NEVER Do (Expert Anti-Patterns)
Networking & Scale
- NEVER sync all 100 players every frame; strictly use a Relevancy System to sync high-freq data only for players within ~100m. Far players sync at ~5Hz.
- NEVER use
TRANSFER_MODE_RELIABLE for movement data; strictly use Unreliable to prevent packet backup and network congestion.
- NEVER focus on client-side hit detection; strictly use Authoritative Server Validation where the server confirms "Did it hit?" based on state history.
- NEVER trust the client for game state; strictly validate all movement, looting, and inventory changes exclusively on the authoritative server.
- NEVER run a dedicated server with visuals; strictly use Headless Mode (
--headless) or dummy drivers to save massive CPU/GPU resources.
- NEVER call RPCs before connection; strictly wait for the
connected_to_server signal before attempting synchronization logic.
Mechanics & Performance
- NEVER pick a fully random center for the Safe Zone; strictly target centers that ensure the new circle is completely contained within the current one.
- NEVER allow "Storm Tunneling"; strictly use a Distance-to-Center calculation rather than a simple collision perimeter to prevent skips at low tick rates.
- NEVER spawn loot without Object Pooling; strictly pre-instantiate and toggle visibility/collision to avoid GC spikes during dense spawns.
- NEVER ignore
VisibilityNotifier3D; strictly disable AnimationPlayer, _process(), and heavy AI logic for players that are not visible to the observer.
- NEVER print in tight server loops; strictly avoid
print() as console I/O is blocking and will tank server performance in high-player-count matches.
Available Scripts
MANDATORY: Read the appropriate script before implementing the corresponding pattern.
Zone / Storm
storm_system.gd
MANDATORY for any zone/storm work — phase radii, contained next-center selection, distance-to-center damage (anti-tunneling). Do not paste inline zone_manager tutorials.
Networking & Multiplayer
kill_feed_bus.gd
Global elimination signal bus with match stat tracking.
headless_branch_logic.gd
Expert dedicated server initialization that branches logic based on headless execution and server-specific feature flags.
enet_br_server.gd
High-player-capacity ENet server setup optimized for 100+ concurrent peers over UDP.
state_replication_unreliable.gd
Pattern for synchronizing player transforms via TRANSFER_MODE_UNRELIABLE to minimize network congestion in large matches.
authoritative_looting.gd
Authoritative server-side validation logic for preventing cheat-based item collection and infinite looting.
targeted_rpc_relay.gd
Optimized communication pattern using rpc_id() to target specific peers and reduce wasted packet broadcasts.
server_state_buffer.gd
Handling network jitter and out-of-order UDP packets via sequential state buffering and tick-based sorting.
Performance & Optimization
rid_loot_spawner.gd
Bypassing the node hierarchy for massive loot density. Uses RenderingServer directly to eliminate CPU overhead for item drops.
async_map_loader.gd
Non-blocking map sector streaming using ResourceLoader background threads for seamless open-world exploration.
multimesh_vegetation.gd
Drawing dense foliage and environment assets (100k+ instances) via MultiMeshInstance3D to maximize rendering performance.
threaded_ai_manager.gd
Offloading server-side bot behavior and pathfinding logic to the WorkerThreadPool to prevent main-thread stalling.
Restored from baseline
- lag_compensator.gd - Server transform history + hit timestamp rewind validation.
- monster_synchronizer.gd -
MultiplayerSynchronizer delta/on-change replication setup.
NEVER Do in Battle Royale
- NEVER export mobile clients without the INTERNET permission — Communication will silently fail on Android/iOS if the manifest is missing the networking permission.
- NEVER use
get_var(true) on untrusted data — Deserializing arbitrary objects allows attackers to execute remote code on the server or other clients.
- NEVER synchronize
Object or Resource types over network — Use the MultiplayerSynchronizer strictly for base types (int, float, vec).
- NEVER assume
UNRELIABLE packets arrive in order — Design state interpolation carefully to handle missing or out-of-order ticks.
- NEVER leave
multiplayer_poll false without manual calling — If using custom threads, failing to call multiplayer.poll() freezes all traffic.
Core Loop
Deploy → Loot → Move with storm → Engage → Last standing.
Skill Chain (GDSkills peers only)
Decision Trees (strip inline deploy/loot/zone tutorials)
Zone / Storm
| Need |
Action |
| Phase shrink, contained centers, distance DPS |
MANDATORY storm_system.gd |
| Storm wall VFX |
Inverted SphereMesh + unshaded cull_disabled shader driven by storm radius |
Loot
| Need |
Action |
| Dense drops |
rid_loot_spawner.gd + pooling |
| Anti-cheat pickup |
MANDATORY authoritative_looting.gd |
| Tables / rarity |
Data Resources + peer inventory — not instantiate() loops in SKILL.md |
Deploy
| Need |
Action |
| Plane → freefall → parachute → grounded |
Finite state on player controller; server validates landing inventory |
| Map sectors |
async_map_loader.gd |
Networking
| Need |
Action |
| 100+ peers |
enet_br_server.gd + headless_branch_logic.gd |
| Movement |
state_replication_unreliable.gd |
| Relevancy |
Near ~20Hz+, far ~5Hz; replication_interval / interest management |
| Targeted messages |
targeted_rpc_relay.gd |
| Jitter buffer |
server_state_buffer.gd |
Advanced (keep elite, no deploy/loot re-tutorials)
Lag Compensation
Server keeps transform history; validate client hit timestamps against rewound poses (authoritative). Pair with shooter/combat peers.
Delta-Patching
MultiplayerSynchronizer + REPLICATION_MODE_ON_CHANGE for health/inventory; ALWAYS only for hot transforms. Cap with delta_interval.
Zone Visualizer
Unshaded, cull_disabled spatial shader on inverted sphere scaled by storm_system.gd.
Common Pitfalls
- Too much loot → pool + RID spawner
- Camping → storm forces movement (storm_system.gd)
- Client hit authority → server validate with history
Expert knowledge (on demand)
LLM-ignorance rule: If a general agent would not know it before reading, load the reference — never delete expert deltas.
- expert-battle-royale-patterns.md — restored baseline pedagogy (architecture, WHY, implementation depth)
- lag_compensator.gd
- monster_synchronizer.gd
Reference
Progressive disclosure: open Official Documentation links only when researching a specific API; load Related Skills when routing to a peer domain — do not preload the whole lattice.
Official Documentation
- High-level multiplayer — RPC authority, peer lifecycle, and visibility-aware sync patterns for 100-player relevancy instead of full-mesh broadcasts.
- ENetMultiplayerPeer — UDP host/client peer sized for high concurrent match populations without TCP head-of-line blocking.
- MultiplayerPeer — Reliable vs unreliable/unordered transfer modes so movement snapshots never back up the channel.
- MultiplayerSynchronizer — Property replication,
replication_interval / on-change deltas, and per-peer visibility filters for interest management.
- MultiplayerSpawner — Spawn/despawn replication for players, loot drops, and late-join scene graph consistency.
- Command line tutorial —
--headless and multi-instance CLI launches for dedicated match servers.
- Exporting for dedicated servers — Server export presets and feature tags that strip client-only rendering/input paths.
- Occlusion culling — Bake occlusion for dense building clusters so large BR maps stay GPU-viable.
- Mesh level of detail (LOD) — Distance LODs for terrain props and structures that dominate draw cost at drop-zone scale.
- Optimization using MultiMeshes — Batch foliage/debris into MultiMesh draw calls instead of per-instance nodes.
- Optimization using Servers — RenderingServer RID paths for dense loot visuals without SceneTree node overhead.
- Background loading — Threaded
ResourceLoader sector streaming for non-blocking open-world map loads.
Related Skills
Prerequisites
- godot-multiplayer-networking — Authoritative server RPCs, transfer modes, and lobby/peer lifecycle that BR relevancy and lag compensation build on.
- godot-project-foundations — Autoloads, export feature flags, and project layout for headless dedicated vs client builds.
- godot-3d-world-building — Large terrain chunking, collision generation, and world streaming prerequisites for storm-scale maps.
Complements
- godot-adapt-single-to-multiplayer — Authority split, prediction shells, and snapshot interpolation before applying BR-scale interest management.
- godot-server-architecture — Headless host scaffolding and PhysicsServer/RID patterns used by authoritative match simulation.
- godot-export-builds — Dedicated-server presets, INTERNET permissions, and CLI packaging for multi-instance match tests.
- godot-inventory-system — Backpacks, attachments, and armor state that authoritative looting must validate server-side.
- godot-performance-optimization — LOD, pooling, and CPU budgets when loot density and peer count stress the match server/clients.
- godot-signal-architecture — Kill-feed and match-event buses that stay local while RPCs carry cross-peer eliminations.
- godot-genre-shooter — Hitscan/projectile combat patterns and lag-compensated validation used inside the BR engagement loop.
Downstream / consumers
- godot-monte-carlo-balancer — Simulate zone DPS phases, loot rarity tables, and TTK bands so storm/loot pacing stays fair across 100-player matches.
- godot-ai-navigation — Bot pathfinding and interest-culled AI when filling lobbies with threaded server-side bots.
Master
- godot-master — Library router and mirrored module entry; open when discovering which Domain Skill owns a cross-cutting BR concern.
1---2name: godot-genre-battle-royale3description: Expert blueprint for Battle Royale games including shrinking zone/storm mechanics (phase-based, damage scaling), large-scale networking (relevancy, tick rate optimization), deployment systems (plane, freefall, parachute), loot spawning (weighted tables, rarity), and performance optimization (LOD, occlusion culling, object pooling). Use for multiplayer survival games or last-one-standing formats. Trigger keywords: battle_royale, zone_shrink, storm_damage, deployment_system, loot_spawn, networking_optimization, relevancy_system, snapshot_interpolation.4---5
6## NEVER Do (Expert Anti-Patterns)
7
8### Networking & Scale
9- NEVER sync all 100 players every frame; strictly use a **Relevancy System** to sync high-freq data only for players within ~100m. Far players sync at ~5Hz.
10- NEVER use `TRANSFER_MODE_RELIABLE` for movement data; strictly use **Unreliable** to prevent packet backup and network congestion.
11- NEVER focus on client-side hit detection; strictly use **Authoritative Server Validation** where the server confirms "Did it hit?" based on state history.
12- NEVER trust the client for game state; strictly validate all movement, looting, and inventory changes exclusively on the authoritative server.
13- NEVER run a dedicated server with visuals; strictly use **Headless Mode** (`--headless`) or dummy drivers to save massive CPU/GPU resources.
14- NEVER call RPCs before connection; strictly wait for the `connected_to_server` signal before attempting synchronization logic.
15
16### Mechanics & Performance
17- NEVER pick a fully random center for the Safe Zone; strictly target centers that ensure the new circle is **completely contained** within the current one.
18- NEVER allow "Storm Tunneling"; strictly use a **Distance-to-Center** calculation rather than a simple collision perimeter to prevent skips at low tick rates.
19- NEVER spawn loot without **Object Pooling**; strictly pre-instantiate and toggle visibility/collision to avoid GC spikes during dense spawns.
20- NEVER ignore `VisibilityNotifier3D`; strictly disable `AnimationPlayer`, `_process()`, and heavy AI logic for players that are not visible to the observer.
21- NEVER print in tight server loops; strictly avoid `print()` as console I/O is blocking and will tank server performance in high-player-count matches.
22
23---
24
25## Available Scripts
26
27> **MANDATORY**: Read the appropriate script before implementing the corresponding pattern.
28
29### Zone / Storm
30### [storm_system.gd](scripts/storm_system.gd)
31**MANDATORY for any zone/storm work** — phase radii, contained next-center selection, distance-to-center damage (anti-tunneling). Do not paste inline zone_manager tutorials.
32
33### Networking & Multiplayer
34### [kill_feed_bus.gd](scripts/kill_feed_bus.gd)
35Global elimination signal bus with match stat tracking.
36
37### [headless_branch_logic.gd](scripts/headless_branch_logic.gd)
38Expert dedicated server initialization that branches logic based on `headless` execution and server-specific feature flags.
39
40### [enet_br_server.gd](scripts/enet_br_server.gd)
41High-player-capacity ENet server setup optimized for 100+ concurrent peers over UDP.
42
43### [state_replication_unreliable.gd](scripts/state_replication_unreliable.gd)
44Pattern for synchronizing player transforms via `TRANSFER_MODE_UNRELIABLE` to minimize network congestion in large matches.
45
46### [authoritative_looting.gd](scripts/authoritative_looting.gd)
47Authoritative server-side validation logic for preventing cheat-based item collection and infinite looting.
48
49### [targeted_rpc_relay.gd](scripts/targeted_rpc_relay.gd)
50Optimized communication pattern using `rpc_id()` to target specific peers and reduce wasted packet broadcasts.
51
52### [server_state_buffer.gd](scripts/server_state_buffer.gd)
53Handling network jitter and out-of-order UDP packets via sequential state buffering and tick-based sorting.
54
55### Performance & Optimization
56### [rid_loot_spawner.gd](scripts/rid_loot_spawner.gd)
57Bypassing the node hierarchy for massive loot density. Uses `RenderingServer` directly to eliminate CPU overhead for item drops.
58
59### [async_map_loader.gd](scripts/async_map_loader.gd)
60Non-blocking map sector streaming using `ResourceLoader` background threads for seamless open-world exploration.
61
62### [multimesh_vegetation.gd](scripts/multimesh_vegetation.gd)
63Drawing dense foliage and environment assets (100k+ instances) via `MultiMeshInstance3D` to maximize rendering performance.
64
65### [threaded_ai_manager.gd](scripts/threaded_ai_manager.gd)
66Offloading server-side bot behavior and pathfinding logic to the `WorkerThreadPool` to prevent main-thread stalling.
67
68### Restored from baseline
69- [lag_compensator.gd](scripts/lag_compensator.gd) - Server transform history + hit timestamp rewind validation.
70- [monster_synchronizer.gd](scripts/monster_synchronizer.gd) - `MultiplayerSynchronizer` delta/on-change replication setup.
71
72## NEVER Do in Battle Royale
73
74- **NEVER export mobile clients without the INTERNET permission** — Communication will silently fail on Android/iOS if the manifest is missing the networking permission.
75- **NEVER use `get_var(true)` on untrusted data** — Deserializing arbitrary objects allows attackers to execute remote code on the server or other clients.
76- **NEVER synchronize `Object` or `Resource` types over network** — Use the `MultiplayerSynchronizer` strictly for base types (int, float, vec).
77- **NEVER assume `UNRELIABLE` packets arrive in order** — Design state interpolation carefully to handle missing or out-of-order ticks.
78- **NEVER leave `multiplayer_poll` false without manual calling** — If using custom threads, failing to call `multiplayer.poll()` freezes all traffic.
79
80---
81
82## Core Loop
83Deploy → Loot → Move with storm → Engage → Last standing.
84
85## Skill Chain (GDSkills peers only)
86
87| Phase | Skills | Purpose |
88|-------|--------|---------|
89| 1. Net | [godot-multiplayer-networking](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-multiplayer-networking/SKILL.md) | Authoritative server, relevancy, RPCs |
90| 2. Map | [godot-3d-world-building](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-3d-world-building/SKILL.md), [godot-genre-open-world](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-genre-open-world/SKILL.md) | Terrain scale, streaming, HLOD |
91| 3. Items | [godot-inventory-system](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-inventory-system/SKILL.md) | Backpack / attachments / armor |
92| 4. Combat | [godot-genre-shooter](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-genre-shooter/SKILL.md), [godot-combat-system](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-combat-system/SKILL.md) | Hitscan/projectile + damage validation |
93| 5. Zone | **MANDATORY** [storm_system.gd](scripts/storm_system.gd) | Storm phases / DPS / contained centers |
94| 6. Balance | [godot-monte-carlo-balancer](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-monte-carlo-balancer/SKILL.md) | Zone DPS, loot rarity, TTK bands |
95
96---
97
98## Decision Trees (strip inline deploy/loot/zone tutorials)
99
100### Zone / Storm
101| Need | Action |
102|------|--------|
103| Phase shrink, contained centers, distance DPS | **MANDATORY** [storm_system.gd](scripts/storm_system.gd) |
104| Storm wall VFX | Inverted SphereMesh + unshaded `cull_disabled` shader driven by storm radius |
105
106### Loot
107| Need | Action |
108|------|--------|
109| Dense drops | [rid_loot_spawner.gd](scripts/rid_loot_spawner.gd) + pooling |
110| Anti-cheat pickup | **MANDATORY** [authoritative_looting.gd](scripts/authoritative_looting.gd) |
111| Tables / rarity | Data Resources + peer inventory — not `instantiate()` loops in SKILL.md |
112
113### Deploy
114| Need | Action |
115|------|--------|
116| Plane → freefall → parachute → grounded | Finite state on player controller; server validates landing inventory |
117| Map sectors | [async_map_loader.gd](scripts/async_map_loader.gd) |
118
119### Networking
120| Need | Action |
121|------|--------|
122| 100+ peers | [enet_br_server.gd](scripts/enet_br_server.gd) + [headless_branch_logic.gd](scripts/headless_branch_logic.gd) |
123| Movement | [state_replication_unreliable.gd](scripts/state_replication_unreliable.gd) |
124| Relevancy | Near ~20Hz+, far ~5Hz; `replication_interval` / interest management |
125| Targeted messages | [targeted_rpc_relay.gd](scripts/targeted_rpc_relay.gd) |
126| Jitter buffer | [server_state_buffer.gd](scripts/server_state_buffer.gd) |
127
128---
129
130## Advanced (keep elite, no deploy/loot re-tutorials)
131
132### Lag Compensation
133Server keeps transform history; validate client hit timestamps against rewound poses (authoritative). Pair with shooter/combat peers.
134
135### Delta-Patching
136`MultiplayerSynchronizer` + `REPLICATION_MODE_ON_CHANGE` for health/inventory; `ALWAYS` only for hot transforms. Cap with `delta_interval`.
137
138### Zone Visualizer
139Unshaded, `cull_disabled` spatial shader on inverted sphere scaled by [storm_system.gd](scripts/storm_system.gd).
140
141## Common Pitfalls
142
1431. Too much loot → pool + RID spawner
1442. Camping → storm forces movement ([storm_system.gd](scripts/storm_system.gd))
1453. Client hit authority → server validate with history
146
147## Expert knowledge (on demand)
148
149> **LLM-ignorance rule:** If a general agent would not know it before reading, load the reference — never delete expert deltas.
150
151- [expert-battle-royale-patterns.md](references/expert-battle-royale-patterns.md) — restored baseline pedagogy (architecture, WHY, implementation depth)
152- [lag_compensator.gd](scripts/lag_compensator.gd)
153- [monster_synchronizer.gd](scripts/monster_synchronizer.gd)
154
155## Reference
156
157> Progressive disclosure: open Official Documentation links only when researching a specific API; load Related Skills when routing to a peer domain — do not preload the whole lattice.
158
159### Official Documentation
160- [High-level multiplayer](https://docs.godotengine.org/en/stable/tutorials/networking/high_level_multiplayer.html) — RPC authority, peer lifecycle, and visibility-aware sync patterns for 100-player relevancy instead of full-mesh broadcasts.
161- [ENetMultiplayerPeer](https://docs.godotengine.org/en/stable/classes/class_enetmultiplayerpeer.html) — UDP host/client peer sized for high concurrent match populations without TCP head-of-line blocking.
162- [MultiplayerPeer](https://docs.godotengine.org/en/stable/classes/class_multiplayerpeer.html) — Reliable vs unreliable/unordered transfer modes so movement snapshots never back up the channel.
163- [MultiplayerSynchronizer](https://docs.godotengine.org/en/stable/classes/class_multiplayersynchronizer.html) — Property replication, `replication_interval` / on-change deltas, and per-peer visibility filters for interest management.
164- [MultiplayerSpawner](https://docs.godotengine.org/en/stable/classes/class_multiplayerspawner.html) — Spawn/despawn replication for players, loot drops, and late-join scene graph consistency.
165- [Command line tutorial](https://docs.godotengine.org/en/stable/tutorials/editor/command_line_tutorial.html) — `--headless` and multi-instance CLI launches for dedicated match servers.
166- [Exporting for dedicated servers](https://docs.godotengine.org/en/stable/tutorials/export/exporting_for_dedicated_servers.html) — Server export presets and feature tags that strip client-only rendering/input paths.
167- [Occlusion culling](https://docs.godotengine.org/en/stable/tutorials/3d/occlusion_culling.html) — Bake occlusion for dense building clusters so large BR maps stay GPU-viable.
168- [Mesh level of detail (LOD)](https://docs.godotengine.org/en/stable/tutorials/3d/mesh_lod.html) — Distance LODs for terrain props and structures that dominate draw cost at drop-zone scale.
169- [Optimization using MultiMeshes](https://docs.godotengine.org/en/stable/tutorials/performance/using_multimesh.html) — Batch foliage/debris into MultiMesh draw calls instead of per-instance nodes.
170- [Optimization using Servers](https://docs.godotengine.org/en/stable/tutorials/performance/using_servers.html) — RenderingServer RID paths for dense loot visuals without SceneTree node overhead.
171- [Background loading](https://docs.godotengine.org/en/stable/tutorials/io/background_loading.html) — Threaded `ResourceLoader` sector streaming for non-blocking open-world map loads.
172
173### Related Skills
174
175#### Prerequisites
176- [godot-multiplayer-networking](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-multiplayer-networking/SKILL.md) — Authoritative server RPCs, transfer modes, and lobby/peer lifecycle that BR relevancy and lag compensation build on.
177- [godot-project-foundations](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-project-foundations/SKILL.md) — Autoloads, export feature flags, and project layout for headless dedicated vs client builds.
178- [godot-3d-world-building](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-3d-world-building/SKILL.md) — Large terrain chunking, collision generation, and world streaming prerequisites for storm-scale maps.
179
180#### Complements
181- [godot-adapt-single-to-multiplayer](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-adapt-single-to-multiplayer/SKILL.md) — Authority split, prediction shells, and snapshot interpolation before applying BR-scale interest management.
182- [godot-server-architecture](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-server-architecture/SKILL.md) — Headless host scaffolding and PhysicsServer/RID patterns used by authoritative match simulation.
183- [godot-export-builds](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-export-builds/SKILL.md) — Dedicated-server presets, INTERNET permissions, and CLI packaging for multi-instance match tests.
184- [godot-inventory-system](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-inventory-system/SKILL.md) — Backpacks, attachments, and armor state that authoritative looting must validate server-side.
185- [godot-performance-optimization](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-performance-optimization/SKILL.md) — LOD, pooling, and CPU budgets when loot density and peer count stress the match server/clients.
186- [godot-signal-architecture](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-signal-architecture/SKILL.md) — Kill-feed and match-event buses that stay local while RPCs carry cross-peer eliminations.
187- [godot-genre-shooter](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-genre-shooter/SKILL.md) — Hitscan/projectile combat patterns and lag-compensated validation used inside the BR engagement loop.
188
189#### Downstream / consumers
190- [godot-monte-carlo-balancer](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-monte-carlo-balancer/SKILL.md) — Simulate zone DPS phases, loot rarity tables, and TTK bands so storm/loot pacing stays fair across 100-player matches.
191- [godot-ai-navigation](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-ai-navigation/SKILL.md) — Bot pathfinding and interest-culled AI when filling lobbies with threaded server-side bots.
192
193#### Master
194- [godot-master](https://github.com/thedivergentai/gd-agentic-skills/blob/main/skills/godot-master/SKILL.md) — Library router and mirrored module entry; open when discovering which Domain Skill owns a cross-cutting BR concern.