Add demo_plugin and plugin host integration tests

Minimal in-tree add-on (DP_HELLO) validates registry, ribbon merge, and try_dispatch. Five new lib tests; EntryKind gains PartialEq for test helpers.

docs/PR-plugin-host.md

@@ -51,7 +51,7 @@ cargo build
 cargo test --lib
 ```
 
-No domain plugin is registered in this branch; existing core tests should pass unchanged.
+A minimal **`demo_plugin`** add-on registers at compile time for smoke tests (`DP_HELLO` command, Demo Plugin ribbon tab). Remove or gate it before release if maintainers prefer zero in-tree add-ons.
 
 ## Review questions
 

docs/issue-78-comment.txt

@@ -0,0 +1,36 @@
+@HakanSeven12 @schoeller — following up with a concrete architecture proposal and an implementation ready for review.
+
+### Proposal
+
+I've drafted a **QGIS-style add-on model** on my fork:
+
+- **Spec:** [docs/plugin-architecture.md](https://github.com/mf4633/OpenCADStudio/blob/feature/plugin-host/docs/plugin-architecture.md)
+- **Scaffold:** [docs/plugin-template/](https://github.com/mf4633/OpenCADStudio/tree/feature/plugin-host/docs/plugin-template)
+- **Framework PR:** #80 — **host only, no Storm Sewer in core**
+
+**Three layers:** host core → add-on package (plugin.toml, ribbon, commands) → optional headless engine crate. Domain data lives on DWG entities (XDATA), not a proprietary project DB.
+
+**Phase 1 (PR #80):** in-process plugins via inventory::submit!(PluginRegistration), HostSession API, per-document plugin state, command routing without editing commands.rs.
+
+**Phase 2:** user install folder + dynamic .dll/.so with the same plugin.toml.
+
+### Storm Sewer (separate)
+
+Storm Sewer stays on a separate branch as the reference consumer — not in core: [feature/storm-sewer-module](https://github.com/mf4633/OpenCADStudio/tree/feature/storm-sewer-module).
+
+### Re: script languages (@schoeller, #29)
+
+Agree this shouldn't be either/or. Suggested sequencing:
+
+1. Native Rust add-ons + stable HostSession / ocs_plugin_api
+2. Python (or similar) as **bindings over that same API** — one extension surface, two authoring paths
+
+Phase 1 defers embedded scripting until the native API is stable.
+
+### Questions for maintainers
+
+1. ocs_plugin_api as a workspace crate with semver — OK?
+2. Should the main repo ship **zero** discipline modules, or optional built-ins for dev?
+3. Priority: extract API crate (1b) vs dynamic loading (2)?
+
+— Michael

src/app/mod.rs

@@ -1475,6 +1475,22 @@ impl OpenCADStudio {
         app
     }
 
+    #[cfg(test)]
+    pub(crate) fn new_for_test() -> Self {
+        Self::new()
+    }
+
+    #[cfg(test)]
+    pub(crate) fn command_history_info(&self) -> Vec<String> {
+        use crate::ui::command_line::EntryKind;
+        self.command_line
+            .history
+            .iter()
+            .filter(|e| e.kind == EntryKind::Info)
+            .map(|e| e.text.clone())
+            .collect()
+    }
+
     /// Boot function for `iced::daemon`: returns initial state plus a task that
     /// opens the primary application window.
     fn boot() -> (Self, Task<Message>) {

src/modules/demo_plugin/dispatch.rs

@@ -0,0 +1,11 @@
+use crate::plugin::host::HostSession;
+
+pub fn handle(host: &mut HostSession<'_>, cmd: &str) -> bool {
+    match cmd {
+        "DP_HELLO" => {
+            host.push_info("Hello from demo_plugin (plugin host OK).");
+            true
+        }
+        _ => false,
+    }
+}

src/modules/demo_plugin/manifest.rs

@@ -0,0 +1,14 @@
+use crate::plugin::manifest::{ApiVersion, PluginManifest};
+
+pub const PLUGIN_ID: &str = "opencad.demo_plugin";
+
+pub static MANIFEST: PluginManifest = PluginManifest {
+    id: PLUGIN_ID,
+    name: "Demo Plugin",
+    version: "0.1.0",
+    description: "Minimal add-on for plugin-host integration tests",
+    api_version: ApiVersion::CURRENT,
+    ribbon_order: 99,
+    xdata_apps: &[],
+    command_prefixes: &["DP_"],
+};

src/modules/demo_plugin/mod.rs

@@ -0,0 +1,47 @@
+// Minimal in-tree add-on — validates plugin host on `feature/plugin-host`.
+
+pub mod dispatch;
+pub mod manifest;
+pub mod plugin;
+pub mod register;
+
+use crate::modules::{CadModule, IconKind, ModuleEvent, RibbonGroup, RibbonItem, ToolDef};
+
+inventory::submit!(crate::command::CommandRegistration {
+    names: &["DP_HELLO"]
+});
+
+pub struct DemoPluginModule;
+
+impl CadModule for DemoPluginModule {
+    fn id(&self) -> &'static str {
+        "demo_plugin"
+    }
+
+    fn title(&self) -> &'static str {
+        "Demo Plugin"
+    }
+
+    fn ribbon_groups(&self) -> Vec<RibbonGroup> {
+        vec![RibbonGroup {
+            title: "Smoke",
+            tools: vec![RibbonItem::LargeTool(ToolDef {
+                id: "DP_HELLO",
+                label: "Hello",
+                icon: IconKind::Glyph("★"),
+                event: ModuleEvent::Command("DP_HELLO".to_string()),
+            })],
+        }]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::plugin::all_ribbon_modules;
+
+    #[test]
+    fn ribbon_tab_is_registered() {
+        let titles: Vec<&str> = all_ribbon_modules().iter().map(|m| m.title()).collect();
+        assert!(titles.contains(&"Demo Plugin"), "tabs: {titles:?}");
+    }
+}

src/modules/demo_plugin/plugin.rs

@@ -0,0 +1,21 @@
+use crate::plugin::host::{BuiltinPlugin, HostSession};
+use crate::plugin::manifest::PluginManifest;
+
+use super::dispatch;
+use super::manifest;
+
+pub struct DemoPlugin;
+
+impl BuiltinPlugin for DemoPlugin {
+    fn manifest(&self) -> &'static PluginManifest {
+        &manifest::MANIFEST
+    }
+
+    fn ribbon(&self) -> Box<dyn crate::modules::CadModule> {
+        Box::new(super::DemoPluginModule)
+    }
+
+    fn dispatch(&self, host: &mut HostSession<'_>, cmd: &str) -> bool {
+        dispatch::handle(host, cmd)
+    }
+}

src/modules/demo_plugin/plugin.toml

@@ -0,0 +1,13 @@
+[plugin]
+id = "opencad.demo_plugin"
+name = "Demo Plugin"
+version = "0.1.0"
+description = "Minimal add-on for plugin-host integration tests"
+author = "Open CAD Studio contributors"
+license = "GPL-3.0-only"
+
+[opencad]
+api_version = 1
+ribbon_order = 99
+command_prefixes = ["DP_"]
+xdata_apps = []

src/modules/demo_plugin/register.rs

@@ -0,0 +1,7 @@
+use super::plugin::DemoPlugin;
+
+inventory::submit! {
+    crate::plugin::registry::PluginRegistration {
+        construct: || Box::new(DemoPlugin),
+    }
+}

src/modules/mod.rs

@@ -139,6 +139,7 @@ pub mod home;
 pub mod insert;
 pub mod model;
 pub mod layout;
+pub mod demo_plugin;
 pub mod manage;
 pub mod view;
 

src/plugin/registry.rs

@@ -40,3 +40,49 @@ pub(crate) fn try_dispatch(app: &mut OpenCADStudio, tab: usize, cmd: &str) -> bo
     }
     false
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::app::OpenCADStudio;
+    #[test]
+    fn discovers_registered_plugins() {
+        let plugins = all_plugins();
+        assert!(
+            !plugins.is_empty(),
+            "expected at least one PluginRegistration (demo_plugin)"
+        );
+        assert!(
+            plugins
+                .iter()
+                .any(|p| p.manifest().id == "opencad.demo_plugin"),
+            "demo_plugin missing; ids: {:?}",
+            plugins.iter().map(|p| p.manifest().id).collect::<Vec<_>>()
+        );
+    }
+
+    #[test]
+    fn addon_ribbon_tabs_merge_after_core() {
+        let titles: Vec<&str> = all_ribbon_modules().iter().map(|m| m.title()).collect();
+        assert!(titles.contains(&"Demo Plugin"), "ribbon tabs: {titles:?}");
+        let core = core_registry::all_modules();
+        assert_eq!(titles.len(), core.len() + all_plugins().len());
+    }
+
+    #[test]
+    fn try_dispatch_routes_demo_command() {
+        let mut app = OpenCADStudio::new_for_test();
+        assert!(try_dispatch(&mut app, 0, "DP_HELLO"));
+        let info = app.command_history_info();
+        assert!(
+            info.iter().any(|t| t.contains("demo_plugin") && t.contains("plugin host OK")),
+            "info history: {info:?}"
+        );
+    }
+
+    #[test]
+    fn unknown_plugin_command_falls_through() {
+        let mut app = OpenCADStudio::new_for_test();
+        assert!(!try_dispatch(&mut app, 0, "DP_NOPE"));
+    }
+}

src/ui/command_line.rs

@@ -49,7 +49,7 @@ pub struct HistoryEntry {
     pub created_at: Instant,
 }
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub enum EntryKind {
     Command,
     Output,