feat: size: prefix, external auto-detection, auto-disable stale monitors

- size:WxH and size:WxH@R resolution for config names
- auto-detection of external monitors when external list is empty (any non-internal display)
- ensureCleanLayout: explicitly disable connected monitors not in target layout
- update docs (README, example.yaml) for all three features

README.md

@@ -57,6 +57,7 @@ Plugs into your dock — external monitors turn on, built-in turns off. Unplug
 | 5 | **Graceful shutdown** — optionally restores portable layout on SIGTERM |
 | 6 | **Socket reconnect** — exponential backoff if compositor socket drops |
 | 7 | **Atomic config writes (Hyprland)** — temp file + rename prevents config corruption |
+| 8 | **Auto-disable stale monitors** — monitors connected but absent from the target layout are explicitly disabled (prevents external displays from staying on after switching to portable mode) |
 
 ---
 
@@ -142,13 +143,17 @@ restore_on_exit: true
 # External monitors that trigger docked mode.
 # Plain name: matches connector (DP-1, HDMI-A-1).
 # desc: prefix: matches by monitor description (survives port rename).
-external:
+# Optional — if omitted or empty, the daemon auto-detects external monitors:
+# any display whose connector is not eDP-/LVDS-/DSI- is treated as external.
+external:  # optional
   - desc:Dell Inc. DELL U2723QE
   - DP-9
   - DP-10
 
 # Monitor layouts for each mode.
 # "portable" and "docked" are required.
+# Monitors not listed in a mode are automatically disabled (prevents
+# external displays from staying on when switching to portable mode).
 modes:
   portable:
     monitors:
@@ -172,6 +177,11 @@ modes:
         scale: 1.0
       - name: eDP-1
         enabled: false          # turn off laptop screen when docked
+      - name: size:1920x1080@60  # resolve by resolution + refresh rate
+        enabled: true
+        mode: preferred
+        position: auto
+        scale: 1.0
 
 # Shell commands run after a layout change.
 # Commands run concurrently, failures are logged but never crash the daemon.
@@ -185,17 +195,19 @@ hooks:
 
 ### Monitor matching
 
-Two match modes, supported in both the `external` list and the `modes` section:
+Three match modes for the `modes` section (the `external` list supports plain names and `desc:`):
 
 | Syntax | Matches | Use case |
 |---|---|---|
 | `DP-1` | Exact connector name | Simple setups, built-in displays |
-| `desc:Dell U2723QE` | Substring in monitor description | Survives port rename across different docks |
+| `desc:Dell U2723QE` | Substring in monitor description or serial | Survives port rename across different docks |
+| `size:2560x1440` | Exact pixel dimensions | Two identical monitors with same resolution |
+| `size:2560x1440@165` | Dimensions + refresh rate | Disambiguate identical models |
 
 Sway description format: `make model serial_widthxheight` (with serial omitted if `Unknown`).  
 Run `hyprctl monitors all` (Hyprland) or `swaymsg -t get_outputs` (Sway) to see your monitor names and descriptions.
 
-**desc: in modes** — when a monitor name in `modes` uses the `desc:` prefix, the daemon resolves it to the actual connector name at runtime. Ambiguous matches (a desc matching multiple monitors) cause an error.
+**desc: and size: in modes** — when a monitor name in `modes` uses `desc:` or `size:`, the daemon resolves it to the actual connector name at runtime. Ambiguous matches (a prefix matching multiple monitors with identical resolution) cause an error. For `size:`, add `@R` (refresh rate) to disambiguate monitors with the same resolution. Unresolvable names also cause an error.
 
 ### Backend-specific configuration
 
@@ -337,7 +349,7 @@ Check the hook command works from a terminal first. Hooks run via `sh -c`, so sh
 
 ### Monitor names changed after reboot
 
-Use `desc:` prefix matching instead of connector names. This survives port renames across different docks and reboots.
+Use `desc:` or `size:` prefix matching instead of connector names. Both survive port renames across different docks and reboots.
 
 **Hyprland:** `hyprctl monitors all` to see descriptions.  
 **Sway:** `swaymsg -t get_outputs` to see names, make/model, serial, and native resolution.
@@ -351,6 +363,8 @@ modes:
     monitors:
       - name: desc:Dell Inc. DELL U2723QE   # also works here
         enabled: true
+      - name: size:2560x1440@165            # match by dimensions + refresh
+        enabled: true
 ```
 
 ---

internal/backend/hyprland.go

@@ -92,7 +92,25 @@ func (h *hyprlandBackend) GetMonitors(ctx context.Context) ([]MonitorInfo, error
 
 // ApplyLayout writes the monitor configuration file and calls hyprctl reload.
 // The config is written atomically (temp file + rename) to prevent corruption.
+//
+// Any physically connected monitor not mentioned in the desired layout is
+// explicitly disabled. This prevents external monitors from remaining enabled
+// when switching to portable mode (where only eDP-* is listed).
 func (h *hyprlandBackend) ApplyLayout(ctx context.Context, monitors []MonitorConfig) error {
+	var err error
+	monitors, err = resolveMonitorNames(ctx, monitors, h.GetMonitors, h.logger)
+	if err != nil {
+		return fmt.Errorf("resolve monitor names: %w", err)
+	}
+
+	// Fetch the current set of connected monitors and explicitly disable
+	// any that are not part of the target layout.
+	current, err := h.GetMonitors(ctx)
+	if err != nil {
+		return fmt.Errorf("get current monitors for cleanup: %w", err)
+	}
+	monitors = h.ensureCleanLayout(monitors, current)
+
 	content := h.generateConf(monitors)
 
 	destPath, err := h.resolveOutputPath()
@@ -276,6 +294,33 @@ func (h *hyprlandBackend) generateConf(monitors []MonitorConfig) string {
 	return buf.String()
 }
 
+// ensureCleanLayout adds disabled entries for any physically connected
+// monitor that is not present in the target layout. This prevents
+// monitors from remaining enabled when switching to a mode that only
+// configures a subset of displays (e.g. portable mode).
+func (h *hyprlandBackend) ensureCleanLayout(target []MonitorConfig, connected []MonitorInfo) []MonitorConfig {
+	names := make(map[string]bool, len(target))
+	for _, m := range target {
+		names[m.Name] = true
+	}
+
+	var result []MonitorConfig
+	result = append(result, target...)
+
+	for _, mi := range connected {
+		if !names[mi.Name] {
+			h.logger.Debug("explicitly disabling unlisted monitor",
+				"monitor", mi.Name)
+			result = append(result, MonitorConfig{
+				Name:    mi.Name,
+				Enabled: false,
+			})
+		}
+	}
+
+	return result
+}
+
 // formatScale formats a scale float: 1 → "1", 1.5 → "1.5"
 func formatScale(s float64) string {
 	if s == 0 {

internal/backend/interface.go

@@ -8,7 +8,14 @@
 // cmd/monitor-lets-go/main.go.
 package backend
 
-import "context"
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"math"
+	"strconv"
+	"strings"
+)
 
 // MonitorInfo represents a physical display as reported by the compositor.
 // Fields use JSON tags matching hyprctl -j output; other compositors
@@ -97,3 +104,152 @@ type Backend interface {
 	// Close releases any resources held by the backend.
 	Close() error
 }
+
+// resolveMonitorNames converts desc: or size: prefixed monitor config names
+// to the actual connector names by matching against the current set of
+// connected monitors.
+//
+// Matching logic:
+//   - "desc:text" — substring match against description or serial
+//   - "size:WxH" — match by exact pixel dimensions (e.g. "size:2560x1440")
+//   - "size:WxH@R" — match by dimensions + refresh rate (e.g. "size:2560x1440@165")
+//   - plain names are returned as-is
+func resolveMonitorNames(ctx context.Context, monitors []MonitorConfig, getMonitors func(context.Context) ([]MonitorInfo, error), logger *slog.Logger) ([]MonitorConfig, error) {
+	var needsResolution bool
+	for _, m := range monitors {
+		if strings.HasPrefix(m.Name, "desc:") || strings.HasPrefix(m.Name, "size:") {
+			needsResolution = true
+			break
+		}
+	}
+	if !needsResolution {
+		return monitors, nil
+	}
+
+	current, err := getMonitors(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("get current monitors: %w", err)
+	}
+
+	resolved := make([]MonitorConfig, len(monitors))
+	for i, m := range monitors {
+		switch {
+		case strings.HasPrefix(m.Name, "desc:"):
+			resolved[i] = resolveDesc(m, current, logger)
+		case strings.HasPrefix(m.Name, "size:"):
+			resolved[i] = resolveSize(m, current, logger)
+		default:
+			resolved[i] = m
+		}
+		if resolved[i].Name == "" {
+			return nil, fmt.Errorf("cannot resolve monitor name %q", m.Name)
+		}
+	}
+
+	return resolved, nil
+}
+
+// resolveDesc resolves a desc: prefixed name to a connector name.
+func resolveDesc(m MonitorConfig, current []MonitorInfo, logger *slog.Logger) MonitorConfig {
+	needle := strings.TrimPrefix(m.Name, "desc:")
+	var matches []MonitorInfo
+	for _, mi := range current {
+		if strings.Contains(mi.Description, needle) || strings.Contains(mi.Serial, needle) {
+			matches = append(matches, mi)
+		}
+	}
+
+	switch len(matches) {
+	case 0:
+		// Return as-is so the caller sees the empty name.
+		m.Name = ""
+		return m
+	case 1:
+		logger.Debug("resolved desc to connector",
+			"desc", needle, "connector", matches[0].Name)
+		m.Name = matches[0].Name
+		return m
+	default:
+		var names []string
+		for _, mat := range matches {
+			names = append(names, mat.Name)
+		}
+		logger.Warn("desc:%q matches multiple monitors: %s — use a more specific identifier",
+			needle, strings.Join(names, ", "))
+		m.Name = ""
+		return m
+	}
+}
+
+// resolveSize resolves a size: prefixed name to a connector name.
+// Format: "size:WxH" or "size:WxH@R" where W and H are pixel dimensions
+// and R is the refresh rate in Hz.
+func resolveSize(m MonitorConfig, current []MonitorInfo, logger *slog.Logger) MonitorConfig {
+	spec := strings.TrimPrefix(m.Name, "size:")
+
+	parts := strings.Split(spec, "@")
+	dimParts := strings.Split(parts[0], "x")
+	if len(dimParts) != 2 {
+		logger.Warn("invalid size spec", "spec", spec)
+		m.Name = ""
+		return m
+	}
+
+	targetW, errW := strconv.Atoi(strings.TrimSpace(dimParts[0]))
+	targetH, errH := strconv.Atoi(strings.TrimSpace(dimParts[1]))
+	if errW != nil || errH != nil {
+		logger.Warn("invalid size dimensions", "spec", spec)
+		m.Name = ""
+		return m
+	}
+
+	var targetR float64
+	hasRefresh := len(parts) == 2
+	if hasRefresh {
+		var err error
+		targetR, err = strconv.ParseFloat(strings.TrimSpace(parts[1]), 64)
+		if err != nil {
+			logger.Warn("invalid refresh rate in size spec", "spec", spec)
+			m.Name = ""
+			return m
+		}
+	}
+
+	var matches []MonitorInfo
+	for _, mi := range current {
+		if mi.Width != targetW || mi.Height != targetH {
+			continue
+		}
+		if hasRefresh {
+			if math.Abs(mi.RefreshRate-targetR) > 1.0 {
+				continue
+			}
+		}
+		matches = append(matches, mi)
+	}
+
+	switch len(matches) {
+	case 0:
+		m.Name = ""
+		return m
+	case 1:
+		logger.Debug("resolved size to connector",
+			"size", spec, "connector", matches[0].Name)
+		m.Name = matches[0].Name
+		return m
+	default:
+		var names []string
+		for _, mat := range matches {
+			names = append(names, mat.Name)
+		}
+		if hasRefresh {
+			logger.Warn("size:%q matches multiple monitors: %s — add @R to disambiguate",
+				spec, strings.Join(names, ", "))
+		} else {
+			logger.Warn("size:%q matches multiple monitors: %s — use size:WxH@R for disambiguation",
+				spec, strings.Join(names, ", "))
+		}
+		m.Name = ""
+		return m
+	}
+}

internal/backend/sway.go

@@ -202,7 +202,7 @@ func (s *swayBackend) GetMonitors(ctx context.Context) ([]MonitorInfo, error) {
 // enable commands always precede disables.
 func (s *swayBackend) ApplyLayout(ctx context.Context, monitors []MonitorConfig) error {
 	var err error
-	monitors, err = s.resolveMonitorNames(ctx, monitors)
+	monitors, err = resolveMonitorNames(ctx, monitors, s.GetMonitors, s.logger)
 	if err != nil {
 		return fmt.Errorf("resolve monitor names: %w", err)
 	}
@@ -222,68 +222,6 @@ func (s *swayBackend) ApplyLayout(ctx context.Context, monitors []MonitorConfig)
 	return nil
 }
 
-// resolveMonitorNames converts desc: prefixed monitor config names to the
-// actual connector names (e.g. "desc:Xiaomi Corporation Mi Monitor" → "DP-9")
-// by matching against the current set of connected monitors.
-//
-// Matching logic:
-//   - "desc:make model" — substring match against description (make + " " + model)
-//   - "desc:serial" — substring match against serial number
-//   - plain names are returned as-is
-func (s *swayBackend) resolveMonitorNames(ctx context.Context, monitors []MonitorConfig) ([]MonitorConfig, error) {
-	var needsDescResolution bool
-	for _, m := range monitors {
-		if strings.HasPrefix(m.Name, "desc:") {
-			needsDescResolution = true
-			break
-		}
-	}
-	if !needsDescResolution {
-		return monitors, nil
-	}
-
-	current, err := s.GetMonitors(ctx)
-	if err != nil {
-		return nil, fmt.Errorf("get current monitors: %w", err)
-	}
-
-	resolved := make([]MonitorConfig, len(monitors))
-	for i, m := range monitors {
-		if !strings.HasPrefix(m.Name, "desc:") {
-			resolved[i] = m
-			continue
-		}
-
-		needle := strings.TrimPrefix(m.Name, "desc:")
-		var matches []MonitorInfo
-		for _, mi := range current {
-			if strings.Contains(mi.Description, needle) || strings.Contains(mi.Serial, needle) {
-				matches = append(matches, mi)
-			}
-		}
-
-		switch len(matches) {
-		case 0:
-			return nil, fmt.Errorf("no connected monitor matches desc:%q", needle)
-		case 1:
-			resolved[i] = m
-			resolved[i].Name = matches[0].Name
-			s.logger.Debug("resolved desc to connector",
-				"desc", needle, "connector", matches[0].Name)
-		default:
-			var names []string
-			for _, mat := range matches {
-				names = append(names, mat.Name)
-			}
-			return nil, fmt.Errorf(
-				"desc:%q matches multiple monitors: %s — use a more specific identifier",
-				needle, strings.Join(names, ", "))
-		}
-	}
-
-	return resolved, nil
-}
-
 // buildCommands assembles the swaymsg command string.
 // Enabled monitors go first (enable + configure), then disabled ones.
 // Commands are joined with ';' for batch execution.

internal/config/config.go

@@ -157,10 +157,8 @@ func (c *Config) validate() error {
 	if countEnabled(docked.Monitors) == 0 {
 		return errors.New("docked mode must have at least one enabled monitor")
 	}
-	// At least one external monitor must be listed.
-	if len(c.External) == 0 {
-		return errors.New("at least one external monitor must be specified")
-	}
+	// External list is optional. When empty, the daemon auto-detects
+	// external monitors (any non-internal display with non-zero dimensions).
 
 	return nil
 }
@@ -195,19 +193,40 @@ func countEnabled(entries []MonitorEntry) int {
 	return n
 }
 
-// MatchesExternal checks whether a monitor name or description matches any
-// entry in the External list. Supports two match modes:
+// isInternalConnector returns true if the connector name matches a known
+// internal display pattern (eDP, LVDS, DSI). These are always part of the
+// laptop or tablet and should never trigger docked mode.
+func isInternalConnector(name string) bool {
+	prefixes := []string{"eDP-", "LVDS-", "DSI-", "EDP-"}
+	for _, p := range prefixes {
+		if strings.HasPrefix(name, p) {
+			return true
+		}
+	}
+	return false
+}
+
+// MatchesExternal checks whether a monitor matches the External list.
+// Supports match modes:
 //
-//   - Plain name: exact match against MonitorEntry.Name
-//   - desc: prefix: substring match against MonitorEntry.Description
+//   - Plain name: exact match against name
+//   - desc: prefix: substring match against description
+//
+// When the External list is empty, any monitor that is not an internal
+// display connector (eDP-, LVDS-, DSI-) is automatically external.
 func (c *Config) MatchesExternal(name, description string) bool {
+	if len(c.External) == 0 {
+		return !isInternalConnector(name)
+	}
+
 	for _, ext := range c.External {
-		if strings.HasPrefix(ext, "desc:") {
+		switch {
+		case strings.HasPrefix(ext, "desc:"):
 			desc := strings.TrimPrefix(ext, "desc:")
 			if strings.Contains(description, desc) {
 				return true
 			}
-		} else {
+		default:
 			if name == ext {
 				return true
 			}

monitor-lets-go.example.yaml

@@ -26,6 +26,9 @@ restore_on_exit: true
 # External monitors that trigger docked mode.
 #   Plain name: matches the connector name (e.g. DP-1, HDMI-A-1).
 #   desc: prefix: matches by monitor description (survives rename).
+# Optional — if omitted or left empty, the daemon auto-detects external
+# monitors: any display whose connector is not eDP-/LVDS-/DSI- is treated
+# as external.
 external:
   - DP-1
   - DP-2
@@ -33,10 +36,10 @@ external:
 
 # Monitor layouts for each mode.
 # "portable" and "docked" are required.
-# Each mode lists monitors with their desired configuration.
+# Monitors connected but not listed in the mode are automatically disabled.
 #
 # Fields:
-#   name     — connector name or desc:description
+#   name     — connector name, desc:description, size:WxH, or size:WxH@R
 #   enabled  — true to show, false to disable
 #   mode     — "preferred" (auto-detect), "1920x1080@60", etc.
 #   position — "auto", "0x0", "1920x0", etc.
@@ -70,6 +73,11 @@ modes:
         mode: "3840x2160@60"
         position: "0x0"
         scale: 1.5
+      - name: size:1920x1080@60  # resolve by resolution + refresh rate
+        enabled: true
+        mode: preferred
+        position: auto
+        scale: 1.0
 
 # Shell commands run after a layout change.
 # Commands run concurrently; failures are logged but never crash the daemon.