ext-stage-dock: transparent strip, surface hugs cards, fix re-minimize after empty

Builds on the kernel per-pixel-alpha + set_size-resize capabilities.

- Transparent strip: body.dock background #1c1c1ee6 -> transparent, so the
  windows beneath show through everywhere the cards don't cover; cards keep their
  solid #2e2e32 panel. data-attr-src preview, Noto Sans, and the d1 slot-enter
  animation are intact.
- Surface hugs the card stack: height = surface_height(count) =
  max(1, 2*pad + count*card + (count-1)*gap) (0->1px hidden, 1->140, 2->272, …),
  never the full output height, so the transparent area doesn't needlessly
  capture input. The empty dock is a positive 1px hidden placeholder (the substrate
  rejects 0 geometry); grows/shrinks via set_size on minimize/restore.
- Fix: re-minimize after the dock empties was a no-op. do_restore relied on
  on_toplevel_focused re-firing, but a restored window was never seat-defocused,
  so focus() is a seat no-op and the event never fires — leaving focused_ stale,
  so the next Super+M's focused_ guard rejected it (a new toplevel mapping
  unstuck it). Fix: set focused_ = tl directly in restore. No kernel change.

Tests: new policy cases (surface_height always positive; hug heights 0/140/272/536)
and a glue minimize->restore->minimize 1->0->1 cycle with has_focused() probe.
ext-stage-dock 2/2 green on build + build-asan (no sanitizer reports). Real-seat
verified: transparent strip, dock visible, cards float, re-minimize works.
Edits confined to packages/ext-stage-dock/.

5 files changed, 206 insertions, 8 deletions

diff --git a/packages/ext-stage-dock/src/dock_layout.hpp b/packages/ext-stage-dock/src/dock_layout.hpp
index 43ee910..b02d819 100644
--- a/packages/ext-stage-dock/src/dock_layout.hpp
+++ b/packages/ext-stage-dock/src/dock_layout.hpp
@@ -86,6 +86,20 @@ struct DockMetrics {
     return 2 * m.pad + count * m.slot_height + (count - 1) * m.gap;
 }
 
+// The POSITIVE surface height that hugs `count` cards: content_height(count)
+// clamped to a strictly-positive minimum. The ui substrate REJECTS a surface
+// with non-positive geometry (create_surface/set_size return nullptr + log an
+// error), so the empty dock (count 0 -> content_height 0) must still be created
+// / resized at a positive size and merely hidden (set_visible(false)), never at
+// height 0. Returns max(content_height(count), 1): >= 1 for every count >= 0,
+// equal to content_height once there is at least one card. (Width never hits 0
+// in practice — dock_width is a fixed positive constant — but callers should
+// likewise guard it; this helper covers the height, which is the count-driven
+// dimension.)
+[[nodiscard]] inline auto surface_height(const DockMetrics& m, int count) -> int {
+    return std::max(1, content_height(m, count));
+}
+
 // The on-screen rect of slot `i` (0-based) within the dock content, given the
 // current vertical `scroll` offset (px scrolled DOWN; 0 = top). The slot's
 // content-space top is pad + i*(slot_height+gap); subtracting `scroll` yields
diff --git a/packages/ext-stage-dock/src/extension.cpp b/packages/ext-stage-dock/src/extension.cpp
index 82814e2..e5261e4 100644
--- a/packages/ext-stage-dock/src/extension.cpp
+++ b/packages/ext-stage-dock/src/extension.cpp
@@ -56,6 +56,21 @@ constexpr std::uint32_t kMinimizeMods = WLR_MODIFIER_LOGO;  // Super/LOGO
 // dock sits fully revealed (no reveal animation); d1 animates dock_box(f).
 constexpr int kDockWidth = 240;
 
+// Card-stack metrics, in px, that MIRROR the kDockRml RCSS so the surface rect
+// can be sized (via dock_layout::content_height) to hug the rendered card stack
+// rather than the full output height. dp == px (substrate dp-ratio is 1.0), so
+// these are the RCSS dp values:
+//   kCardHeight  — one div.slot's OUTER (border-box) height: padding 6dp*2 (=12)
+//     + img.preview 84dp + span.title (margin-top 4dp + ~one 13dp line). Rounded
+//     UP to 124 so RmlUi's exact line-box height never clips a card (over-sizing
+//     the transparent surface by a few px is harmless; clipping a card is not).
+//   kCardGap     — the inter-card vertical space (div.slot margin-bottom: 8dp).
+//   kStripPad    — the strip's inner top/bottom margin (body.dock padding: 8dp).
+// content_height(count) = 2*kStripPad + count*kCardHeight + (count-1)*kCardGap.
+constexpr int kCardHeight = 124;
+constexpr int kCardGap = 8;
+constexpr int kStripPad = 8;
+
 // A minimized window's dock entry: the live Toplevel* borrow (valid until its
 // unmapped event), the frozen Preview (owns the imported texture; null when the
 // substrate has no GL path), and a copied title (the Toplevel's title() view is
@@ -73,7 +88,21 @@ struct Slot {
 // rounded like the Stage-Manager reference. d1 ADDS the RCSS animation on top of
 // c2's static document — without touching the data model (same "slots" list,
 // same per-row preview/title/restore bindings). data-model "ui" (the substrate
-// default). The img src is the Preview source_uri(), bound via
+// default).
+//
+// TRANSPARENT STRIP (per-pixel alpha). The substrate composites this surface
+// with per-pixel alpha (ui.hpp UiSurface §PER-PIXEL ALPHA): any pixel body.dock
+// does not paint is fully transparent and the windows BELOW show through. So
+// `body.dock` paints NO background (`background-color: transparent`) — only the
+// `div.slot` CARDS paint (their `#2e2e32ff` panel), reading as cards floating
+// over the window with the empty strip see-through. NOTE the substrate still
+// consumes pointer/touch over the whole surface RECT regardless of visual
+// transparency (slice-5 consumption model), so the surface is sized to HUG the
+// card stack (see content_height in create/refresh) — the rest of the screen
+// stays interactive. A real input-transparent strip needs a deferred
+// UiSurfaceSpec flag (report change-req).
+//
+// The img src is the Preview source_uri(), bound via
 // `data-attr-src="row.preview"` — RmlUi interpolates {{ }} only in TEXT, so an
 // element attribute must use the data-attr-<attr> attribute-binding form
 // (verified against vendored RmlUi 6.2: data_binding/options samples). The
@@ -110,7 +139,7 @@ constexpr const char* kDockRml = R"RML(<rml>
 <head>
 <style>
 body.dock {
-    background-color: #1c1c1ee6;
+    background-color: transparent;
     padding: 8dp;
     font-family: Noto Sans;
     transform: translateX(-100%);
@@ -171,6 +200,7 @@ public:
     void minimize_focused() override { do_minimize_focused(); }
     void restore(std::size_t i) override { do_restore(i); }
     [[nodiscard]] auto slot_count() const -> std::size_t override { return slots_.size(); }
+    [[nodiscard]] auto has_focused() const -> bool override { return focused_ != nullptr; }
 
     void activate(Host& host) override {
         host_ = &host;
@@ -278,7 +308,20 @@ private:
         slots_.erase(slots_.begin() + static_cast<std::ptrdiff_t>(i));
         if (tl != nullptr) {
             tl->show();
-            tl->focus(); // produces on_toplevel_focused -> updates focused_
+            tl->focus();
+            // Re-establish focused_ DIRECTLY rather than relying on focus()
+            // re-emitting on_toplevel_focused. KEY: hide() never moved keyboard
+            // focus at the seat, so when we minimize the only window the seat
+            // STILL holds focus on the (now hidden) window; our local focused_
+            // went nullptr only because first_non_minimized_other() found no
+            // other window. On restore, tl->focus() is then focusing the
+            // already-seat-focused window, which the kernel treats as a no-op and
+            // does NOT re-emit on_toplevel_focused — leaving focused_ stale at
+            // nullptr, so the next Super+M (guarded on focused_ != nullptr) was a
+            // no-op until a new map set focused_. We KNOW tl is the focused window
+            // now (we just restored + focused it), so set it here. If the event
+            // does also fire it just re-sets the same value (idempotent).
+            focused_ = tl;
         }
         refresh_slots();
     }
@@ -329,6 +372,14 @@ private:
     //     -> the body slides back out; we DEFER set_visible(false) until the
     //     slide-out finishes (on_dock_settled, fired by RmlUi's transitionend
     //     through the existing event binding) so the close animation is seen.
+    // The surface rect tracks the slot count: whenever there is at least one
+    // slot we set_size the height to content_height(count) so the rect hugs the
+    // card stack (brief §3 — minimize the input-capturing area). We do NOT
+    // shrink to 0 the instant the dock empties: that would collapse the surface
+    // mid slide-OUT and the close animation would not be seen. Instead we keep
+    // the last non-empty height through the slide and shrink to 0 in
+    // on_dock_settled (with set_visible(false)). The width is fixed (kDockWidth).
+    //
     // No-op on the visual when the surface is null (no-GL backend); the model is
     // still tracked, and slot_count()/the c2 invariants are unchanged.
     void refresh_slots() {
@@ -337,6 +388,13 @@ private:
         }
         dock_surface_->dirty("slots");
 
+        // Resize the rect to hug the cards while non-empty (growing OR shrinking
+        // by one of several). When empty, defer the collapse to on_dock_settled.
+        if (!slots_.empty()) {
+            const int w = layout::dock_box(dock_metrics(), 1.0).w;
+            dock_surface_->set_size(w, surface_height_for(slots_.size()));
+        }
+
         const bool want_open = !slots_.empty();
         if (want_open == open_) {
             return; // reveal state unchanged (e.g. minimize a 2nd window)
@@ -366,13 +424,27 @@ private:
     void on_dock_settled() {
         if (dock_surface_ != nullptr && closing_ && !open_) {
             dock_surface_->set_visible(false);
+            // Collapse the rect now that the slide-out is done and the surface is
+            // hidden: a hidden empty dock captures NO input. Deferred to here (not
+            // refresh_slots) so the card stack stays sized through the slide. The
+            // height is the positive 1px placeholder (count==0), never 0.
+            const int w = layout::dock_box(dock_metrics(), 1.0).w;
+            dock_surface_->set_size(w, surface_height_for(slots_.size())); // count==0 -> 1px
         }
         closing_ = false;
     }
 
-    // Create the dock UiSurface (overlay, left edge, full output height) and
-    // register all data bindings BEFORE the first frame. Null surface (no-GL
-    // backend) is fine — we just skip it and the model is still tracked.
+    // Create the dock UiSurface (overlay, left edge) and register all data
+    // bindings BEFORE the first frame. The surface rect HUGS the card stack: its
+    // width is the dock_box width, its height is content_height(slot count) —
+    // NOT the full output height — because the substrate consumes pointer/touch
+    // over the whole rect regardless of visual transparency, so a transparent
+    // full-height strip would still eat clicks over the empty area (brief §3).
+    // Height tracks the slot count via set_size in refresh_slots(); at create
+    // the dock is empty so the height is a POSITIVE 1px placeholder (the
+    // substrate rejects non-positive geometry — see surface_height_for) and the
+    // surface is hidden (spec.visible=false) until the first slot. Null surface
+    // (no-GL backend) is fine — we just skip it and the model is still tracked.
     void create_dock_surface() {
         const layout::DockMetrics m = dock_metrics();
         const layout::Box frame = layout::dock_box(m, 1.0); // fully revealed (c2)
@@ -383,7 +455,7 @@ private:
         spec.x = frame.x;
         spec.y = frame.y;
         spec.width = frame.w;
-        spec.height = frame.h;
+        spec.height = surface_height_for(slots_.size()); // hug the card stack
         spec.layer = kernel::SceneLayer::overlay;
         spec.visible = false; // shown when slot count > 0
 
@@ -424,7 +496,9 @@ private:
 
     // Dock metrics from the first output's size (queried via output_layout). On
     // a backend with no output yet, falls back to 0x0 (the dock is hidden until
-    // a slot exists anyway). The dock keeps its fixed width and full height.
+    // a slot exists anyway). The dock keeps its fixed width; its HEIGHT now hugs
+    // the card stack (content_height), not the full output (input caveat, §3).
+    // The card-stack dims (slot_height/gap/pad) mirror the kDockRml RCSS.
     [[nodiscard]] auto dock_metrics() const -> layout::DockMetrics {
         int ow = 0;
         int oh = 0;
@@ -445,9 +519,28 @@ private:
         m.output_w = ow;
         m.output_h = oh;
         m.dock_width = kDockWidth;
+        // Card-stack dims mirror the kDockRml RCSS so content_height() yields the
+        // surface height that hugs the rendered cards (see kCardHeight et al.).
+        m.slot_height = kCardHeight;
+        m.gap = kCardGap;
+        m.pad = kStripPad;
         return m;
     }
 
+    // The POSITIVE surface HEIGHT that hugs `count` cards: the strip's content
+    // height (2*pad + count*card + (count-1)*gap) per dock_layout, CLAMPED to a
+    // strictly-positive minimum (>= 1). The substrate REJECTS non-positive
+    // geometry (create_surface/set_size return nullptr + log
+    // "surface needs positive geometry"), so the EMPTY dock (count 0 ->
+    // content_height 0) must be created/resized at a positive size and merely
+    // hidden (set_visible(false)), never at height 0. The substrate consumes
+    // input over the whole rect, so sizing height to the card stack (not the
+    // full output) leaves the rest of the screen interactive (brief §3 caveat);
+    // the empty-dock 1px placeholder is hidden, so it captures nothing.
+    [[nodiscard]] auto surface_height_for(std::size_t count) const -> int {
+        return layout::surface_height(dock_metrics(), static_cast<int>(count));
+    }
+
     const kernel::Manifest manifest_{
         .id = "stage-dock",
         .tier = kernel::Tier::standard,
diff --git a/packages/ext-stage-dock/src/probe.hpp b/packages/ext-stage-dock/src/probe.hpp
index 9ea49db..77d9a3b 100644
--- a/packages/ext-stage-dock/src/probe.hpp
+++ b/packages/ext-stage-dock/src/probe.hpp
@@ -41,6 +41,12 @@ public:
 
     // The current number of dock slots (minimized windows).
     [[nodiscard]] virtual auto slot_count() const -> std::size_t = 0;
+
+    // Whether the dock currently has a focused window (focused_ != nullptr) — the
+    // exact guard do_minimize_focused()/the Super+M filter check before acting.
+    // After a restore the dock MUST report a focused window (restore re-focuses
+    // the shown window), or the next minimize would be a no-op. Glue-test only.
+    [[nodiscard]] virtual auto has_focused() const -> bool = 0;
 };
 
 struct ExtensionWithProbe {
diff --git a/packages/ext-stage-dock/tests/test_glue.cpp b/packages/ext-stage-dock/tests/test_glue.cpp
index 69985ff..c72cd9d 100644
--- a/packages/ext-stage-dock/tests/test_glue.cpp
+++ b/packages/ext-stage-dock/tests/test_glue.cpp
@@ -275,6 +275,11 @@ TEST_CASE("ext-stage-dock c2: minimize hides the focused window + adds a slot; r
     probe->restore(0);
     CHECK(probe->slot_count() == 0);          // slot dropped (Preview, if any, freed)
     CHECK(tree->node.enabled == true);        // show() re-enabled the scene node
+    // INVARIANT: restore must re-establish focused_ on the shown window, else the
+    // next minimize (guarded on focused_ != nullptr) is a no-op (the real-seat
+    // bug). With ONE window, minimize had set focused_=nullptr, so this is the
+    // re-establishment the restore path is responsible for.
+    CHECK(probe->has_focused() == true);
 
     // A guarded out-of-range restore is a no-op.
     probe->restore(5);
@@ -284,6 +289,36 @@ TEST_CASE("ext-stage-dock c2: minimize hides the focused window + adds a slot; r
         pump(*server, c.display);
     }
 
+    // --- RE-MINIMIZE the same window after the dock fully emptied (1->0->1) ----
+    // Real-seat regression: with ONE window, minimize sets focused_=nullptr (no
+    // OTHER window to focus), and restore must RE-ESTABLISH focused_ to the shown
+    // window. hide() never moves seat keyboard focus, so the restoring focus() is
+    // a no-op at the seat and on_toplevel_focused does NOT re-fire — so the glue
+    // must set focused_ itself on restore. If it does not, this second
+    // minimize_focused() (guarded on focused_ != nullptr) is a no-op and the slot
+    // count stays 0. The fix makes the SAME window minimizable again with NO new
+    // window mapped. This is the SAME tl (never unmapped); its borrow is still
+    // live (observer still holds it).
+    CHECK(observer->mapped() == tl);          // still the only mapped window
+    CHECK(tree->node.enabled == true);        // restored + visible before re-minimize
+    CHECK(probe->has_focused() == true);      // dock still tracks a focused window
+    probe->minimize_focused();
+    CHECK(probe->slot_count() == 1);          // re-minimized into the dock (the bug fix)
+    CHECK(tree->node.enabled == false);       // hide() disabled it again
+    CHECK(observer->mapped() == tl);          // still NOT unmapped
+
+    for (int i = 0; i < 10; ++i) {
+        pump(*server, c.display);
+    }
+    // Restore once more so we tear down from a clean (empty, shown) state.
+    probe->restore(0);
+    CHECK(probe->slot_count() == 0);
+    CHECK(tree->node.enabled == true);
+
+    for (int i = 0; i < 10; ++i) {
+        pump(*server, c.display);
+    }
+
     // Teardown: destroy the client toplevel; on_toplevel_unmapped fires and the
     // dock forgets the window. Dropping the server destroys extensions in reverse
     // activation order; within the dock, Subscriptions release first, then the
diff --git a/packages/ext-stage-dock/tests/test_policy.cpp b/packages/ext-stage-dock/tests/test_policy.cpp
index c2b057f..a62a5fa 100644
--- a/packages/ext-stage-dock/tests/test_policy.cpp
+++ b/packages/ext-stage-dock/tests/test_policy.cpp
@@ -187,6 +187,56 @@ TEST_CASE("content_height: 0/1/many slots") {
     CHECK(lay::content_height(m, 3) == 2 * 20 + 3 * 100 + 2 * 10); // 360
 }
 
+// The glue (src/extension.cpp) sizes the dock SURFACE rect to HUG the card stack
+// via content_height(card-stack metrics, slot count) instead of the full output
+// height — so the transparent strip captures input only over the cards (brief
+// §3: the substrate consumes input over the whole rect regardless of visual
+// transparency). These are the exact px values the surface height takes, with
+// the card-stack metrics that mirror the kDockRml RCSS (kCardHeight=124 outer
+// card height, kCardGap=8 inter-card margin, kStripPad=8 body padding). Keep in
+// lockstep with src/extension.cpp's kCard*/kStripPad constants + dock_metrics().
+TEST_CASE("dock surface height hugs the card stack (content_height with RCSS card metrics)") {
+    // Mirror src/extension.cpp: kCardHeight=124, kCardGap=8, kStripPad=8.
+    lay::DockMetrics card{.output_w = 1920, .output_h = 1080, .dock_width = 240,
+                          .slot_height = 124, .gap = 8, .pad = 8};
+    // Empty dock -> 0 content (but the SURFACE is clamped positive, below).
+    CHECK(lay::content_height(card, 0) == 0);
+    // One card -> 2*pad + card (no trailing gap).
+    CHECK(lay::content_height(card, 1) == 2 * 8 + 124);                   // 140
+    // Two cards -> +gap between them.
+    CHECK(lay::content_height(card, 2) == 2 * 8 + 2 * 124 + 1 * 8);       // 272
+    // Many cards grow linearly and stay FAR under the full output height, so the
+    // surface never spans the whole left edge (the hug-the-cards property).
+    CHECK(lay::content_height(card, 4) == 2 * 8 + 4 * 124 + 3 * 8);       // 536
+    CHECK(lay::content_height(card, 4) < card.output_h);                  // < 1080
+}
+
+// REGRESSION GUARD (0-geometry boot bug): the ui substrate REJECTS a surface
+// with non-positive geometry ("surface needs positive geometry") and returns
+// nullptr, so the EMPTY dock must be created/resized at a POSITIVE height, not 0.
+// surface_height() — the helper the glue's surface_height_for() delegates to —
+// clamps content_height to >= 1, so create_surface/set_size are never called
+// with height 0. Cover EVERY count the glue can produce, especially the empty
+// case the headless test cannot distinguish from the substrate-null path.
+TEST_CASE("surface_height is ALWAYS positive (empty-dock 0-geometry guard)") {
+    lay::DockMetrics card{.output_w = 1920, .output_h = 1080, .dock_width = 240,
+                          .slot_height = 124, .gap = 8, .pad = 8};
+    // The empty dock: content_height is 0, but the surface height is clamped to 1.
+    CHECK(lay::content_height(card, 0) == 0);
+    CHECK(lay::surface_height(card, 0) == 1);   // positive placeholder (hidden)
+    // Once there is at least one card, surface_height == content_height (>0).
+    CHECK(lay::surface_height(card, 1) == lay::content_height(card, 1));
+    CHECK(lay::surface_height(card, 4) == lay::content_height(card, 4));
+    // Never non-positive for any plausible count (incl. a negative/degenerate).
+    for (int n = -2; n <= 20; ++n) {
+        CHECK(lay::surface_height(card, n) >= 1);
+    }
+    // Even with degenerate (zeroed) metrics — defensive: still >= 1, never 0.
+    lay::DockMetrics zero{};
+    CHECK(lay::surface_height(zero, 0) >= 1);
+    CHECK(lay::surface_height(zero, 3) >= 1);
+}
+
 TEST_CASE("slot_box: vertical stacking by stride, inset width") {
     auto m = metrics(); // pad 20, slot 100, gap 10, dock_width 300
     auto s0 = lay::slot_box(m, 0, 0);