some guard rails

src/main/java/com/gregor/jprototerm/Compositor.java

@@ -114,7 +114,7 @@ public final class Compositor {
     public void setFont(String family, double size) {
         metrics.setFont(family, size);
         paneContentVersion.clear();
-        lastWidth = -1.0; // force a redraw on the next frame
+        layoutVersion++; // recomposite with the new metrics on the next frame
     }
 
     // ---- Tabs and panes -------------------------------------------------------------
@@ -123,8 +123,9 @@ public final class Compositor {
         return tabs.isEmpty();
     }
 
+    /** The active pane of the current tab, or {@code null} when no tab is left. */
     public TerminalPane activePane() {
-        return currentTab().activePane();
+        return isEmpty() ? null : currentTab().activePane();
     }
 
     public void navigate(Direction direction) {
@@ -173,10 +174,7 @@ public final class Compositor {
     }
 
     public void closeActivePane() {
-        if (isEmpty()) {
+        TerminalPane active = activePane();
-            return;
-        }
-        TerminalPane active = currentTab().activePane();
         if (active != null) {
             closePane(active);
         }
@@ -214,7 +212,8 @@ public final class Compositor {
     public void newTab() {
         // Open the new tab in the currently active pane's working directory, so it lands where the
         // user currently is rather than always in home.
-        String workingDirectory = isEmpty() ? null : currentTab().activePane().currentWorkingDirectory();
+        TerminalPane active = activePane();
+        String workingDirectory = active != null ? active.currentWorkingDirectory() : null;
         tabs.add(new Tab(config, metrics, workingDirectory, this::closePane));
         currentTabIndex = tabs.size() - 1;
         layoutVersion++;
@@ -454,11 +453,11 @@ public final class Compositor {
     private void handleMouseReleased(MouseEvent event) {
         TerminalPane pane = paneAt(event.getX(), event.getY());
         if (pane == null) {
-            pane = activePane();
+            pane = activePane(); // released outside every pane (e.g. mid-drag): route to the active one
         }
 
         MouseButton button = pressedButton == MouseButton.UNKNOWN ? mouseButton(event) : pressedButton;
-        MouseTarget target = mouseTarget(pane);
+        MouseTarget target = pane == null ? null : mouseTarget(pane);
         if (target != null) {
             send(pane, target, MouseInput.release(button, localX(event.getX(), pane, target), localY(event.getY(), pane, target), modifiers(event)), false, event);
         }
@@ -469,7 +468,10 @@ public final class Compositor {
     private void handleMouseDragged(MouseEvent event) {
         TerminalPane pane = paneAt(event.getX(), event.getY());
         if (pane == null) {
-            pane = activePane();
+            pane = activePane(); // dragged outside every pane: route to the active one
+        }
+        if (pane == null) {
+            return;
         }
 
         MouseButton button = pressedButton == MouseButton.UNKNOWN ? mouseButton(event) : pressedButton;

src/main/java/com/gregor/jprototerm/Daemon.java

@@ -9,6 +9,7 @@ import java.nio.channels.ServerSocketChannel;
 import java.nio.channels.SocketChannel;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
+import java.nio.file.LinkOption;
 import java.nio.file.Path;
 import java.nio.file.attribute.PosixFilePermissions;
 
@@ -23,6 +24,11 @@ import java.nio.file.attribute.PosixFilePermissions;
  * (mode 0700), so only the owning user can connect.
  */
 public final class Daemon {
+    // One request is a single line holding a filesystem path; anything bigger is bogus.
+    private static final int MAX_REQUEST_BYTES = 4096;
+    // The accept loop is single-threaded, so a client that stalls must not wedge the daemon.
+    private static final long READ_TIMEOUT_NANOS = 5_000_000_000L;
+
     private Daemon() {
     }
 
@@ -31,9 +37,9 @@ public final class Daemon {
         Path socket = socketPath();
         try {
             Files.createDirectories(socket.getParent());
-            trySecureDir(socket.getParent());
+            secureDir(socket.getParent());
         } catch (IOException ex) {
-            System.err.println("jprototerm: cannot create socket dir " + socket.getParent() + ": " + ex.getMessage());
+            System.err.println("jprototerm: cannot secure socket dir " + socket.getParent() + ": " + ex.getMessage());
             return;
         }
 
@@ -107,14 +113,22 @@ public final class Daemon {
             manager.openWindow(workingDirectory == null || workingDirectory.isBlank()
                     ? null
                     : workingDirectory.trim());
+            connection.configureBlocking(true);
             connection.write(ByteBuffer.wrap("OK\n".getBytes(StandardCharsets.UTF_8)));
         }
     }
 
+    // Reads the request line non-blocking with a deadline and a size cap: the accept loop is
+    // single-threaded, so a client that stalls or never sends a newline must fail the connection
+    // (an IOException logged by run()) rather than wedge the daemon or grow the buffer unbounded.
     private static String readLine(SocketChannel channel) throws IOException {
+        channel.configureBlocking(false);
+        long deadline = System.nanoTime() + READ_TIMEOUT_NANOS;
         ByteArrayOutputStream out = new ByteArrayOutputStream();
         ByteBuffer buffer = ByteBuffer.allocate(4096);
-        while (channel.read(buffer) != -1) {
+        while (true) {
+            int n = channel.read(buffer);
+            if (n > 0) {
                 buffer.flip();
                 while (buffer.hasRemaining()) {
                     byte b = buffer.get();
@@ -122,10 +136,25 @@ public final class Daemon {
                         return out.toString(StandardCharsets.UTF_8);
                     }
                     out.write(b);
+                    if (out.size() > MAX_REQUEST_BYTES) {
+                        throw new IOException("request line too long");
+                    }
                 }
                 buffer.clear();
-        }
+            } else if (n == -1) {
                 return out.size() == 0 ? null : out.toString(StandardCharsets.UTF_8);
+            } else {
+                if (System.nanoTime() >= deadline) {
+                    throw new IOException("request timed out");
+                }
+                try {
+                    Thread.sleep(5);
+                } catch (InterruptedException ex) {
+                    Thread.currentThread().interrupt();
+                    throw new IOException("interrupted while reading request");
+                }
+            }
+        }
     }
 
     private static Path socketPath() {
@@ -136,11 +165,19 @@ public final class Daemon {
         return dir.resolve("daemon.sock");
     }
 
-    private static void trySecureDir(Path dir) {
+    // Make the socket dir private, and refuse to use it if it is not ours. The /tmp fallback
+    // path is predictable, so another user could have pre-created it (the classic /tmp race);
+    // binding a socket inside a directory someone else owns would hand them control of it.
+    private static void secureDir(Path dir) throws IOException {
         try {
             Files.setPosixFilePermissions(dir, PosixFilePermissions.fromString("rwx------"));
-        } catch (IOException | UnsupportedOperationException ignored) {
+        } catch (UnsupportedOperationException ignored) {
-            // Best effort: XDG_RUNTIME_DIR is already user-private; the /tmp fallback we try to lock.
+            return; // not a POSIX filesystem: nothing more we can check
+        }
+        String owner = Files.getOwner(dir, LinkOption.NOFOLLOW_LINKS).getName();
+        String user = System.getProperty("user.name");
+        if (!owner.equals(user)) {
+            throw new IOException(dir + " is owned by '" + owner + "', not '" + user + "'");
         }
     }
 }

src/main/java/com/gregor/jprototerm/GlyphCache.java

@@ -29,6 +29,11 @@ final class GlyphCache {
     record Glyph(int width, int height, byte[] alpha) {
     }
 
+    // Bounds the atlas so pathological glyph diversity (e.g. a dump of distinct CJK/emoji cells)
+    // can't grow it without limit; on overflow it clears and rebuilds on demand, like any
+    // metrics change.
+    private static final int MAX_GLYPHS = 4096;
+
     private final TerminalMetrics metrics;
     private final Map<String, Glyph> glyphs = new HashMap<>();
     // The metrics snapshot the cached glyphs were rasterized for; a mismatch clears the cache.
@@ -43,7 +48,16 @@ final class GlyphCache {
 
     Glyph glyph(String text) {
         ensureCurrent();
-        return glyphs.computeIfAbsent(text, this::renderGlyph);
+        Glyph cached = glyphs.get(text);
+        if (cached != null) {
+            return cached;
+        }
+        if (glyphs.size() >= MAX_GLYPHS) {
+            glyphs.clear();
+        }
+        Glyph rendered = renderGlyph(text);
+        glyphs.put(text, rendered);
+        return rendered;
     }
 
     // Drop the rasterized masks if the font/cell geometry changed since they were built. Cheap to

src/main/java/com/gregor/jprototerm/KeyBinding.java

@@ -5,17 +5,19 @@ import javafx.scene.input.KeyEvent;
 
 import java.util.Locale;
 
-public record KeyBinding(boolean alt, boolean control, boolean shift, KeyCode code) {
+public record KeyBinding(boolean alt, boolean control, boolean shift, boolean meta, KeyCode code) {
     public static KeyBinding parse(String value) {
         boolean alt = false;
         boolean control = false;
         boolean shift = false;
+        boolean meta = false;
         KeyCode code = null;
 
         for (String part : value.split("\\+")) {
             String token = part.trim().toUpperCase(Locale.ROOT);
             switch (token) {
-                case "ALT", "META" -> alt = true;
+                case "ALT" -> alt = true;
+                case "META", "SUPER" -> meta = true;
                 case "CTRL", "CONTROL" -> control = true;
                 case "SHIFT" -> shift = true;
                 default -> code = keyCode(token);
@@ -25,13 +27,14 @@ public record KeyBinding(boolean alt, boolean control, boolean shift, KeyCode co
         if (code == null) {
             throw new IllegalArgumentException("Key binding has no key code: " + value);
         }
-        return new KeyBinding(alt, control, shift, code);
+        return new KeyBinding(alt, control, shift, meta, code);
     }
 
     public boolean matches(KeyEvent event) {
         return event.isAltDown() == alt
                 && event.isControlDown() == control
                 && event.isShiftDown() == shift
+                && event.isMetaDown() == meta
                 && event.getCode() == code;
     }
 
@@ -44,6 +47,9 @@ public record KeyBinding(boolean alt, boolean control, boolean shift, KeyCode co
         if (alt) {
             builder.append("ALT+");
         }
+        if (meta) {
+            builder.append("META+");
+        }
         if (shift) {
             builder.append("SHIFT+");
         }

src/main/java/com/gregor/jprototerm/LinuxPty.java

@@ -317,6 +317,10 @@ public final class LinuxPty implements AutoCloseable {
     }
 
     private void closeMaster() {
+        // Note: closing the master fd does NOT wake a reader thread blocked in read() on it —
+        // the reader unblocks via EOF when the child exits and the slave end closes. The signal
+        // here usually does that; if the child ignores it, the SIGKILL escalation in reap()
+        // guarantees it shortly after.
         callKill(pid, closeSignal);
         callInt(CLOSE, masterFd);
     }

src/main/java/com/gregor/jprototerm/StartupTiming.java

@@ -22,8 +22,11 @@ final class StartupTiming {
     private StartupTiming() {
     }
 
-    /** Records a phase boundary, printing the delta since the previous mark and since JVM start. */
+    /**
-    static void mark(String phase) {
+     * Records a phase boundary, printing the delta since the previous mark and since JVM start.
+     * Synchronized because marks come from both the launcher thread and the FX thread.
+     */
+    static synchronized void mark(String phase) {
         if (!ENABLED) {
             return;
         }
@@ -38,7 +41,7 @@ final class StartupTiming {
      * Records the first rendered frame exactly once, then becomes a no-op. Safe and cheap to call
      * from the render loop every frame (it only ever touches FX-thread state).
      */
-    static void firstFrame() {
+    static synchronized void firstFrame() {
         if (!ENABLED || firstFrameSeen) {
             return;
         }

src/main/java/com/gregor/jprototerm/Tab.java

@@ -18,6 +18,14 @@ import java.util.stream.Stream;
  * return whether they actually changed anything so it can bump its layout version.
  */
 final class Tab implements AutoCloseable {
+    // Floating-pane sizing policy: a fraction of the tab's size with a floor so panes stay
+    // usable in small windows, cascaded diagonally per pane, kept off the window edge.
+    private static final double FLOATING_SIZE_FRACTION = 0.58;
+    private static final double FLOATING_MIN_WIDTH = 420.0;
+    private static final double FLOATING_MIN_HEIGHT = 260.0;
+    private static final double FLOATING_CASCADE_OFFSET = 28.0;
+    private static final double FLOATING_EDGE_MARGIN = 12.0;
+
     private final AppConfig config;
     private final TerminalMetrics metrics;
     // Notified (on the FX thread) when one of this tab's panes' process exits on its own, so the
@@ -142,13 +150,15 @@ final class Tab implements AutoCloseable {
             tiled.get(i).bounds(i * tileWidth, topInset, tileWidth, availHeight);
         }
 
-        double floatingWidth = Math.max(420, width * 0.58);
+        double floatingWidth = Math.max(FLOATING_MIN_WIDTH, width * FLOATING_SIZE_FRACTION);
-        double floatingHeight = Math.max(260, availHeight * 0.58);
+        double floatingHeight = Math.max(FLOATING_MIN_HEIGHT, availHeight * FLOATING_SIZE_FRACTION);
         for (int i = 0; i < floating.size(); i++) {
-            double offset = i * 28.0;
+            double offset = i * FLOATING_CASCADE_OFFSET;
             floating.get(i).bounds(
-                    Math.min(width - floatingWidth - 12.0, ((width - floatingWidth) / 2.0) + offset),
+                    Math.min(width - floatingWidth - FLOATING_EDGE_MARGIN,
-                    Math.min(height - floatingHeight - 12.0, topInset + ((availHeight - floatingHeight) / 2.0) + offset),
+                            ((width - floatingWidth) / 2.0) + offset),
+                    Math.min(height - floatingHeight - FLOATING_EDGE_MARGIN,
+                            topInset + ((availHeight - floatingHeight) / 2.0) + offset),
                     floatingWidth,
                     floatingHeight);
         }
@@ -384,7 +394,9 @@ final class Tab implements AutoCloseable {
     private double[] paneSize(boolean asFloating) {
         double availHeight = lastHeight - lastTopInset;
         if (asFloating) {
-            return new double[] {Math.max(420, lastWidth * 0.58), Math.max(260, availHeight * 0.58)};
+            return new double[] {
+                    Math.max(FLOATING_MIN_WIDTH, lastWidth * FLOATING_SIZE_FRACTION),
+                    Math.max(FLOATING_MIN_HEIGHT, availHeight * FLOATING_SIZE_FRACTION)};
         }
         // A new tiled pane joins the row, so each gets 1/(n+1) of the width.
         return new double[] {lastWidth / (tiled.size() + 1), availHeight};

src/main/java/com/gregor/jprototerm/TerminalPane.java

@@ -18,6 +18,7 @@ import javafx.scene.shape.Shape;
 
 import java.util.Optional;
 import java.util.concurrent.atomic.AtomicLong;
+import java.util.function.Supplier;
 
 /**
  * One terminal: owns its ghostty {@link Terminal}, the {@link ShellSession}/pty driving it,
@@ -80,8 +81,8 @@ public final class TerminalPane implements AutoCloseable, RenderTarget {
     public static TerminalPane create(AppConfig config, TerminalMetrics metrics, Runnable onContentChange,
             double widthPx, double heightPx, String workingDirectory) {
         TerminalPane pane = newPane(config, metrics, onContentChange, widthPx, heightPx);
-        pane.attach(ShellSession.start(config.shell(), config.envOverride(), pane, pane.columns, pane.rows,
+        attachOrShowError(pane, () -> ShellSession.start(config.shell(), config.envOverride(), pane,
-                workingDirectory, config.closeSignalNumber()));
+                pane.columns, pane.rows, workingDirectory, config.closeSignalNumber()));
         return pane;
     }
 
@@ -93,11 +94,23 @@ public final class TerminalPane implements AutoCloseable, RenderTarget {
     public static TerminalPane createWithCommand(AppConfig config, TerminalMetrics metrics, Runnable onContentChange,
             double widthPx, double heightPx, String workingDirectory, String command) {
         TerminalPane pane = newPane(config, metrics, onContentChange, widthPx, heightPx);
-        pane.attach(ShellSession.startCommand(config.envOverride(), pane, pane.columns, pane.rows,
+        attachOrShowError(pane, () -> ShellSession.startCommand(config.envOverride(), pane,
-                workingDirectory, command, config.closeSignalNumber()));
+                pane.columns, pane.rows, workingDirectory, command, config.closeSignalNumber()));
         return pane;
     }
 
+    // Start the pane's process, but never let a spawn failure (e.g. a bad `shell` in config)
+    // propagate and crash window/pane creation. ShellSession has already written the error into
+    // the pane, so the pane opens showing it; with no session attached it is inert (sends are
+    // dropped) and the user closes it with the close-pane key.
+    private static void attachOrShowError(TerminalPane pane, Supplier<ShellSession> start) {
+        try {
+            pane.attach(start.get());
+        } catch (RuntimeException ex) {
+            System.err.println("jprototerm: " + ex.getMessage());
+        }
+    }
+
     private static TerminalPane newPane(AppConfig config, TerminalMetrics metrics, Runnable onContentChange,
             double widthPx, double heightPx) {
         int columns = widthPx > 0 ? metrics.columnsFor(widthPx) : config.columns();

src/main/java/com/gregor/jprototerm/TerminalWindow.java

@@ -138,8 +138,7 @@ final class TerminalWindow {
         }
         String encoded = KeyEncoder.encode(event);
         if (encoded != null) {
-            compositor.activePane().send(encoded);
+            sendToActivePane(encoded, event);
-            event.consume();
         }
     }
 
@@ -150,15 +149,25 @@ final class TerminalWindow {
 
         String text = event.getCharacter();
         if (text != null && !text.isEmpty() && text.charAt(0) >= 0x20 && text.charAt(0) != 0x7f) {
-            compositor.activePane().send(text);
+            sendToActivePane(text, event);
+        }
+    }
+
+    // Key handlers run on every keystroke, including any that race the window's teardown, so
+    // tolerate the no-pane-left state instead of assuming one exists.
+    private void sendToActivePane(String text, KeyEvent event) {
+        TerminalPane active = compositor.activePane();
+        if (active != null) {
+            active.send(text);
             event.consume();
         }
     }
 
     private void pasteFromClipboard() {
+        TerminalPane active = compositor.activePane();
         Clipboard clipboard = Clipboard.getSystemClipboard();
-        if (clipboard.hasString()) {
+        if (active != null && clipboard.hasString()) {
-            compositor.activePane().paste(clipboard.getString());
+            active.paste(clipboard.getString());
         }
     }
 
@@ -206,17 +215,22 @@ final class TerminalWindow {
     }
 
     private void openScrollbackInEditor() {
-        try {
         // Capture the active pane's scrollback before opening the floating pane, since that
         // makes the new pane active.
+        TerminalPane active = compositor.activePane();
+        if (active == null) {
+            return;
+        }
+        try {
             Path file = Files.createTempFile("jprototerm-scrollback-", ".txt");
-            Files.writeString(file, compositor.activePane().scrollbackText());
+            Files.writeString(file, active.scrollbackText());
-            file.toFile().deleteOnExit();
 
             // Run the editor as the floating pane's process (via /bin/sh -c) rather than typing the
             // command into an interactive shell. The command runs deterministically from the start
-            // — no shell startup/rc race — and the pane auto-closes when the editor exits.
+            // — no shell startup/rc race — and the pane auto-closes when the editor exits. The
-            compositor.openFloatingPane(scrollbackEditorCommand(file));
+            // trailing rm removes the file (which holds terminal contents) when the editor exits;
+            // deleteOnExit would leak files for the JVM's whole lifetime in daemon mode.
+            compositor.openFloatingPane(scrollbackEditorCommand(file) + "; rm -f " + shellQuote(file.toString()));
         } catch (IOException ex) {
             System.err.println("Could not open scrollback in editor: " + ex.getMessage());
         }