diff --git a/.claude/rules/filters/lua-development.md b/.claude/rules/filters/lua-development.md
index fdc9659e09..dc881078f1 100644
--- a/.claude/rules/filters/lua-development.md
+++ b/.claude/rules/filters/lua-development.md
@@ -142,6 +142,25 @@ if quarto.log.debug then
 end
 ```
 
+## External Command Execution
+
+Use `pandoc.pipe()` instead of `io.popen()` for calling external programs:
+
+```lua
+-- ✅ Correct - pandoc.pipe passes args as array, no shell interpretation
+local ok, result = pcall(pandoc.pipe, command, {"arg1", "arg2"}, "")
+if not ok then
+  quarto.log.error("Command failed: " .. tostring(result))
+end
+
+-- ❌ Wrong - io.popen uses shell, breaks on paths with spaces
+local handle = io.popen(command .. " arg1 arg2", "r")
+```
+
+`io.popen()` passes a string to the shell, which breaks when paths contain spaces (e.g., `C:\Program Files\...`). `pandoc.pipe()` calls the executable directly with arguments as an array — no shell, no quoting issues.
+
+Reference: `quarto-pre/shiny.lua`, `quarto-post/pdf-images.lua`
+
 ## Filter Return Values
 
 ```lua
diff --git a/news/changelog-1.9.md b/news/changelog-1.9.md
index c6f919abb1..23b93a4d99 100644
--- a/news/changelog-1.9.md
+++ b/news/changelog-1.9.md
@@ -86,6 +86,7 @@ All changes included in 1.9:
 - ([#13978](https://github.com/quarto-dev/quarto-cli/pull/13978)): Keep term and description together in definition lists to avoid breaking across pages. (author: @mcanouil)
 - ([#13878](https://github.com/quarto-dev/quarto-cli/issues/13878)): Typst now uses Pandoc's skylighting for syntax highlighting by default (consistent with other formats). Use `syntax-highlighting: idiomatic` to opt-in to Typst's native syntax highlighting instead.
 - ([#14126](https://github.com/quarto-dev/quarto-cli/issues/14126)): Fix Skylighting code blocks in Typst lacking full-width background, padding, and border radius. A postprocessor patches the Pandoc-generated Skylighting function to add `width: 100%`, `inset: 8pt`, and `radius: 2pt` to the block call, matching the styling of native code blocks. Brand `monospace-block.background-color` also now correctly applies to Skylighting output. This workaround will be removed once the fix is upstreamed to Skylighting.
+- ([#14202](https://github.com/quarto-dev/quarto-cli/issues/14202)): Fix CSS inlining (`juice`) failing on Windows when Quarto is installed in a path with spaces (e.g., `C:\Program Files\Quarto\`).
 
 ### `pdf`
 
diff --git a/src/resources/filters/normalize/astpipeline.lua b/src/resources/filters/normalize/astpipeline.lua
index 1065d70562..881d935dd9 100644
--- a/src/resources/filters/normalize/astpipeline.lua
+++ b/src/resources/filters/normalize/astpipeline.lua
@@ -65,28 +65,19 @@ function quarto_ast_pipeline()
         jin:write(htmltext)
         jin:flush()
         local quarto_path = quarto.config.cli_path()
-        local jout, jerr = io.popen(quarto_path .. ' run ' ..
-            pandoc.path.join({os.getenv('QUARTO_SHARE_PATH'), 'scripts', 'juice.ts'}) .. ' ' ..
-            juice_in, 'r')
-        if not jout then
-          quarto.log.error('Running juice failed with message: ' .. (jerr or "Unknown error"))
+        local juice_script = pandoc.path.join({os.getenv('QUARTO_SHARE_PATH'), 'scripts', 'juice.ts'})
+        local ok, content = pcall(pandoc.pipe, quarto_path, {'run', juice_script, juice_in}, '')
+        if not ok then
+          quarto.log.error('Running juice failed: ' .. tostring(content))
           return htmltext
         end
-        local content = jout:read('a')
-        local success, _, exitCode = jout:close()
-        -- Check the exit status
-        if not success then
-          quarto.log.error("Running juice failed with exit code: " .. (exitCode or "unknown exit code"))
-          return htmltext
-        else
-          local index = 1
-          content = content:gsub(data_uri_uuid:gsub('-', '%%-'), function(_)
-            local data_uri = data_uris[index]
-            index = index + 1
-            return data_uri
-          end)
-          return content
-        end
+        local index = 1
+        content = content:gsub(data_uri_uuid:gsub('-', '%%-'), function(_)
+          local data_uri = data_uris[index]
+          index = index + 1
+          return data_uri
+        end)
+        return content
       end)
     end   
     local function should_handle_raw_html_as_table(el)