panic: byte index out of bounds in chat response rendering when response contains triple backticks

[sandikodev]

Bug Report

Version: kiro-cli 1.25.1
OS: Debian GNU/Linux 12 (bookworm), kernel 6.1.0-44-amd64, x86_64
Install method: Official install script from kiro.dev (curl)
Binary location: /home/dev/.local/bin/kiro-cli

Description

The application panics with a byte index out of bounds error when the AI response contains triple backticks (```````) in the rendered output.

Steps to Reproduce

1. Start a chat session: kiro-cli chat
2. Ask a question that causes the AI to respond with a message containing triple backticks (e.g., a code block or a message referencing backtick syntax)
3. The application crashes mid-response

Panic Output

The application panicked (crashed).
Message:  byte index 536 is out of bounds of `...`[...]
Location: crates/chat-cli/src/cli/chat/mod.rs:3849

Root Cause Analysis

In crates/chat-cli/src/cli/chat/mod.rs, the response rendering loop uses a byte offset to track parsing progress:

let input = Partial::new(&buf[offset..]);
// ...
offset += parsed.offset_from(&input);

parsed.offset_from(&input) returns a byte count relative to the input slice. This is accumulated into offset, which is used as a byte index into buf. When buf contains multi-byte UTF-8 characters (e.g., non-ASCII text, emoji, or characters adjacent to triple backticks), the accumulated offset can land in the middle of a multi-byte character boundary, causing the panic on the next iteration when &buf[offset..] is evaluated.

Suggested Fix

Validate that offset falls on a valid UTF-8 character boundary before slicing, or use buf.get(offset..) which returns None instead of panicking:

// Instead of:
let input = Partial::new(&buf[offset..]);

// Use:
let Some(slice) = buf.get(offset..) else { break };
let input = Partial::new(slice);

Alternatively, ensure offset is always advanced using ceil_char_boundary or equivalent to stay on valid UTF-8 boundaries.

Additional Context

This panic is reproducible when the AI response includes triple backticks in its text content (not just code blocks), particularly when the surrounding text contains non-ASCII characters.