diff --git a/crates/tranquil-pds/src/cache_keys.rs b/crates/tranquil-pds/src/cache_keys.rs
index 9fd03d5..6625577 100644
--- a/crates/tranquil-pds/src/cache_keys.rs
+++ b/crates/tranquil-pds/src/cache_keys.rs
@@ -39,3 +39,10 @@ pub fn scope_ref_key(cid: &CidLink) -> String {
 pub fn auto_verify_sent_key(did: &Did) -> String {
     format!("auto_verify_sent:{}", did)
 }
+
+pub fn permission_set_key(nsid: &str, aud: Option<&str>) -> String {
+    match aud {
+        Some(a) => format!("permset:{}:{}", nsid, a),
+        None => format!("permset:{}", nsid),
+    }
+}
diff --git a/crates/tranquil-pds/src/oauth/mod.rs b/crates/tranquil-pds/src/oauth/mod.rs
index 53707c3..d5ba187 100644
--- a/crates/tranquil-pds/src/oauth/mod.rs
+++ b/crates/tranquil-pds/src/oauth/mod.rs
@@ -1,5 +1,6 @@
 pub mod client;
 pub mod db;
+pub mod permission_set_resolver;
 pub mod scopes;
 pub mod verify;
 
@@ -20,6 +21,7 @@ pub use tranquil_oauth::{
     compute_pkce_challenge, verify_client_auth,
 };
 
+pub use permission_set_resolver::expand_scopes;
 pub use scopes::{AccountAction, AccountAttr, RepoAction, ScopeError, ScopePermissions};
 pub use verify::{
     OAuthAuthError, OAuthUser, VerifyResult, generate_dpop_nonce, verify_oauth_access_token,
diff --git a/crates/tranquil-pds/src/oauth/permission_set_resolver.rs b/crates/tranquil-pds/src/oauth/permission_set_resolver.rs
new file mode 100644
index 0000000..2f51d8a
--- /dev/null
+++ b/crates/tranquil-pds/src/oauth/permission_set_resolver.rs
@@ -0,0 +1,182 @@
+use crate::cache::Cache;
+use crate::cache_keys::permission_set_key;
+use serde::{Deserialize, Serialize};
+use std::time::Duration;
+use tranquil_scopes::{
+    fetch_and_expand, parse_include_scope, ExpansionOutcome, FailedSet, ResolveFailure,
+    ResolvedSetGroup, ScopeExpansionError,
+};
+use tranquil_types::Nsid;
+
+#[derive(Serialize, Deserialize)]
+struct CachedPermissionSet {
+    scope: String,
+    title: Option<String>,
+    detail: Option<String>,
+}
+
+const PERMISSION_SET_CACHE_TTL_SECS: u64 = 24 * 60 * 60;
+
+pub async fn expand_scopes(cache: &dyn Cache, scope_string: &str) -> ExpansionOutcome {
+    let mut outcome = ExpansionOutcome::default();
+    for tok in scope_string.split_whitespace() {
+        match tok.strip_prefix("include:") {
+            None => outcome.passthrough.push(tok.to_string()),
+            Some(rest) => {
+                let (nsid, aud) = parse_include_scope(rest);
+                match resolve_one(cache, nsid, aud).await {
+                    Ok(group) => outcome.sets.push(group),
+                    Err(reason) => outcome.failures.push(FailedSet {
+                        nsid: nsid.to_string(),
+                        aud: aud.map(str::to_string),
+                        reason,
+                    }),
+                }
+            }
+        }
+    }
+    outcome
+}
+
+async fn resolve_one(
+    cache: &dyn Cache,
+    nsid: &str,
+    aud: Option<&str>,
+) -> Result<ResolvedSetGroup, ResolveFailure> {
+    let key = permission_set_key(nsid, aud);
+    // Cache hit
+    if let Some(json) = cache.get(&key).await
+        && let Ok(v) = serde_json::from_str::<CachedPermissionSet>(&json)
+    {
+        return Ok(group_from(nsid, aud, v.scope, v.title, v.detail));
+    }
+    // Miss → network fetch → cache
+    let parsed = Nsid::new(nsid).map_err(|_| ResolveFailure::Invalid)?;
+    match fetch_and_expand(&parsed, aud).await {
+        Ok(fetched) => {
+            let stored = CachedPermissionSet {
+                scope: fetched.expanded.clone(),
+                title: fetched.title.clone(),
+                detail: fetched.detail.clone(),
+            };
+            if let Ok(json) = serde_json::to_string(&stored) {
+                let _ = cache
+                    .set(&key, &json, Duration::from_secs(PERMISSION_SET_CACHE_TTL_SECS))
+                    .await;
+            }
+            Ok(group_from(nsid, aud, fetched.expanded, fetched.title, fetched.detail))
+        }
+        Err(e) => Err(map_err(&e)),
+    }
+}
+
+fn group_from(
+    nsid: &str,
+    aud: Option<&str>,
+    scope: String,
+    title: Option<String>,
+    detail: Option<String>,
+) -> ResolvedSetGroup {
+    ResolvedSetGroup {
+        nsid: nsid.to_string(),
+        aud: aud.map(str::to_string),
+        title,
+        detail,
+        expanded: scope.split_whitespace().map(str::to_string).collect(),
+    }
+}
+
+fn map_err(e: &ScopeExpansionError) -> ResolveFailure {
+    use ScopeExpansionError as E;
+    match e {
+        E::InvalidNsid(_) | E::UnexpectedType(_) | E::EmptyPermissions | E::MissingDefinition(_) => {
+            ResolveFailure::Invalid
+        }
+        E::DnsResolution(_) | E::HttpFailed(_) | E::DidResolution(_) => ResolveFailure::NetworkError,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::cache::{Cache, CacheError};
+    use std::collections::HashMap;
+    use std::sync::Mutex;
+    use std::time::Duration;
+
+    #[derive(Default)]
+    struct MapCache(Mutex<HashMap<String, String>>);
+
+    #[async_trait::async_trait]
+    impl Cache for MapCache {
+        async fn get(&self, key: &str) -> Option<String> {
+            self.0.lock().unwrap().get(key).cloned()
+        }
+        async fn set(&self, key: &str, value: &str, _ttl: Duration) -> Result<(), CacheError> {
+            self.0
+                .lock()
+                .unwrap()
+                .insert(key.to_string(), value.to_string());
+            Ok(())
+        }
+        async fn delete(&self, key: &str) -> Result<(), CacheError> {
+            self.0.lock().unwrap().remove(key);
+            Ok(())
+        }
+        async fn get_bytes(&self, _key: &str) -> Option<Vec<u8>> {
+            None
+        }
+        async fn set_bytes(&self, _k: &str, _v: &[u8], _t: Duration) -> Result<(), CacheError> {
+            Ok(())
+        }
+    }
+
+    fn seed(cache: &MapCache, nsid: &str, scope: &str) {
+        let key = crate::cache_keys::permission_set_key(nsid, None);
+        let val = serde_json::to_string(&CachedPermissionSet {
+            scope: scope.to_string(),
+            title: Some("Basic".into()),
+            detail: None,
+        })
+        .unwrap();
+        cache.0.lock().unwrap().insert(key, val);
+    }
+
+    #[tokio::test]
+    async fn cache_hit_expands_without_network() {
+        let cache = MapCache::default();
+        seed(
+            &cache,
+            "io.atcr.authFullApp",
+            "repo:io.atcr.manifest?action=create identity:*",
+        );
+        let out = expand_scopes(&cache, "atproto include:io.atcr.authFullApp").await;
+        assert!(out.failures.is_empty());
+        assert_eq!(out.passthrough, vec!["atproto".to_string()]);
+        assert_eq!(out.sets.len(), 1);
+        assert_eq!(out.sets[0].nsid, "io.atcr.authFullApp");
+        assert!(
+            out.flat_scopes()
+                .iter()
+                .any(|s| s == "repo:io.atcr.manifest?action=create")
+        );
+    }
+
+    #[tokio::test]
+    async fn passthrough_scopes_untouched() {
+        let cache = MapCache::default();
+        let out = expand_scopes(&cache, "atproto repo:app.bsky.feed.post?action=create").await;
+        assert!(out.failures.is_empty());
+        assert!(out.sets.is_empty());
+        assert_eq!(out.flat_scopes().len(), 2);
+    }
+
+    #[tokio::test]
+    async fn cache_miss_unresolvable_is_a_failure() {
+        let cache = MapCache::default(); // empty → miss → network fetch of a fake NSID fails fast
+        let out = expand_scopes(&cache, "include:nonexistent.fake.permissionSet").await;
+        assert_eq!(out.sets.len(), 0);
+        assert_eq!(out.failures.len(), 1);
+        assert_eq!(out.failures[0].nsid, "nonexistent.fake.permissionSet");
+    }
+}
diff --git a/crates/tranquil-scopes/src/lib.rs b/crates/tranquil-scopes/src/lib.rs
index fd01786..ec35354 100644
--- a/crates/tranquil-scopes/src/lib.rs
+++ b/crates/tranquil-scopes/src/lib.rs
@@ -15,5 +15,8 @@ pub use parser::{
     AccountAction, AccountAttr, AccountScope, BlobScope, IdentityAttr, IdentityScope, IncludeScope,
     ParsedScope, RepoAction, RepoScope, RpcScope, parse_scope, parse_scope_string,
 };
-pub use permission_set::{ScopeExpansionError, expand_include_scopes};
+pub use permission_set::{
+    ExpansionOutcome, FailedSet, FetchedSet, ResolveFailure, ResolvedSetGroup,
+    ScopeExpansionError, expand_include_scopes, fetch_and_expand, parse_include_scope,
+};
 pub use permissions::ScopePermissions;
diff --git a/crates/tranquil-scopes/src/permission_set.rs b/crates/tranquil-scopes/src/permission_set.rs
index 7c60469..a19b342 100644
--- a/crates/tranquil-scopes/src/permission_set.rs
+++ b/crates/tranquil-scopes/src/permission_set.rs
@@ -26,6 +26,50 @@ pub enum ScopeExpansionError {
     EmptyPermissions,
 }
 
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ResolveFailure {
+    NotFound,
+    NetworkError,
+    Invalid,
+}
+
+#[derive(Debug, Clone)]
+pub struct FailedSet {
+    pub nsid: String,
+    pub aud: Option<String>,
+    pub reason: ResolveFailure,
+}
+
+#[derive(Debug, Clone)]
+pub struct ResolvedSetGroup {
+    pub nsid: String,
+    pub aud: Option<String>,
+    pub title: Option<String>,
+    pub detail: Option<String>,
+    pub expanded: Vec<String>,
+}
+
+#[derive(Debug, Clone, Default)]
+pub struct ExpansionOutcome {
+    pub passthrough: Vec<String>,
+    pub sets: Vec<ResolvedSetGroup>,
+    pub failures: Vec<FailedSet>,
+}
+
+impl ExpansionOutcome {
+    pub fn flat_scopes(&self) -> Vec<String> {
+        let mut out = self.passthrough.clone();
+        for s in &self.sets {
+            out.extend(s.expanded.iter().cloned());
+        }
+        out
+    }
+    /// Space-joined `flat_scopes`.
+    pub fn to_scope_string(&self) -> String {
+        self.flat_scopes().join(" ")
+    }
+}
+
 static LEXICON_CACHE: LazyLock<RwLock<HashMap<String, CachedLexicon>>> =
     LazyLock::new(|| RwLock::new(HashMap::new()));
 
@@ -63,6 +107,10 @@ struct LexiconDoc {
 struct LexiconDef {
     #[serde(rename = "type")]
     def_type: String,
+    #[serde(default)]
+    title: Option<String>,
+    #[serde(default)]
+    detail: Option<String>,
     permissions: Option<Vec<PermissionEntry>>,
 }
 
@@ -98,7 +146,7 @@ pub async fn expand_include_scopes(scope_string: &str) -> Result<String, ScopeEx
         .map(|v| v.join(" "))
 }
 
-fn parse_include_scope(rest: &str) -> (&str, Option<&str>) {
+pub fn parse_include_scope(rest: &str) -> (&str, Option<&str>) {
     rest.split_once('?')
         .map(|(nsid, params)| {
             let aud = params.split('&').find_map(|p| p.strip_prefix("aud="));
@@ -126,33 +174,8 @@ async fn expand_permission_set(
         }
     }
 
-    let lexicon = fetch_lexicon_via_atproto(nsid).await?;
-
-    let main_def = lexicon
-        .defs
-        .get("main")
-        .ok_or(ScopeExpansionError::MissingDefinition("main".to_string()))?;
-
-    if main_def.def_type != "permission-set" {
-        return Err(ScopeExpansionError::UnexpectedType(
-            main_def.def_type.clone(),
-        ));
-    }
-
-    let permissions =
-        main_def
-            .permissions
-            .as_ref()
-            .ok_or(ScopeExpansionError::MissingDefinition(
-                "permissions".to_string(),
-            ))?;
-
-    let namespace_authority = extract_namespace_authority(nsid);
-    let expanded = build_expanded_scopes(permissions, aud, &namespace_authority);
-
-    if expanded.is_empty() {
-        return Err(ScopeExpansionError::EmptyPermissions);
-    }
+    let fetched = fetch_and_expand(nsid, aud).await?;
+    let expanded = fetched.expanded;
 
     {
         let mut cache = LEXICON_CACHE.write().await;
@@ -169,6 +192,44 @@ async fn expand_permission_set(
     Ok(expanded)
 }
 
+pub struct FetchedSet {
+    pub expanded: String,
+    pub title: Option<String>,
+    pub detail: Option<String>,
+}
+
+pub async fn fetch_and_expand(
+    nsid: &Nsid,
+    aud: Option<&str>,
+) -> Result<FetchedSet, ScopeExpansionError> {
+    let lexicon = fetch_lexicon_via_atproto(nsid).await?;
+    let main_def = lexicon
+        .defs
+        .get("main")
+        .ok_or(ScopeExpansionError::MissingDefinition("main".to_string()))?;
+    if main_def.def_type != "permission-set" {
+        return Err(ScopeExpansionError::UnexpectedType(
+            main_def.def_type.clone(),
+        ));
+    }
+    let permissions = main_def
+        .permissions
+        .as_ref()
+        .ok_or(ScopeExpansionError::MissingDefinition(
+            "permissions".to_string(),
+        ))?;
+    let namespace_authority = extract_namespace_authority(nsid);
+    let expanded = build_expanded_scopes(permissions, aud, &namespace_authority);
+    if expanded.is_empty() {
+        return Err(ScopeExpansionError::EmptyPermissions);
+    }
+    Ok(FetchedSet {
+        expanded,
+        title: main_def.title.clone(),
+        detail: main_def.detail.clone(),
+    })
+}
+
 async fn fetch_lexicon_via_atproto(nsid: &Nsid) -> Result<LexiconDoc, ScopeExpansionError> {
     let parts: Vec<&str> = nsid.split('.').collect();
     let authority = parts[..parts.len() - 1]
@@ -678,4 +739,55 @@ mod tests {
             "bookmarks.lexicon.community"
         );
     }
+
+    #[test]
+    fn expansion_outcome_flat_scopes_and_string() {
+        let out = ExpansionOutcome {
+            passthrough: vec!["atproto".into()],
+            sets: vec![ResolvedSetGroup {
+                nsid: "io.atcr.authFullApp".into(),
+                aud: None,
+                title: Some("T".into()),
+                detail: None,
+                expanded: vec![
+                    "repo:io.atcr.manifest?action=create".into(),
+                    "rpc:io.atcr.getManifest".into(),
+                ],
+            }],
+            failures: vec![FailedSet {
+                nsid: "nonexistent.fake.permissionSet".into(),
+                aud: None,
+                reason: ResolveFailure::NotFound,
+            }],
+        };
+        let flat = out.flat_scopes();
+        assert_eq!(
+            flat,
+            vec![
+                "atproto",
+                "repo:io.atcr.manifest?action=create",
+                "rpc:io.atcr.getManifest"
+            ]
+        );
+        assert_eq!(
+            out.to_scope_string(),
+            "atproto repo:io.atcr.manifest?action=create rpc:io.atcr.getManifest"
+        );
+    }
+
+    #[test]
+    fn test_lexicon_def_captures_title_and_detail() {
+        let json = serde_json::json!({
+            "defs": { "main": {
+                "type": "permission-set",
+                "title": "Basic App",
+                "detail": "Posts and interactions",
+                "permissions": [{ "resource": "repo", "collection": ["io.atcr.manifest"] }]
+            }}
+        });
+        let doc: LexiconDoc = serde_json::from_value(json).unwrap();
+        let main = doc.defs.get("main").unwrap();
+        assert_eq!(main.title.as_deref(), Some("Basic App"));
+        assert_eq!(main.detail.as_deref(), Some("Posts and interactions"));
+    }
 }