story-kit: start 192_bug_code_fences_lose_newlines_when_pasted_from_agent_output

.story_kit/work/2_current/192_bug_code_fences_lose_newlines_when_pasted_from_agent_output.md

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+---
+name: "Code fences lose newlines when pasted from agent output"
+---
+
+# Bug 192: Code fences lose newlines when pasted from agent output
+
+## Description
+
+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
+2. The function `mentions_bot()` from the matrix bot module was used as the test case
+3. Observe the rendered output in Matrix
+
+## Actual Result
+
+The first portion of the code block renders with proper newlines, but partway through (around the `let short = format!(...)` line), all remaining lines collapse into a single line with no line breaks.
+
+## Expected Result
+
+The entire code block should render with proper newlines preserved, matching the original source formatting.
+
+## Acceptance Criteria
+
+- [ ] Code fences with multi-line content preserve all newlines when sent through the Matrix bot interface
+- [ ] Verify the issue is not a Matrix client rendering bug vs. a message sending bug (inspect the raw message content)