feat(simulation): persist SelectedBookmark across save/load (#863, #862)

Adds Serialize/Deserialize to SelectedBookmark and wires it into
SaveStateV1 so a loaded game remembers which bookmark and starting
location the player picked. Replaces the TODO at bookmark/mod.rs:95
(originally deferred to Sprint 37 alongside #614).

Also refactors BookmarkPlugin to accept an injected BookmarkRegistry
via BookmarkPlugin::new(registry) (#862). The Default constructor
still wires the canonical tycoon registry — injection is for tests
and future TOML loading. Flagged in PR #132 review as a follow-up.

Updates bookmark spec §4.4 to remove the v0.2-deferred scope note.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/bookmark/mod.rs

@@ -20,7 +20,11 @@ use crate::knowledge::{resolve_culture, CultureResolver};
 ///
 /// Built once during `BookmarkPlugin::build`, read-only at runtime.
 /// `BTreeMap` for deterministic iteration (D-010 principle 4, D-041).
-#[derive(Resource, Debug, Default)]
+///
+/// `Clone` is required by `BookmarkPlugin::build` which moves the registry into
+/// the Bevy `App` via `insert_resource` while retaining the value from `self`
+/// (#862 injection pattern).
+#[derive(Resource, Debug, Default, Clone)]
 pub struct BookmarkRegistry {
     entries: BTreeMap<String, BookmarkDefinition>,
 }
@@ -88,18 +92,15 @@ impl BookmarkRegistry {
 }
 
 /// The confirmed bookmark selection for the current session.
-/// Populated when `ConfirmBookmark` is processed. `None` during the
-/// character-creation phase (before confirm) and always `None` in a
-/// fresh session.
 ///
-/// **v0.2 scope: transient only.** Not serialized — save/load of
-/// `SelectedBookmark` is deferred to Sprint 37 (follow-up ticket
-/// filed alongside #614). Add `Serialize`/`Deserialize` derives and
-/// wire into `SaveState` when that ticket is claimed.
+/// Populated when `ConfirmBookmark` is processed. `None` fields during the
+/// character-creation phase (before confirm) and in a fresh session.
+///
+/// Serialized into `SaveStateV1.selected_bookmark` (#863) so that a loaded
+/// game remembers which bookmark and starting location were chosen.
 ///
 /// Downstream systems (apartment generator, skill seeder) read from this resource.
-// TODO(sprint-37): serialize — see #863
-#[derive(Resource, Debug, Clone, Default)]
+#[derive(Resource, Debug, Clone, Default, serde::Serialize, serde::Deserialize)]
 pub struct SelectedBookmark {
     pub bookmark_id: Option<String>,
     pub starting_location_id: Option<String>,
@@ -109,14 +110,47 @@ pub struct SelectedBookmark {
 ///
 /// Registers `BookmarkRegistry`, `SelectedBookmark`, and the startup system that
 /// stages the initial catalog in `SnapshotBuffer` for tick-0 delivery.
-pub struct BookmarkPlugin;
+///
+/// **Default construction** uses the canonical tycoon registry:
+/// ```ignore
+/// app.add_plugins(BookmarkPlugin::default());
+/// ```
+///
+/// **Injection** substitutes a custom registry (for tests and future TOML loading):
+/// ```ignore
+/// let mut registry = BookmarkRegistry::default();
+/// // populate ...
+/// app.add_plugins(BookmarkPlugin::new(registry));
+/// ```
+pub struct BookmarkPlugin {
+    registry: BookmarkRegistry,
+}
+
+impl BookmarkPlugin {
+    /// Create a plugin with an injected registry.
+    ///
+    /// Useful in tests (inject a minimal registry with fixed entries) and
+    /// for future TOML loading (caller constructs the registry from disk,
+    /// then hands it to the plugin).
+    pub fn new(registry: BookmarkRegistry) -> Self {
+        Self { registry }
+    }
+}
+
+impl Default for BookmarkPlugin {
+    /// Default plugin pre-populates the canonical tycoon registry via
+    /// `register_default_bookmarks`. Equivalent to the v0.2 behaviour before
+    /// injection was introduced.
+    fn default() -> Self {
+        let mut registry = BookmarkRegistry::default();
+        register_default_bookmarks(&mut registry);
+        Self { registry }
+    }
+}
 
 impl Plugin for BookmarkPlugin {
     fn build(&self, app: &mut App) {
-        let mut registry = BookmarkRegistry::default();
-        register_default_bookmarks(&mut registry);
-
-        app.insert_resource(registry)
+        app.insert_resource(self.registry.clone())
             .init_resource::<SelectedBookmark>()
             .add_systems(Startup, prime_initial_catalog);