diff --git a/server/src/chat/timer.rs b/server/src/chat/timer.rs
index 4525b33f..61b43ae3 100644
--- a/server/src/chat/timer.rs
+++ b/server/src/chat/timer.rs
@@ -483,10 +483,8 @@ fn strip_mention<'a>(message: &'a str, bot_name: &str, bot_user_id: &str) -> &'a
 }
 
 fn strip_prefix_ci<'a>(text: &'a str, prefix: &str) -> Option<&'a str> {
-    if text.len() < prefix.len() {
-        return None;
-    }
-    if !text[..prefix.len()].eq_ignore_ascii_case(prefix) {
+    let candidate = text.get(..prefix.len())?;
+    if !candidate.eq_ignore_ascii_case(prefix) {
         return None;
     }
     let rest = &text[prefix.len()..];
diff --git a/server/src/chat/transport/matrix/assign.rs b/server/src/chat/transport/matrix/assign.rs
index 2313e790..ce598b32 100644
--- a/server/src/chat/transport/matrix/assign.rs
+++ b/server/src/chat/transport/matrix/assign.rs
@@ -254,10 +254,8 @@ fn strip_mention<'a>(message: &'a str, bot_name: &str, bot_user_id: &str) -> &'a
 }
 
 fn strip_prefix_ci<'a>(text: &'a str, prefix: &str) -> Option<&'a str> {
-    if text.len() < prefix.len() {
-        return None;
-    }
-    if !text[..prefix.len()].eq_ignore_ascii_case(prefix) {
+    let candidate = text.get(..prefix.len())?;
+    if !candidate.eq_ignore_ascii_case(prefix) {
         return None;
     }
     let rest = &text[prefix.len()..];
@@ -354,6 +352,18 @@ mod tests {
         assert_eq!(cmd, None);
     }
 
+    #[test]
+    fn extract_assign_command_multibyte_prefix_no_panic() {
+        // "xxxx⏺ assign 42 opus" — ⏺ (U+23FA) is 3 bytes, starting at byte 4.
+        // "@timmy" has len 6 so text[..6] lands inside ⏺ — panics without the fix.
+        let cmd = extract_assign_command(
+            "xxxx\u{23FA} assign 42 opus",
+            "Timmy",
+            "@timmy:home.local",
+        );
+        assert_eq!(cmd, None);
+    }
+
     // -- resolve_agent_name --------------------------------------------------
 
     #[test]
diff --git a/server/src/chat/transport/matrix/delete.rs b/server/src/chat/transport/matrix/delete.rs
index 4b990156..7e1a94ef 100644
--- a/server/src/chat/transport/matrix/delete.rs
+++ b/server/src/chat/transport/matrix/delete.rs
@@ -206,10 +206,8 @@ fn strip_mention<'a>(message: &'a str, bot_name: &str, bot_user_id: &str) -> &'a
 }
 
 fn strip_prefix_ci<'a>(text: &'a str, prefix: &str) -> Option<&'a str> {
-    if text.len() < prefix.len() {
-        return None;
-    }
-    if !text[..prefix.len()].eq_ignore_ascii_case(prefix) {
+    let candidate = text.get(..prefix.len())?;
+    if !candidate.eq_ignore_ascii_case(prefix) {
         return None;
     }
     let rest = &text[prefix.len()..];
diff --git a/server/src/chat/transport/matrix/htop.rs b/server/src/chat/transport/matrix/htop.rs
index 243c971c..98226df9 100644
--- a/server/src/chat/transport/matrix/htop.rs
+++ b/server/src/chat/transport/matrix/htop.rs
@@ -110,10 +110,8 @@ fn strip_mention<'a>(message: &'a str, bot_name: &str, bot_user_id: &str) -> &'a
 }
 
 fn strip_prefix_ci<'a>(text: &'a str, prefix: &str) -> Option<&'a str> {
-    if text.len() < prefix.len() {
-        return None;
-    }
-    if !text[..prefix.len()].eq_ignore_ascii_case(prefix) {
+    let candidate = text.get(..prefix.len())?;
+    if !candidate.eq_ignore_ascii_case(prefix) {
         return None;
     }
     let rest = &text[prefix.len()..];
diff --git a/server/src/chat/transport/matrix/rebuild.rs b/server/src/chat/transport/matrix/rebuild.rs
index 9da471d3..bec3627a 100644
--- a/server/src/chat/transport/matrix/rebuild.rs
+++ b/server/src/chat/transport/matrix/rebuild.rs
@@ -74,10 +74,8 @@ fn strip_mention<'a>(message: &'a str, bot_name: &str, bot_user_id: &str) -> &'a
 }
 
 fn strip_prefix_ci<'a>(text: &'a str, prefix: &str) -> Option<&'a str> {
-    if text.len() < prefix.len() {
-        return None;
-    }
-    if !text[..prefix.len()].eq_ignore_ascii_case(prefix) {
+    let candidate = text.get(..prefix.len())?;
+    if !candidate.eq_ignore_ascii_case(prefix) {
         return None;
     }
     let rest = &text[prefix.len()..];
diff --git a/server/src/chat/transport/matrix/reset.rs b/server/src/chat/transport/matrix/reset.rs
index afe5c936..cca78812 100644
--- a/server/src/chat/transport/matrix/reset.rs
+++ b/server/src/chat/transport/matrix/reset.rs
@@ -76,10 +76,8 @@ fn strip_mention<'a>(message: &'a str, bot_name: &str, bot_user_id: &str) -> &'a
 }
 
 fn strip_prefix_ci<'a>(text: &'a str, prefix: &str) -> Option<&'a str> {
-    if text.len() < prefix.len() {
-        return None;
-    }
-    if !text[..prefix.len()].eq_ignore_ascii_case(prefix) {
+    let candidate = text.get(..prefix.len())?;
+    if !candidate.eq_ignore_ascii_case(prefix) {
         return None;
     }
     let rest = &text[prefix.len()..];
diff --git a/server/src/chat/transport/matrix/rmtree.rs b/server/src/chat/transport/matrix/rmtree.rs
index 8baf632e..867dbff5 100644
--- a/server/src/chat/transport/matrix/rmtree.rs
+++ b/server/src/chat/transport/matrix/rmtree.rs
@@ -136,10 +136,8 @@ fn strip_mention<'a>(message: &'a str, bot_name: &str, bot_user_id: &str) -> &'a
 }
 
 fn strip_prefix_ci<'a>(text: &'a str, prefix: &str) -> Option<&'a str> {
-    if text.len() < prefix.len() {
-        return None;
-    }
-    if !text[..prefix.len()].eq_ignore_ascii_case(prefix) {
+    let candidate = text.get(..prefix.len())?;
+    if !candidate.eq_ignore_ascii_case(prefix) {
         return None;
     }
     let rest = &text[prefix.len()..];
diff --git a/server/src/chat/transport/matrix/start.rs b/server/src/chat/transport/matrix/start.rs
index 683b176a..b2362bdc 100644
--- a/server/src/chat/transport/matrix/start.rs
+++ b/server/src/chat/transport/matrix/start.rs
@@ -197,10 +197,8 @@ fn strip_mention<'a>(message: &'a str, bot_name: &str, bot_user_id: &str) -> &'a
 }
 
 fn strip_prefix_ci<'a>(text: &'a str, prefix: &str) -> Option<&'a str> {
-    if text.len() < prefix.len() {
-        return None;
-    }
-    if !text[..prefix.len()].eq_ignore_ascii_case(prefix) {
+    let candidate = text.get(..prefix.len())?;
+    if !candidate.eq_ignore_ascii_case(prefix) {
         return None;
     }
     let rest = &text[prefix.len()..];