fix: harden subprocess output decoding across lessons

s07_skill_loading/code.py

@@ -138,24 +138,14 @@ SYSTEM = build_system_prompt()
 
 # -- Tools --
 
-# s07: Fix Windows subprocess encoding crash (fallback UTF-8 -> GBK with error replacement)
-def safe_decode(data: bytes) -> str:
-    if not data:
-        return ""
-    try:
-        return data.decode('utf-8')
-    except UnicodeDecodeError:
-        return data.decode('gbk')
-
-
 def run_bash(command: str) -> str:
     try:
-        r = subprocess.run(command, shell=True, cwd=WORKDIR,
-                           capture_output=True, timeout=120)
-        stdout = safe_decode(r.stdout)
-        stderr = safe_decode(r.stderr)
-        out = (stdout + stderr).strip()
-        return out[:50000] if out else "(no output)"
+        result = subprocess.run(
+            command, shell=True, cwd=WORKDIR,
+            capture_output=True, text=True, errors="replace", timeout=120,
+        )
+        output = (result.stdout + result.stderr).strip()
+        return output[:50000] if output else "(no output)"
     except subprocess.TimeoutExpired:
         return "Error: Timeout (120s)"