fix: prevent UTF-8 corruption when RTK truncation splits multi-byte codepoints (FAR-19)

The trunc function in the RTK filter script now walks back from the
truncation point past continuation bytes and checks whether the full
codepoint fits, avoiding replacement characters from mid-codepoint slicing.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/server/job-manifest.ts

@@ -47,7 +47,8 @@ export function buildRtkSetupCommands(maxOutputBytes: number): string {
     `if(typeof s!=='string')return s;`,
     `const b=Buffer.from(s,'utf-8');`,
     `if(b.length<=MAX)return s;`,
-    `return b.slice(0,MAX).toString('utf-8')+'\\n[...'+(b.length-MAX)+' bytes truncated by paperclip-rtk]';`,
+    `let e=MAX;if(e>0){let p=e-1;while(p>0&&(b[p]&0xC0)===0x80)p--;const l=b[p];let n=1;if((l&0xE0)===0xC0)n=2;else if((l&0xF0)===0xE0)n=3;else if((l&0xF8)===0xF0)n=4;if(p+n>e)e=p;}`,
+    `return b.slice(0,e).toString('utf-8')+'\\n[...'+(b.length-e)+' bytes truncated by paperclip-rtk]';`,
     `}`,
     `const tr=o&&(o.tool_response||o.tool_result);`,
     `if(tr){`,