feat(plugin): marketplace — install plugins from a curated registry

Add a Plugin Manager marketplace that installs external add-ons from a
GitHub repo's Releases. A curated registry (plugins/registry.json in this
repo, extended by PR) lists discoverable plugins; the host fetches it,
shows each entry with a release dropdown, and on install downloads the
asset matching the user's platform plus plugin.toml into the plugins
folder (API-version checked first). Users can also link arbitrary
owner/repo manually. Linked repos persist in settings.

Desktop only (ureq + serde_json); the install path reuses the phase-2
loader. Part of the #100 extensibility epic (phase 2).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/ui/plugin_manager.rs

@@ -5,11 +5,21 @@
 //! `docs/plugin-architecture.md`.
 
 use crate::app::Message;
-use crate::plugin::external::ExternalPlugin;
+use crate::plugin::external::{ExternalPlugin, RegistryEntry};
 use crate::plugin::manifest::PluginManifest;
-use iced::widget::{button, column, container, row, scrollable, text, Space};
+use iced::widget::{button, column, container, pick_list, row, scrollable, text, text_input, Space};
 use iced::{Background, Border, Color, Element, Fill, Theme};
-use rustc_hash::FxHashSet;
+use rustc_hash::{FxHashMap, FxHashSet};
+
+/// Marketplace state passed to the Plugin Manager view.
+pub struct MarketView<'a> {
+    pub registry: &'a [RegistryEntry],
+    pub input: &'a str,
+    pub repos: &'a [String],
+    pub release_tags: &'a FxHashMap<String, Vec<String>>,
+    pub selected_tag: &'a FxHashMap<String, String>,
+    pub status: &'a str,
+}
 
 // Register the command names for autocomplete.
 inventory::submit!(crate::command::CommandRegistration {
@@ -199,11 +209,131 @@ fn external_card<'a>(p: &ExternalPlugin, loaded: bool) -> Element<'a, Message> {
         .into()
 }
 
+fn pill_button<'a>(label: &str, msg: Message, bg: Color) -> Element<'a, Message> {
+    button(text(label.to_string()).size(12).color(WHITE))
+        .padding([4, 12])
+        .on_press(msg)
+        .style(move |_: &Theme, status| {
+            let c = if matches!(status, button::Status::Hovered | button::Status::Pressed) {
+                Color { r: bg.r + 0.08, g: bg.g + 0.08, b: bg.b + 0.08, a: 1.0 }
+            } else {
+                bg
+            };
+            button::Style {
+                background: Some(Background::Color(c)),
+                text_color: WHITE,
+                border: Border { radius: 4.0.into(), ..Default::default() },
+                ..Default::default()
+            }
+        })
+        .into()
+}
+
+const GREEN: Color = Color { r: 0.2, g: 0.45, b: 0.28, a: 1.0 };
+const RED: Color = Color { r: 0.4, g: 0.25, b: 0.25, a: 1.0 };
+
+/// Release dropdown + Install (+ optional unlink) for one repo.
+fn install_controls<'a>(
+    repo: &str,
+    tags: Vec<String>,
+    selected: Option<String>,
+    removable: bool,
+) -> Element<'a, Message> {
+    let repo_s = repo.to_string();
+    let picker: Element<'_, Message> = if tags.is_empty() {
+        text("no releases").size(11).color(DIM).into()
+    } else {
+        let r = repo_s.clone();
+        pick_list(tags, selected, move |tag| {
+            Message::PluginReleaseSelect(r.clone(), tag)
+        })
+        .text_size(12)
+        .into()
+    };
+    let mut controls = row![
+        picker,
+        Space::new().width(8),
+        pill_button("Install", Message::PluginInstall(repo_s.clone()), GREEN),
+    ]
+    .align_y(iced::Center)
+    .spacing(4);
+    if removable {
+        controls = controls.push(Space::new().width(6));
+        controls = controls.push(pill_button("✕", Message::PluginRepoRemove(repo_s), RED));
+    }
+    controls.into()
+}
+
+fn market_card<'a>(body: iced::widget::Column<'a, Message>) -> Element<'a, Message> {
+    container(body.spacing(4).padding([10, 12]))
+        .width(Fill)
+        .style(|_: &Theme| container::Style {
+            background: Some(Background::Color(CARD)),
+            border: Border { color: BORDER, width: 1.0, radius: 6.0.into() },
+            ..Default::default()
+        })
+        .into()
+}
+
+fn marketplace_section<'a>(m: &MarketView) -> Element<'a, Message> {
+    let mut col = column![text("Available plugins").size(13).color(ACCENT)].spacing(6);
+
+    // Curated registry entries (from the OpenCADStudio repo).
+    for e in m.registry {
+        let tags = m.release_tags.get(&e.repo).cloned().unwrap_or_default();
+        let selected = m.selected_tag.get(&e.repo).cloned();
+        let header = row![
+            text(e.name.clone()).size(14).color(WHITE),
+            Space::new().width(Fill),
+            install_controls(&e.repo, tags, selected, false),
+        ]
+        .align_y(iced::Center);
+        let mut body = column![header, text(e.repo.clone()).size(11).color(ACCENT)];
+        if !e.description.is_empty() {
+            body = body.push(text(e.description.clone()).size(12).color(DIM));
+        }
+        col = col.push(market_card(body));
+    }
+
+    // Manual: link any repo by owner/repo.
+    col = col.push(Space::new().height(6));
+    col = col.push(text("Add a repository").size(12).color(DIM));
+    col = col.push(
+        row![
+            text_input("owner/repo", m.input)
+                .on_input(Message::PluginRepoInput)
+                .on_submit(Message::PluginRepoAdd)
+                .size(13)
+                .width(Fill),
+            Space::new().width(8),
+            pill_button("Add", Message::PluginRepoAdd, Color { r: 0.2, g: 0.4, b: 0.62, a: 1.0 }),
+        ]
+        .align_y(iced::Center),
+    );
+    for repo in m.repos {
+        let tags = m.release_tags.get(repo).cloned().unwrap_or_default();
+        let selected = m.selected_tag.get(repo).cloned();
+        let header = row![
+            text(repo.clone()).size(13).color(WHITE),
+            Space::new().width(Fill),
+            install_controls(repo, tags, selected, true),
+        ]
+        .align_y(iced::Center);
+        col = col.push(market_card(column![header]));
+    }
+
+    if !m.status.is_empty() {
+        col = col.push(text(m.status.to_string()).size(11).color(DIM));
+    }
+    col.into()
+}
+
 pub fn view_window<'a>(
     plugins: &[&'static PluginManifest],
     disabled: &FxHashSet<String>,
     externals: &[ExternalPlugin],
     loaded: &FxHashSet<String>,
+    market: MarketView,
 ) -> Element<'a, Message> {
     let title = text("Installed Plugins").size(20).color(WHITE);
     let subtitle = text(format!(
@@ -235,6 +365,9 @@ pub fn view_window<'a>(
             list = list.push(external_card(p, loaded.contains(&p.id)));
         }
     }
+    // Marketplace: install from a linked repository's releases.
+    list = list.push(Space::new().height(14));
+    list = list.push(marketplace_section(&market));
     let body: Element<'_, Message> = scrollable(list.width(Fill)).height(Fill).into();
 
     container(