Disable kernel tracing stack

custom/modules/default.nix

@@ -114,13 +114,13 @@
             #
             GOOGLE_FIRMWARE = lib.mkForce no;
             #
-            TRACING = no;
-            FUNCTION_GRAPH_TRACER = no;
-            DYNAMIC_FTRACE = no;
-            #
+            TRACING = lib.mkForce no;
             FTRACE = lib.mkForce no;
+            FUNCTION_GRAPH_TRACER = lib.mkForce no;
+            DYNAMIC_FTRACE = lib.mkForce no;
             FUNCTION_PROFILER = lib.mkForce no;
             FUNCTION_TRACER = lib.mkForce no;
+            CONTEXT_SWITCH_TRACER = lib.mkForce no;
             SCHED_TRACER = lib.mkForce no;
             STACK_TRACER = lib.mkForce no;
           }

todo.md

@@ -27,6 +27,7 @@
 - The custom kernel helper now normalizes config-only `kernelPatches` entries to `{ patch = null; ... }` before calling `buildLinux`, which fixes `devenv shell -- build` failing during kernel evaluation.
 - The kernel build does invoke `sccache` during live builds, but relying on the in-sandbox wrapper to create `/var/cache/sccache/nix-builds/kernel` made host-side observation ambiguous.
 - The host NixOS config should create and expose `/var/cache/sccache/nix-builds/{packages,kernel}` explicitly so sandboxed builds and host-side inspection see the same cache paths.
+- The kernel `fentry` failure was caused by tracing options being enabled indirectly. Forcing `TRACING`, `FTRACE`, `FUNCTION_TRACER`, `FUNCTION_GRAPH_TRACER`, `DYNAMIC_FTRACE`, `FUNCTION_PROFILER`, `CONTEXT_SWITCH_TRACER`, `SCHED_TRACER`, and `STACK_TRACER` to `no` got the build past the old `Compiler does not support fentry?` stop and into real kernel compilation.
 
 ## Next Checks
 
@@ -38,3 +39,4 @@
 - The same helper may also be needed on the outer package if the subpackage is fixed but the wrapper package then stalls at its own CMake configure.
 - Run a minimal hello-world derivation with the new `sccacheStdenv` and confirm repeated compiles produce cache hits.
 - If that works, switch current consumers to the ccache-style path and remove obsolete wrapper-patching logic.
+- After the host Nix daemon picks up the new sandbox path config, re-check kernel cache growth under `/var/cache/sccache/nix-builds/kernel` during a bounded kernel build.