fix(env): keep the batch-size constant reachable without pulling in PyYAML

ac5e7d54c4 removed a duplicated literal by having the tuning handler take
BATCH_SIZE from the client that owns it. That import walks straight out of the
stdlib:

  handlers/__init__ -> i18n/tuning -> client -> languages -> cache.yaml -> yaml

and the .env generator runs on the bare bootstrap python, before any dependency
is installed. The client needs SOURCE_LANGUAGE from the language table, so it
can never satisfy that contract itself.

The constant moves into a module with no imports of its own, which the handler
README names as the allowed shape: a handler may import any repo module whose
own closure is stdlib-only. Both the client and the handler read it from there,
so the literal still exists once.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

utils/env/handlers/infinito/i18n/tuning.py

@@ -7,7 +7,7 @@ import json
 from pathlib import Path
 from typing import TYPE_CHECKING
 
-from utils.i18n.client import BATCH_SIZE
+from utils.i18n.limits import BATCH_SIZE
 
 if TYPE_CHECKING:
     from utils.env.builder import BuildContext, EnvBuilder

utils/i18n/client.py

@@ -16,13 +16,13 @@ from dataclasses import dataclass
 from typing import TYPE_CHECKING
 
 from utils.i18n.languages import SOURCE_LANGUAGE
+from utils.i18n.limits import BATCH_SIZE
 from utils.i18n.placeholders import has_words, mask, unmask
 
 if TYPE_CHECKING:
     from collections.abc import Iterable
 
 SERVER_CODES = {"zh": "zh-Hans"}
-BATCH_SIZE = 20
 POLL_SECONDS = 5
 REQUEST_TIMEOUT_SECONDS = 600
 RETRY_ATTEMPTS = 4

utils/i18n/limits.py

@@ -0,0 +1,10 @@
+"""Client limits the env generator and the translator must agree on.
+
+They live apart from the client itself because the generator runs on the bare
+bootstrap interpreter: importing the client would pull in the language table and
+with it a YAML parser the generator is not allowed to need.
+"""
+
+from __future__ import annotations
+
+BATCH_SIZE = 20