Project-M/Docs/Vault/_Meta/CLAUDE_Build_Gotchas_Archive.md

title, type, created

title	type	created
CLAUDE.md Build-Gotchas Archive	reference	2026-06-04

CLAUDE.md Build-Gotchas Archive

This note holds the full, verbose build-gotcha entries that were condensed out of the committed CLAUDE.md on 2026-06-04 to keep that file under its 40 KB context-load limit. The condensed one-liners in CLAUDE.md link here and to the per-milestone Decision Records (Docs/Vault/07_Sessions/_Decisions/DR-###). Nothing was deleted — this is the long-form source of truth for the operational lessons; the DRs carry the design rationale.

When a gotcha here is later proven wrong or superseded, strike it through and note the superseding DR rather than deleting it.

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Version history & stack status

✅ Reconciled 2026-06-02: manifest.json pins aligned to the resolved Unity 6.4.7 lock (entities/entities.graphics 6.4.0, URP 17.4.0, test-framework 1.6.0, ugui 2.0.0, multiplayer.center 1.0.1) — a no-op re-resolve (lock unchanged, console clean). The values in the CLAUDE.md stack table match packages-lock.json. See DR-008_M5_HomeBase_BaseLayer_Storage.

Version history & status (2026-05-30): built on 6.4.7 (6000.4.7f1; Netcode 1.13.2 / Physics 1.4.6 / Entities 6.4.0). Briefly upgraded to 6.6.0a6, where Netcode→6.6.0, Physics→6.5.0, Entities→6.5.0 all renumbered into the editor line — BUT the alpha's Netcode/Transport runtime is broken (all in-editor connections fail with "invalid wrapped network interface"; confirmed engine bug via a zero-gameplay repro — see Docs/Vault DR-002 and Docs/UnityBugReport-Netcode-Transport-6.6.0a6.md). → Reverting to Unity 6.4.7 for stable netcode runtime. If returning to 6.6 later, expect the renumber and re-test the runtime. The M1 player slice should port to 6.4 / Netcode 1.13.2 with no or minimal changes — recompile and read_console after the downgrade.

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Build gotchas (learned — M1, 2026-05-30)

• Unity.Transforms must be a DIRECT asmdef reference for any assembly whose source-gen'd systems use LocalTransform/LocalToWorld. It is its own assembly; transitive visibility compiles your hand-written code but the Entities generator emits CS0246 inside the *.g.cs.
• Authoring asmdefs need Unity.Entities.Hybrid (defines Baker<T>) and Unity.Collections (baking source-gen). A nested baker class must not be named Baker (it shadows Baker<T> → CS0308/CS0246) — name it FooBaker.
• Never name an IComponentData PlayerInput, and don't using UnityEngine.InputSystem; in a file that references such a component: it collides with UnityEngine.InputSystem.PlayerInput, and the Entities generator binds RefRW<…> to the managed class → a misleading CS8377 "must be a non-nullable value type". Fully-qualify Input System types (UnityEngine.InputSystem.Keyboard.current) instead.
• IInputComponentData requires implementing FixedString512Bytes ToFixedString().
• An input-gather system that reads the managed Input System belongs in GhostInputSystemGroup as a non-Burst ISystem (or SystemBase), never inside the prediction loop.

Build gotchas (learned — M2 combat, 2026-05-31)

• The generated Input Actions C# wrapper must live inside an asmdef any system needs to reference. By default it generates next to the .inputactions (e.g. Assets/Settings/), which has no asmdef → it compiles into Assembly-CSharp, and asmdef assemblies (ProjectM.Client) cannot reference that. Fix: set the importer's wrapperCodePath (in the .inputactions.meta) to a path inside the consuming asmdef, e.g. Assets/_Project/Scripts/Client/Input/ProjectMInput.cs, and delete the old generated file. Read the action map via a managed SystemBase holding the wrapper; gather Fire as a netcode InputEvent (reset the field each frame, .Set() on the press edge — netcode latches the absolute Count into the command buffer; the live component value is only the per-tick delta).
• Predicted-spawn classification cannot be [BurstCompile]d (Netcode 1.13.2). The cross-assembly generic Unity.NetCode.LowLevel.SnapshotDataBufferComponentLookup.TryGetComponentDataFromSnapshotHistory<T>() trips a Burst internal compiler error (type-hash resolution). Make the classifier a plain non-Burst ISystem (it only runs when spawns are received — cold path). In 1.13.2 that method takes ref DynamicBuffer<SnapshotDataBuffer> (the public HelloNetcode sample's by-value data is from an older version).
• A Burst internal compiler error corrupts the editor's Burst incremental cache. After the error is fixed in code, newly-added [BurstCompile] entry points (systems and generated ghost-component serializers) keep logging "... is not a known Burst entry point" and run managed-fallback (slow → server tick-batching, ~30–40s play-enter). A clean compile + green tests + working runtime confirm the code is fine. Clear it with an editor restart (or delete Library/BurstCache while closed) — a domain reload alone does not.
• Projectile/area hit tests must be swept, not point checks. A point distance check tunnels straight through a target when the per-tick step exceeds the target radius — at high projectile speed or whenever the server tick-batches under load. Test the segment the projectile traversed this tick ([curPos - dir*speed*dt, curPos]) against each target; order the damage system [UpdateAfter(MoveSystem)]. (Caught at runtime, not by a point-based unit test — cover hit detection with a tunnelling regression test.)
• In-editor input injection needs a focused Game view — unless you change two settings. By default the Input System ignores injected/real device input while the Game view is unfocused, so headless (MCP execute_code) keypress simulation won't drive IInputComponentData. Fix (both now set in this project): InputSettings.editorInputBehaviorInPlayMode = AllDeviceInputAlwaysGoesToGameView + Application.runInBackground = true. For deterministic, device-independent validation prefer the editor-only DebugInputInjectionSystem (ProjectM.Client, #if UNITY_EDITOR): poke its statics from execute_code — DebugInputInjectionSystem.Fire() / .SetMove(x,z) / .SetAim(x,z) / .Stop() — to drive the local player's PlayerInput through the authentic command→prediction pipeline. (Validated: SetMove drives + replicates movement. One-shot Fire propagation needs a healthy editor — tick-batching under a degraded/corrupt-Burst editor drops one-shot InputEvents while continuous values survive.)
• Prototype presentation glue lives in ProjectM.Client as MonoBehaviours. PrototypeCameraRig (on the Main Camera) is a tunable player-following ARPG cam (default mid 3/4 ~45° perspective) that reads the local player ghost's LocalTransform each LateUpdate. Bright prototype URP-Lit materials are in Assets/_Project/Materials/ (player cyan, dummy red, projectile yellow, ground grey). ProjectM.Client now references Unity.Transforms directly (the rig reads LocalTransform).

Build gotchas (learned — M5 physics-in-prediction, 2026-06-01)

• Editing Assets .cs with the raw Write tool does NOT reliably trigger a Unity recompile on an unfocused editor — refresh_unity did a domain reload without recompiling, so tests + execute_code ran a stale assembly (symptom: behaviour that exists in neither the old nor new source). Always edit Assets .cs via MCP apply_text_edits / create_script (Unity's own scripting pipeline) — never Write. (Write/Edit are fine for non-asset files: vault, asmdef JSON, etc.) See 2026-06-01_M5_Physics_In_Prediction.
• Predicted physics is implicit — there is no PredictedPhysics toggle. With the netcode-physics package present (Unity.NetCode.Physics, …Physics.Hybrid) and predicted ghosts carrying physics components, Netcode relocates PhysicsSystemGroup into the PredictedFixedStepSimulationSystemGroup (a child of PredictedSimulationSystemGroup, marked OrderFirst). NetCodePhysicsConfig only tunes lag-comp / run-mode / history. Put one in the gameplay subscene with PhysicGroupRunMode = LagCompensationEnabledOrAnyPhysicsEntities so the group runs whenever physics entities exist.
• Unity Physics 1.x bakes built-in UnityEngine colliders + Rigidbody — the old PhysicsShapeAuthoring/PhysicsBodyAuthoring (Physics 0.x) are gone (unity_reflect finds neither). Author a dynamic body with a CapsuleCollider/BoxCollider + Rigidbody (useGravity=false → planar/PhysicsGravityFactor=0; isKinematic=false; interpolation=Interpolate → PhysicsGraphicalSmoothing). Static colliders = collider, no Rigidbody, baked into the subscene (present identically in server + client worlds, deterministic, no replication).
• PhysicsVelocity auto-replicates — Netcode ships PhysicsVelocityDefaultVariant + a generated serializer, so a predicted-physics ghost needs no hand-written [GhostField] for velocity (LocalTransform is already replicated). Drive the character by writing PhysicsVelocity.Linear, not by teleporting LocalTransform.
• Rigidbody.FreezeRotation is NOT honored by the DOTS baker (baked PhysicsMass.InverseInertia stays non-zero). Hold a top-down character's facing by zeroing angular velocity each tick + writing rotation directly (PlayerAimSystem); set PhysicsMass.InverseInertia = float3.zero in a baker/system if a hard lock is needed.
• Gravity-off bodies accumulate vertical contact impulses permanently (a capsule rides up a box edge and floats away — looks like tunnelling, isn't). Pin players to the movement plane after the physics step: a system in PredictedSimulationSystemGroup [UpdateAfter(PredictedFixedStepSimulationSystemGroup)] clamping Y to PlayerSpawner.SpawnPoint.y + zeroing Linear.y (PlayerPlanarConstraintSystem).
• The predicted physics group is OrderFirst, so a system in PredictedSimulationSystemGroup with [UpdateBefore(PredictedFixedStepSimulationSystemGroup)] is ignored (OrderFirst/OrderLast wins) → 1-tick velocity offset (consistent across server/client/rollback — prediction stays in sync). For same-tick application, put the system inside PredictedFixedStepSimulationSystemGroup [UpdateBefore(Unity.Physics.Systems.PhysicsSystemGroup)] (verified to sort before the step) — but expect cosmetic "invalid UpdateBefore" warnings from the relocation.

Note (M5b): PlayerMoveSystem + PlayerPlanarConstraintSystem from this milestone were deleted when the player became a Unity Character Controller. The predicted-physics infra (NetCodePhysicsConfig, baked static walls) is kept. See the M5b section.

Build gotchas (learned — M5b Unity Character Controller, 2026-06-01)

• The player is now a Unity Character Controller kinematic character, NOT a dynamic Rigidbody. PlayerMoveSystem + PlayerPlanarConstraintSystem (M5) are deleted. Movement: PlayerControlSystem maps PlayerInput.Move × EffectiveCharacterStats.MoveSpeed → CharacterControl (via the unit-tested CharacterControlMath.DesiredMovement); CharacterProcessor (collide-and-slide) consumes it in CharacterPhysicsUpdateSystem ([UpdateInGroup(KinematicCharacterPhysicsUpdateGroup)], relocated into the predicted loop). The DR-006 predicted-physics infra (NetCodePhysicsConfig, baked static walls) is kept — the CC character sweeps against that same PhysicsWorld.
• A package declaring an older com.unity.entities/com.unity.physics dependency can still resolve on our renumbered stack — Unity treats the dep as a SemVer floor, so Entities 6.4.0 satisfies a 1.3.15 requirement and is NOT downgraded. Don't trust a version-string mismatch as "incompatible": probe (add the package, confirm packages-lock.json kept Entities 6.4.0 / Physics 1.4.6 / Netcode 1.13.2 + a clean compile; rollback if not). CC 1.4.2 verified this way.
• CC 1.4.2 API shape = IKinematicCharacterProcessor<T> + KinematicCharacterDataAccess + static KinematicCharacterUtilities.Update_*. The legacy KinematicCharacterAspect (IAspect, instance Update_*) also exists but is NOT what the 1.4.x samples use — verify the installed shape with unity_reflect, don't assume. (A sub-agent's package-cache read disagreed with reflect; reflect + first-try clean compile won.)
• KinematicCharacterUtilities.BakeCharacter aborts (logs an error, adds nothing) if the GameObject has a Rigidbody and requires uniform (1,1,1) scale. The player prefab keeps its CapsuleCollider (baked into PhysicsCollider) but the M5 Rigidbody was removed. Two bakers on one prefab GameObject (PlayerAuthoring + PlayerCharacterAuthoring) is fine — both resolve the same entity.
• CharacterInterpolation must be PredictedClient-only. BakeCharacter adds it to all prefab versions; a DefaultVariantSystemBase registers CharacterInterpolation → [GhostComponent(PrefabType = GhostPrefabType.PredictedClient)] so it's stripped from server + interpolated-client prefabs (else double-interp on remotes). Verified: server ghost has no CharacterInterpolation, client ghost does.
• Do NOT copy the CC sample's global LocalTransform → DontSerializeVariant. It is project-wide and would break the non-character ghosts here (projectiles/dummies/pickups) that rely on stock LocalTransform replication. Our CC character replicates position via the normal owner-predicted LocalTransform path; only the CharacterInterpolation variant is registered.
• Top-down CC config (planar, no gravity): AuthoringKinematicCharacterProperties with SnapToGround=false, InterpolateRotation=false (rotation owned by PlayerAimSystem), SimulateDynamicBody=false (players don't physically push each other); gravity is handled in the processor by feeding float3.zero to Update_GroundPushing and never adding a gravity term. Result: stays on the spawn plane (y≈1) with no planar-pin system.

Build gotchas (learned — M5 home base + shared storage, 2026-06-02)

• Ownerless interpolated ghost ≠ owner-predicted for buffer replication. A server-spawned ownerless ghost (e.g. the shared storage chest) replicates a [GhostField] IBufferElementData to all clients with no OwnerSendType and no GhostOwner — server mutations just propagate. [GhostComponent(OwnerSendType = SendToOwnerType.All)] (per StatModifier) is only for the predicting owner to recompute its own state; adding it (or a GhostOwner) to an ownerless ghost is wrong.
• One-off shared-state actions belong on an IRpcCommand, not a predicted InputEvent. RPCs are reliable, so deposit/withdraw landed even while the server tick-batched (the M2 one-shot Fire InputEvent drops under batching). RPC payloads are plain blittable fields — no [GhostField]; store an op as a byte, not an enum (cross-assembly enum-Burst hazard, same one that de-Bursted ProjectileClassificationSystem). For a single shared target, resolve it as a server singleton — never put an Entity (not stable cross-world) in the command; only reach for a ghost-id+spawn-tick (SpawnedGhostEntityMap) when there are many targets (and that lookup may force the handler off Burst).
• Apply server-only RPC effects in the server SimulationSystemGroup, NOT the predicted loop — the predicted loop re-runs on rollback and would double-apply. (Mutating a DynamicBuffer is not a structural change, so it's safe to do while iterating a different entity query, e.g. the RPC requests.)
• Build-grid math must be deterministic + integer-stable. Corner-origin + center-returning + half-open cell bounds + math.floor (not truncation — negatives). Lock CellSize/PlotSize as a coordinate space once: M6 placement builds on it; changing them later invalidates placed structures. (BaseGridMath, unit-tested in EditMode like PlayerSpawnMath.)
• Runtime-spawn shared ghosts; don't bake them into the subscene. A one-shot server spawner (mirrors UpgradePickup/TrainingDummy) keeps the subscene ghost-free and dodges the prespawn section-ack/CRC handshake. Do not add such a ghost to a connection's LinkedEntityGroup if it must survive that player's disconnect (the shared base is world-owned).
• Build a correctly-configured ghost prefab by duplicating an existing one (UpgradePickup.prefab → Storage.prefab, then swap the authoring MonoBehaviour via manage_prefabs modify_contents) rather than hand-adding GhostAuthoringComponent — its ownerless/interpolated settings (HasOwner=0, DefaultGhostMode=Interpolated) + LinkedEntityGroupAuthoring come along for free.
• execute_code runs as a method body — no using directives (they parse as statements → "Identifier expected"); fully-qualify every type (Unity.Entities.World, ProjectM.Simulation.BaseAnchor, …). Also: world flags overlap a shared Game bit, so identify worlds by world.Name == "ServerWorld"/"ClientWorld" rather than (Flags & GameServer).
• An unfocused editor throttles Edit mode to near-idle → MCP pings time out and the bridge looks hung (it still queues commands — telemetry_ping succeeds). Application.runInBackground only helps in Play mode. If it wedges, focus or restart the editor; don't pile refresh_unity calls onto a blocked main thread. Prefer refresh_unity scope=scripts for code-only changes (scope=all force is heavy and contributed to a mid-session hang).

Build gotchas (learned — M5.5 game feel & identity, 2026-06-02)

• Move an ownerless INTERPOLATED enemy ghost SERVER-ONLY in the plain SimulationSystemGroup, never in PredictedSimulationSystemGroup (interpolated ghosts aren't predicted; the server has no rollback). Use [UpdateAfter(PredictedSimulationSystemGroup)], NOT [UpdateBefore] — the predicted group is OrderFirst in SimulationSystemGroup, so UpdateBefore/After it is silently ignored (Unity logs "Ignoring invalid UpdateBefore… OrderFirst/OrderLast has higher precedence"). A plain-SimulationSystemGroup server system therefore always runs after the predicted group, so a contact DamageEvent it appends drains the following tick (~16ms, fine for melee). Stock LocalTransform replication carries position — no hand-written [GhostField]. Build the enemy ghost by duplicating an existing interpolated ghost (UpgradePickup.prefab → Enemy.prefab) so the ownerless/interpolated GhostAuthoringComponent comes free — the training dummy is not a ghost (server-only → invisible to clients). See DR-009_GameFeel_Identity_FirstBlood.
• Derive an enableable gate from already-replicated state instead of replicating it. Player Dead = a LOCAL enableable derived every predicted tick from the replicated Health<=0 (PlayerDeathStateSystem, runs in both worlds, before movement/aim/fire) — the same derive-don't-replicate idiom as StatRecomputeSystem/EffectiveCharacterStats; rollback-correct on server + owner-client with no [GhostEnabledBit]. To write the bit on a currently-disabled entity the query must visit it: .WithPresent<Dead>() (write) vs .WithDisabled<Dead>() (alive-only run); .WithAll<Simulate>() ANDs independently. Bake the enableable DISABLED (AddComponent<T>(e); SetComponentEnabled<T>(e, false); in the baker) so instances spawn in the off state (instantiated entities inherit the prefab's enabled state). Respawn TIMING is server-only (SimulationSystemGroup, after the predicted group).
• All juice/HUD = client-only managed SystemBase in PresentationSystemGroup (once per frame, no rollback double-fire) that OBSERVES replicated state — never mutates the sim. Read ECS via SystemAPI.Query inside OnUpdate + EntityManager.CompleteDependencyBeforeRO<T>() — NOT from a MonoBehaviour LateUpdate (that throws the job-safety exception the camera rig hit). Entity is a stable client dict key for a ghost's lifetime — prune the cache each frame (a pruned enemy = a kill → death VFX at its last pos; never DestroyEntity a ghost from the client — GhostDespawnSystem owns despawn). Netcode-safe "hit-stop" = a camera punch, never Time.timeScale (it would corrupt the deterministic sim).
• Asset-free presentation: procedural AudioClip.Create SFX; a runtime ParticleSystem pool (Sprites/Default material + HDR start color so bursts bloom); a code-built uGUI HUD (RawImage over Texture2D.whiteTexture for anchor-driven bars + legacy Text with Resources.GetBuiltinResource<Font>("LegacyRuntime.ttf")). To edit a prefab asset's component in code: PrefabUtility.LoadPrefabContents → modify → SaveAsPrefabAsset(root, path) → UnloadPrefabContents (SavePrefabAsset rejects the contents root — "Can't save a Prefab instance"). Watch shared-material bleed when re-tinting (M_Dummy doubled as the wall material → orange walls; Husks got their own M_Husk). ACES tonemapping needs the URP asset color grading mode = HDR (m_ColorGradingMode = 1).
• The "0 = ready" raw-uint cooldown sentinel can collide at tick wraparound — a computed ServerTick + delay can equal 0. Route every cooldown/spawn "next tick" write through TickUtil.NonZero(...) (coerce 0→1), and compare stored ticks with new NetworkTick(raw).IsNewerThan(serverTick) / .TicksSince(...) — never raw < / subtraction — the HUD cooldown bar included. (Caught by the adversarial review; RespawnMath already guarded it.)
• An unfocused editor stalls EditMode test INIT ("tests did not start within timeout") and slows play-enter domain reloads — pass run_tests(init_timeout=120000) and retry; ask the operator to focus Unity for heavy build/test sessions (Application.runInBackground only helps in Play mode).

Build gotchas (learned — art import / Synty packs → URP, 2026-06-03)

The imported store art (BefourStudios; future Synty) is HDRP-authored but we run URP 17.4 + Entities Graphics → source M_* materials render magenta. The reusable converter is Assets/_Project/Scripts/Editor/EnvArtTools.cs (menu ProjectM/Art/1. Convert Curated Env Materials); it outputs stock URP/Lit to Assets/_Project/Materials/Env/. See DR-010_Art_Import_URP_Conversion_Visual_Upgrade.

• Convert, don't switch pipelines. Re-author to stock URP/Lit (933532a4…, the same shader our prototypes use → DOTS-instancing/Entities-Graphics compatible). FBX meshes + T_*_B/_N/_ORM textures are reusable as-is; the auto-generated MI_* URP stubs are blank. Switching the project to HDRP is NOT an option (breaks Entities Graphics).
• A dark-lit screenshot MASKS material bugs — verify material values, not just the render. S_General exposes a float _BaseColorMultiply and the real Color in _AlbedoTint. HasProperty("_BaseColorMultiply") is true but GetColor() on a float returns (0,0,0) (and logs a "doesn't have a color property" warning) → black albedo everywhere. Always shader.GetPropertyType(idx)-guard before GetColor/GetFloat/GetTexture.
• Gate source emission on the _Emissive (0/1) flag AND a fixture name — S_General carries a non-zero default _EmissiveColor even when off; reading it unconditionally makes crates/walls/domes glow (flat color can't reproduce the source emission mask).
• VolumeProfile.Add<T>() does NOT persist the override — on save the components list serializes {fileID:0} nulls (works in-session, gone after reload). Use AssetDatabase.AddObjectToAsset(component, profile) per effect, then SaveAssets; verify non-null refs on disk.
• LocalTransform.FromPosition() resets Scale=1, silently discarding a ghost prefab's authored scale (Scale is a replicated [GhostField] → consistent-but-wrong, not a desync). Server spawners must read the prefab's baked LocalTransform and override only Position (fixed in UpgradePickupSpawnSystem/SharedStorageSpawnSystem).
• High metallic + no reflection probe + dark skybox = near-black. Keep converted env metallic low (0.1–0.2); rely on albedo + direct light.
• Static decor goes in the gameplay subscene (Entities Graphics renders only baked/EG-spawned entities; a SampleScene MeshRenderer renders via classic URP). Strip colliders from cosmetic props (else they bake into the static PhysicsWorld the CC sweeps) and put no GhostAuthoring on scenery. Edit the subscene via manage_scene load … additive → place → SaveScene → close_scene (re-bakes on Play); the baked-entity view disappears while it's open additively — verify placement via execute_code over the scene roots, not the game view.
• HUD-free beauty shot = a positioned game_view capture (view_position/view_rotation) — direct camera rendering excludes Screen-Space-Overlay UI. scene_view rejects positioned capture.
• VFX (GabrielAguiar) is now imported (499 prefabs, ~94% Shuriken; 27 VFX-Graph). Wired into combat via DR-011_Synty_World_VFX_Integration — see the VFX gotchas below. VFX-Graph (hits/beams) packs still need separate URP setup if wanted.

Build gotchas (learned — Synty world + GabrielAguiar VFX, 2026-06-03)

The world is now a cohesive Synty sci-fi colony + GabrielAguiar combat VFX. See DR-011_Synty_World_VFX_Integration / 2026-06-03_Synty_World_And_VFX.

• Synty is URP-native — NO conversion (unlike the HDRP BefourStudios art). The grounded world is built as cosmetic classic-URP GameObjects in SampleScene (SyntyWorld root), NOT the DOTS subscene — the custom Synty/Generic_Basic shader just renders, and you never have to verify its Entities-Graphics DOTS-instancing. Only the gameplay subscene needs Entities Graphics + the baked PhysicsWorld.
• Cosmetic SampleScene colliders are inert to gameplay — classic PhysX is separate from the DOTS PhysicsWorld (baked only from the subscene); the planar-pinned CC never sees them. So a cosmetic world needs no collider stripping for gameplay.
• "Grounded" = surround + horizon, not a bigger plane — a skyline ring of tall buildings + a planet/asteroid backdrop + a Skybox/6 Sided space skybox + light fog killed the floating-plane far better than extending the ground.
• Swap a subscene object's VISUAL while keeping collision: disable its MeshRenderer but keep the BoxCollider — the collider still bakes to the static PhysicsCollider, and a disabled renderer bakes no RenderMesh (invisible wall, collision intact). Used to retire the BefourStudios walls under the Synty world.
• A GA "projectile" prefab is NOT a passive trail — it ships a non-kinematic Rigidbody + collider + ProjectileMoveScript (self-propels, collides, spawns secondary muzzle/hit VFX). Any authored VFX dropped into a cosmetic slot must be stripped to particles: destroy Rigidbody/Collider and disable Projectile/Move-named MonoBehaviours BEFORE their Start runs (CombatFeedbackSystem.StripCosmetic). Verify a prefab's components, not its name.
• VFX prefab → client SystemBase bridge: a MonoBehaviour with a static Instance + prefab fields in the bootstrap scene (VFXConfig, mirrors PrototypeCameraRig) hands authored assets to the managed CombatFeedbackSystem; keep a procedural fallback so a null slot still runs. Derive VFX TTL from the prefab's longest ParticleSystem (not a blanket constant) and cap concurrent VFX to bound GC churn under swarms.
• Projectile-follow VFX: query SystemAPI.Query<RefRO<LocalTransform>>().WithAll<Projectile>() each presentation frame; dict-by-Entity spawn/reposition/prune (same idiom as the Health FX cache). The one-shot Fire InputEvent still drops under the unfocused editor, so fire-driven VFX (muzzle/trail/enemy-death) need a focused editor / real client to fire.

Build gotchas (learned — aim controls: mouse cursor + gamepad, 2026-06-03)

The KBM/gamepad aim rework is DR-012_Aim_Controls_Cursor_Gamepad / 2026-06-03_Aim_Controls_Cursor_Gamepad.

• Client-derived aim rides the EXISTING PlayerInput.Aim [GhostField] — no new netcode surface. Mouse-cursor aim is computed client-side in PlayerInputGatherSystem (managed SystemBase, GhostInputSystemGroup, once/frame): Mouse.current.position → Camera.main.ScreenPointToRay → AimMath.PlanarAimFromRay (pure, Burst-safe, unit-tested) against the player's movement plane → write the player→cursor direction as Aim. Only the resulting direction crosses the wire; predicted/server systems are unchanged. Movement (Move) is already decoupled from facing (Aim/PlayerFacing), so strafe-while-aiming is free the moment Aim is the cursor. Don't add a mouse binding to the Aim action — the gather reads the device directly (no .inputactions edit → no wrapper regen).
• Active input scheme = last-meaningful-actuation-wins, replicated as a byte (NOT an enum). Detect KBM vs gamepad each frame (stick/trigger/button past a 0.04 lengthsq deadzone vs mouse-delta/click/movement-key; InputDevice.lastUpdateTime breaks ties; hold last when idle) and stream PlayerInput.Scheme (InputSchemeId.KeyboardMouse=0/Gamepad=1). It is a byte because it is compared inside the Burst-compiled AbilityFireSystem (the cross-assembly enum-in-Burst ICE hazard). The server gates the AutoTarget cone to applied.InternalInput.Scheme == Gamepad (read at the fire tick from the same GetDataAtTick lookup) → precise mouse, gamepad-only assist; mouse then predicts == server (fewer reconcile snaps).
• A static presentation bridge must reset on play-enter. AimPresentation.Scheme (mirrors PrototypeCameraRig/VFXConfig statics) needs [UnityEngine.RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.SubsystemRegistration)] to reset — statics survive fast-enter-playmode domain reloads, and a stale value flashes the wrong cursor/reticle for the first frames (caught by the adversarial review).
• Cursor/reticle = client PresentationSystemGroup SystemBase (AimReticleSystem) that OBSERVES, never mutates. A flat world-space ground ring (primitive quad, Sprites/Default with a null-guard fallback, procedural ring texture) is the aim indicator for BOTH schemes — KBM at the cursor's ground-projection point, gamepad a fixed distance ahead along replicated PlayerFacing. The hardware cursor is hidden while aiming + focused (Application.isFocused-gated) and restored on focus-loss / OnDestroy. A radial dead-zone (AimMath.PlanarAimFromRay deadZoneRadius) holds facing when the cursor is over the character. The KBM ground point is re-raycast INSIDE AimReticleSystem (PresentationSystemGroup runs after the follow-cam's LateUpdate), not latched from the gather (GhostInputSystemGroup, before the move) — latching there drifts the ring a frame behind the cursor under the moving camera. Optional camera aim look-ahead (PrototypeCameraRig.AimLeadDistance, tunable) leads the framed point toward PlayerFacing (not the live cursor projection, to avoid a feedback loop). Headless validation: drive DebugInputInjectionSystem (now stamps Scheme) + force AimPresentation.Scheme; the real cursor / live device-switch needs a focused Game view (the unfocused editor can't inject mouse position).

Build gotchas (learned — M6 Aether Cycle core loop, 2026-06-03)

The M6 core-loop slice (Expedition→Defend→Build) + the base/expedition world split. See DR-013_M6_Aether_Cycle_Region_Split / 2026-06-03_M6_Aether_Cycle_CoreLoop. Stages 0–1 done; 2–4 are the continuation.

• Base/expedition split = coordinate-region + per-connection GhostRelevancy, NOT SceneSystem streaming (supersedes DR-008's framing). One server world; the expedition lives at base + (1000,0,0); a server RegionRelevancySystem in GhostSimulationSystemGroup (before GhostSendSystem) sets GhostRelevancyMode.SetIsIrrelevant and each tick marks region-tagged ghosts irrelevant to connections whose player is in a different region. Use SetIsIrrelevant (not SetIsRelevant) so untagged/global ghosts (the future cycle director) stay relevant to everyone for free — you only enumerate cross-region ghosts to hide. Verify the API on the installed Netcode (1.13.2) with unity_reflect: GhostRelevancy singleton has GhostRelevancyMode + NativeParallelHashMap<RelevantGhostForConnection,int> GhostRelevancySet; RelevantGhostForConnection{ int Connection; int Ghost } (Connection=NetworkId.Value, Ghost=GhostInstance.ghostId). RegionTag{byte Region} is server-only (NOT a [GhostField]) — the server makes all relevancy decisions; the client just gains/loses ghosts. Reuses the runtime-ghost spawn path verbatim (no baked ghosts → no prespawn handshake), no async-load race; co-op drop-in is free.
• Region transit + cycle phase use the established byte-RPC + tick-safe + server-SimulationSystemGroup patterns. RegionTransitRequest{byte TargetRegion} (resolve sender via ReceiveRpcCommandRequest.SourceConnection→NetworkId→GhostOwner, flip RegionTag, teleport LocalTransform). The macro loop is a server-only CycleState singleton ([GhostField]-pre-annotated for the later CycleDirector ghost) driven by CyclePhaseSystem ([UpdateBefore(WaveSystem)]); it gates WaveSystem with a one-line if (TryGetSingleton<CycleState>(out var c) && c.Phase != CyclePhase.Defend) return;. All phase timers are wrap-safe NetworkTick (TickUtil.NonZero + IsNewerThan), never raw uint <.
• Editing an existing [BurstCompile] ISystem's SystemAPI query set on an UNFOCUSED editor can leave a STALE Burst binary (managed assembly recompiles with shifted source-gen query indices, Burst's async recompile doesn't finish) → runtime InvalidOperationException: "… required component type was not declared in the EntityQuery" thrown from an unrelated GetSingleton<T> in that system. Tell: the Burst stack reports the old line number for the failing call. Same family as the M2 Burst-cache gotcha. Workaround: Jobs ▸ Burst ▸ Enable Compilation OFF for the session (verify BurstCompiler.Options.EnableBurstCompilation==false) — everything runs the fresh managed source-gen. Permanent fix = restart Unity to clear the cache, then re-enable Burst. Prefer a focused editor for Burst-affecting edits.
• Shared GLOBAL game-state (cycle phase, resource ledger, goal meter) rides an UNTAGGED ghost, never a region-tagged one — SetIsIrrelevant hides a region-tagged ghost (e.g. the base storage) from players in the other region. The M6 resource ledger is a StorageEntry buffer on the global CycleDirector ghost, resolved via a distinct ResourceLedger tag — never GetSingleton<StorageEntry> (the base storage container owns a second StorageEntry buffer → "multiple instances" throw). Runtime-proven: the director stays relevant to an expedition player while the base storage despawns.
• A hit/area sweep that runs in the PLAIN SimulationSystemGroup must NOT use SystemAPI.Time.DeltaTime — that group sees the variable wall-frame delta, not the fixed tick step, so a cur - dir*Speed*dt segment is wrong. Store the per-tick step on the projectile (Projectile.LastStep, written by ProjectileMoveSystem in the fixed-step predicted group) and reconstruct the swept segment as cur - dir*LastStep — tunnel-safe with zero dependence on the consuming system's clock. ResourceHarvestSystem runs [UpdateAfter(PredictedSimulationSystemGroup)] so it only sees projectiles that survived ProjectileDamageSystem (relies on the ~1000u base/expedition coordinate gap so a base shot can't reach a node). A node hit by N projectiles in one tick: deposit per hit but ecb.DestroyEntity at-most-once (destroyed-bitset + local Remaining copy — a double destroy throws at Playback); persist the decremented [GhostField] Remaining via SetComponent so depletion carries across ticks.
• New ghost prefab recipe (proven M6): manage_asset duplicate UpgradePickup.prefab → manage_prefabs modify_contents (swap the authoring MonoBehaviour; strip MeshFilter+MeshRenderer for an invisible state-holder, keep them for a visible node). Wire the baked spawner into the gameplay subscene: manage_scene load additive → set_active_scene Gameplay → manage_gameobject create (+ manage_components set_property for the prefab ref, verify via mcpforunity://scene/gameobject/{id}/component/...) → save → set_active_scene SampleScene → close_scene (re-bakes on Play).
• Run an adversarial design-review Workflow (3 critics: netcode/relevancy, determinism/prediction, reuse/scope → synthesize) BEFORE coding a netcode-heavy slice — for M6 Stage 2 it caught every one of the above pre-implementation (relevancy trap, singleton collision, dt-trap, double-destroy, lazy-create hazard).
• manage_gameobject create component_properties SILENTLY DROPS enum + Vector3 fields (it set object-refs and simple scalars, but baked authoring enums/Vector3 stayed at their C# defaults — two gates baked identical, one worked only by coincidence). Always set those via a follow-up manage_components set_property (with a properties dict) and VERIFY through the mcpforunity://scene/gameobject/{id}/component/{Type} resource (or, for a ghost, by reading the baked component in execute_code after Play). Same caveat applies to manage_prefabs modify_contents component_properties. Per-renderer color via manage_material set_renderer_color defaults to a runtime PropertyBlock that does NOT persist into Play — create a material asset (manage_material create) and assign_material_to_renderer, or use a prefab-stage assign, for colors that survive a domain reload.
• Walk-in region gates (M6 visibility pass): a baked ExpeditionGate{FromRegion,ToRegion,Radius,ArrivalPos} entity (visible primitive, collider stripped so you pass through) + a server ExpeditionGateSystem (plain group, [UpdateAfter(CyclePhaseSystem)]) proximity-transits a player whose RegionTag matches FromRegion (flip RegionTag + teleport to ArrivalPos, offset from the destination gate so no re-trigger). Returning to base mid-Expedition expires the cycle timer → Defend ("timer cap + early return"). The expedition is a place = cosmetic ground/pillars in SampleScene at the +1000 offset (classic URP, like SyntyWorld), not the DOTS subscene; gameplay nodes/gates are the baked subscene entities.
• Build/automation foundation (M6 Stage 3, the M7 contract): generic PlacedStructure{[GhostField] byte Type; int2 Cell (server-only); uint NextTick; uint LastProcessedTick} on an ownerless interpolated ghost (RegionTag{Base}, world-owned, runtime-spawned). Bake the two tick fields NOW — the turret reuses NextTick as its fire cooldown, and they are the deterministic-offline-catch-up linchpin M7 needs and that can't be reconstructed retroactively. Only Type replicates (client derives Cell from LocalTransform via BaseGridMath.WorldToCell). Data-driven StructureCatalog buffer ({byte Type; Entity Prefab; byte CostResourceId; int CostAmount}, modeled on AbilityPrefabElement); M7 adds a recipe column additively. Occupancy is DERIVED by scanning live structure ghosts into a Temp NativeHashSet<int2> (structures are the source of truth — restart/replay-safe), NEVER a mutable buffer on the immutable baked BaseAnchor.
• Co-op placement atomicity: BuildPlaceSystem commits the StorageMath.Withdraw + cell-reservation IN-PLACE inside the RPC foreach (only the Instantiate goes through the ECB) — the StorageOpReceiveSystem idiom — so two same-tick BuildPlaceRequests for one cell can't both pass (validated: → exactly one structure + one withdraw). RPC carries int CellX/CellZ scalars, not int2 (scalar-only RPC precedent).
• Buildable turret = hitscan = reversed EnemyAISystem: snapshot living Husks, nearest-in-same-region-within-Range, on the NextTick cooldown append a direct DamageEvent{Damage, SourceNetworkId=-1} → reuses HealthApplyDamageSystem (despawns at HP≤0). NO projectile → no tunnelling, no friendly-fire/team model. Plain server group [UpdateAfter(PredictedSimulationSystemGroup)].
• Resource-gated ability tiers reuse StatModifier — no new replicated component. AbilityUpgradeSystem spends Aether and grows ONE StatModifier{Target=Damage, Op=PercentAdd, SourceId=<sentinel>} on the player (replace-by-SourceId so the [InternalBufferCapacity(8)] buffer stays bounded — repeated upgrades grow one row, not append); StatRecomputeSystem folds it into EffectiveAbilityStats.Damage on both worlds (the UpgradePickup path). GoalProgress{[GhostField] int Charge, Target} lives on the global CycleDirector ghost, single-writer in CyclePhaseSystem. Disk-persistence writer is deferred to post-M7 (in-session-only state, per DR-008); freeze the save schema + bake the structure tick fields now so it's additive. See DR-014_M6_Build_Structures_Automation_Foundation.