Restructure refimpl into go-lang and python subdirectories

Move Go reference implementation to refimpl/go-lang/ and add new
Python reference implementation in refimpl/python/. Update build.sh
with renamed draft and simplified tool paths.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

refimpl/python/ect/config.py

@@ -0,0 +1,61 @@
+"""Production config from environment."""
+
+from __future__ import annotations
+
+import os
+from dataclasses import dataclass
+
+ENV_IAT_MAX_AGE_MINUTES = "ECT_IAT_MAX_AGE_MINUTES"
+ENV_IAT_MAX_FUTURE_SEC = "ECT_IAT_MAX_FUTURE_SEC"
+ENV_DEFAULT_EXPIRY_MIN = "ECT_DEFAULT_EXPIRY_MIN"
+ENV_JTI_REPLAY_CACHE_SIZE = "ECT_JTI_REPLAY_CACHE_SIZE"
+ENV_JTI_REPLAY_TTL_MIN = "ECT_JTI_REPLAY_TTL_MIN"
+
+
+@dataclass
+class Config:
+    iat_max_age_sec: int = 900
+    iat_max_future_sec: int = 30
+    default_expiry_sec: int = 600
+    jti_replay_size: int = 0
+    jti_replay_ttl_sec: int = 3600
+
+    def create_options(self, key_id: str) -> "CreateOptions":
+        from ect.create import CreateOptions
+        return CreateOptions(
+            key_id=key_id,
+            default_expiry_sec=self.default_expiry_sec,
+        )
+
+    def verify_options(self) -> "VerifyOptions":
+        from ect.verify import VerifyOptions
+        from ect.dag import default_dag_config
+        return VerifyOptions(
+            iat_max_age_sec=self.iat_max_age_sec,
+            iat_max_future_sec=self.iat_max_future_sec,
+            dag=default_dag_config(),
+        )
+
+
+def default_config() -> Config:
+    return Config()
+
+
+def _int_env(name: str, default: int) -> int:
+    v = os.environ.get(name)
+    if v is None or v == "":
+        return default
+    try:
+        return int(v)
+    except ValueError:
+        return default
+
+
+def load_config_from_env() -> Config:
+    c = default_config()
+    c.iat_max_age_sec = _int_env(ENV_IAT_MAX_AGE_MINUTES, 15) * 60
+    c.iat_max_future_sec = _int_env(ENV_IAT_MAX_FUTURE_SEC, 30)
+    c.default_expiry_sec = _int_env(ENV_DEFAULT_EXPIRY_MIN, 10) * 60
+    c.jti_replay_size = _int_env(ENV_JTI_REPLAY_CACHE_SIZE, 0)
+    c.jti_replay_ttl_sec = _int_env(ENV_JTI_REPLAY_TTL_MIN, 60) * 60
+    return c