diff --git a/crates/aura-cli/src/backend/direct.rs b/crates/aura-cli/src/backend/direct.rs
index 6d301c5e3..a1cdacde2 100644
--- a/crates/aura-cli/src/backend/direct.rs
+++ b/crates/aura-cli/src/backend/direct.rs
@@ -340,8 +340,10 @@ impl DirectBackend {
         let selected = get_selected_model();
         let mut req = Self::build_chat_request(messages, tools, selected);
 
+        let session =
+            aura::SessionId::new(session_id).map_err(|e| anyhow::anyhow!("session id: {e}"))?;
         let setup =
-            handlers::prepare_request(&self.app_state, &mut req, session_id, &self.extra_headers)
+            handlers::prepare_request(&self.app_state, &mut req, &session, &self.extra_headers)
                 .await
                 .map_err(|e| anyhow::anyhow!("{e}"))?;
 
@@ -406,8 +408,10 @@ impl DirectBackend {
             tools: None,
         };
 
+        let session =
+            aura::SessionId::new(session_id).map_err(|e| anyhow::anyhow!("session id: {e}"))?;
         let setup =
-            handlers::prepare_request(&self.app_state, &mut req, session_id, &self.extra_headers)
+            handlers::prepare_request(&self.app_state, &mut req, &session, &self.extra_headers)
                 .await
                 .map_err(|e| anyhow::anyhow!("{e}"))?;
 
diff --git a/crates/aura-events/src/lib.rs b/crates/aura-events/src/lib.rs
index 9884eba95..54f17218c 100644
--- a/crates/aura-events/src/lib.rs
+++ b/crates/aura-events/src/lib.rs
@@ -161,6 +161,12 @@ macro_rules! nonempty_string_newtype {
                 }
             }
 
+            /// The identifier `value` names, or `None` for the empty string:
+            /// for a boundary where a blank and an absent value mean the same.
+            pub fn non_empty(value: impl Into<String>) -> Option<Self> {
+                Self::new(value).ok()
+            }
+
             pub fn as_str(&self) -> &str {
                 &self.0
             }
@@ -236,7 +242,7 @@ impl std::fmt::Display for EmptyId {
 
 impl std::error::Error for EmptyId {}
 
-string_newtype! {
+nonempty_string_newtype! {
     /// Identifier for a session: an agent's identity over time, and the key
     /// its [`SessionEvent`](run::SessionEvent) stream is ordered under.
     SessionId
diff --git a/crates/aura-events/src/run.rs b/crates/aura-events/src/run.rs
index 22c481981..cff119121 100644
--- a/crates/aura-events/src/run.rs
+++ b/crates/aura-events/src/run.rs
@@ -296,7 +296,7 @@ mod tests {
 
     fn envelope(seq: u64, run: Option<RunId>, payload: SessionEventPayload) -> SessionEvent {
         SessionEvent {
-            session_id: SessionId::new("sess_1"),
+            session_id: SessionId::new("sess_1").unwrap(),
             run_id: run,
             seq: SequenceNumber::try_from(seq).expect("a sequence starts at 1"),
             at: Timestamp::from_unix_millis(1_700_000_000_000),
@@ -631,7 +631,7 @@ mod tests {
     fn ids_serialize_as_bare_strings() {
         assert_eq!(serde_json::to_value(run_id()).unwrap(), json!(RUN));
         assert_eq!(
-            serde_json::to_value(SessionId::new("sess_1")).unwrap(),
+            serde_json::to_value(SessionId::new("sess_1").unwrap()).unwrap(),
             json!("sess_1")
         );
         assert_eq!(
@@ -688,6 +688,36 @@ mod tests {
         );
     }
 
+    /// A session named by the empty string names nothing, like an observer
+    /// or a checkpoint, so neither the constructor nor deserialization will
+    /// build one, and a stream keyed by it cannot exist.
+    #[test]
+    fn an_empty_session_id_is_refused() {
+        let err = SessionId::new("").unwrap_err();
+        assert_eq!(err.to_string(), "SessionId cannot be empty");
+        assert!(SessionId::try_from(String::new()).is_err());
+        assert!(serde_json::from_value::<SessionId>(json!("")).is_err());
+        assert_eq!(
+            serde_json::from_value::<SessionId>(json!("sess_1")).unwrap(),
+            "sess_1"
+        );
+    }
+
+    #[test]
+    fn a_blank_names_no_session() {
+        assert_eq!(SessionId::non_empty(""), None);
+        assert_eq!(SessionId::non_empty(String::new()), None);
+        assert_eq!(
+            SessionId::non_empty("sess_1"),
+            Some(SessionId::new("sess_1").unwrap())
+        );
+        assert_eq!(
+            Some("sess_1".to_string()).and_then(SessionId::non_empty),
+            Some(SessionId::new("sess_1").unwrap())
+        );
+        assert_eq!(Some(String::new()).and_then(SessionId::non_empty), None);
+    }
+
     /// The refusal reaches the envelope: an attach naming an empty observer
     /// does not parse into an event.
     #[test]
diff --git a/crates/aura-web-server/src/handlers.rs b/crates/aura-web-server/src/handlers.rs
index 1eae4aef2..06f03799f 100644
--- a/crates/aura-web-server/src/handlers.rs
+++ b/crates/aura-web-server/src/handlers.rs
@@ -231,7 +231,7 @@ pub struct RequestSetup {
 pub async fn prepare_request(
     data: &AppState,
     req: &mut ChatCompletionRequest,
-    chat_session_id: &str,
+    chat_session_id: &aura::SessionId,
     req_headers_map: &HashMap<String, String>,
 ) -> Result<RequestSetup, PrepareError> {
     // Client-side tools are gated per-agent by `[agent].enable_client_tools`
@@ -298,10 +298,8 @@ pub async fn prepare_request(
     // server-generated session id is echoed back via `X-Chat-Session-Id`, so
     // the client may adopt it on its next request, and an id that is never
     // reused just leaves TTL-bounded orphan records.
-    let skill_log = aura::session_store::SkillLogKey::new(
-        aura::SessionId::new(chat_session_id),
-        config.agent_id(),
-    );
+    let skill_log =
+        aura::session_store::SkillLogKey::new(chat_session_id.clone(), config.agent_id());
     let skill_recorder = (!config.agent.skills.local.is_empty()).then(|| {
         Arc::new(aura::skill_tool::SkillInvocationRecorder::new(
             data.session_store.skills(),
@@ -1341,8 +1339,15 @@ pub async fn resolve_approval(
 /// A blank value counts as none given. Taken as given, every client that sends
 /// one would share a single session, and with it each other's recorded skill
 /// invocations; orchestration persistence would refuse it outright.
-fn chat_session_id(metadata: Option<&HashMap<String, String>>, headers: &HeaderMap) -> String {
-    let given = |value: &str| (!value.trim().is_empty()).then(|| value.to_owned());
+fn chat_session_id(
+    metadata: Option<&HashMap<String, String>>,
+    headers: &HeaderMap,
+) -> aura::SessionId {
+    let given = |value: &str| {
+        (!value.trim().is_empty())
+            .then(|| value.to_owned())
+            .and_then(aura::SessionId::non_empty)
+    };
     let header = |name: &str| {
         headers
             .get(name)
@@ -1358,8 +1363,9 @@ fn chat_session_id(metadata: Option<&HashMap<String, String>>, headers: &HeaderM
 }
 
 /// Generate a chat session ID (simple GUID)
-fn generate_chat_session_id() -> String {
-    format!("cs_{}", Uuid::new_v4().simple())
+fn generate_chat_session_id() -> aura::SessionId {
+    aura::SessionId::new(format!("cs_{}", Uuid::new_v4().simple()))
+        .expect("a generated id carries its prefix, so it is never empty")
 }
 
 /// The HMAC-ON ingress path for `resolve_approval`: buffer the raw bytes
@@ -1526,7 +1532,7 @@ mod tests {
             let first = chat_session_id(Some(&metadata("")), &blank);
             let second = chat_session_id(Some(&metadata("")), &blank);
 
-            assert!(first.starts_with("cs_"), "got: {first}");
+            assert!(first.as_str().starts_with("cs_"), "got: {first}");
             assert_ne!(first, second);
         }
     }
@@ -3141,13 +3147,13 @@ source = '{}'
                 skill_agent(dir.path(), "agent-a", "# Agent A instructions"),
                 skill_agent(dir.path(), "agent-b", "# Agent B instructions"),
             ]);
-            let session = "sess-switch";
+            let session = aura::SessionId::new("sess-switch").unwrap();
             // Agent A loaded `shared` during the session's first turn.
             state
                 .session_store
                 .skills()
                 .record(
-                    &SkillLogKey::new(aura::SessionId::new(session), "agent-a"),
+                    &SkillLogKey::new(session.clone(), "agent-a"),
                     SkillInvocationRecord {
                         version: SKILL_INVOCATION_RECORD_VERSION,
                         invocation: SkillInvocation::LoadSkill {
@@ -3165,7 +3171,7 @@ source = '{}'
             // The client keeps the session id and switches to agent B, which
             // configures a skill of the same name it never loaded.
             let setup =
-                prepare_request(&state, &mut follow_up("agent-b"), session, &HashMap::new())
+                prepare_request(&state, &mut follow_up("agent-b"), &session, &HashMap::new())
                     .await
                     .unwrap();
             assert!(
@@ -3177,7 +3183,7 @@ source = '{}'
 
             // Agent A, back on the same session, still gets its own.
             let setup =
-                prepare_request(&state, &mut follow_up("agent-a"), session, &HashMap::new())
+                prepare_request(&state, &mut follow_up("agent-a"), &session, &HashMap::new())
                     .await
                     .unwrap();
             assert_eq!(setup.rehydrated_skills, ["shared"]);
diff --git a/crates/aura-web-server/tests/file_session_store_test.rs b/crates/aura-web-server/tests/file_session_store_test.rs
index e3c1d0075..1e804363a 100644
--- a/crates/aura-web-server/tests/file_session_store_test.rs
+++ b/crates/aura-web-server/tests/file_session_store_test.rs
@@ -525,7 +525,7 @@ fn skill_record(name: &str, anchor: u32, seq: u32) -> SkillInvocationRecord {
 }
 
 fn skill_log(session_id: &str) -> SkillLogKey {
-    SkillLogKey::new(SessionId::new(session_id), "agent")
+    SkillLogKey::new(SessionId::new(session_id).unwrap(), "agent")
 }
 
 fn skill_store(dir: &tempfile::TempDir, ttl_secs: Option<u64>) -> FileSkillInvocationStore {
@@ -633,7 +633,7 @@ async fn skill_sessions_are_isolated_and_a_hostile_id_stays_inside_the_root() {
 async fn skill_agents_sharing_a_session_are_isolated() {
     let dir = tempfile::tempdir().unwrap();
     let store = skill_store(&dir, Some(60));
-    let session = SessionId::new("sess-switch");
+    let session = SessionId::new("sess-switch").unwrap();
     let first = SkillLogKey::new(session.clone(), "agent-a");
     let second = SkillLogKey::new(session, "agent-b");
 
diff --git a/crates/aura-web-server/tests/redis_session_store_test.rs b/crates/aura-web-server/tests/redis_session_store_test.rs
index 4490618c1..179c19ce7 100644
--- a/crates/aura-web-server/tests/redis_session_store_test.rs
+++ b/crates/aura-web-server/tests/redis_session_store_test.rs
@@ -1481,7 +1481,7 @@ async fn corrupt_record_is_skipped_from_list() {
 // ---------------------------------------------------------------------------
 
 fn skill_log(session_id: &str) -> SkillLogKey {
-    SkillLogKey::new(SessionId::new(session_id), "agent")
+    SkillLogKey::new(SessionId::new(session_id).unwrap(), "agent")
 }
 
 /// The Redis key holding `log`, per the store's key schema.
@@ -1614,7 +1614,7 @@ async fn skill_sessions_are_isolated_by_prefix_and_session() {
 #[tokio::test]
 async fn skill_agents_sharing_a_session_are_isolated() {
     let skills = connect(&test_config(60)).await.skills();
-    let session = SessionId::new("sess-switch");
+    let session = SessionId::new("sess-switch").unwrap();
     let first = SkillLogKey::new(session.clone(), "agent-a");
     let second = SkillLogKey::new(session, "agent-b");
 
diff --git a/crates/aura/src/builder.rs b/crates/aura/src/builder.rs
index 92868e045..417691985 100644
--- a/crates/aura/src/builder.rs
+++ b/crates/aura/src/builder.rs
@@ -392,7 +392,7 @@ impl PreparedAgent {
                 session_id: config_owned
                     .session_id
                     .clone()
-                    .map(crate::config::SessionId::new),
+                    .and_then(crate::config::SessionId::non_empty),
             };
             let wrapper = Arc::new(crate::hitl::HitlApprovalWrapper::new(
                 hitl.patterns.clone(),
diff --git a/crates/aura/src/hitl/route.rs b/crates/aura/src/hitl/route.rs
index 56c7ecc7f..9009691bd 100644
--- a/crates/aura/src/hitl/route.rs
+++ b/crates/aura/src/hitl/route.rs
@@ -867,7 +867,7 @@ mod tests {
             scope: AgentScope::Worker {
                 run_id,
                 task: crate::orchestration::TaskIdentity::new(2, Some("k8s-agent".to_string())),
-                session_id: Some(crate::config::SessionId::new("sess-abc".to_string())),
+                session_id: Some(crate::config::SessionId::new("sess-abc").unwrap()),
             },
             origin: ApprovalOrigin::AgentRequested {
                 reason: "deleting prod ns".to_string(),
diff --git a/crates/aura/src/orchestration/orchestrator.rs b/crates/aura/src/orchestration/orchestrator.rs
index 21c6d204c..3053808fb 100644
--- a/crates/aura/src/orchestration/orchestrator.rs
+++ b/crates/aura/src/orchestration/orchestrator.rs
@@ -962,7 +962,7 @@ impl Orchestrator {
             let scope = crate::hitl::AgentScope::Worker {
                 run_id,
                 task: super::TaskIdentity::new(task_id, worker_name.map(String::from)),
-                session_id: session_id_owned.map(crate::config::SessionId::new),
+                session_id: session_id_owned.and_then(crate::config::SessionId::non_empty),
             };
             let mut gate = crate::hitl::HitlApprovalWrapper::new(
                 hitl.patterns.clone(),
@@ -1207,7 +1207,7 @@ impl Orchestrator {
             .map(|run_id| crate::hitl::AgentScope::Worker {
                 run_id,
                 task: super::TaskIdentity::new(task_id, worker_name.map(String::from)),
-                session_id: session_id.map(crate::config::SessionId::new),
+                session_id: session_id.and_then(crate::config::SessionId::non_empty),
             })
     }
 
diff --git a/crates/aura/src/session_store/memory.rs b/crates/aura/src/session_store/memory.rs
index ceca707e3..a99ff017b 100644
--- a/crates/aura/src/session_store/memory.rs
+++ b/crates/aura/src/session_store/memory.rs
@@ -534,7 +534,7 @@ mod tests {
     }
 
     fn skill_log(session_id: impl Into<String>, agent_id: &str) -> SkillLogKey {
-        SkillLogKey::new(SessionId::new(session_id), agent_id)
+        SkillLogKey::new(SessionId::new(session_id).unwrap(), agent_id)
     }
 
     #[tokio::test]
diff --git a/crates/aura/src/session_store/record.rs b/crates/aura/src/session_store/record.rs
index 48d020650..e9feaf594 100644
--- a/crates/aura/src/session_store/record.rs
+++ b/crates/aura/src/session_store/record.rs
@@ -179,7 +179,7 @@ impl TryFrom<ScopeRecord> for AgentScope {
     fn try_from(record: ScopeRecord) -> Result<Self, Self::Error> {
         Ok(match record {
             ScopeRecord::Single { session_id } => AgentScope::Single {
-                session_id: session_id.map(SessionId::new),
+                session_id: session_id.and_then(SessionId::non_empty),
             },
             ScopeRecord::Worker {
                 run_id,
@@ -189,7 +189,7 @@ impl TryFrom<ScopeRecord> for AgentScope {
             } => AgentScope::Worker {
                 run_id: parse_run_id(&run_id)?,
                 task: TaskIdentity::new(task_id, worker),
-                session_id: session_id.map(SessionId::new),
+                session_id: session_id.and_then(SessionId::non_empty),
             },
             ScopeRecord::Coordinator { run_id } => AgentScope::Coordinator {
                 run_id: parse_run_id(&run_id)?,
@@ -281,7 +281,7 @@ mod tests {
     fn single_scope_round_trips() {
         assert_round_trip(parked(
             AgentScope::Single {
-                session_id: Some(SessionId::new("sess-9")),
+                session_id: Some(SessionId::new("sess-9").unwrap()),
             },
             ApprovalOrigin::ConfigGate {
                 matched_pattern: "kubectl_*".to_string(),
@@ -332,6 +332,30 @@ mod tests {
         assert_eq!(json["origin"]["kind"], "agent_requested");
     }
 
+    /// A stored scope carrying an empty session id restores as a scope with
+    /// no session rather than failing to decode.
+    #[test]
+    fn a_blank_session_id_in_a_stored_scope_restores_as_none() {
+        let single = ScopeRecord::Single {
+            session_id: Some(String::new()),
+        };
+        assert_eq!(
+            AgentScope::try_from(single).unwrap(),
+            AgentScope::Single { session_id: None }
+        );
+
+        let worker = ScopeRecord::Worker {
+            run_id: "0191e8c0-1111-7000-8000-000000000000".to_string(),
+            task_id: 1,
+            worker: None,
+            session_id: Some(String::new()),
+        };
+        let AgentScope::Worker { session_id, .. } = AgentScope::try_from(worker).unwrap() else {
+            panic!("a worker scope restores as one");
+        };
+        assert_eq!(session_id, None);
+    }
+
     #[test]
     fn malformed_run_id_is_an_invalid_record() {
         let scope = ScopeRecord::Coordinator {
diff --git a/crates/aura/src/skill_rehydration.rs b/crates/aura/src/skill_rehydration.rs
index c6dfcda48..bdc27eb08 100644
--- a/crates/aura/src/skill_rehydration.rs
+++ b/crates/aura/src/skill_rehydration.rs
@@ -406,7 +406,7 @@ mod tests {
         let dir = TempDir::new().unwrap();
         let skills = vec![make_skill(dir.path(), "alpha", "# Alpha instructions")];
         let store = Arc::new(InMemorySkillInvocationStore::new());
-        let log = SkillLogKey::new(crate::config::SessionId::new("sess-loop"), "agent");
+        let log = SkillLogKey::new(crate::config::SessionId::new("sess-loop").unwrap(), "agent");
 
         // Turn N: history [user], anchor = 0 + 1. The LLM calls load_skill.
         let recorder = Arc::new(SkillInvocationRecorder::new(store.clone(), log.clone(), 1));
diff --git a/crates/aura/src/skill_tool.rs b/crates/aura/src/skill_tool.rs
index b308be76a..3af7d1ba8 100644
--- a/crates/aura/src/skill_tool.rs
+++ b/crates/aura/src/skill_tool.rs
@@ -870,7 +870,10 @@ mod tests {
         let dir = TempDir::new().unwrap();
         let configs = make_skill_configs(dir.path());
         let store = Arc::new(InMemorySkillInvocationStore::new());
-        let log = SkillLogKey::new(crate::config::SessionId::new("sess-reuse"), "agent");
+        let log = SkillLogKey::new(
+            crate::config::SessionId::new("sess-reuse").unwrap(),
+            "agent",
+        );
         let turn = |id: &str, anchor| {
             let recorder = Arc::new(SkillInvocationRecorder::new(
                 store.clone(),