diff --git a/rsworkspace/crates/acp-nats/src/agent/bridge.rs b/rsworkspace/crates/acp-nats/src/agent/bridge.rs
index 2ae7baf8b..f38303636 100644
--- a/rsworkspace/crates/acp-nats/src/agent/bridge.rs
+++ b/rsworkspace/crates/acp-nats/src/agent/bridge.rs
@@ -146,7 +146,7 @@ where
         &self,
         subject: &impl crate::nats::markers::SessionCommand,
         args: &Req,
-        session_id: &str,
+        session_id: &crate::session_id::AcpSessionId,
     ) -> Result<Res>
     where
         Req: serde::Serialize,
diff --git a/rsworkspace/crates/acp-nats/src/agent/close_session.rs b/rsworkspace/crates/acp-nats/src/agent/close_session.rs
index 83b3b8c56..5beaeef10 100644
--- a/rsworkspace/crates/acp-nats/src/agent/close_session.rs
+++ b/rsworkspace/crates/acp-nats/src/agent/close_session.rs
@@ -39,11 +39,7 @@ where
     let subject = session::agent::CloseSubject::new(prefix, &session_id);
 
     let result = bridge
-        .session_request::<CloseSessionRequest, CloseSessionResponse>(
-            &subject,
-            &args,
-            session_id.as_str(),
-        )
+        .session_request::<CloseSessionRequest, CloseSessionResponse>(&subject, &args, &session_id)
         .await;
 
     bridge.metrics.record_request(
diff --git a/rsworkspace/crates/acp-nats/src/agent/fork_session.rs b/rsworkspace/crates/acp-nats/src/agent/fork_session.rs
index 42d3683be..9027ca493 100644
--- a/rsworkspace/crates/acp-nats/src/agent/fork_session.rs
+++ b/rsworkspace/crates/acp-nats/src/agent/fork_session.rs
@@ -39,11 +39,7 @@ where
     let subject = session::agent::ForkSubject::new(prefix, &session_id);
 
     let result = bridge
-        .session_request::<ForkSessionRequest, ForkSessionResponse>(
-            &subject,
-            &args,
-            session_id.as_str(),
-        )
+        .session_request::<ForkSessionRequest, ForkSessionResponse>(&subject, &args, &session_id)
         .await;
 
     if let Ok(ref response) = result {
diff --git a/rsworkspace/crates/acp-nats/src/agent/js_request.rs b/rsworkspace/crates/acp-nats/src/agent/js_request.rs
index 93d1f959b..b7b8045d5 100644
--- a/rsworkspace/crates/acp-nats/src/agent/js_request.rs
+++ b/rsworkspace/crates/acp-nats/src/agent/js_request.rs
@@ -23,7 +23,7 @@ pub async fn js_request<J, Req, Res, S>(
     request: &Req,
     serializer: &S,
     prefix: &AcpPrefix,
-    session_id: &str,
+    session_id: &crate::session_id::AcpSessionId,
     req_id: &str,
     operation_timeout: Duration,
 ) -> agent_client_protocol::Result<Res>
@@ -61,7 +61,7 @@ where
 
     let mut headers = async_nats::HeaderMap::new();
     headers.insert(REQ_ID_HEADER, req_id);
-    headers.insert(SESSION_ID_HEADER, session_id);
+    headers.insert(SESSION_ID_HEADER, session_id.as_str());
 
     js.publish_with_headers(subject.to_string(), headers, Bytes::from(payload_bytes))
         .await
@@ -114,11 +114,16 @@ mod tests {
     use trogon_nats::jetstream::mocks::*;
 
     use crate::agent::test_support::MockJs;
+    use crate::session_id::AcpSessionId;
 
     fn test_prefix() -> AcpPrefix {
         AcpPrefix::new("acp").expect("test prefix")
     }
 
+    fn test_sid(s: &str) -> AcpSessionId {
+        AcpSessionId::new(s).expect("test session id")
+    }
+
     fn make_nats_msg(payload: &[u8]) -> async_nats::Message {
         async_nats::Message {
             subject: "test".into(),
@@ -147,7 +152,7 @@ mod tests {
             &agent_client_protocol::PromptRequest::new("s1", vec![]),
             &trogon_std::StdJsonSerialize,
             &test_prefix(),
-            "s1",
+            &test_sid("s1"),
             "req-1",
             Duration::from_secs(5),
         )
@@ -173,7 +178,7 @@ mod tests {
             &agent_client_protocol::PromptRequest::new("s1", vec![]),
             &trogon_std::StdJsonSerialize,
             &test_prefix(),
-            "s1",
+            &test_sid("s1"),
             "req-1",
             Duration::from_secs(5),
         )
@@ -193,7 +198,7 @@ mod tests {
             &agent_client_protocol::PromptRequest::new("s1", vec![]),
             &trogon_std::StdJsonSerialize,
             &test_prefix(),
-            "s1",
+            &test_sid("s1"),
             "req-1",
             Duration::from_secs(5),
         )
@@ -220,7 +225,7 @@ mod tests {
             &agent_client_protocol::PromptRequest::new("s1", vec![]),
             &trogon_std::StdJsonSerialize,
             &test_prefix(),
-            "s1",
+            &test_sid("s1"),
             "req-1",
             Duration::from_secs(5),
         )
@@ -245,7 +250,7 @@ mod tests {
             &agent_client_protocol::PromptRequest::new("s1", vec![]),
             &trogon_std::StdJsonSerialize,
             &test_prefix(),
-            "s1",
+            &test_sid("s1"),
             "req-1",
             Duration::from_secs(5),
         )
@@ -267,7 +272,7 @@ mod tests {
             &agent_client_protocol::PromptRequest::new("s1", vec![]),
             &trogon_std::StdJsonSerialize,
             &test_prefix(),
-            "s1",
+            &test_sid("s1"),
             "req-1",
             Duration::from_millis(10),
         )
@@ -304,7 +309,7 @@ mod tests {
             &agent_client_protocol::PromptRequest::new("s1", vec![]),
             &trogon_std::StdJsonSerialize,
             &test_prefix(),
-            "s1",
+            &test_sid("s1"),
             "req-1",
             Duration::from_secs(5),
         )
@@ -329,7 +334,7 @@ mod tests {
             &agent_client_protocol::PromptRequest::new("s1", vec![]),
             &trogon_std::StdJsonSerialize,
             &test_prefix(),
-            "s1",
+            &test_sid("s1"),
             "req-1",
             Duration::from_secs(5),
         )
@@ -361,7 +366,7 @@ mod tests {
             &agent_client_protocol::PromptRequest::new("s1", vec![]),
             &trogon_std::StdJsonSerialize,
             &test_prefix(),
-            "s1",
+            &test_sid("s1"),
             "req-1",
             Duration::from_secs(5),
         )
@@ -383,7 +388,7 @@ mod tests {
             &agent_client_protocol::PromptRequest::new("s1", vec![]),
             &trogon_std::FailNextSerialize::new(1),
             &test_prefix(),
-            "s1",
+            &test_sid("s1"),
             "req-1",
             Duration::from_secs(5),
         )
diff --git a/rsworkspace/crates/acp-nats/src/agent/load_session.rs b/rsworkspace/crates/acp-nats/src/agent/load_session.rs
index e60292831..08e612410 100644
--- a/rsworkspace/crates/acp-nats/src/agent/load_session.rs
+++ b/rsworkspace/crates/acp-nats/src/agent/load_session.rs
@@ -39,11 +39,7 @@ where
     let subject = session::agent::LoadSubject::new(prefix, &session_id);
 
     let result = bridge
-        .session_request::<LoadSessionRequest, LoadSessionResponse>(
-            &subject,
-            &args,
-            session_id.as_str(),
-        )
+        .session_request::<LoadSessionRequest, LoadSessionResponse>(&subject, &args, &session_id)
         .await;
 
     if result.is_ok() {
diff --git a/rsworkspace/crates/acp-nats/src/agent/prompt.rs b/rsworkspace/crates/acp-nats/src/agent/prompt.rs
index 79ccdea1c..7ebb57f10 100644
--- a/rsworkspace/crates/acp-nats/src/agent/prompt.rs
+++ b/rsworkspace/crates/acp-nats/src/agent/prompt.rs
@@ -86,9 +86,8 @@ where
     // Create consumers BEFORE publishing — same principle as subscribe-before-publish.
     // JetStream consumers with DeliverAll replay from stream start, so they'll see the
     // response even if the runner responds before we start consuming.
-    let sid = session_id.as_str();
     let notifications_stream = streams::notifications_stream_name(prefix);
-    let notif_config = consumers::prompt_notifications_consumer(prefix, sid, req_id);
+    let notif_config = consumers::prompt_notifications_consumer(prefix, session_id, req_id);
     let notif_stream = js.get_stream(&notifications_stream).await.map_err(|e| {
         Error::new(
             ErrorCode::InternalError.into(),
@@ -112,7 +111,7 @@ where
     })?;
 
     let responses_stream = streams::responses_stream_name(prefix);
-    let resp_config = consumers::prompt_response_consumer(prefix, sid, req_id);
+    let resp_config = consumers::prompt_response_consumer(prefix, session_id, req_id);
     let resp_stream = js.get_stream(&responses_stream).await.map_err(|e| {
         Error::new(
             ErrorCode::InternalError.into(),
@@ -154,7 +153,7 @@ where
 
     let mut headers = async_nats::HeaderMap::new();
     headers.insert(REQ_ID_HEADER, req_id);
-    headers.insert(SESSION_ID_HEADER, sid);
+    headers.insert(SESSION_ID_HEADER, session_id.as_str());
 
     let prompt_subject = session::agent::PromptSubject::new(prefix, session_id);
     js.publish_with_headers(prompt_subject, headers, Bytes::from(payload_bytes))
diff --git a/rsworkspace/crates/acp-nats/src/agent/resume_session.rs b/rsworkspace/crates/acp-nats/src/agent/resume_session.rs
index 94d26e5a0..a88225c90 100644
--- a/rsworkspace/crates/acp-nats/src/agent/resume_session.rs
+++ b/rsworkspace/crates/acp-nats/src/agent/resume_session.rs
@@ -44,7 +44,7 @@ where
         .session_request::<ResumeSessionRequest, ResumeSessionResponse>(
             &subject,
             &args,
-            session_id.as_str(),
+            &session_id,
         )
         .await;
 
diff --git a/rsworkspace/crates/acp-nats/src/agent/set_session_config_option.rs b/rsworkspace/crates/acp-nats/src/agent/set_session_config_option.rs
index 5231fe146..2cb8b435d 100644
--- a/rsworkspace/crates/acp-nats/src/agent/set_session_config_option.rs
+++ b/rsworkspace/crates/acp-nats/src/agent/set_session_config_option.rs
@@ -44,7 +44,7 @@ where
         .session_request::<SetSessionConfigOptionRequest, SetSessionConfigOptionResponse>(
             &subject,
             &args,
-            session_id.as_str(),
+            &session_id,
         )
         .await;
 
diff --git a/rsworkspace/crates/acp-nats/src/agent/set_session_mode.rs b/rsworkspace/crates/acp-nats/src/agent/set_session_mode.rs
index 0585ce7bf..1587dc609 100644
--- a/rsworkspace/crates/acp-nats/src/agent/set_session_mode.rs
+++ b/rsworkspace/crates/acp-nats/src/agent/set_session_mode.rs
@@ -44,7 +44,7 @@ where
         .session_request::<SetSessionModeRequest, SetSessionModeResponse>(
             &subject,
             &args,
-            session_id.as_str(),
+            &session_id,
         )
         .await;
 
diff --git a/rsworkspace/crates/acp-nats/src/agent/set_session_model.rs b/rsworkspace/crates/acp-nats/src/agent/set_session_model.rs
index 8189b1515..f281a7144 100644
--- a/rsworkspace/crates/acp-nats/src/agent/set_session_model.rs
+++ b/rsworkspace/crates/acp-nats/src/agent/set_session_model.rs
@@ -44,7 +44,7 @@ where
         .session_request::<SetSessionModelRequest, SetSessionModelResponse>(
             &subject,
             &args,
-            session_id.as_str(),
+            &session_id,
         )
         .await;
 
diff --git a/rsworkspace/crates/acp-nats/src/jetstream/consumers.rs b/rsworkspace/crates/acp-nats/src/jetstream/consumers.rs
index 5e4a19a77..8364daaeb 100644
--- a/rsworkspace/crates/acp-nats/src/jetstream/consumers.rs
+++ b/rsworkspace/crates/acp-nats/src/jetstream/consumers.rs
@@ -2,11 +2,17 @@ use async_nats::jetstream::consumer::pull::Config;
 use async_nats::jetstream::consumer::{AckPolicy, DeliverPolicy, ReplayPolicy};
 
 use crate::acp_prefix::AcpPrefix;
+use crate::session_id::AcpSessionId;
 
-pub fn prompt_notifications_consumer(prefix: &AcpPrefix, session_id: &str, req_id: &str) -> Config {
+pub fn prompt_notifications_consumer(
+    prefix: &AcpPrefix,
+    session_id: &AcpSessionId,
+    req_id: &str,
+) -> Config {
     let pfx = prefix.as_str();
+    let sid = session_id.as_str();
     Config {
-        filter_subject: format!("{pfx}.session.{session_id}.agent.update.{req_id}"),
+        filter_subject: format!("{pfx}.session.{sid}.agent.update.{req_id}"),
         deliver_policy: DeliverPolicy::All,
         ack_policy: AckPolicy::Explicit,
         replay_policy: ReplayPolicy::Instant,
@@ -14,10 +20,15 @@ pub fn prompt_notifications_consumer(prefix: &AcpPrefix, session_id: &str, req_i
     }
 }
 
-pub fn prompt_response_consumer(prefix: &AcpPrefix, session_id: &str, req_id: &str) -> Config {
+pub fn prompt_response_consumer(
+    prefix: &AcpPrefix,
+    session_id: &AcpSessionId,
+    req_id: &str,
+) -> Config {
     let pfx = prefix.as_str();
+    let sid = session_id.as_str();
     Config {
-        filter_subject: format!("{pfx}.session.{session_id}.agent.prompt.response.{req_id}"),
+        filter_subject: format!("{pfx}.session.{sid}.agent.prompt.response.{req_id}"),
         deliver_policy: DeliverPolicy::All,
         ack_policy: AckPolicy::Explicit,
         replay_policy: ReplayPolicy::Instant,
@@ -25,10 +36,11 @@ pub fn prompt_response_consumer(prefix: &AcpPrefix, session_id: &str, req_id: &s
     }
 }
 
-pub fn response_consumer(prefix: &AcpPrefix, session_id: &str, req_id: &str) -> Config {
+pub fn response_consumer(prefix: &AcpPrefix, session_id: &AcpSessionId, req_id: &str) -> Config {
     let pfx = prefix.as_str();
+    let sid = session_id.as_str();
     Config {
-        filter_subject: format!("{pfx}.session.{session_id}.agent.response.{req_id}"),
+        filter_subject: format!("{pfx}.session.{sid}.agent.response.{req_id}"),
         deliver_policy: DeliverPolicy::All,
         ack_policy: AckPolicy::Explicit,
         replay_policy: ReplayPolicy::Instant,
@@ -57,9 +69,13 @@ mod tests {
         AcpPrefix::new(s).expect("test prefix")
     }
 
+    fn sid(s: &str) -> AcpSessionId {
+        AcpSessionId::new(s).expect("test session id")
+    }
+
     #[test]
     fn prompt_notifications_consumer_filter() {
-        let config = prompt_notifications_consumer(&p("acp"), "sess-1", "req-abc");
+        let config = prompt_notifications_consumer(&p("acp"), &sid("sess-1"), "req-abc");
         assert_eq!(
             config.filter_subject,
             "acp.session.sess-1.agent.update.req-abc"
@@ -68,7 +84,7 @@ mod tests {
 
     #[test]
     fn prompt_notifications_consumer_delivers_all() {
-        let config = prompt_notifications_consumer(&p("acp"), "s1", "r1");
+        let config = prompt_notifications_consumer(&p("acp"), &sid("s1"), "r1");
         assert_eq!(config.deliver_policy, DeliverPolicy::All);
         assert_eq!(config.ack_policy, AckPolicy::Explicit);
         assert_eq!(config.replay_policy, ReplayPolicy::Instant);
@@ -76,7 +92,7 @@ mod tests {
 
     #[test]
     fn prompt_response_consumer_filter() {
-        let config = prompt_response_consumer(&p("acp"), "sess-1", "req-abc");
+        let config = prompt_response_consumer(&p("acp"), &sid("sess-1"), "req-abc");
         assert_eq!(
             config.filter_subject,
             "acp.session.sess-1.agent.prompt.response.req-abc"
@@ -98,7 +114,7 @@ mod tests {
 
     #[test]
     fn response_consumer_filter() {
-        let config = response_consumer(&p("acp"), "sess-1", "req-abc");
+        let config = response_consumer(&p("acp"), &sid("sess-1"), "req-abc");
         assert_eq!(
             config.filter_subject,
             "acp.session.sess-1.agent.response.req-abc"
@@ -107,7 +123,7 @@ mod tests {
 
     #[test]
     fn response_consumer_delivers_all() {
-        let config = response_consumer(&p("acp"), "s1", "r1");
+        let config = response_consumer(&p("acp"), &sid("s1"), "r1");
         assert_eq!(config.deliver_policy, DeliverPolicy::All);
         assert_eq!(config.ack_policy, AckPolicy::Explicit);
         assert_eq!(config.replay_policy, ReplayPolicy::Instant);
@@ -115,13 +131,13 @@ mod tests {
 
     #[test]
     fn response_consumer_custom_prefix() {
-        let config = response_consumer(&p("myapp"), "s1", "r1");
+        let config = response_consumer(&p("myapp"), &sid("s1"), "r1");
         assert_eq!(config.filter_subject, "myapp.session.s1.agent.response.r1");
     }
 
     #[test]
     fn custom_prefix_in_consumers() {
-        let config = prompt_response_consumer(&p("myapp"), "s1", "r1");
+        let config = prompt_response_consumer(&p("myapp"), &sid("s1"), "r1");
         assert_eq!(
             config.filter_subject,
             "myapp.session.s1.agent.prompt.response.r1"