diff --git a/codex-rs/core-plugins/src/manifest.rs b/codex-rs/core-plugins/src/manifest.rs
index 2352fdbef..14d7a4fe4 100644
--- a/codex-rs/core-plugins/src/manifest.rs
+++ b/codex-rs/core-plugins/src/manifest.rs
@@ -1,10 +1,11 @@
 use codex_config::HooksFile;
 use codex_utils_absolute_path::AbsolutePathBuf;
+use codex_utils_path_uri::PathConvention;
+use codex_utils_path_uri::PathUri;
 use codex_utils_plugins::find_plugin_manifest_path;
 use serde::Deserialize;
 use serde_json::Value as JsonValue;
 use std::fs;
-use std::path::Component;
 use std::path::Path;
 const MAX_DEFAULT_PROMPT_COUNT: usize = 3;
 const MAX_DEFAULT_PROMPT_LEN: usize = 128;
@@ -16,6 +17,8 @@ pub type PluginManifestMcpServers =
     codex_plugin::manifest::PluginManifestMcpServers<AbsolutePathBuf>;
 pub type PluginManifestPaths = codex_plugin::manifest::PluginManifestPaths<AbsolutePathBuf>;
 
+pub(crate) type UriPluginManifest = codex_plugin::manifest::PluginManifest<PathUri>;
+
 #[derive(Debug, Default, Deserialize)]
 #[serde(rename_all = "camelCase")]
 struct RawPluginManifest {
@@ -141,6 +144,19 @@ pub(crate) fn parse_plugin_manifest(
     manifest_path: &Path,
     contents: &str,
 ) -> Result<PluginManifest, serde_json::Error> {
+    let plugin_root_uri =
+        PathUri::from_host_native_path(plugin_root).map_err(serde_json::Error::io)?;
+    let manifest_path_uri =
+        PathUri::from_host_native_path(manifest_path).map_err(serde_json::Error::io)?;
+    parse_plugin_manifest_uri(&plugin_root_uri, &manifest_path_uri, contents)?
+        .try_map_resources(|path| path.to_abs_path().map_err(serde_json::Error::io))
+}
+
+pub(crate) fn parse_plugin_manifest_uri(
+    plugin_root: &PathUri,
+    manifest_path: &PathUri,
+    contents: &str,
+) -> Result<UriPluginManifest, serde_json::Error> {
     let RawPluginManifest {
         name: raw_name,
         version,
@@ -153,11 +169,10 @@ pub(crate) fn parse_plugin_manifest(
         interface,
     } = serde_json::from_str::<RawPluginManifest>(contents)?;
     let name = plugin_root
-        .file_name()
-        .and_then(|entry| entry.to_str())
+        .basename()
         .filter(|_| raw_name.trim().is_empty())
-        .unwrap_or(&raw_name)
-        .to_string();
+        .unwrap_or(raw_name);
+    let manifest_path_for_warning = manifest_path.to_string();
     let version = version.and_then(|version| {
         let version = version.trim();
         (!version.is_empty()).then(|| version.to_string())
@@ -181,7 +196,7 @@ pub(crate) fn parse_plugin_manifest(
             screenshots,
         } = interface;
 
-        let interface = PluginManifestInterface {
+        let interface = codex_plugin::manifest::PluginManifestInterface {
             display_name,
             short_description,
             long_description,
@@ -191,7 +206,10 @@ pub(crate) fn parse_plugin_manifest(
             website_url,
             privacy_policy_url,
             terms_of_service_url,
-            default_prompt: resolve_default_prompts(manifest_path, default_prompt.as_ref()),
+            default_prompt: resolve_default_prompts(
+                &manifest_path_for_warning,
+                default_prompt.as_ref(),
+            ),
             brand_color,
             composer_icon: resolve_interface_asset_path(
                 plugin_root,
@@ -234,12 +252,12 @@ pub(crate) fn parse_plugin_manifest(
 
         has_fields.then_some(interface)
     });
-    Ok(PluginManifest {
+    Ok(codex_plugin::manifest::PluginManifest {
         name,
         version,
         description,
         keywords,
-        paths: PluginManifestPaths {
+        paths: codex_plugin::manifest::PluginManifestPaths {
             skills: resolve_manifest_paths(plugin_root, "skills", skills.as_ref()),
             mcp_servers: resolve_manifest_mcp_servers(plugin_root, mcp_servers),
             apps: resolve_manifest_path(plugin_root, "apps", apps.as_deref()),
@@ -250,25 +268,28 @@ pub(crate) fn parse_plugin_manifest(
 }
 
 fn resolve_manifest_hooks(
-    plugin_root: &Path,
+    plugin_root: &PathUri,
     hooks: Option<RawPluginManifestHooks>,
-) -> Option<PluginManifestHooks> {
+) -> Option<codex_plugin::manifest::PluginManifestHooks<PathUri>> {
     match hooks? {
         RawPluginManifestHooks::Path(path) => {
             resolve_manifest_path(plugin_root, "hooks", Some(&path))
-                .map(|path| PluginManifestHooks::Paths(vec![path]))
+                .map(|path| codex_plugin::manifest::PluginManifestHooks::Paths(vec![path]))
         }
         RawPluginManifestHooks::Paths(paths) => {
             let hooks = paths
                 .iter()
                 .filter_map(|path| resolve_manifest_path(plugin_root, "hooks", Some(path)))
                 .collect::<Vec<_>>();
-            (!hooks.is_empty()).then_some(PluginManifestHooks::Paths(hooks))
+            (!hooks.is_empty()).then_some(codex_plugin::manifest::PluginManifestHooks::Paths(hooks))
         }
-        RawPluginManifestHooks::Inline(hooks) => Some(PluginManifestHooks::Inline(vec![hooks])),
-        RawPluginManifestHooks::InlineList(hooks) => {
-            (!hooks.is_empty()).then_some(PluginManifestHooks::Inline(hooks))
+        RawPluginManifestHooks::Inline(hooks) => {
+            Some(codex_plugin::manifest::PluginManifestHooks::Inline(vec![
+                hooks,
+            ]))
         }
+        RawPluginManifestHooks::InlineList(hooks) => (!hooks.is_empty())
+            .then_some(codex_plugin::manifest::PluginManifestHooks::Inline(hooks)),
         RawPluginManifestHooks::Invalid(value) => {
             tracing::warn!(
                 "ignoring hooks: expected a string, string array, object, or object array; found {}",
@@ -280,16 +301,18 @@ fn resolve_manifest_hooks(
 }
 
 fn resolve_manifest_mcp_servers(
-    plugin_root: &Path,
+    plugin_root: &PathUri,
     mcp_servers: Option<RawPluginManifestMcpServers>,
-) -> Option<PluginManifestMcpServers> {
+) -> Option<codex_plugin::manifest::PluginManifestMcpServers<PathUri>> {
     match mcp_servers? {
         RawPluginManifestMcpServers::Path(path) => {
             resolve_manifest_path(plugin_root, "mcpServers", Some(&path))
-                .map(PluginManifestMcpServers::Path)
+                .map(codex_plugin::manifest::PluginManifestMcpServers::Path)
         }
         RawPluginManifestMcpServers::Object(servers) => match serde_json::to_string(&servers) {
-            Ok(servers) => Some(PluginManifestMcpServers::Object(servers)),
+            Ok(servers) => Some(codex_plugin::manifest::PluginManifestMcpServers::Object(
+                servers,
+            )),
             Err(err) => {
                 tracing::warn!("ignoring mcpServers: failed to serialize object: {err}");
                 None
@@ -306,15 +329,15 @@ fn resolve_manifest_mcp_servers(
 }
 
 fn resolve_interface_asset_path(
-    plugin_root: &Path,
+    plugin_root: &PathUri,
     field: &'static str,
     path: Option<&str>,
-) -> Option<AbsolutePathBuf> {
+) -> Option<PathUri> {
     resolve_manifest_path(plugin_root, field, path)
 }
 
 fn resolve_default_prompts(
-    manifest_path: &Path,
+    manifest_path: &str,
     value: Option<&RawPluginManifestDefaultPrompt>,
 ) -> Option<Vec<String>> {
     match value? {
@@ -370,7 +393,7 @@ fn resolve_default_prompts(
     }
 }
 
-fn resolve_default_prompt_str(manifest_path: &Path, field: &str, prompt: &str) -> Option<String> {
+fn resolve_default_prompt_str(manifest_path: &str, field: &str, prompt: &str) -> Option<String> {
     let prompt = prompt.split_whitespace().collect::<Vec<_>>().join(" ");
     if prompt.is_empty() {
         warn_invalid_default_prompt(manifest_path, field, "prompt must not be empty");
@@ -387,11 +410,8 @@ fn resolve_default_prompt_str(manifest_path: &Path, field: &str, prompt: &str) -
     Some(prompt)
 }
 
-fn warn_invalid_default_prompt(manifest_path: &Path, field: &str, message: &str) {
-    tracing::warn!(
-        path = %manifest_path.display(),
-        "ignoring {field}: {message}"
-    );
+fn warn_invalid_default_prompt(manifest_path: &str, field: &str, message: &str) {
+    tracing::warn!(path = %manifest_path, "ignoring {field}: {message}");
 }
 
 fn json_value_type(value: &JsonValue) -> &'static str {
@@ -406,10 +426,10 @@ fn json_value_type(value: &JsonValue) -> &'static str {
 }
 
 fn resolve_manifest_paths(
-    plugin_root: &Path,
+    plugin_root: &PathUri,
     field: &'static str,
     paths: Option<&RawPluginManifestPaths>,
-) -> Vec<AbsolutePathBuf> {
+) -> Vec<PathUri> {
     match paths {
         Some(RawPluginManifestPaths::Path(path)) => {
             resolve_manifest_path(plugin_root, field, Some(path))
@@ -432,12 +452,10 @@ fn resolve_manifest_paths(
 }
 
 fn resolve_manifest_path(
-    plugin_root: &Path,
+    plugin_root: &PathUri,
     field: &'static str,
     path: Option<&str>,
-) -> Option<AbsolutePathBuf> {
-    // `plugin.json` paths are required to be relative to the plugin root and we return the
-    // normalized absolute path to the rest of the system.
+) -> Option<PathUri> {
     let path = path?;
     if path.is_empty() {
         return None;
@@ -451,27 +469,40 @@ fn resolve_manifest_path(
         return None;
     }
 
-    let mut normalized = std::path::PathBuf::new();
-    for component in Path::new(relative_path).components() {
-        match component {
-            Component::Normal(component) => normalized.push(component),
-            Component::ParentDir => {
-                tracing::warn!("ignoring {field}: path must not contain '..'");
-                return None;
-            }
-            _ => {
-                tracing::warn!("ignoring {field}: path must stay within the plugin root");
-                return None;
-            }
+    let convention = plugin_root.infer_path_convention();
+    let has_parent_component = match convention {
+        Some(PathConvention::Windows) => relative_path
+            .split(['/', '\\'])
+            .any(|component| component == ".."),
+        Some(PathConvention::Posix) | None => {
+            relative_path.split('/').any(|component| component == "..")
         }
+    };
+    if has_parent_component {
+        tracing::warn!("ignoring {field}: path must not contain '..'");
+        return None;
     }
 
-    AbsolutePathBuf::try_from(plugin_root.join(normalized))
-        .map_err(|err| {
-            tracing::warn!("ignoring {field}: path must resolve to an absolute path: {err}");
-            err
-        })
-        .ok()
+    let has_windows_root = convention == Some(PathConvention::Windows)
+        && (relative_path.starts_with('\\')
+            || matches!(relative_path.as_bytes(), [drive, b':', ..] if drive.is_ascii_alphabetic()));
+    if relative_path.starts_with('/') || has_windows_root {
+        tracing::warn!("ignoring {field}: path must stay within the plugin root");
+        return None;
+    }
+
+    let resolved = match plugin_root.join(relative_path) {
+        Ok(resolved) => resolved,
+        Err(err) => {
+            tracing::warn!("ignoring {field}: path must resolve under plugin root: {err}");
+            return None;
+        }
+    };
+    if !resolved.starts_with(plugin_root) {
+        tracing::warn!("ignoring {field}: path must stay within the plugin root");
+        return None;
+    }
+    Some(resolved)
 }
 
 #[cfg(test)]
@@ -486,6 +517,7 @@ mod tests {
     use codex_protocol::capabilities::CapabilityRootLocation;
     use codex_protocol::capabilities::SelectedCapabilityRoot;
     use codex_utils_absolute_path::AbsolutePathBuf;
+    use codex_utils_path_uri::PathUri;
     use pretty_assertions::assert_eq;
     use std::fs;
     use std::path::Path;
@@ -695,6 +727,46 @@ mod tests {
         );
     }
 
+    #[test]
+    fn uri_manifest_uses_the_root_path_convention() {
+        let windows_root =
+            PathUri::parse("file:///C:/plugins/demo-plugin").expect("Windows plugin root URI");
+        let posix_root =
+            PathUri::parse("file:///plugins/demo-plugin").expect("POSIX plugin root URI");
+        let composer_icon = r"./assets\..\icon.svg";
+
+        assert_eq!(parse_uri_composer_icon(&windows_root, composer_icon), None);
+        assert_eq!(
+            parse_uri_composer_icon(&posix_root, composer_icon),
+            Some(
+                posix_root
+                    .join(r"assets\..\icon.svg")
+                    .expect("composer icon URI")
+            )
+        );
+    }
+
+    fn parse_uri_composer_icon(plugin_root: &PathUri, composer_icon: &str) -> Option<PathUri> {
+        let manifest_path = plugin_root
+            .join(".codex-plugin/plugin.json")
+            .expect("manifest URI");
+        let composer_icon_json =
+            serde_json::to_string(composer_icon).expect("serialize composer icon");
+        let contents = format!(
+            r#"{{
+  "name": "demo-plugin",
+  "interface": {{
+    "displayName": "Demo Plugin",
+    "composerIcon": {composer_icon_json}
+  }}
+}}"#
+        );
+        super::parse_plugin_manifest_uri(plugin_root, &manifest_path, &contents)
+            .expect("URI manifest")
+            .interface
+            .and_then(|interface| interface.composer_icon)
+    }
+
     #[tokio::test]
     async fn host_and_executor_sources_parse_the_same_manifest() {
         let temp_dir = tempdir().expect("tempdir");
diff --git a/codex-rs/core-plugins/src/marketplace.rs b/codex-rs/core-plugins/src/marketplace.rs
index f5024ab25..3190e0449 100644
--- a/codex-rs/core-plugins/src/marketplace.rs
+++ b/codex-rs/core-plugins/src/marketplace.rs
@@ -86,11 +86,12 @@ impl MarketplacePluginManifestFallback {
     }
 
     pub(crate) fn parse_for_listing(&self) -> Option<crate::manifest::PluginManifest> {
-        // Git sources have no plugin root before install. Parse against a synthetic absolute root,
-        // then discard path-bearing fields so listings expose metadata only.
+        // Git sources have no plugin root before install. Parse against a host-native synthetic
+        // absolute root, then discard path-bearing fields so listings expose metadata only.
+        let plugin_root = Path::new(if cfg!(windows) { r"C:\" } else { "/" });
         let mut manifest = crate::manifest::parse_plugin_manifest(
-            Path::new("/"),
-            Path::new("/.codex-plugin/plugin.json"),
+            plugin_root,
+            &fallback_plugin_manifest_path(plugin_root),
             &self.contents,
         )
         .ok()?;
diff --git a/codex-rs/plugin/src/manifest.rs b/codex-rs/plugin/src/manifest.rs
index eb8e1f7d9..89cfd8d0b 100644
--- a/codex-rs/plugin/src/manifest.rs
+++ b/codex-rs/plugin/src/manifest.rs
@@ -90,7 +90,8 @@ impl<Resource> PluginManifest<Resource> {
             .unwrap_or(&self.name)
     }
 
-    pub(crate) fn try_map_resources<Mapped, Error>(
+    /// Maps every path-bearing resource in the manifest.
+    pub fn try_map_resources<Mapped, Error>(
         self,
         mut map: impl FnMut(Resource) -> Result<Mapped, Error>,
     ) -> Result<PluginManifest<Mapped>, Error> {
diff --git a/codex-rs/utils/path-uri/src/lib.rs b/codex-rs/utils/path-uri/src/lib.rs
index 9794e7c70..650343209 100644
--- a/codex-rs/utils/path-uri/src/lib.rs
+++ b/codex-rs/utils/path-uri/src/lib.rs
@@ -265,10 +265,18 @@ impl PathUri {
             return false;
         }
 
-        let Some(path_segments) = containment_path_segments(&self.0) else {
+        let Some(path_segments) = containment_path_segments(
+            &self.0,
+            self.infer_path_convention()
+                .unwrap_or(PathConvention::Posix),
+        ) else {
             return false;
         };
-        let Some(base_segments) = containment_path_segments(&base.0) else {
+        let Some(base_segments) = containment_path_segments(
+            &base.0,
+            base.infer_path_convention()
+                .unwrap_or(PathConvention::Posix),
+        ) else {
             return false;
         };
         path_segments.starts_with(&base_segments)
@@ -569,7 +577,7 @@ fn is_windows_drive_uri_segment(segment: &str) -> bool {
     matches!(segment.as_bytes(), [drive, b':'] if drive.is_ascii_alphabetic())
 }
 
-fn containment_path_segments(url: &Url) -> Option<Vec<&str>> {
+fn containment_path_segments(url: &Url, convention: PathConvention) -> Option<Vec<&str>> {
     let segments = url
         .path_segments()?
         .filter(|segment| !segment.is_empty())
@@ -577,7 +585,7 @@ fn containment_path_segments(url: &Url) -> Option<Vec<&str>> {
     (!segments.iter().any(|segment| {
         urlencoding::decode_binary(segment.as_bytes())
             .iter()
-            .any(|byte| matches!(*byte, b'/' | b'\\'))
+            .any(|byte| *byte == b'/' || (convention == PathConvention::Windows && *byte == b'\\'))
     }))
     .then_some(segments)
 }
diff --git a/codex-rs/utils/path-uri/src/tests.rs b/codex-rs/utils/path-uri/src/tests.rs
index c52c3f9e6..1eead137f 100644
--- a/codex-rs/utils/path-uri/src/tests.rs
+++ b/codex-rs/utils/path-uri/src/tests.rs
@@ -748,6 +748,11 @@ fn starts_with_uses_uri_segment_boundaries() {
         (
             "file:///workspace/plugin/%5C..%5Coutside",
             "file:///workspace/plugin",
+            true,
+        ),
+        (
+            "file:///C:/plugins/foo/%5C..%5Coutside",
+            "file:///C:/plugins/foo",
             false,
         ),
     ] {