[nexxeln]

Follow-up to #43 | Stack: #46 ← #47

Why the change

The stderr tail attached to RPC failures is cut to its last 8 KiB by bytes, so a failure message could start with a stray � where the cut split a multi-byte character.

Special things to note

• Stacked on fix(opencode): settle RPCs when Rift exits, not when stderr closes #46. Merge that first.
• Test abort signals go from 1.5 s to 3 s, and the three-call regression test gets a 15 s budget. The old limits included a cold node start and timed out now and then under load.

Change outline

The tail is still cut by bytes. When it's formatted, any leading UTF-8 continuation bytes (10xxxxxx) are skipped, so the message starts on a whole character.

 describe(message)
+  skip leading bytes where (byte & 0xc0) === 0x80
   detail = tail.toString().trim()
   return detail ? `${message}: ${detail}` : message