diff --git a/bin/only-commit-source.js b/bin/only-commit-source.js
index 77ad0d981..f18a91132 100755
--- a/bin/only-commit-source.js
+++ b/bin/only-commit-source.js
@@ -18,11 +18,32 @@ function findBuiltFiles( dir ) {
     }
 
     const isProbablyBuilt = filePath.endsWith('.css');
+    const basename = path.basename( filePath, '.css' );
+
+    // `.css` files exactly 2 directories below `_imports/` are source files
+    // in the reorganized third-party library structure (e.g. Bootstrap 4/5).
+    // They use `.css` extension by convention and are not build artifacts.
+    const isLibrarySource = /_imports\/[^/]+\/[^/]+\/[^/]+\.css$/.test( relativePath );
+
+    // `core-styles.*.css` files are consumer-facing entry points in `_imports/`;
+    // they aggregate @imports for a client library and must be published.
+    const isEntryPoint = /_imports\/core-styles\.[^/]+\.css$/.test( relativePath );
+
+    // Files whose name starts with `demo` / `example`, or contains `.demo`,
+    // are Fractal-only demo helpers and are never compiled into the package.
+    const isDemoOrExample = /(?:^demo(?:[.-]|$)|\.demo(?:[.-]|$)|^example(?:[.-]|$))/.test( basename );
+
+    // `_imports/vendors/` exists on epic/v3 but is removed on epic/v3--reorg;
+    // this rule becomes a no-op once the reorg merges in.
+    const isVendored = relativePath.includes( '_imports/vendors' );
+
     const shouldIgnore = (
-      /_imports\/[^/]+\/[^/]+\/[^/]+\.css$/.test(relativePath) ||
+      isLibrarySource ||
       filePath.endsWith('fractality.server.refresh.css') ||
-      relativePath.includes('_imports/vendors') ||
-      filePath.endsWith('README.css')
+      isVendored ||
+      filePath.endsWith('README.css') ||
+      isEntryPoint ||
+      isDemoOrExample
     );
 
     if ( isProbablyBuilt && ! shouldIgnore ) {
diff --git a/src/lib/_imports/components/c-tag.postcss b/src/lib/_imports/components/c-tag.postcss
index 2a1c1734a..de4acb4a1 100644
--- a/src/lib/_imports/components/c-tag.postcss
+++ b/src/lib/_imports/components/c-tag.postcss
@@ -1,4 +1,4 @@
-@import url("../tools/x-tag.css");
+@import url("../tools/x-tag.postcss");
 
 @import url("./c-tag.selectors.postcss");
 
diff --git a/src/lib/_imports/djangocms-blog/cms-pagination.css b/src/lib/_imports/djangocms-blog/cms-pagination.postcss
similarity index 100%
rename from src/lib/_imports/djangocms-blog/cms-pagination.css
rename to src/lib/_imports/djangocms-blog/cms-pagination.postcss
diff --git a/src/lib/_imports/objects/o-offset-content.postcss b/src/lib/_imports/objects/o-offset-content.postcss
index e848cfc21..1b91cecbb 100644
--- a/src/lib/_imports/objects/o-offset-content.postcss
+++ b/src/lib/_imports/objects/o-offset-content.postcss
@@ -8,7 +8,7 @@ Content that should be:
 Styleguide Objects.OffsetContent
 */
 @import url("../tools/media-queries.postcss");
-@import url("../tools/x-offset-content.css");
+@import url("../tools/x-offset-content.postcss");
 
 .o-offset-content--left,
 .o-offset-content--right {
diff --git a/src/lib/_imports/tools/x-offset-content.demo.css b/src/lib/_imports/tools/x-offset-content.demo.css
index a75988d81..6645ff34c 100644
--- a/src/lib/_imports/tools/x-offset-content.demo.css
+++ b/src/lib/_imports/tools/x-offset-content.demo.css
@@ -1,6 +1,6 @@
 /* This CSS is ONLY for the pattern library. It is NOT part of the pattern. */
 
-@import url("./x-offset-content.css");
+@import url("./x-offset-content.postcss");
 
 .x-offset-content--left,
 .x-offset-content--right {
diff --git a/src/lib/_imports/tools/x-offset-content.css b/src/lib/_imports/tools/x-offset-content.postcss
similarity index 100%
rename from src/lib/_imports/tools/x-offset-content.css
rename to src/lib/_imports/tools/x-offset-content.postcss
diff --git a/src/lib/_imports/tools/x-pill.demo.css b/src/lib/_imports/tools/x-pill.demo.css
index 29f65efef..d4c05e55b 100644
--- a/src/lib/_imports/tools/x-pill.demo.css
+++ b/src/lib/_imports/tools/x-pill.demo.css
@@ -1,4 +1,4 @@
-@import url("./x-pill.css");
+@import url("./x-pill.postcss");
 
 /* FAQ: Wrapped to deter clients from using `.x-pill` */
 /* HACK: Not in `x-pill/demo.css` because it is not processed */
diff --git a/src/lib/_imports/tools/x-pill.css b/src/lib/_imports/tools/x-pill.postcss
similarity index 100%
rename from src/lib/_imports/tools/x-pill.css
rename to src/lib/_imports/tools/x-pill.postcss
diff --git a/src/lib/_imports/tools/x-tag.demo.css b/src/lib/_imports/tools/x-tag.demo.css
index 6ee8e9617..c0d71d00d 100644
--- a/src/lib/_imports/tools/x-tag.demo.css
+++ b/src/lib/_imports/tools/x-tag.demo.css
@@ -1,4 +1,4 @@
-@import url("./x-tag.css");
+@import url("./x-tag.postcss");
 
 /* FAQ: Wrapped to deter clients from using `.x-tag` */
 /* HACK: Not in `x-tag/demo.css` because it is not processed */
diff --git a/src/lib/_imports/tools/x-tag.css b/src/lib/_imports/tools/x-tag.postcss
similarity index 100%
rename from src/lib/_imports/tools/x-tag.css
rename to src/lib/_imports/tools/x-tag.postcss