include/halp/halp.cppm exports the halp convenience layer (import halp;) pulling in
only halp's own deps -- no binding/score/ossia/Qt -- so it builds standalone. Built
into avnd_halp_module (gated on CMAKE_CXX_SCAN_FOR_MODULES), reused by every backend.
Validated: builds with gcc-16 via avendish's own CMake (FILE_SET CXX_MODULES).

A user object written as a .cppm module (export module <c_name>; import halp;) now
builds through the same per-backend prototype as a header object: the prototype's
single "pull in the user code" line becomes @AVND_MAIN_IMPORT@, configured to either
#include the header or import the module -- no duplicated module_prototype files.
Helpers (avendish.modules.cmake): avnd_main_import (the prototype line), and
avnd_add_object_to_base / avnd_add_object_to_backend, which compile a .cppm once in
the object's base library (exported BMI) and have backend targets link it to import,
or compile a header as before. Module-ness is auto-detected from the extension; the
module name is the object's C_NAME by convention.
Wired through avnd_register (base) + the dump backend. Validated with gcc-16: the
non-module dump path is unchanged and a .cppm object builds, links, and runs.

Each backend prototype now uses the shared @AVND_MAIN_IMPORT@ line (computed once in
_avnd_dispatch_backend, or explicitly for dump/ossia/example_host) and consumes the
user object via avnd_add_object_to_backend (link the base library that compiled the
.cppm, or source the header as before). No duplicated per-backend module prototypes.
Full configure is clean across all backends; the non-module path is unchanged and a
.cppm object builds + runs through the dump backend (gcc-16).
Known limitation (next): GCC requires a module BMI's exception/rtti dialect to match
its consumers, but avendish backends differ (dump uses exceptions, plugin backends
use DisableExceptions / -fno-exceptions -fno-rtti), so one shared module can't yet
serve both -- a dialect decision is needed.

GCC requires a module BMI's exception/rtti dialect to match every consumer
exactly, so a single shared halp BMI cannot serve both the exception backends
(dump/python/ossia) and the -fno-exceptions -fno-rtti plugin backends. Compile
the slim halp module and the user object into each backend target instead, in
that backend's own dialect; both are one small object, so the duplication is
cheap and every backend stays self-contained. This replaces the shared
avnd_halp_module STATIC library and its base-library compilation.
Also move `import` after the avnd binding includes in the 9 prototypes that had
it first. A module-linkage processor type whose `import` precedes the avnd
introspection headers makes value-init concepts (inputs_is_value, ...) diverge,
leaving effect_container<T> incomplete and the example process() constraints
unsatisfied; including avnd first -- the order dump/vst3/fuzz/standalone already
used -- fixes it for both the header and module paths with one shared prototype.
Requires a generator with module support (Ninja; the Makefiles generator drops
-fmodules) and -DCMAKE_CXX_SCAN_FOR_MODULES=ON. Validated with gcc-16 on the
same object across dialects: dump (exceptions) and example (no-exceptions) build
and run, vintage (no-exceptions/no-rtti) builds its plugin .so.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>