figterm paste handler panics with non-UTF-8 input (from_utf8_lossy length mismatch)

[malikdraz]

Bug

The figterm paste handler in crates/figterm/src/input/mod.rs panics when pasting content with bytes that are not valid UTF-8:

thread 'kiro-cli-term-runtime-worker-7' panicked at crates/figterm/src/input/mod.rs:1774:56:
range end index 2258 out of range for slice of length 2256

This is a re-report of #2002 which was closed without a fix. The figterm crate was removed from this repo but the bug persists in downstream consumers (Kiro CLI v0.10.32).

Root Cause

In process_bytes, the Pasting state handler computes bytes to advance using pasted.len() (the byte length of the lossy-converted UTF-8 string) instead of idx (the raw byte offset returned by find_subsequence):

let pasted = String::from_utf8_lossy(&self.buf.as_slice()[0..idx]).to_string();
self.advance_buf(pasted.len() + end_paste.len());  // BUG: pasted.len() >= idx

String::from_utf8_lossy replaces each invalid byte with U+FFFD (3 UTF-8 bytes), so pasted.len() can exceed idx, causing advance_buf to slice out-of-bounds.

Fix

self.advance_buf(idx + end_paste.len());

Use the raw byte offset idx for buffer arithmetic. The lossy conversion is only needed for the event payload.