Fix spawn placement under the top bar, add per-window minimum sizes, and clean up maximize

Four reports after restarting into today's build, with a screenshot. The
screenshot was measured, not eyeballed: top bar y=0..29, a 4px accent border
at y=30..33, titlebar from y=34, bottom border at y=1027..1030, and 49px of
bare desktop below it.

Windows spawning too close to the top bar. A remembered position was
validated only by asking whether it landed on some monitor's full_geometry,
which includes the strip a top bar reserves, so an app whose remembered y was
small reopened with its titlebar under the bar. That is why it was
"sometimes": it depended on the stored value, and the live store holds
wezterm at y=44 and firefox at y=69 against a 30px bar. Remembered positions
are now clamped into the monitor's usable area.

Placement not surviving a logout. Window memory does persist, but five of the
eleven entries in the live store were saved with a second monitor attached,
at x >= 2000. Those points match no current monitor and were discarded
outright, falling back to a fresh cascade, so those apps appeared to remember
nothing. Such a position is now clamped onto a monitor that exists instead.

Per-window minimum sizes. One global floor is wrong in both directions.
Three sources now, in increasing precedence: the global floor, the client's
own declared minimum (xdg_toplevel.set_min_size or ICCCM hints), and a
min_width/min_height window rule overriding both. A rule wins permanently --
the backend refreshes the client's declared minimum on every decoration
redraw and must not undo a deliberate override.

Maximize, three faults in one report. A maximized window now draws no
border: its edges are the screen's edges, and the only place maximize stops
short is the bar strip, which is exactly where the measured line was.
maximize_geometry_for no longer subtracts a bottom-anchored dock's exclusive
zone, so maximize runs to the bottom of the screen and the dock floats over
it; top, left and right are still honoured.
general.maximize_covers_dock = false restores the old behaviour. With the
border gone the window sits flush under the bar instead of with an accent
line crowding it.

Verified: seven new tests on the real numbers from the live store, and
maximize geometry measured live in a nested instance (a window maximized on a
split half reports exactly that half's rect). NOT confirmed on screen: the
border removal and the dock behaviour - the nested backend has no bar or
dock to reserve a zone, and an attempt to check the border produced a failing
control, since srd set border_width only affects windows created after it.

515 tests pass, clippy clean.

1 files changed, 39 insertions, 5 deletions

diff --git a/crates/core/src/manager/windows.rs b/crates/core/src/manager/windows.rs
index bd13b0c..0186679 100644
--- a/crates/core/src/manager/windows.rs
+++ b/crates/core/src/manager/windows.rs
@@ -60,6 +60,10 @@ impl WindowManager {
             if let Some(margin) = a.resize_margin {
                 window.resize_margin = Some(margin);
             }
+            if let Some(min) = a.min_size {
+                window.min_size = min;
+                window.min_size_from_rule = true;
+            }
             if let Some(ratio) = a.aspect_ratio {
                 window.aspect_ratio = Some(ratio);
             }
@@ -87,8 +91,8 @@ impl WindowManager {
         let mut remembered_position: Option<(i32, i32)> = None;
         if !window.app_id.is_empty() && !window.is_dialog {
             if let Some((x, y, w, h)) = self.remembered_geometry.get(&window.app_id).copied() {
-                window.geometry.width = w.max(MIN_WINDOW_WIDTH);
-                window.geometry.height = h.max(MIN_WINDOW_HEIGHT);
+                window.geometry.width = w.max(window.min_size.0);
+                window.geometry.height = h.max(window.min_size.1);
                 remembered_position = Some((x, y));
             }
         }
@@ -137,7 +141,16 @@ impl WindowManager {
         // current monitor's own *full* geometry (not the exclusive-zone-
         // shrunk usable one): a remembered position under where a bar now
         // sits is still "a real monitor, just partly covered", not invalid.
-        let remembered_monitor = remembered_position.and_then(|(x, y)| self.monitors.iter().find(|m| m.full_geometry.contains_point(x, y)));
+        // Whichever monitor a remembered position lands on, else the one
+        // the window would have been placed on anyway - a position saved
+        // while a second monitor was connected must not be thrown away
+        // just because that monitor is gone. Clamped onto the surviving
+        // monitor below instead, which keeps "reopen where I left it"
+        // meaningful across a docking change rather than silently falling
+        // back to a fresh cascade.
+        let remembered_monitor = remembered_position
+            .and_then(|(x, y)| self.monitors.iter().find(|m| m.full_geometry.contains_point(x, y)))
+            .or(target_monitor);
         // A dialog is centred, and neither cascaded nor restored to a
         // remembered spot. Reported as "even dialog/starter windows spawn
         // that side, most times should be centered".
@@ -160,8 +173,25 @@ impl WindowManager {
             }
         } else if let (Some((x, y)), Some(monitor)) = (remembered_position, remembered_monitor) {
             window.monitor = monitor.id;
-            window.geometry.x = x;
-            window.geometry.y = y;
+            // Clamped into the monitor's *usable* area, not its full one.
+            //
+            // The check above only asked whether the remembered point was
+            // on some monitor at all, and `full_geometry` includes the
+            // strip a top bar reserves - so an app whose remembered `y`
+            // was small reopened with its titlebar tucked under the bar,
+            // unreachable. Reported as windows spawning "so close to top
+            // bar", and "sometimes" precisely because it depended on the
+            // remembered value: this store currently holds a window at
+            // y=44 with a 30px bar above it.
+            //
+            // The same clamp is what makes a position from a
+            // now-disconnected monitor usable rather than discarded: it is
+            // pulled back onto a monitor that exists, keeping as much of
+            // the remembered placement as still fits.
+            let area = monitor.geometry;
+            let (w, h) = (window.geometry.width as i32, window.geometry.height as i32);
+            window.geometry.x = x.clamp(area.x, (area.right() - w).max(area.x));
+            window.geometry.y = y.clamp(area.y, (area.bottom() - h).max(area.y));
         } else if let Some(monitor) = target_monitor {
             window.monitor = monitor.id;
             let layout_name = self.workspace(workspace).map(|w| w.layout.clone()).unwrap_or_default();
@@ -280,6 +310,10 @@ impl WindowManager {
         if let Some(margin) = actions.resize_margin {
             window.resize_margin = Some(margin);
         }
+        if let Some(min) = actions.min_size {
+            window.min_size = min;
+            window.min_size_from_rule = true;
+        }
         if let Some(ratio) = actions.aspect_ratio {
             window.aspect_ratio = Some(ratio);
         }