refactor(api): TOML 配置 SSOT、统一错误契约、Auth/事务加固与可观测性 (#33)

配置 SSOT（TOML + .env）
统一错误契约
Auth 与事务边界
Redis / Celery 可靠性:业务 Redis（DB/0）与 Celery broker/backend（DB/1）显式拆分；连接池、sync client
可观测性（OpenTelemetry + LGTM）

api/app/core/agent_logging.py

@@ -29,6 +29,7 @@ from opentelemetry.trace import Status, StatusCode
 
 from app.core.config import settings
 from app.core.telemetry import get_tracer
+from app.core.runtime_constants import agent_log_defaults
 
 _dedup_lock = threading.Lock()
 _last_prompt_sha256_by_label: dict[str, str] = {}
@@ -52,14 +53,14 @@ def agent_summary_enabled() -> bool:
     """是否输出单行 INFO 摘要（耗时、规模等），不依赖全局 DEBUG。"""
     if agent_verbose_enabled():
         return True
-    return bool(settings.log_agent_verbose)
+    return bool(agent_log_defaults.agent_verbose)
 
 
 def truncate_for_log(text: str | None, *, max_chars: int | None = None) -> str:
     """截断过长文本，避免日志爆量。max_chars / AGENT_LOG_MAX_CHARS 为 0 表示不截断。"""
     if text is None:
         return ""
-    max_c = max_chars if max_chars is not None else settings.agent_log_max_chars
+    max_c = max_chars if max_chars is not None else agent_log_defaults.max_chars
     s = str(text)
     if max_c <= 0 or len(s) <= max_c:
         return s
@@ -105,7 +106,7 @@ def agent_span(
     def _log_end(ms: float) -> None:
         if agent_verbose_enabled():
             logger.debug("agent_span_end {} duration_ms={:.2f} {}", operation, ms, ctx)
-        elif settings.log_agent_verbose:
+        elif agent_log_defaults.agent_verbose:
             logger.info("agent_span {} duration_ms={:.2f} {}", operation, ms, ctx)
 
     if settings.otel_enabled:
@@ -153,7 +154,7 @@ def log_agent_payload(
     sha12 = digest[:12]
 
     is_prompt = label.endswith(".prompt")
-    if is_prompt and settings.agent_log_prompt_dedup:
+    if is_prompt and agent_log_defaults.prompt_dedup:
         with _dedup_lock:
             if _last_prompt_sha256_by_label.get(label) == digest:
                 logger.debug(
@@ -169,14 +170,14 @@ def log_agent_payload(
     extra_note = ""
     if (
         is_prompt
-        and settings.agent_log_json_prompt_prefix_chars > 0
-        and total_len > settings.agent_log_json_prompt_prefix_only_if_len_gt
+        and agent_log_defaults.json_prompt_prefix_chars > 0
+        and total_len > agent_log_defaults.json_prompt_prefix_only_if_len_gt
     ):
-        skip = settings.agent_log_json_prompt_prefix_chars
+        skip = agent_log_defaults.json_prompt_prefix_chars
         preview_source = raw[skip:]
         extra_note = f" skipped_prefix_chars={skip}"
 
-    mode = (settings.agent_log_prompt_mode or "preview").strip().lower()
+    mode = (agent_log_defaults.prompt_mode or "preview").strip().lower()
     if is_prompt and mode == "hash_only":
         logger.debug(
             "agent_payload label={} total_len={} sha12={} mode=hash_only{}",