feat: Plugin developer guide and CI coverage for example plugins

[gmh5225]

Background

NeverD exposes a pure C plugin ABI (NeverDPlugin.h) with loader/processor/UI plugin types and session events. An example plugin ships under plugins/example/, built with -DNEVERD_BUILD_PLUGINS=ON (default OFF).

The CLI supports listing and running plugins (neverd plugins), and load paths are documented in README (<neverd-dir>/plugins, ~/.neverd/plugins, $NEVERD_PLUGIN_PATH). However:

• There is no plugin developer guide
• Plugins are not built or tested in CI
• Integrators lack a minimal “hello plugin” walkthrough beyond the example source

Roadmap §4 mentions expanding the plugin ABI for new formats/loaders over time.

Goal

Make the plugin system discoverable, documented, and regression-tested so third parties (and AI agents) can extend NeverD without forking core code.

Current state

Item	Location
Plugin header	include/neverd/sdk/NeverDPlugin.h
C API	include/neverd/sdk/NeverDCAPI.h
Example plugin	plugins/example/example_plugin.c
Build flag	NEVERD_BUILD_PLUGINS (default OFF)
CLI	neverd plugins command

Acceptance criteria

Documentation

• Add docs/plugins.md (or section in architecture docs) covering:
  • Plugin types (NEVERD_PLUGIN_LOADER, PROCESSOR, UI, GENERIC)
  • Required exported symbol: neverd_plugin → neverd_plugin_t
  • Event model (NEVERD_EVT_BINARY_LOADED, ANALYSIS_DONE, PATCH_APPLIED, …)
  • Build instructions: -DNEVERD_BUILD_PLUGINS=ON, link against libneverd
  • Install / load paths and $NEVERD_PLUGIN_PATH
  • Minimal step-by-step: build example → copy to plugins dir → neverd plugins list/run

CI integration (depends on #1)

• CI job (or matrix leg) builds with -DNEVERD_BUILD_PLUGINS=ON
• Smoke test: load example plugin via CLI (neverd plugins list shows it, or run a documented subcommand)
• Plugin build works on Linux, macOS, and Windows (or document platform gaps explicitly)

Example plugin quality

• Example plugin demonstrates at least one event handler with clear comments
• Optional: tiny integration test under unittests/ that loads the plugin in-process if a stable test hook exists; otherwise CLI smoke test in CI is sufficient

README

• Link to plugin docs from README SDK and plugins section

Implementation notes (for implementers / AI agents)

1. Read NeverDPlugin.h, plugins/example/example_plugin.c, and CLI plugin command implementation under tools/neverd/
2. Keep the plugin API pure C — no C++ in plugin examples unless clearly isolated
3. Do not break existing default builds (NEVERD_BUILD_PLUGINS=OFF remains default)
4. If Windows DLL export requires __declspec(dllexport), document it in the guide

Out of scope

• New plugin types or ABI breaking changes
• GUI plugin hosting (no GUI in repo today)
• Publishing plugins to a central registry
• EVM/Solana loaders as plugins (separate roadmap issues)

Deliverables

1. docs/plugins.md (+ README link)
2. CI step building and smoke-testing the example plugin
3. Any small fixes needed for cross-platform plugin loading

References

• README SDK section: README.md
• Example: plugins/example/
• Roadmap §4: docs/roadmap/README.md
• Related: feat: Add cross-platform CI/CD — build NeverD and run the test suite #1 (CI/CD), docs issue docs: Add CONTRIBUTING guide and architecture documentation #5