Make NNUE eval the default, same convention as the EGTB path default

main.c's InitializeOptions now tries to load "eval.nnue" (a file next
to the binary, matching typhoon_nnue's own NNUE_WEIGHTS default --
typically a symlink into head_reference/nnue/current/weights.nnue)
after argument parsing, if the user hasn't already enabled NNUE
explicitly via --nnueweights or an interactive "nnue load"/"nnue on".
Same hardcoded-default-path convention main.c already uses for
--egtbpath (/zscratch/egtb).

Fails soft: a checkout without eval.nnue present, or one where it
fails to load, just falls back to HCE eval exactly as before -- this
is a default, not a requirement, so there's no UtilPanic the way
--nnueweights's own explicit-request failure path has. The existing
interactive "nnue off" command remains the way to explicitly opt back
out of NNUE for a given session; a script that wants guaranteed HCE
(e.g. an apples-to-apples eval comparison) should add "nnue off;" to
its own --command string rather than relying on the old no-flag
default.

Verified: clean release build, clean DEBUG=1 TEST=1 self-test run (no
assertion failures), and manually confirmed both the default-load path
(eval.nnue present in cwd) and the silent-fallback path (run from a
directory without it) behave as expected; --nnueweights still works
unchanged.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

1 files changed, 26 insertions, 0 deletions

diff --git a/src/main.c b/src/main.c
index 2f5428e..73b3758 100644
--- a/src/main.c
+++ b/src/main.c
@@ -521,6 +521,32 @@ Return value:
 
         i++;
     }
+
+    // 2026-10-25: NNUE is now the default evaluator, same convention
+    // as szEGTBPath's hardcoded /zscratch/egtb default above -- try to
+    // load a weights file sitting next to the binary (matching
+    // typhoon_nnue's own NNUE_WEIGHTS default) if the user didn't
+    // already enable NNUE explicitly via --nnueweights or an
+    // interactive "nnue load"/"nnue on". Fails soft: a checkout
+    // without eval.nnue present (or a bad/missing file) just falls
+    // back to HCE, exactly like it always did -- this is a default,
+    // not a requirement, so there's no UtilPanic here the way
+    // --nnueweights's own explicit-request failure path has.
+    if ((FALSE == g_fUseNnueEval) &&
+        (TRUE == SystemDoesFileExist("eval.nnue")))
+    {
+        if (NnueLoadWeights("eval.nnue"))
+        {
+            g_fUseNnueEval = TRUE;
+            Trace("Loaded default NNUE weights \"eval.nnue\", "
+                  "NNUE eval enabled.\n");
+        }
+        else
+        {
+            Trace("Found \"eval.nnue\" but failed to load it; "
+                  "falling back to HCE eval.\n");
+        }
+    }
 }