diff --git a/cli/src/main.rs b/cli/src/main.rs
index 339005036eea2b7c0f98ab9b3007854de8ffaf2c..eff3e415a7995378b3286efd5af06a1259d0ef45 100644
--- a/cli/src/main.rs
+++ b/cli/src/main.rs
@@ -585,29 +585,35 @@ fn print_thread(resp: &ThreadDetailResponse) {
         );
     }
     for (i, item) in resp.items.iter().enumerate() {
-        match item {
+        let xml = match item {
             ThreadItem::Post {
                 index,
                 ts,
+                actor,
+                delegate,
                 body,
                 ..
-            } => {
-                let timeago = slug_types::timeago::timeago_compact(now_ms, *ts);
-                let body = body.trim();
-                println!("<post index=\"{index}\" timeago=\"{timeago}\">");
-                println!("{body}");
-                println!("</post>");
-            }
+            } => slug_types::thread_xml::format_post_at(
+                now_ms,
+                *index,
+                *ts,
+                actor,
+                delegate.as_deref(),
+                body,
+            ),
             ThreadItem::System { ts, text } => {
                 let timeago = slug_types::timeago::timeago_compact(now_ms, *ts);
-                println!("<system timeago=\"{}\">{}</system>", timeago, text.trim());
+                slug_types::thread_xml::format_system(&timeago, text)
             }
-        }
+        };
+        print!("{xml}");
         if i + 1 < resp.items.len() {
-            println!();
-            println!();
+            print!("{}", slug_types::thread_xml::ITEM_SEPARATOR);
         }
     }
+    if !resp.items.is_empty() {
+        println!();
+    }
 }
 
 /// Parse a Unix ms timestamp or YYYY-MM-DD date string to ms since epoch.
diff --git a/server/src/api/rpc.rs b/server/src/api/rpc.rs
index a0f8ee1d658bdba4d2168e5198c1104918b3575d..0b7070a2b7289e5c40778c8d062bd4150285a8df 100644
--- a/server/src/api/rpc.rs
+++ b/server/src/api/rpc.rs
@@ -478,6 +478,7 @@ fn rpc_forum_thread_detail(
                         index: idx,
                         ts: ing.ts,
                         actor: ing.principal.clone(),
+                        delegate: ing.delegate.clone(),
                         body: if redacted { String::new() } else { ing.raw.clone() },
                         truncated: false,
                         redacted,
@@ -538,6 +539,7 @@ fn rpc_forum_thread_detail(
                 index: idx,
                 ts: ing.ts,
                 actor: ing.principal.clone(),
+                delegate: ing.delegate.clone(),
                 body,
                 truncated,
                 redacted,
diff --git a/server/src/html/forum/copy.rs b/server/src/html/forum/copy.rs
index 29057c68856cea85106e9f911a8d9466eedfc870..4c878921a51e23ff4fdf1bc28037847f69098876 100644
--- a/server/src/html/forum/copy.rs
+++ b/server/src/html/forum/copy.rs
@@ -3,7 +3,7 @@ use crate::form_template::template_json_compact;
 use crate::reducer::{scope_from_room_wire, ReducerState, ScopeId};
 use crate::state::AppState;
 use maud::{html, Markup};
-use slug_types::timeago::timeago_compact;
+use slug_types::thread_xml;
 
 use super::access::user_can_view_room;
 use super::ingest::thread_ui_fetch_onclick;
@@ -11,7 +11,7 @@ use super::nav::ThreadNav;
 use crate::html::ui_action::HtmlUiAction;
 use crate::html::{JsBuilder, now_ms};
 
-/// CLI `forum show` text (`print_thread` in `cli/src/main.rs`).
+/// CLI `forum show` and browser copy-thread text (`slug_types::thread_xml`).
 pub(crate) fn format_thread_cli_text(
     reduced: &ReducerState,
     scope: &ScopeId,
@@ -32,19 +32,22 @@ pub(crate) fn format_thread_cli_text(
             continue;
         };
         if i > 0 {
-            out.push_str("\n\n\n");
+            out.push_str(thread_xml::ITEM_SEPARATOR);
         }
-        let index = i;
-        let timeago = timeago_compact(now_ms, ing.ts);
         let redacted = reduced.redacted_posts.contains(&ing.id);
         let body = if redacted {
             String::new()
         } else {
             ing.raw.trim().to_string()
         };
-        out.push_str(&format!("<post index=\"{index}\" timeago=\"{timeago}\">\n"));
-        out.push_str(&body);
-        out.push_str("\n</post>");
+        out.push_str(&thread_xml::format_post_at(
+            now_ms,
+            i,
+            ing.ts,
+            &ing.principal,
+            ing.delegate.as_deref(),
+            &body,
+        ));
     }
     out
 }
diff --git a/types/src/lib.rs b/types/src/lib.rs
index d747e509094d75124573f252ee4b6c73186b4c24..0a6f7c2cd9acbb83acb9b3d9db629e6b9603dd8b 100644
--- a/types/src/lib.rs
+++ b/types/src/lib.rs
@@ -5,6 +5,7 @@ pub mod item_wire;
 pub mod item_id;
 pub mod paths;
 pub mod timeago;
+pub mod thread_xml;
 
 pub use item_id::ItemId;
 pub use item_wire::{
@@ -163,6 +164,9 @@ pub enum ThreadItem {
         index: usize,
         ts: i64,
         actor: String,
+        /// Agent delegate (`uuid:rig:provider/model`) when present; omitted in JSON when absent.
+        #[serde(default, skip_serializing_if = "Option::is_none")]
+        delegate: Option<String>,
         body: String,
         truncated: bool,
         /// Author redacted this post; body is empty and garden contributions were removed.
diff --git a/types/src/thread_xml.rs b/types/src/thread_xml.rs
new file mode 100644
index 0000000000000000000000000000000000000000..e7b42646de727c7660793b83fff3fef0403797be
--- /dev/null
+++ b/types/src/thread_xml.rs
@@ -0,0 +1,110 @@
+//! Thread timeline as XML for CLI `forum show` and browser copy-thread.
+
+use crate::timeago::timeago_compact;
+
+/// Blank line block between consecutive thread rows in CLI / copy output.
+pub const ITEM_SEPARATOR: &str = "\n\n\n";
+
+fn escape_xml_attr(s: &str) -> String {
+    let mut out = String::with_capacity(s.len());
+    for c in s.chars() {
+        match c {
+            '&' => out.push_str("&amp;"),
+            '"' => out.push_str("&quot;"),
+            '<' => out.push_str("&lt;"),
+            _ => out.push(c),
+        }
+    }
+    out
+}
+
+/// Opening tag for one forum post (body omitted).
+pub fn post_open_tag(
+    index: usize,
+    timeago: &str,
+    principal: &str,
+    delegate: Option<&str>,
+) -> String {
+    let delegate_attr = delegate.unwrap_or("");
+    format!(
+        "<post index=\"{}\" timeago=\"{}\" principal=\"{}\" delegate=\"{}\">",
+        index,
+        escape_xml_attr(timeago),
+        escape_xml_attr(principal),
+        escape_xml_attr(delegate_attr),
+    )
+}
+
+/// One forum post element: opening tag, trimmed body, closing tag.
+pub fn format_post(
+    index: usize,
+    timeago: &str,
+    principal: &str,
+    delegate: Option<&str>,
+    body: &str,
+) -> String {
+    format!(
+        "{}\n{}\n</post>",
+        post_open_tag(index, timeago, principal, delegate),
+        body.trim(),
+    )
+}
+
+/// One room system line in thread XML.
+pub fn format_system(timeago: &str, text: &str) -> String {
+    format!(
+        "<system timeago=\"{}\">{}</system>",
+        escape_xml_attr(timeago),
+        text.trim(),
+    )
+}
+
+/// Format a post row using wall-clock `now_ms` for the `timeago` attribute.
+pub fn format_post_at(
+    now_ms: i64,
+    index: usize,
+    ts: i64,
+    principal: &str,
+    delegate: Option<&str>,
+    body: &str,
+) -> String {
+    let timeago = timeago_compact(now_ms, ts);
+    format_post(index, &timeago, principal, delegate, body)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn post_includes_principal_and_delegate() {
+        let xml = format_post(
+            2,
+            "1h2m3s",
+            "alice",
+            Some("00000000-0000-0000-0000-000000000000:test:local/dev"),
+            "hello\n",
+        );
+        assert!(xml.starts_with(
+            "<post index=\"2\" timeago=\"1h2m3s\" principal=\"alice\" delegate=\"00000000-0000-0000-0000-000000000000:test:local/dev\">"
+        ));
+        assert!(xml.ends_with("\nhello\n</post>"));
+    }
+
+    #[test]
+    fn post_empty_delegate_when_human() {
+        let xml = format_post(0, "5s", "bob", None, "hi");
+        assert!(xml.starts_with(
+            "<post index=\"0\" timeago=\"5s\" principal=\"bob\" delegate=\"\">"
+        ));
+    }
+
+    #[test]
+    fn escapes_attribute_values() {
+        let xml = post_open_tag(0, "1s", "a&b", Some("d\"q"));
+        assert_eq!(
+            xml,
+            "<post index=\"0\" timeago=\"1s\" principal=\"a&amp;b\" delegate=\"d&quot;q\">"
+        );
+    }
+}