feat(api): Memory compaction 管线与调度修复，同步环境变量示例

Memory compaction（近重复 chunk 软排除）
- 新增 compaction 调度：Redis debounce、scheduler gate、增量游标；任务结束时 finalize，避免 gate 长期占用并处理运行期新 trigger。
- Celery memory_compaction_run：debounce 未到点则 retry；用户级 Redis 锁；成功路径更新游标并 finalize；异常时释放 scheduler gate 并 self.retry，避免静默卡死调度与瞬时失败不重试。
- compaction_service：多层判定 + canonical 打分；无 embedding 时停止前移游标（awaiting_embeddings）；curation details 补全 trigger 等上下文。
- ingest_transcript_sync：同步路径尽力写入 embedding，与异步 ingest 行为对齐，避免 compaction 永远扫不到无向量 chunk。
- repo：新增 update_chunk_embedding_sync。
测试
- 扩展 test_memory_compaction：调度合并、finalize、ingest embedding、无向量游标、异常路径 gate+retry 等回归用

api/app/tasks/memory_compaction_tasks.py

@@ -0,0 +1,79 @@
+"""Celery：memory compaction（近重复 chunk 软排除）。"""
+
+from __future__ import annotations
+
+import time
+from datetime import datetime
+from typing import Any
+
+from celery import shared_task
+
+from app.core.config import settings
+from app.core.db import get_sync_db
+from app.core.logging import get_logger
+from app.core.memory_compaction_schedule import (
+    finalize_memory_compaction_run,
+    read_debounce_deadline_ts,
+    release_scheduler_gate,
+    set_incremental_cursor_pair,
+)
+from app.core.redis_lock import acquire_redis_lock, release_redis_lock
+from app.features.memory.compaction_service import run_memory_compaction_sync
+
+logger = get_logger(__name__)
+
+
+@shared_task(bind=True, max_retries=12, default_retry_delay=20)
+def memory_compaction_run(
+    self, user_id: str, context: dict[str, Any] | None = None
+) -> dict[str, Any]:
+    if not settings.memory_compaction_enabled:
+        return {"skipped": True, "reason": "disabled"}
+
+    ctx = dict(context or {})
+    deadline = read_debounce_deadline_ts(user_id)
+    now = time.time()
+    if deadline is not None and now < deadline:
+        delay = max(1.0, deadline - now)
+        raise self.retry(countdown=int(delay))
+
+    lock = acquire_redis_lock(
+        f"lock:memory_compaction:{user_id}",
+        ttl_seconds=settings.memory_compaction_lock_ttl_seconds,
+    )
+    if lock is None:
+        logger.info(
+            "memory_compaction_skipped user_id={} skipped_reason=lock_not_acquired",
+            user_id,
+        )
+        out = {"skipped": True, "reason": "lock_not_acquired"}
+        finalize_memory_compaction_run(
+            user_id,
+            observed_deadline_ts=deadline,
+            context=ctx,
+        )
+        return out
+
+    try:
+        with get_sync_db() as session:
+            out = run_memory_compaction_sync(session, user_id, ctx)
+            session.commit()
+
+        if out.get("new_cursor_ts") and out.get("new_cursor_id") is not None:
+            set_incremental_cursor_pair(
+                user_id,
+                datetime.fromisoformat(out["new_cursor_ts"]),
+                str(out["new_cursor_id"]),
+            )
+        finalize_memory_compaction_run(
+            user_id,
+            observed_deadline_ts=deadline,
+            context=ctx,
+        )
+        return out
+    except Exception as exc:
+        logger.warning("memory_compaction_run failed user_id={} err={}", user_id, exc)
+        release_scheduler_gate(user_id)
+        raise self.retry(exc=exc)
+    finally:
+        release_redis_lock(lock)