fix(combat): track targets with retail camera

Port ClientCombatSystem's Keep in View consumer through CameraSet's pivot-to-target boom heading, including the transformed half-metre target offset and melee/missile validity gates. Preserve the existing stateful chase damping and collision architecture, with conformance coverage and named-retail pseudocode.

Co-Authored-By: Codex <codex@openai.com>

docs/research/2026-07-11-combat-target-camera-pseudocode.md

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+# Retail combat target camera pseudocode
+
+Source: Sept 2013 EoR named retail client.
+
+- `ClientCombatSystem::UpdateTargetTracking` (`0x0056A950`)
+- `ClientCombatSystem::TrackTarget` (`0x0056AED0`)
+- `CameraSet::TrackTarget` (`0x00458280`)
+- `CameraSet::SetTargetForOffset` (`0x004576E0`)
+- `CameraManager::SetTargetObject` (`0x00456380`)
+- `CameraManager::UpdateCamera` (`0x00456660`)
+
+## Option consumer
+
+```text
+UpdateTargetTracking():
+    if ViewCombatTarget is enabled
+       and combat mode is Melee or Missile
+       and current attack target is valid:
+        camera.TrackTarget(attackTarget)
+    else:
+        camera.TrackTarget(0)
+```
+
+## Camera state
+
+```text
+CameraSet.TrackTarget(targetId):
+    if targetId != 0:
+        targeting = true
+        camera.SetTargetObject(targetId, wholeObject)
+        camera.targetOffset = (0, 0, 0.5 metres)
+    else:
+        targeting = false
+
+    SetTargetForOffset(camera.viewerOffset)
+
+SetTargetForOffset(viewerOffset), while targeting:
+    camera.targetStatus = LOOK_AT_OBJECT | LOOK_AT_PIVOT
+```
+
+## Per-frame pose
+
+```text
+pivot = player part position + transformed pivotOffset
+direction = zero
+
+if targetStatus contains LOOK_AT_OBJECT and target object exists:
+    targetPoint = target.position localToGlobal targetOffset
+    direction += normalize(targetPoint - pivot)
+
+headingFrame = frameWhoseForwardIs(direction)
+desiredEye = pivot + headingFrame.transformVector(viewerOffset)
+
+if targetStatus contains LOOK_AT_PIVOT:
+    desiredForward = normalize(pivot - desiredEye)
+
+damp current viewer toward (desiredEye, desiredForward)
+```
+
+The target therefore changes the direction of the boom around the player; it
+does not replace the player as the boom's pivot. `LOOK_AT_PIVOT` keeps the
+player centered while the target-facing boom keeps the combat target in view.
+
+## Port mapping
+
+- `GameWindow.GetCombatCameraTargetPoint` applies the option/mode/valid-target
+  gates and transforms the target-local 0.5 metre Z offset.
+- `RetailChaseCamera.ComputeTrackedHeading` ports the pivot-to-target direction.
+- Existing `RetailChaseCamera` boom construction and damping consume that
+  heading unchanged.
+- The diagnostic legacy `ChaseCamera` remains intentionally non-retail under
+  existing divergence row TS-19; the production retail camera owns this behavior.
+
+The ACE and ACME reference trees are not present in this worktree (only the
+in-tree WorldBuilder reference is available), so no interpretation-aid cross
+check was possible. The named retail functions above are complete for this
+behavior and remain the ground truth.