts on this flag, however — the reset loop was scaffolded but never completed, and was removed as dead code in #148.

What needs to happen

After each process cycle, any control input port flagged `kMethcla_Trigger` should be reset to `0.f` (one-shot / edge-trigger semantics). The sending side writes a non-zero value once; the engine zeros it on the next block so the synth sees exactly one non-zero sample.

Required changes

All changes are internal to the engine; the plugin API (kMethcla_Trigger) is already public.

src/Methcla/Audio/Synth.hpp — Synth::Flags

Add a hasTriggerInput bit:

struct Flags
{
    unsigned int state          : 2;
    unsigned int hasTriggerInput : 1;
};

src/Methcla/Audio/Synth.cpp — construction

After the port-counting loop (around line 100), scan control input port descriptors and set the flag:

Methcla_PortDescriptor desc;
for (Methcla_PortCount i = 0; i < numControlInputs; i++) {
    synthDef.portDescriptor(options, controlInputPortIndex(i), &desc);
    if (desc.flags & kMethcla_Trigger) {
        synth->m_flags.hasTriggerInput = 1;
        break;
    }
}

(The exact port index arithmetic depends on how control input indices map to global port indices — verify against the existing counting loop.)

src/Methcla/Audio/Synth.cpp — Synth::doProcess

At the end of the kStateActive block, after the output-write loop:

if (m_flags.hasTriggerInput) {
    Methcla_PortDescriptor desc;
    for (Methcla_PortCount i = 0; i < numControlInputs(); i++) {
        synthDef().portDescriptor(nullptr, controlInputPortIndex(i), &desc);
        if (desc.flags & kMethcla_Trigger)
            controlInput(i) = 0.f;
    }
}

Note: portDescriptor takes a Methcla_SynthOptions*; pass nullptr here since options are only needed at construction. Verify this is safe with the existing implementation in SynthDef.cpp.

Out of scope

• Changes to plugin.h or the public C API
• Exposing trigger-port semantics through the OSC/C++ client API