feat(trace-pipeline): memory triage, async job queue, and NDJSON streaming

Three proposals addressing the 2026-02-25 trace pipeline OOM crash (114K CIDs):

1. trace-events-memory-triage: fetchmany iterator (read_sql_df_slow_iter),
   admission control (50K CID limit for non-MSD), cache skip for large queries,
   early memory release with gc.collect()

2. trace-async-job-queue: RQ-based async jobs for queries >20K CIDs,
   separate worker process with isolated memory, frontend polling via
   useTraceProgress composable, systemd service + deploy scripts

3. trace-streaming-response: chunked Redis storage (TRACE_STREAM_BATCH_SIZE=5000),
   NDJSON stream endpoint (GET /api/trace/job/<id>/stream), frontend
   ReadableStream consumer for progressive rendering, backward-compatible
   with legacy single-key storage

All three proposals archived. 1101 tests pass, frontend builds clean.

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

tests/test_database_slow_iter.py

@@ -0,0 +1,119 @@
+# -*- coding: utf-8 -*-
+"""Unit tests for read_sql_df_slow_iter (fetchmany iterator)."""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock, patch
+
+import mes_dashboard.core.database as db
+
+
+@patch.object(db, "oracledb")
+@patch.object(db, "_get_slow_query_semaphore")
+@patch.object(db, "get_db_runtime_config")
+def test_slow_iter_yields_batches(mock_runtime, mock_sem_fn, mock_oracledb):
+    """read_sql_df_slow_iter should yield (columns, rows) batches via fetchmany."""
+    mock_runtime.return_value = {
+        "slow_call_timeout_ms": 60000,
+        "slow_fetchmany_size": 2,
+        "tcp_connect_timeout": 10,
+        "retry_count": 1,
+        "retry_delay": 1.0,
+    }
+
+    sem = MagicMock()
+    sem.acquire.return_value = True
+    mock_sem_fn.return_value = sem
+
+    cursor = MagicMock()
+    cursor.description = [("COL_A",), ("COL_B",)]
+    cursor.fetchmany.side_effect = [
+        [("r1a", "r1b"), ("r2a", "r2b")],
+        [("r3a", "r3b")],
+        [],
+    ]
+
+    conn = MagicMock()
+    conn.cursor.return_value = cursor
+    mock_oracledb.connect.return_value = conn
+
+    batches = list(db.read_sql_df_slow_iter("SELECT 1", {"p0": "x"}, batch_size=2))
+
+    assert len(batches) == 2
+    assert batches[0] == (["COL_A", "COL_B"], [("r1a", "r1b"), ("r2a", "r2b")])
+    assert batches[1] == (["COL_A", "COL_B"], [("r3a", "r3b")])
+    cursor.fetchmany.assert_called_with(2)
+    conn.close.assert_called_once()
+    sem.release.assert_called_once()
+
+
+@patch.object(db, "oracledb")
+@patch.object(db, "_get_slow_query_semaphore")
+@patch.object(db, "get_db_runtime_config")
+def test_slow_iter_empty_result(mock_runtime, mock_sem_fn, mock_oracledb):
+    """read_sql_df_slow_iter should yield nothing for empty result."""
+    mock_runtime.return_value = {
+        "slow_call_timeout_ms": 60000,
+        "slow_fetchmany_size": 5000,
+        "tcp_connect_timeout": 10,
+        "retry_count": 1,
+        "retry_delay": 1.0,
+    }
+
+    sem = MagicMock()
+    sem.acquire.return_value = True
+    mock_sem_fn.return_value = sem
+
+    cursor = MagicMock()
+    cursor.description = [("ID",)]
+    cursor.fetchmany.return_value = []
+
+    conn = MagicMock()
+    conn.cursor.return_value = cursor
+    mock_oracledb.connect.return_value = conn
+
+    batches = list(db.read_sql_df_slow_iter("SELECT 1"))
+
+    assert batches == []
+    conn.close.assert_called_once()
+    sem.release.assert_called_once()
+
+
+@patch.object(db, "oracledb")
+@patch.object(db, "_get_slow_query_semaphore")
+@patch.object(db, "get_db_runtime_config")
+def test_slow_iter_releases_on_error(mock_runtime, mock_sem_fn, mock_oracledb):
+    """Semaphore and connection should be released even on error."""
+    mock_runtime.return_value = {
+        "slow_call_timeout_ms": 60000,
+        "slow_fetchmany_size": 5000,
+        "tcp_connect_timeout": 10,
+        "retry_count": 1,
+        "retry_delay": 1.0,
+    }
+
+    sem = MagicMock()
+    sem.acquire.return_value = True
+    mock_sem_fn.return_value = sem
+
+    conn = MagicMock()
+    conn.cursor.side_effect = RuntimeError("cursor failed")
+    mock_oracledb.connect.return_value = conn
+
+    try:
+        list(db.read_sql_df_slow_iter("SELECT 1"))
+    except RuntimeError:
+        pass
+
+    conn.close.assert_called_once()
+    sem.release.assert_called_once()
+
+
+def test_runtime_config_includes_fetchmany_size():
+    """get_db_runtime_config should include slow_fetchmany_size."""
+    # Force refresh to pick up current config
+    db._DB_RUNTIME_CONFIG = None
+    runtime = db.get_db_runtime_config(refresh=True)
+    assert "slow_fetchmany_size" in runtime
+    assert isinstance(runtime["slow_fetchmany_size"], int)
+    assert runtime["slow_fetchmany_size"] > 0