Fix Parser Test Runner JSON mode, Filter Simulator PQ syntax, dropdown source

- backend/routers/quality.py
 * Add GET /api/quality/parsers (lists actual files in /app/parsers)
 * Support SDL JSON auto-extract parsers ($=json{parse=json}$)
 * Apply parser rewrite blocks with correct $0/$N backref translation
 * Accept single JSON / JSON array / NDJSON in test-parser body
 * Flatten JSON inside 'message' for Field Population coverage
- backend/routers/ingest.py
 * Rewrite simulate-filter PowerQuery to valid SDL syntax
 * Correct field name: src.name -> dataSource.name
- frontend/index.html
 * Parser dropdown loads from /api/quality/parsers
 * Add 'Last 7d' lookback option
 * Render JSON-mode test results with badges + payload counter

backend/routers/quality.py

@@ -2,11 +2,26 @@ from fastapi import APIRouter, HTTPException
 from pydantic import BaseModel
 from datetime import datetime, timedelta
 from services import s1_client
+import os
 import re
 
 router = APIRouter()
 
 
+@router.get("/parsers")
+def list_parser_files():
+    """List parser filenames available under /app/parsers/ for the Test Runner."""
+    parsers_dir = "/app/parsers"
+    try:
+        names = sorted(
+            e.name for e in os.scandir(parsers_dir)
+            if e.is_file() and not e.name.startswith(".")
+        )
+    except FileNotFoundError:
+        names = []
+    return {"parsers": names, "count": len(names)}
+
+
 def _date_range_hours(hours: int) -> tuple[str, str]:
     now = datetime.utcnow()
     return (
@@ -52,11 +67,41 @@ class TestParserRequest(BaseModel):
 # Helpers
 # ---------------------------------------------------------------------------
 
+def _flatten_dict(d: dict, prefix: str = "", out: dict | None = None) -> dict:
+    """Recursively flatten a nested dict into dotted keys."""
+    if out is None:
+        out = {}
+    if not isinstance(d, dict):
+        return out
+    for k, v in d.items():
+        key = f"{prefix}.{k}" if prefix else k
+        if isinstance(v, dict):
+            _flatten_dict(v, key, out)
+        else:
+            out[key] = v
+    return out
+
+
 def _flatten_event(event: dict) -> dict:
-    """Return a flat field→value dict from a PowerQuery result row."""
-    if isinstance(event, dict):
-        return {k: v for k, v in event.items()}
-    return {}
+    """Return a flat field→value dict from a PowerQuery result row.
+
+    If the row only carries a JSON-stringified payload in `message` (i.e. the
+    parser wasn't applied at query time), parse and flatten it inline so the
+    UI can measure field population accurately. The original raw `message`
+    is preserved under its own key.
+    """
+    if not isinstance(event, dict):
+        return {}
+    flat = dict(event)
+    msg = flat.get("message")
+    if isinstance(msg, str) and msg.startswith("{") and msg.endswith("}"):
+        try:
+            parsed = __import__("json").loads(msg)
+            if isinstance(parsed, dict):
+                flat.update(_flatten_dict(parsed))
+        except Exception:
+            pass
+    return flat
 
 
 def _extract_format_strings(content: str) -> list[str]:
@@ -204,6 +249,117 @@ async def test_parser(req: TestParserRequest):
 
     format_strings = _extract_format_strings(content)
 
+    # ── JSON auto-extract path ──────────────────────────────────────────────
+    # SDL parsers that use `$=json{parse=json}$` (or any format containing
+    # `parse=json`) auto-extract every top-level JSON key as an attribute.
+    # The regex-based path can't model that — handle it explicitly so users
+    # can test JSON-shaped logs against JSON-mode parsers.
+    log_input = req.log_line.strip()
+    is_json_mode = any("parse=json" in f for f in format_strings) or log_input.startswith("{")
+    if is_json_mode:
+        import json as _json
+        # Support multi-line input (one JSON object per line, or a JSON array)
+        lines = [ln for ln in (l.strip() for l in log_input.splitlines()) if ln]
+        payloads: list[dict] = []
+        parse_errors: list[str] = []
+        # Single line: try direct parse; if it's a JSON array, expand.
+        if len(lines) == 1:
+            try:
+                obj = _json.loads(lines[0])
+            except Exception as e:
+                return {
+                    "parser_name": req.parser_name,
+                    "matched": False,
+                    "message": f"Parser expects JSON but log line could not be parsed as JSON: {e}",
+                    "fields": [],
+                }
+            if isinstance(obj, list):
+                payloads = [x for x in obj if isinstance(x, dict)]
+            elif isinstance(obj, dict):
+                payloads = [obj]
+            else:
+                return {
+                    "parser_name": req.parser_name,
+                    "matched": False,
+                    "message": "Parser expects a JSON object (got scalar).",
+                    "fields": [],
+                }
+        else:
+            # Multi-line: one JSON object per line (NDJSON)
+            for i, ln in enumerate(lines, 1):
+                try:
+                    obj = _json.loads(ln)
+                    if isinstance(obj, dict):
+                        payloads.append(obj)
+                    else:
+                        parse_errors.append(f"line {i}: not a JSON object")
+                except Exception as e:
+                    parse_errors.append(f"line {i}: {e}")
+
+        if not payloads:
+            return {
+                "parser_name": req.parser_name,
+                "matched": False,
+                "message": "No valid JSON objects found. " + " | ".join(parse_errors[:3]),
+                "fields": [],
+            }
+
+        # Use the first payload for the detail table; report totals.
+        payload = payloads[0]
+        extracted = _flatten_dict(payload)
+        # Apply lightweight rewrites if present (input/output/match/replace blocks).
+        # We only handle simple literal/regex matches with $0 or string replacements;
+        # this is best-effort, intended for quick visual verification.
+        rewrites_applied = []
+        rewrite_re = re.compile(
+            r'\{\s*input:\s*"([^"]+)"\s*,\s*output:\s*"([^"]+)"\s*,\s*match:\s*"((?:[^"\\]|\\.)*)"\s*,\s*replace:\s*"((?:[^"\\]|\\.)*)"\s*\}',
+            re.DOTALL,
+        )
+        derived: dict[str, str] = {}
+        for m in rewrite_re.finditer(content):
+            in_field, out_field, match_pat, replace_val = m.group(1), m.group(2), m.group(3), m.group(4)
+            src_val = extracted.get(in_field)
+            if src_val is None:
+                continue
+            try:
+                m2 = re.search(match_pat, str(src_val))
+            except re.error:
+                continue
+            if not m2:
+                continue
+            # SDL uses $0 for whole match, $1.. for groups. Translate to Python
+            # \g<0>, \g<1>, ... so re.sub doesn't read \0 as a null byte.
+            def _to_py_backref(s: str) -> str:
+                return re.sub(r"\$(\d+)", lambda mm: f"\\g<{mm.group(1)}>", s)
+            try:
+                val = re.sub(match_pat, _to_py_backref(replace_val), str(src_val), count=1)
+            except re.error:
+                val = replace_val
+            derived[out_field] = val
+            rewrites_applied.append({
+                "input": in_field, "input_value": src_val,
+                "output": out_field, "matched_on": match_pat, "result": val,
+            })
+
+        fields = (
+            [{"field": k, "value": v, "source": "json-extract"} for k, v in sorted(extracted.items())]
+            + [{"field": k, "value": v, "source": "rewrite"}     for k, v in sorted(derived.items())]
+        )
+        return {
+            "parser_name": req.parser_name,
+            "matched": True,
+            "mode": "json",
+            "format_matched": "$=json{parse=json}$",
+            "fields": fields,
+            "rewrites_applied": rewrites_applied,
+            "extracted_count": len(extracted),
+            "derived_count": len(derived),
+            "payload_count": len(payloads),
+            "parse_errors": parse_errors,
+            "showing_payload": 1,
+        }
+
+    # ── Regex format-string path (original) ─────────────────────────────────
     for fmt in format_strings:
         try:
             compiled, py_to_sdl = _sdl_format_to_regex(fmt)
@@ -221,6 +377,7 @@ async def test_parser(req: TestParserRequest):
             return {
                 "parser_name": req.parser_name,
                 "matched": True,
+                "mode": "regex",
                 "format_matched": fmt,
                 "fields": fields,
             }