story-kit: create 192_bug_code_fences_lose_newlines_when_pasted_from_agent_output

.story_kit/work/1_upcoming/192_bug_code_fences_lose_newlines_when_pasted_from_agent_output.md

@@ -8,6 +8,44 @@ name: "Code fences lose newlines when pasted from agent output"
 
 When the assistant pastes a multi-line Rust function using a fenced code block, the second half of the code loses its line breaks and renders as a single long line. This has been reproduced twice in the Matrix chat interface.
 
+Here is the function that the Matrix claude instance was asked to format in chat: 
+
+```rust
+pub fn mentions_bot(body: &str, bot_user_id: &OwnedUserId) -> bool {
+    let full_id = bot_user_id.as_str();
+    if body.contains(full_id) {
+        return true;
+    }
+
+    let short = format!("@{}", bot_user_id.localpart());
+    let mut start = 0;
+    while let Some(rel) = body[start..].find(short.as_str()) {
+        let abs = start + rel;
+        let after = abs + short.len();
+        let next = body[after..].chars().next();
+        let is_word_end =
+            next.is_none_or(|c| !c.is_alphanumeric() && c != '-' && c != '_');
+        if is_word_end {
+            return true;
+        }
+        start = abs + 1;
+    }
+    false
+}
+```
+
+This part rendered fine: 
+
+```rust
+pub fn mentions_bot(body: &str, bot_user_id: &OwnedUserId) -> bool {
+    let full_id = bot_user_id.as_str();
+    if body.contains(full_id) {
+        return true;
+    }
+```
+
+however everything after that (starting with the newline) came out non-formatted and garbled. 
+
 ## How to Reproduce
 
 1. Ask the assistant to paste a multi-line Rust function in a fenced code block