diff --git a/.env b/.env
index 4550c22ff..070e7f471 100644
--- a/.env
+++ b/.env
@@ -12,7 +12,7 @@ PROJECT_NAME="airstack"
 # If you've run ./airstack.sh setup, then this will auto-generate from the git commit hash every time a change is made 
 # to a Dockerfile or docker-compose.yaml file. Otherwise this can also be set explicitly to make a release version.
 # auto-generated from git commit hash
-VERSION="0.20.7"
+VERSION="0.20.8"
 # Image-tag discriminator ONLY (appears in the image tag suffix, e.g. ..._robot-x86-64_dev).
 # No Dockerfile consumes it: "prebuilt" does NOT bake the built ros_ws into the image today —
 # a real prebuilt (workspace-baked) stage is future work. Keep "dev" (mounted code, built live).
diff --git a/docs/release_notes/index.md b/docs/release_notes/index.md
index 5cc036570..5fb6e7398 100644
--- a/docs/release_notes/index.md
+++ b/docs/release_notes/index.md
@@ -21,6 +21,17 @@ its own notes. -->
 
 - Nothing yet.
 
+## 0.20.8 — 2026-09-04
+
+- **Docs builds no longer copy AirSim scene binaries.** The `same-dir`
+  plugin publishes the whole repo tree as site content, and the downloaded
+  Microsoft AirSim UE4 scenes (`simulation/ms-airsim/assets/scenes/`) and
+  environments (`simulation/ms-airsim/environments/`) were not excluded —
+  every `mkdocs build` or `docs serve` on a machine with scenes fetched
+  copied ~15 GB of Unreal `.debug` binaries and zips into the site
+  directory. Both directories are now listed in `exclude_docs`. No pages or
+  links referenced them.
+
 ## 0.20.7 — 2026-08-30
 
 - **Fixed 404s on every README-sourced docs page.** The `exclude_docs`
diff --git a/mkdocs.yml b/mkdocs.yml
index 06db3374d..99460b788 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -20,6 +20,11 @@ exclude_docs: |
   **/ros_ws/install
   **/kit-app-template/**
   **/isaac_sim_data/**
+  # Downloaded AirSim UE4 scene binaries (fetched by assets/scenes/fetch_scene.sh)
+  # and environments: multi-GB, gitignored, never doc content. Without this the
+  # same-dir plugin copies them into every site build (~15 GB per build).
+  simulation/ms-airsim/assets/scenes/**
+  simulation/ms-airsim/environments/**
   # Fetched module checkouts (RFC #379 §9): the docs deploy workflows clone the
   # registry index + each registered module repo into the gitignored modules/
   # dir. Their content is linked from docs/modules/ (generated by
diff --git a/tests/meta/test_docs_catalog_contract.py b/tests/meta/test_docs_catalog_contract.py
index 91dc24143..5db415e28 100644
--- a/tests/meta/test_docs_catalog_contract.py
+++ b/tests/meta/test_docs_catalog_contract.py
@@ -151,7 +151,12 @@ def test_module_pages_carry_the_contracted_sections():
 
 
 def _load_mkdocs() -> dict:
-    """Parse mkdocs.yml, tolerating the !!python/name superfences tag."""
+    """Parse mkdocs.yml, tolerating the tags MkDocs resolves at load time.
+
+    ``!!python/name:`` (pymdownx superfences) collapses to the dotted name;
+    mkdocs' ``!ENV`` (``!ENV VAR`` or ``!ENV [VAR, default]``) collapses to
+    the default (or None), so a bare SafeLoader does not choke on it.
+    """
 
     class Loader(yaml.SafeLoader):
         pass
@@ -159,6 +164,14 @@ class Loader(yaml.SafeLoader):
     Loader.add_multi_constructor(
         "tag:yaml.org,2002:python/name:", lambda loader, suffix, node: suffix
     )
+
+    def _env_tag(loader, node):
+        if isinstance(node, yaml.SequenceNode):
+            values = loader.construct_sequence(node)
+            return values[-1] if len(values) > 1 else None
+        return None
+
+    Loader.add_constructor("!ENV", _env_tag)
     return yaml.load(MKDOCS_YML.read_text(), Loader=Loader)