diff --git a/_extensions/code-window/code-window.lua b/_extensions/code-window/code-window.lua
index 350cfd9..55586c0 100644
--- a/_extensions/code-window/code-window.lua
+++ b/_extensions/code-window/code-window.lua
@@ -40,7 +40,23 @@ local VALID_STYLES = { ['default'] = true, ['macos'] = true, ['windows'] = true
 --- schema declares and the internal label the language module writes alike.
 local ATTRIBUTE_PREFIX = 'code-window-'
 
-local DEFAULTS = {
+--- Defaults for the two cases where the schema cannot answer: a format the
+--- extension does not act on, where the check never runs, and a schema that
+--- could not be read, which is a state this extension renders through rather
+--- than stopping for. Everywhere else _schema.yml decides these seven, so the
+--- values below are a fallback and not a second place to change one of them.
+--- The hotfix defaults are a different story, and are still kept by hand in
+--- HOTFIX_DEFAULTS: they are nested in the schema and read on their own path,
+--- so changing one in _schema.yml alone still changes nothing.
+--- All seven stay listed, because the second case has nothing else to read
+--- from, and an option added to the schema needs an entry here as well or it
+--- has no default at all on a format the extension does not act on.
+--- Where the two disagree, the schema wins on html and typst, and a format
+--- the extension does not act on reads "enabled" alone, which is the one that
+--- chooses whether a block's attributes are checked. So keep that one in step
+--- with the schema, and treat a difference in the other six as a thing to
+--- correct rather than a thing that shows.
+local FALLBACK_DEFAULTS = {
   ['enabled'] = 'true',
   ['auto-filename'] = 'true',
   ['style'] = 'macos',
@@ -782,8 +798,32 @@ function Meta(meta)
   -- read below, because the report says what the extension cannot use and the
   -- document renders either way. Only a format the extension acts on reports,
   -- because nothing it could say applies anywhere else.
+  -- The check also answers what the schema declares each option defaults to,
+  -- so those values are kept rather than dropped and rebuilt by hand here.
+  -- They arrive typed, and every comparison below reads a string, so each one
+  -- goes through stringify_bool on the way into the table.
+  local schema_defaults = {}
   if acts_on_format() then
-    checker:options(meta)
+    schema_defaults = checker:options(meta)
+  end
+
+  -- The schema is read first and the fallback fills only what it leaves
+  -- unanswered, so on html and typst an option added to _schema.yml and to the
+  -- key list below needs nothing more. Anywhere else the check above never
+  -- runs, so the same option also needs an entry in FALLBACK_DEFAULTS or it
+  -- has no default there. Reading the fallback first would have made it the
+  -- list of options allowed to have a default at all, on every format, which
+  -- is the coupling this change exists to remove. What arrives is one entry
+  -- per option that declares a default of its own, and get_options reads only
+  -- the keys named below.
+  local defaults = {}
+  for key, declared in pairs(schema_defaults) do
+    defaults[key] = stringify_bool(declared)
+  end
+  for key, fallback in pairs(FALLBACK_DEFAULTS) do
+    if defaults[key] == nil then
+      defaults[key] = fallback
+    end
   end
 
   local opts = meta_mod.get_options({
@@ -792,7 +832,7 @@ function Meta(meta)
       'enabled', 'auto-filename', 'style', 'cell-output', 'wrapper', 'collapse', 'lines-label',
     },
     meta = meta,
-    defaults = DEFAULTS,
+    defaults = defaults,
   })
 
   -- checker:options (above) already reports an unrecognised "style" value in
diff --git a/tests/fixtures/wrapper-default.qmd b/tests/fixtures/wrapper-default.qmd
new file mode 100644
index 0000000..9598b66
--- /dev/null
+++ b/tests/fixtures/wrapper-default.qmd
@@ -0,0 +1,16 @@
+---
+title: "The Typst wrapper name"
+filters:
+  - code-window
+format:
+  typst:
+    keep-typ: true
+---
+
+The block below is framed, so the document calls the wrapper function by the
+name the configuration gives it. Nothing here sets that name, so the default
+decides, and the schema is where the default is written down.
+
+```{.python filename="a.py"}
+x = 1
+```
diff --git a/tests/run.sh b/tests/run.sh
index 31e0e19..cae2fc8 100755
--- a/tests/run.sh
+++ b/tests/run.sh
@@ -235,6 +235,51 @@ else
 		"a default class, a cw-auto class, and data-filename=\"foo\" on the block"
 fi
 
+# ============================================================================
+# The schema is where an option's default is written down
+# ============================================================================
+
+# The schema declares a default for every option, and so did a table in the
+# Lua. Changing the schema alone has to change the render, or the two can
+# disagree with nothing to say so. The wrapper name is the option under test
+# because it reaches the Typst output word for word.
+render wrapper-default typst
+if grep -q '^#code-window(' "${work_dir}/wrapper-default.typ"; then
+	report pass "wrapper-default: the schema default names the wrapper"
+else
+	report fail "wrapper-default: the schema default names the wrapper" \
+		"a #code-window( call in wrapper-default.typ"
+fi
+
+sed -i.aside 's/default: "code-window"/default: "my-window"/' \
+	"${work_dir}/_extensions/code-window/_schema.yml"
+render wrapper-default typst
+mv "${work_dir}/_extensions/code-window/_schema.yml.aside" \
+	"${work_dir}/_extensions/code-window/_schema.yml"
+
+# The old name has to be gone as well as the new one present, because a rename
+# that missed a call site would leave both in the document.
+if grep -q '^#my-window(' "${work_dir}/wrapper-default.typ" &&
+	! grep -q '^#code-window(' "${work_dir}/wrapper-default.typ"; then
+	report pass "wrapper-default: a default changed in the schema alone is followed"
+else
+	report fail "wrapper-default: a default changed in the schema alone is followed" \
+		"a #my-window( call and no #code-window( call in wrapper-default.typ"
+fi
+
+# With no schema to read, the fallback in the Lua answers instead, and the
+# document still renders rather than stopping.
+mv "${work_dir}/_extensions/code-window/_schema.yml" "${work_dir}/schema.yml.aside"
+render wrapper-default typst
+mv "${work_dir}/schema.yml.aside" "${work_dir}/_extensions/code-window/_schema.yml"
+
+if grep -q '^#code-window(' "${work_dir}/wrapper-default.typ"; then
+	report pass "wrapper-default: the fallback answers when the schema cannot be read"
+else
+	report fail "wrapper-default: the fallback answers when the schema cannot be read" \
+		"a #code-window( call in wrapper-default.typ"
+fi
+
 # ============================================================================
 
 printf '\n%s passed, %s failed\n' "${passed}" "${failed}"