refactor(plugin): extract ocs_plugin_api crate for the stable add-on contract

Move the dependency-free, semver-versioned half of the plugin contract into a
standalone workspace crate `crates/ocs_plugin_api`:

- manifest types: PluginManifest, ApiVersion, API_VERSION
- ribbon vocabulary: CadModule trait + ToolDef/RibbonGroup/RibbonItem/IconKind/
  ModuleEvent/StyleKey

The host re-exports them from `crate::plugin::manifest` and `crate::modules`, so
every existing call site is unchanged. The acadrust-typed runtime surface
(HostSession) stays in the host binary; lifting it behind a HostApi trait in the
same crate is the remaining phase-1b step.

Part of #100. Docs updated in docs/plugin-architecture.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Cargo.lock

@@ -24,6 +24,7 @@ dependencies = [
  "image",
  "inventory",
  "lzma-sys",
+ "ocs_plugin_api",
  "open",
  "printpdf",
  "rayon",
@@ -3646,6 +3647,10 @@ dependencies = [
  "objc2-foundation 0.2.2",
 ]
 
+[[package]]
+name = "ocs_plugin_api"
+version = "0.1.0"
+
 [[package]]
 name = "once_cell"
 version = "1.21.4"

Cargo.toml

@@ -4,7 +4,13 @@ version = "0.5.6"
 edition = "2021"
 build = "build.rs"
 
+[workspace]
+members = ["crates/ocs_plugin_api"]
+
 [dependencies]
+# Stable, dependency-free add-on contract (manifest + ribbon/CadModule types).
+# Plugin authors target this crate's semver, not OpenCADStudio internals.
+ocs_plugin_api = { path = "crates/ocs_plugin_api" }
 # vtkio (pulled in transitively via truck-meshalgo) depends on xz2 → lzma-sys,
 # which by default links the system liblzma dynamically. On macOS that bakes a
 # Homebrew dylib path (/opt/homebrew/.../liblzma.5.dylib) into the binary, so

crates/ocs_plugin_api/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "ocs_plugin_api"
+version = "0.1.0"
+edition = "2021"
+description = "Stable, dependency-free contract for Open CAD Studio add-on packages: plugin manifest, version handshake, and ribbon/CadModule types."
+license = "GPL-3.0-only"
+
+[dependencies]

crates/ocs_plugin_api/src/lib.rs

@@ -0,0 +1,25 @@
+//! # Open CAD Studio plugin API
+//!
+//! The stable, semver-versioned contract an add-on package targets instead of
+//! the `OpenCADStudio` binary internals. It is intentionally **dependency
+//! free** (no `iced`, no `acadrust`) so engine crates and external tooling can
+//! depend on it cheaply.
+//!
+//! Two pieces live here:
+//!
+//! - [`manifest`] — plugin identity ([`PluginManifest`]) and the host ABI
+//!   version handshake ([`ApiVersion`]).
+//! - [`ribbon`] — the [`CadModule`] trait and the plain-data ribbon types
+//!   ([`RibbonGroup`], [`ToolDef`], …) a plugin uses to describe its tab.
+//!
+//! The runtime host surface a plugin uses at *dispatch* time (document access,
+//! command line, undo) is `acadrust`-typed and therefore lives in the host
+//! binary for now; see `docs/plugin-architecture.md` (phase 1b).
+
+pub mod manifest;
+pub mod ribbon;
+
+pub use manifest::{ApiVersion, PluginManifest, API_VERSION};
+pub use ribbon::{
+    CadModule, IconKind, ModuleEvent, RibbonGroup, RibbonItem, StyleKey, ToolDef,
+};

crates/ocs_plugin_api/src/manifest.rs

@@ -0,0 +1,51 @@
+//! Plugin identity and capability declaration.
+
+/// Host plugin API version. Bump when the host runtime surface breaks
+/// compatibility.
+pub const API_VERSION: u32 = 1;
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct ApiVersion {
+    pub major: u32,
+}
+
+impl ApiVersion {
+    pub const CURRENT: Self = Self { major: API_VERSION };
+
+    pub fn is_compatible_with(host: ApiVersion) -> bool {
+        Self::CURRENT.major == host.major
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn current_matches_const() {
+        assert_eq!(ApiVersion::CURRENT.major, API_VERSION);
+    }
+
+    #[test]
+    fn same_major_is_compatible() {
+        assert!(ApiVersion::is_compatible_with(ApiVersion::CURRENT));
+        assert!(!ApiVersion::is_compatible_with(ApiVersion {
+            major: API_VERSION + 1,
+        }));
+    }
+}
+
+/// Static metadata every plugin supplies at registration time.
+/// Keep fields in sync with `plugin.toml` beside the package.
+#[derive(Clone, Copy, Debug)]
+pub struct PluginManifest {
+    pub id: &'static str,
+    pub name: &'static str,
+    pub version: &'static str,
+    pub description: &'static str,
+    pub api_version: ApiVersion,
+    /// Sort key for add-on ribbon tabs (lower = further left among plugins).
+    pub ribbon_order: i32,
+    pub xdata_apps: &'static [&'static str],
+    pub command_prefixes: &'static [&'static str],
+}

crates/ocs_plugin_api/src/ribbon.rs

@@ -0,0 +1,159 @@
+//! Ribbon description types — the plain-data vocabulary a [`CadModule`] uses to
+//! declare its tab. No UI-framework dependency: the host renders these.
+
+// ── Events ────────────────────────────────────────────────────────────────
+
+/// Events a module tool can emit to the host application.
+#[derive(Debug, Clone)]
+pub enum ModuleEvent {
+    /// Fire a named CAD command (e.g. "LINE", "CIRCLE").
+    Command(String),
+    /// Open the OS file dialog.
+    OpenFileDialog,
+    /// Remove all loaded models from the scene.
+    #[allow(dead_code)]
+    ClearModels,
+    /// Toggle wireframe rendering.
+    SetWireframe(bool),
+    /// Toggle the layer manager panel.
+    ToggleLayers,
+}
+
+// ── Data types ────────────────────────────────────────────────────────────
+
+/// Icon source for a ribbon tool button.
+#[derive(Clone, Copy)]
+pub enum IconKind {
+    /// Unicode glyph rendered as text (fast, no file needed).
+    Glyph(&'static str),
+    /// Raw SVG bytes embedded at compile time via `include_bytes!`.
+    Svg(&'static [u8]),
+}
+
+/// A single tool button shown in the ribbon.
+#[derive(Clone)]
+pub struct ToolDef {
+    /// Unique command id, e.g. "LINE".
+    pub id: &'static str,
+    /// Short label shown under the icon.
+    pub label: &'static str,
+    /// Icon — either a unicode glyph or embedded SVG bytes.
+    pub icon: IconKind,
+    /// Event emitted when the tool is clicked.
+    pub event: ModuleEvent,
+}
+
+/// One item in a ribbon group — plain button or dropdown, in small (1-row) or large (3-row) size.
+#[derive(Clone)]
+pub enum RibbonItem {
+    /// 1-row button — icon only, no label.
+    Tool(ToolDef),
+    /// 3-row button — icon + label below; full ribbon height.
+    LargeTool(ToolDef),
+    /// 1-row dropdown — icon + ▾ on right, no label.
+    Dropdown {
+        id: &'static str,
+        icon: IconKind,
+        items: Vec<(&'static str, &'static str, IconKind)>,
+        default: &'static str,
+    },
+    /// 3-row dropdown — icon + label + ▾ below label; full ribbon height.
+    LargeDropdown {
+        id: &'static str,
+        label: &'static str,
+        icon: IconKind,
+        items: Vec<(&'static str, &'static str, IconKind)>,
+        default: &'static str,
+    },
+    /// Layer combo + two rows of small tools below.
+    /// row2: operates on the layer of a selected object (off/freeze/lock/make-current)
+    /// row3: all-layers operations + match (on/thaw/unlock/match)
+    LayerComboGroup {
+        row2: Vec<ToolDef>,
+        row3: Vec<ToolDef>,
+    },
+    /// Match Properties (large button) + Color / Linetype / Lineweight combos on the right.
+    PropertiesGroup { match_prop: ToolDef },
+    /// A style selector combobox (text / dim / mleader / table style) with
+    /// optional small tool rows below it.
+    StyleComboGroup {
+        /// Which style domain this combo controls.
+        style_key: StyleKey,
+        /// Unique dropdown id (must be unique across the ribbon).
+        combo_id: &'static str,
+        /// Optional command to run when the user opens the style manager.
+        manager_cmd: Option<&'static str>,
+        /// Small tool rows rendered below the combo (0–2 rows).
+        rows: Vec<Vec<ToolDef>>,
+    },
+}
+
+/// Identifies which style list a `StyleComboGroup` refers to.
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+pub enum StyleKey {
+    TextStyle,
+    DimStyle,
+    MLeaderStyle,
+    TableStyle,
+}
+
+impl From<ToolDef> for RibbonItem {
+    fn from(t: ToolDef) -> Self {
+        RibbonItem::Tool(t)
+    }
+}
+
+/// A named group of tool buttons shown together in the ribbon.
+pub struct RibbonGroup {
+    pub title: &'static str,
+    pub tools: Vec<RibbonItem>,
+}
+
+// ── Trait ─────────────────────────────────────────────────────────────────
+
+/// A CAD module owns a set of ribbon groups shown when its tab is active.
+/// Each module is a stateless unit struct — all UI state lives in Ribbon.
+pub trait CadModule: Send + Sync {
+    #[allow(dead_code)]
+    fn id(&self) -> &'static str;
+    fn title(&self) -> &'static str;
+    fn ribbon_groups(&self) -> Vec<RibbonGroup>;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn tool_def_converts_into_small_tool() {
+        let tool = ToolDef {
+            id: "LINE",
+            label: "Line",
+            icon: IconKind::Glyph("／"),
+            event: ModuleEvent::Command("LINE".to_string()),
+        };
+        assert!(matches!(RibbonItem::from(tool), RibbonItem::Tool(_)));
+    }
+
+    #[test]
+    fn cad_module_is_object_safe() {
+        struct Demo;
+        impl CadModule for Demo {
+            fn id(&self) -> &'static str {
+                "demo"
+            }
+            fn title(&self) -> &'static str {
+                "Demo"
+            }
+            fn ribbon_groups(&self) -> Vec<RibbonGroup> {
+                vec![RibbonGroup {
+                    title: "Group",
+                    tools: vec![],
+                }]
+            }
+        }
+        let m: Box<dyn CadModule> = Box::new(Demo);
+        assert_eq!(m.title(), "Demo");
+        assert_eq!(m.ribbon_groups().len(), 1);
+    }
+}

docs/plugin-architecture.md

@@ -15,7 +15,7 @@ This document is the **authoritative spec** for how add-on packages integrate wi
 | Goal | Rationale |
 |------|-----------|
 | **One package, one registration** | Ribbon tab, commands, and manifest ship together — no duplicate hooks in `build.rs` and `commands.rs`. |
-| **Stable host surface** | Plugin authors target `HostSession` / future `ocs_plugin_api` with semver, not `OpenCADStudio` internals. |
+| **Stable host surface** | Plugin authors target the semver-versioned `ocs_plugin_api` crate (manifest + ribbon today) and `HostSession`, not `OpenCADStudio` internals. |
 | **Open-source add-on ergonomics** | Separate git repo + workspace crate is supported; in-tree built-ins use the same layout. |
 | **DWG round-trip** | Domain data on entities (XDATA), not opaque plugin databases. |
 | **Engine reuse** | Headless crates (`stormsewer`, …) run in WASM/CLI without the CAD host. |
@@ -69,7 +69,7 @@ This document is the **authoritative spec** for how add-on packages integrate wi
 |------|-----------------|
 | `metadata.txt` (name, version, author, …) | `plugin.toml` beside the package |
 | `classFactory(iface)` in `__init__.py` | `inventory::submit!(PluginRegistration { construct })` in `register.rs` |
-| `iface` stable API | `HostSession` → future `ocs_plugin_api` crate |
+| `iface` stable API | `ocs_plugin_api` crate (manifest + ribbon) + `HostSession` |
 | User folder `…/python/plugins/<id>/` | Phase 2: `%APPDATA%/OpenCADStudio/plugins/<id>/` |
 | Plugin repository (plugins.qgis.org) | Future: curated index; today = git + in-tree |
 | `qgisMinimumVersion` | `api_version` in manifest (host ABI major) |
@@ -182,7 +182,14 @@ Plugins use `HostSession`, not `OpenCADStudio`:
 | Command line | `push_info`, `push_output`, `push_error`, `set_active_command` |
 | Undo / dirty | `push_undo`, `set_dirty` |
 
-Phase 1b: extract to `crates/ocs_plugin_api` with semver when the surface stabilizes.
+**Status:** The dependency-free half of the contract — `PluginManifest` /
+`ApiVersion` (manifest) and `CadModule` + the ribbon types (`ToolDef`,
+`RibbonGroup`, …) — now lives in the standalone, semver-versioned
+[`crates/ocs_plugin_api`](../crates/ocs_plugin_api) crate. The host re-exports it
+(`crate::plugin::manifest`, `crate::modules`) so in-tree paths are unchanged.
+The `acadrust`-typed runtime surface in the table above (`document_mut`,
+`add_entity`, `set_active_command`, …) stays in the host binary for now; lifting
+it behind a `HostApi` trait in the same crate is the remaining phase-1b step.
 
 ### Command routing
 
@@ -247,7 +254,7 @@ This mirrors QGIS: the application ships core menus; plugins add tabs/tools with
 - [x] Per-tab `plugin_state`
 - [x] Storm Sewer off `commands.rs` monolith
 - [x] Single registration (`plugin.toml` + `BuiltinPlugin::ribbon`)
-- [ ] Extract `ocs_plugin_api` crate
+- [~] Extract `ocs_plugin_api` crate — manifest + ribbon/`CadModule` done; `acadrust`-typed host surface pending
 - [ ] Plugin manager UI stub (list installed, versions)
 
 ### Phase 2 — Dynamic loading (desktop)
@@ -321,7 +328,7 @@ OpenCADStudio/
       storm_sewer/              # add-on (has plugin.toml)
   crates/
     stormsewer/                 # Layer C engine
-    ocs_plugin_api/             # (phase 1b) stable host API
+    ocs_plugin_api/             # stable contract: manifest + ribbon (host API: phase 1b)
   plugins/                      # (phase 2) third-party cdylibs
 ```
 

src/modules/mod.rs

@@ -13,124 +13,14 @@
 //   - mod.rs       : module definition (ribbon groups + tool layout)
 //   - <tool>.rs    : one file per tool (ribbon def + future command logic)
 
-// ── Events ────────────────────────────────────────────────────────────────
-
-/// Events a module tool can emit to the host application.
-#[derive(Debug, Clone)]
-pub enum ModuleEvent {
-    /// Fire a named CAD command (e.g. "LINE", "CIRCLE").
-    Command(String),
-    /// Open the OS file dialog.
-    OpenFileDialog,
-    /// Remove all loaded models from the scene.
-    #[allow(dead_code)]
-    ClearModels,
-    /// Toggle wireframe rendering.
-    SetWireframe(bool),
-    /// Toggle the layer manager panel.
-    ToggleLayers,
-}
-
-// ── Data types ────────────────────────────────────────────────────────────
-
-/// Icon source for a ribbon tool button.
-#[derive(Clone, Copy)]
-pub enum IconKind {
-    /// Unicode glyph rendered as text (fast, no file needed).
-    Glyph(&'static str),
-    /// Raw SVG bytes embedded at compile time via `include_bytes!`.
-    Svg(&'static [u8]),
-}
-
-/// A single tool button shown in the ribbon.
-#[derive(Clone)]
-pub struct ToolDef {
-    /// Unique command id, e.g. "LINE".
-    pub id: &'static str,
-    /// Short label shown under the icon.
-    pub label: &'static str,
-    /// Icon — either a unicode glyph or embedded SVG bytes.
-    pub icon: IconKind,
-    /// Event emitted when the tool is clicked.
-    pub event: ModuleEvent,
-}
-
-/// One item in a ribbon group — plain button or dropdown, in small (1-row) or large (3-row) size.
-#[derive(Clone)]
-pub enum RibbonItem {
-    /// 1-row button — icon only, no label.
-    Tool(ToolDef),
-    /// 3-row button — icon + label below; full ribbon height.
-    LargeTool(ToolDef),
-    /// 1-row dropdown — icon + ▾ on right, no label.
-    Dropdown {
-        id: &'static str,
-        icon: IconKind,
-        items: Vec<(&'static str, &'static str, IconKind)>,
-        default: &'static str,
-    },
-    /// 3-row dropdown — icon + label + ▾ below label; full ribbon height.
-    LargeDropdown {
-        id: &'static str,
-        label: &'static str,
-        icon: IconKind,
-        items: Vec<(&'static str, &'static str, IconKind)>,
-        default: &'static str,
-    },
-    /// Layer combo + two rows of small tools below.
-    /// row2: operates on the layer of a selected object (off/freeze/lock/make-current)
-    /// row3: all-layers operations + match (on/thaw/unlock/match)
-    LayerComboGroup {
-        row2: Vec<ToolDef>,
-        row3: Vec<ToolDef>,
-    },
-    /// Match Properties (large button) + Color / Linetype / Lineweight combos on the right.
-    PropertiesGroup { match_prop: ToolDef },
-    /// A style selector combobox (text / dim / mleader / table style) with
-    /// optional small tool rows below it.
-    StyleComboGroup {
-        /// Which style domain this combo controls.
-        style_key: StyleKey,
-        /// Unique dropdown id (must be unique across the ribbon).
-        combo_id: &'static str,
-        /// Optional command to run when the user opens the style manager.
-        manager_cmd: Option<&'static str>,
-        /// Small tool rows rendered below the combo (0–2 rows).
-        rows: Vec<Vec<ToolDef>>,
-    },
-}
-
-/// Identifies which style list a `StyleComboGroup` refers to.
-#[derive(Clone, Copy, PartialEq, Eq, Debug)]
-pub enum StyleKey {
-    TextStyle,
-    DimStyle,
-    MLeaderStyle,
-    TableStyle,
-}
-
-impl From<ToolDef> for RibbonItem {
-    fn from(t: ToolDef) -> Self {
-        RibbonItem::Tool(t)
-    }
-}
-
-/// A named group of tool buttons shown together in the ribbon.
-pub struct RibbonGroup {
-    pub title: &'static str,
-    pub tools: Vec<RibbonItem>,
-}
-
-// ── Trait ─────────────────────────────────────────────────────────────────
-
-/// A CAD module owns a set of ribbon groups shown when its tab is active.
-/// Each module is a stateless unit struct — all UI state lives in Ribbon.
-pub trait CadModule: Send + Sync {
-    #[allow(dead_code)]
-    fn id(&self) -> &'static str;
-    fn title(&self) -> &'static str;
-    fn ribbon_groups(&self) -> Vec<RibbonGroup>;
-}
+// ── Ribbon vocabulary (CadModule, ToolDef, RibbonGroup, …) ─────────────────
+//
+// These types moved to the dependency-free `ocs_plugin_api` crate so add-ons
+// can target a semver-stable contract. Re-exported here to keep the long-used
+// `crate::modules::{CadModule, ToolDef, …}` paths stable across the codebase.
+pub use ocs_plugin_api::ribbon::{
+    CadModule, IconKind, ModuleEvent, RibbonGroup, RibbonItem, StyleKey, ToolDef,
+};
 
 // ── Module declarations ───────────────────────────────────────────────────
 

src/plugin/manifest.rs

@@ -1,32 +1,7 @@
-// Plugin identity and capability declaration.
+//! Plugin identity and capability declaration.
+//!
+//! These types now live in the standalone, dependency-free `ocs_plugin_api`
+//! crate so external add-ons can target a semver-stable contract. Re-exported
+//! here to keep the `crate::plugin::manifest::*` path stable for in-tree use.
 
-/// Host plugin API version. Bump when HostApi breaks compatibility.
-pub const API_VERSION: u32 = 1;
-
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-pub struct ApiVersion {
-    pub major: u32,
-}
-
-impl ApiVersion {
-    pub const CURRENT: Self = Self { major: API_VERSION };
-
-    pub fn is_compatible_with(host: ApiVersion) -> bool {
-        Self::CURRENT.major == host.major
-    }
-}
-
-/// Static metadata every plugin supplies at registration time.
-/// Keep fields in sync with `plugin.toml` beside the package.
-#[derive(Clone, Copy, Debug)]
-pub struct PluginManifest {
-    pub id: &'static str,
-    pub name: &'static str,
-    pub version: &'static str,
-    pub description: &'static str,
-    pub api_version: ApiVersion,
-    /// Sort key for add-on ribbon tabs (lower = further left among plugins).
-    pub ribbon_order: i32,
-    pub xdata_apps: &'static [&'static str],
-    pub command_prefixes: &'static [&'static str],
-}
+pub use ocs_plugin_api::manifest::*;