diff --git a/client/scripts/autoloads/hud_groups.gd b/client/scripts/autoloads/hud_groups.gd
index 782f8231e..2eb6da5ff 100644
--- a/client/scripts/autoloads/hud_groups.gd
+++ b/client/scripts/autoloads/hud_groups.gd
@@ -1,30 +1,35 @@
 extends Node
 ## HUD visibility group manager (D-170).
 ##
-## Nodes register themselves into groups. When a group's visibility changes,
-## all registered nodes show/hide together. This replaces per-panel manual
-## hide/show of individual HUD elements.
+## Nodes register into hierarchical groups. Groups control show/hide as a unit.
 ##
-## Groups:
-##   "gameplay"  — stance indicator, minimap, health/time, interaction prompts,
-##                 cursor renderer, inventory, news ticker, examine display
-##   "implant"   — star map, travel planner, GTTR reader, station profile
-##   "modal"     — settings, bug report, loading screen, debug console
-##   "debug"     — debug overlay, gauntlet HUD, checklist
-##   "always"    — nodes that never hide (reserved for future use)
+## Hierarchy:
+##   "gameplay"          — stance, minimap, health, prompts, cursor, inventory
+##   "implant/map"       — star map
+##   "implant/wiki"      — GTTR reader
+##   "implant/journal"   — knowledge journal
+##   "implant/travel"    — travel planner
+##   "implant/station"   — station profile
+##   "implant/cargo"     — cargo manifest
+##   "modal"             — settings, bug report, loading (independent layer)
+##   "debug"             — debug overlay, gauntlet HUD (independent layer)
 ##
-## Usage from any node:
+## Rules:
+##   - "gameplay" and any "implant/*" are mutually exclusive.
+##     Opening an implant app hides gameplay.
+##   - "implant/*" apps are mutually exclusive with each other.
+##     Opening implant/map hides implant/wiki.
+##   - "modal" and "debug" are independent — overlay on anything.
+##
+## Usage:
 ##   HudGroups.register(self, "gameplay")
-##   HudGroups.show_group("implant")    # shows implant, hides gameplay
-##   HudGroups.show_group("gameplay")   # shows gameplay, hides implant
-##   HudGroups.toggle_group("implant")  # toggle between gameplay and implant
+##   HudGroups.register(self, "implant/map")
+##   HudGroups.open_app("implant/map")    # hides gameplay + other implant apps
+##   HudGroups.close_app()                # returns to gameplay
+##   HudGroups.toggle_app("implant/map")  # open if closed, close if open
 
-## Which groups are mutually exclusive — showing one hides the others.
-## Modal and debug are independent (they overlay on top of anything).
-const EXCLUSIVE_GROUPS: Array[String] = ["gameplay", "implant"]
-
-var _groups: Dictionary = {}  # group_name -> Array[Control]
-var _active_exclusive: String = "gameplay"
+var _groups: Dictionary = {}         # group_name -> Array[Control]
+var _active_app: String = ""         # currently open implant/* app ("" = none)
 
 
 func register(node: Control, group: String) -> void:
@@ -32,9 +37,11 @@ func register(node: Control, group: String) -> void:
 		_groups[group] = []
 	if node not in _groups[group]:
 		_groups[group].append(node)
-	# Apply current visibility state
-	if group in EXCLUSIVE_GROUPS:
-		node.visible = (group == _active_exclusive)
+	# Apply current visibility
+	if group == "gameplay":
+		node.visible = _active_app.is_empty()
+	elif group.begins_with("implant/"):
+		node.visible = (group == _active_app)
 
 
 func unregister(node: Control, group: String) -> void:
@@ -42,42 +49,55 @@ func unregister(node: Control, group: String) -> void:
 		_groups[group].erase(node)
 
 
-## Show a group. If it's exclusive, hide the other exclusive groups.
-func show_group(group: String) -> void:
-	if group in EXCLUSIVE_GROUPS:
-		_active_exclusive = group
-		for g: String in EXCLUSIVE_GROUPS:
-			_set_group_visible(g, g == group)
+## Open an implant app. Hides gameplay and any other implant app.
+func open_app(app: String) -> void:
+	if not app.begins_with("implant/"):
+		push_warning("HudGroups.open_app: expected implant/* group, got: " + app)
+		return
+
+	# Hide previous app if different
+	if not _active_app.is_empty() and _active_app != app:
+		_set_group_visible(_active_app, false)
+
+	_active_app = app
+	_set_group_visible("gameplay", false)
+	_set_group_visible(app, true)
+
+
+## Close the current implant app. Returns to gameplay.
+func close_app() -> void:
+	if not _active_app.is_empty():
+		_set_group_visible(_active_app, false)
+	_active_app = ""
+	_set_group_visible("gameplay", true)
+
+
+## Toggle an implant app. If it's open, close it. If another is open, switch.
+func toggle_app(app: String) -> void:
+	if _active_app == app:
+		close_app()
 	else:
-		_set_group_visible(group, true)
+		open_app(app)
 
 
-## Hide a group. If exclusive, falls back to "gameplay".
-func hide_group(group: String) -> void:
-	if group in EXCLUSIVE_GROUPS:
-		show_group("gameplay")
-	else:
-		_set_group_visible(group, false)
+## Check if a specific app is currently open.
+func is_app_active(app: String) -> bool:
+	return _active_app == app
 
 
-## Toggle between gameplay and the specified group.
-func toggle_group(group: String) -> void:
-	if _active_exclusive == group:
-		show_group("gameplay")
-	else:
-		show_group(group)
+## Check if any implant app is open.
+func is_implant_active() -> bool:
+	return not _active_app.is_empty()
 
 
-## Check if a group is currently active.
-func is_group_active(group: String) -> bool:
-	if group in EXCLUSIVE_GROUPS:
-		return _active_exclusive == group
-	# Non-exclusive: check if any member is visible
-	if _groups.has(group):
-		for node: Control in _groups[group]:
-			if is_instance_valid(node) and node.visible:
-				return true
-	return false
+## Get the currently active app name, or "" if none.
+func get_active_app() -> String:
+	return _active_app
+
+
+## Show/hide an independent group (modal, debug). Does not affect gameplay/implant.
+func show_group(group: String, vis: bool = true) -> void:
+	_set_group_visible(group, vis)
 
 
 func _set_group_visible(group: String, vis: bool) -> void:
diff --git a/client/ui/star_map.gd b/client/ui/star_map.gd
index 53d594920..e7abc2fd1 100644
--- a/client/ui/star_map.gd
+++ b/client/ui/star_map.gd
@@ -119,7 +119,7 @@ func _ready() -> void:
 	add_child(_info_panel)
 
 	# D-170: Register with HUD visibility groups
-	HudGroups.register(self, "implant")
+	HudGroups.register(self, "implant/map")
 
 	_load_data()
 	if _data_loaded:
@@ -144,9 +144,9 @@ func set_insert_active(active: bool) -> void:
 
 
 ## Toggle visibility via HUD group system (D-170).
-## Shows implant group (hides gameplay) or vice versa.
+## Opens implant/map (hides gameplay) or closes it (returns to gameplay).
 func toggle_visible() -> void:
-	HudGroups.toggle_group("implant")
+	HudGroups.toggle_app("implant/map")
 	if visible:
 		_dirty = true
 
diff --git a/decisions/architecture.md b/decisions/architecture.md
index 43e6d3fe4..67cc0ce74 100644
--- a/decisions/architecture.md
+++ b/decisions/architecture.md
@@ -626,13 +626,18 @@ Technical foundation decisions that constrain implementation: engine, client-ser
 - **Date:** 2026-04-05
 - **Decision:** HUD elements register into named visibility groups via a `HudGroups` autoload. Groups control show/hide of related elements as a unit. Exclusive groups (gameplay, implant) are mutually exclusive — showing one hides the other. Non-exclusive groups (modal, debug) overlay independently.
 - **Rationale:** Full-screen implant panels (star map, travel planner, GTTR reader) need to hide gameplay HUD elements (stance, minimap, health, interaction prompts). Without groups, each panel manually hides/shows individual nodes — error-prone and unsustainable as the panel count grows.
-- **Groups:**
+- **Groups (hierarchical):**
   - `gameplay` — stance indicator, minimap, HUD status, interaction prompts, cursor, inventory, news ticker, examine display. Visible during normal gameplay.
-  - `implant` — star map, travel planner, GTTR reader, station profile. Fullscreen implant overlays. Showing this hides gameplay.
+  - `implant/map` — star map navigator. Mutually exclusive with gameplay and other implant apps.
+  - `implant/wiki` — GTTR reader. Mutually exclusive with gameplay and other implant apps.
+  - `implant/journal` — knowledge journal. Mutually exclusive with gameplay and other implant apps.
+  - `implant/travel` — travel planner. Mutually exclusive with gameplay and other implant apps.
+  - `implant/station` — station profile. Mutually exclusive with gameplay and other implant apps.
+  - `implant/cargo` — cargo manifest. Mutually exclusive with gameplay and other implant apps.
   - `modal` — settings, bug report, loading screen, debug console. Independent — overlays on top of anything.
   - `debug` — debug overlay, gauntlet HUD, checklist. Independent.
-  - `always` — reserved for elements that never hide.
-- **API:** `HudGroups.register(node, "gameplay")`, `HudGroups.show_group("implant")`, `HudGroups.toggle_group("implant")`, `HudGroups.is_group_active("implant")`
+- **Exclusivity rules:** Opening any `implant/*` app hides gameplay and any other implant app. Closing an app returns to gameplay. Modal and debug are independent layers.
+- **API:** `HudGroups.register(node, "implant/map")`, `HudGroups.open_app("implant/map")`, `HudGroups.close_app()`, `HudGroups.toggle_app("implant/map")`, `HudGroups.is_app_active("implant/map")`, `HudGroups.is_implant_active()`
 - **Implementation:** `client/scripts/autoloads/hud_groups.gd` — lightweight autoload, no scene tree manipulation beyond `node.visible`.
 - **Raised by:** Jeroen, 2026-04-05 — "Walk" badge visible over fullscreen star map.
 - **Dissent:** None.