Checkpoint: preserve all uncommitted rust-rewrite worktree work

Safety commit before reconciling this worktree with main, which has
diverged with its own separate fixes today. Nothing here is reviewed
or curated yet - this exists purely so none of this work can be lost
to a git operation, disk issue, or worktree cleanup while that
reconciliation happens.

1 files changed, 106 insertions, 9 deletions

diff --git a/crates/core/src/manager/workspaces.rs b/crates/core/src/manager/workspaces.rs
index 6ffb21b..f502d6b 100644
--- a/crates/core/src/manager/workspaces.rs
+++ b/crates/core/src/manager/workspaces.rs
@@ -30,7 +30,12 @@ impl WindowManager {
         if self.workspaces.len() <= 1 {
             return;
         }
-        let fallback = self.workspaces.iter().map(|w| w.id).find(|&w| w != id).unwrap_or(0);
+        // `unwrap_or(1)` is unreachable in practice - the `len() <= 1`
+        // guard above means `find` always has at least one other workspace
+        // to return - but `1`, not `0`, since workspace ids are 1-based
+        // (see `WindowManager::new`'s own doc comment) and `0` is no longer
+        // a real workspace id this could plausibly fall back to.
+        let fallback = self.workspaces.iter().map(|w| w.id).find(|&w| w != id).unwrap_or(1);
         for w in self.windows.values_mut().filter(|w| w.workspace == id) {
             w.workspace = fallback;
         }
@@ -53,6 +58,23 @@ impl WindowManager {
         if self.workspaces.iter().any(|w| w.id == target) && target != self.current_workspace {
             self.previous_workspace = self.current_workspace;
             self.current_workspace = target;
+            // Keyboard focus otherwise stayed on whatever was focused
+            // *before* the switch - this function only ever touched
+            // `current_workspace`, never `self.focused` - so real input
+            // kept going to a window that had just gone invisible while
+            // whatever's now on screen, if anything, received nothing.
+            // Reported live: switching to a workspace with an open window
+            // left that window unfocused and the previous workspace's
+            // window still receiving keystrokes. Only reassigns focus when
+            // the currently-focused window isn't actually on the new
+            // workspace - an already-correct focus (e.g. `focus_window`'s
+            // own workspace-follow call into this function, where the
+            // target window IS what should end up focused) must not get
+            // silently overridden by "pick the topmost window instead".
+            let focus_still_valid = self.focused.and_then(|id| self.windows.get(&id)).is_some_and(|w| w.workspace == target);
+            if !focus_still_valid {
+                self.focused = self.window_ids_on_workspace_front_to_back(target).into_iter().next();
+            }
         }
     }
 
@@ -60,6 +82,76 @@ impl WindowManager {
         self.current_workspace
     }
 
+    /// The workspace actually showing on `monitor` right now - `current_
+    /// workspace` directly when `per_monitor_workspaces` is `false` (every
+    /// monitor always agrees, by construction, since only `switch_
+    /// workspace` - never `switch_workspace_on_monitor` - can run in that
+    /// mode); otherwise this monitor's own independently-switched
+    /// workspace, or `current_workspace` as the fallback for a monitor
+    /// that has never had one switched independently yet (freshly
+    /// connected, or the mode was just turned on).
+    pub fn workspace_for_monitor(&self, monitor: MonitorId) -> WorkspaceId {
+        if self.per_monitor_workspaces {
+            self.monitor_workspaces.get(&monitor).copied().unwrap_or(self.current_workspace)
+        } else {
+            self.current_workspace
+        }
+    }
+
+    /// Whether `id` is showing on *any* currently-connected monitor right
+    /// now - what `srd workspaces`/AGS's own workspace pills should treat
+    /// as "active" (`crates/platform/src/ipc.rs::workspace_snapshot`).
+    /// Structurally allows more than one workspace to be active at once,
+    /// which only actually happens in `per_monitor_workspaces` mode with
+    /// two monitors on different workspaces - shared mode (the default)
+    /// always has exactly one, same as before this existed.
+    pub fn is_workspace_visible(&self, id: WorkspaceId) -> bool {
+        if self.per_monitor_workspaces {
+            self.monitors.iter().any(|m| self.workspace_for_monitor(m.id) == id)
+        } else {
+            id == self.current_workspace
+        }
+    }
+
+    /// The `per_monitor_workspaces`-aware counterpart to `switch_
+    /// workspace`: switches `monitor`'s own workspace to `id` without
+    /// affecting any other monitor, when the mode is on. Falls straight
+    /// through to the ordinary shared-mode `switch_workspace` (ignoring
+    /// `monitor` entirely) when it's off, so a caller can always use this
+    /// one entry point regardless of which mode is active rather than
+    /// branching on the config flag itself - see its own call site in
+    /// `crates/platform/src/ipc.rs`'s `activate_workspace` handler.
+    ///
+    /// `monitor` is "whichever monitor this switch should apply to", not
+    /// necessarily where the pointer is - the caller decides that (the
+    /// focused window's own monitor, in practice), same as real per-output
+    /// keybinding routing in Hyprland/niri.
+    pub fn switch_workspace_on_monitor(&mut self, id: WorkspaceId, monitor: MonitorId) {
+        if !self.per_monitor_workspaces {
+            self.switch_workspace(id);
+            return;
+        }
+        let current = self.workspace_for_monitor(monitor);
+        let target = if self.auto_back_and_forth && id == current {
+            self.monitor_workspaces.get(&monitor).copied().unwrap_or(self.previous_workspace)
+        } else {
+            id
+        };
+        if !self.workspaces.iter().any(|w| w.id == target) || target == current {
+            return;
+        }
+        self.previous_workspace = current;
+        self.monitor_workspaces.insert(monitor, target);
+        // Same reasoning as `switch_workspace`'s own matching comment:
+        // reassign focus only when the currently-focused window isn't
+        // already correctly on the new workspace, so an already-correct
+        // focus assignment from elsewhere doesn't get silently overridden.
+        let focus_still_valid = self.focused.and_then(|id| self.windows.get(&id)).is_some_and(|w| w.workspace == target);
+        if !focus_still_valid {
+            self.focused = self.window_ids_on_workspace_front_to_back(target).into_iter().next();
+        }
+    }
+
     pub fn workspace(&self, id: WorkspaceId) -> Option<&Workspace> {
         self.workspaces.iter().find(|w| w.id == id)
     }
@@ -74,15 +166,20 @@ impl WindowManager {
         }
     }
 
-    /// Windows that should currently be shown to the user: those on the
-    /// current workspace, and not minimized.
+    /// Windows that should currently be shown to the user: those on
+    /// whichever workspace their own monitor is currently showing, and not
+    /// minimized.
     ///
-    /// `current_workspace` is a single value shared by every monitor --
-    /// srdwm does not have Hyprland-style independent per-monitor
-    /// workspaces, so switching workspace changes what's shown on every
-    /// screen at once. `w.monitor` plays no part in this filter at all.
+    /// In shared mode (`per_monitor_workspaces` off, the default) every
+    /// monitor is always showing `current_workspace`, so this reduces to
+    /// exactly the original single-shared-workspace filter and `w.monitor`
+    /// plays no part in it - switching workspace still changes what's
+    /// shown on every screen at once. In per-monitor mode, each window is
+    /// checked against its *own* monitor's independently-switched
+    /// workspace (`workspace_for_monitor`) instead, so two monitors on two
+    /// different workspaces each correctly show only their own.
     pub fn visible_windows(&self) -> impl Iterator<Item = &Window> {
-        self.windows.values().filter(|w| w.workspace == self.current_workspace && !w.minimized)
+        self.windows.values().filter(|w| w.workspace == self.workspace_for_monitor(w.monitor) && !w.minimized)
     }
 
     /// Same windows as [`Self::visible_windows`], but in real front-to-back
@@ -95,7 +192,7 @@ impl WindowManager {
     /// `self.order` reversed is the same "topmost first" convention
     /// `hit_test`/`window_at` already use.
     pub fn visible_windows_front_to_back(&self) -> impl Iterator<Item = &Window> {
-        self.order.iter().rev().filter_map(|id| self.windows.get(id)).filter(|w| w.workspace == self.current_workspace && !w.minimized)
+        self.order.iter().rev().filter_map(|id| self.windows.get(id)).filter(|w| w.workspace == self.workspace_for_monitor(w.monitor) && !w.minimized)
     }
 
 }