Add SGLANG_CRASH_ON_JIT_COMPILE to forbid on-the-fly JIT compilation (#36615)

Signed-off-by: Shiyan Deng <dsy842974287@meta.com>
Co-authored-by: Lianmin Zheng <lianminzheng@gmail.com>

python/sglang/srt/environ.py

@@ -1095,6 +1095,10 @@ class Envs:
     # is what makes reverting an edit an instant hit instead of a rebuild; set
     # it to trade that away for disk (1 keeps only the most recent build).
     SGLANG_JIT_CACHE_KEEP = EnvInt(None)
+    # Raise instead of compiling when a module misses the cache, so a
+    # deployment that expects a pre-seeded cache fails loudly at startup
+    # rather than silently eating a cold compile.
+    SGLANG_CRASH_ON_JIT_COMPILE = EnvBool(False)
 
     # ===================================================================
     # Expert-parallel dispatch and MoE execution