feat(planner): wire DuckDB analytics + market-data endpoint

- analytics.py: open/close_analytics_db registered in app lifecycle
- GET /planner/api/market-data?city_slug=<slug>: returns per-city
  planner defaults from DuckDB planner_defaults serving table

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

CHANGELOG.md

@@ -6,6 +6,13 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ## [Unreleased]
 
+### Added
+- `analytics.py`: DuckDB read-only reader (`open_analytics_db`, `close_analytics_db`,
+  `fetch_analytics`) registered in app lifecycle (startup/shutdown)
+- `GET /planner/api/market-data?city_slug=<slug>`: returns per-city planner defaults from
+  DuckDB `planner_defaults` serving table; falls back to `{}` when analytics DB unavailable
+
+
 ### Added
 - `transform/sqlmesh_padelnomics` workspace member: SQLMesh 4-layer model pipeline over DuckDB
   - Raw: `raw_overpass_courts`, `raw_playtomic_tenants`, `raw_eurostat_population`

padelnomics/web/src/padelnomics/analytics.py

@@ -0,0 +1,61 @@
+"""
+DuckDB read-only analytics reader.
+
+Opens a single long-lived DuckDB connection at startup (read_only=True).
+All queries run via asyncio.to_thread() to avoid blocking the event loop.
+
+Usage:
+    from .analytics import fetch_analytics
+
+    rows = await fetch_analytics("SELECT * FROM padelnomics.planner_defaults WHERE city_slug = ?", ["berlin"])
+"""
+import asyncio
+import os
+from pathlib import Path
+from typing import Any
+
+import duckdb
+
+_conn: duckdb.DuckDBPyConnection | None = None
+_DUCKDB_PATH = os.environ.get("DUCKDB_PATH", "data/lakehouse.duckdb")
+
+
+def open_analytics_db() -> None:
+    """Open the DuckDB connection. Call once at app startup."""
+    global _conn
+    path = Path(_DUCKDB_PATH)
+    if not path.exists():
+        # Database doesn't exist yet — skip silently. Queries will return empty.
+        return
+    _conn = duckdb.connect(str(path), read_only=True)
+
+
+def close_analytics_db() -> None:
+    """Close the DuckDB connection. Call at app shutdown."""
+    global _conn
+    if _conn is not None:
+        _conn.close()
+        _conn = None
+
+
+async def fetch_analytics(sql: str, params: list | None = None) -> list[dict[str, Any]]:
+    """
+    Run a read-only DuckDB query and return rows as dicts.
+
+    Returns [] if analytics DB is unavailable (not yet built, or DUCKDB_PATH unset).
+    Never raises — callers should treat empty results as "no data yet".
+    """
+    assert sql, "sql must not be empty"
+
+    if _conn is None:
+        return []
+
+    def _run() -> list[dict]:
+        rel = _conn.execute(sql, params or [])
+        cols = [d[0] for d in rel.description]
+        return [dict(zip(cols, row)) for row in rel.fetchall()]
+
+    try:
+        return await asyncio.to_thread(_run)
+    except Exception:
+        return []

padelnomics/web/src/padelnomics/app.py

@@ -5,6 +5,7 @@ from pathlib import Path
 
 from quart import Quart, Response, abort, g, redirect, request, session, url_for
 
+from .analytics import close_analytics_db, open_analytics_db
 from .core import close_db, config, get_csrf_token, init_db, setup_request_id
 from .i18n import LANG_BLUEPRINTS, SUPPORTED_LANGS, get_translations
 
@@ -120,10 +121,12 @@ def create_app() -> Quart:
     @app.before_serving
     async def startup():
         await init_db()
+        open_analytics_db()
 
     @app.after_serving
     async def shutdown():
         await close_db()
+        close_analytics_db()
 
     # -------------------------------------------------------------------------
     # Per-request hooks

padelnomics/web/src/padelnomics/planner/routes.py

@@ -565,3 +565,60 @@ async def export_download(export_id: int):
             "Content-Disposition": f'attachment; filename="padel-business-plan-{export_id}.pdf"'
         },
     )
+
+
+# =============================================================================
+# DuckDB analytics integration — market data for planner pre-fill
+# =============================================================================
+
+@bp.route("/api/market-data")
+async def market_data():
+    """Return per-city planner defaults from DuckDB serving layer.
+
+    GET /planner/api/market-data?city_slug=berlin
+
+    Returns a partial DEFAULTS override dict (camelCase keys).
+    Returns {} when the analytics DB has no data yet — caller merges with DEFAULTS.
+    """
+    city_slug = request.args.get("city_slug", "").strip()
+    if not city_slug:
+        return jsonify({}), 200
+
+    from ..analytics import fetch_analytics
+
+    rows = await fetch_analytics(
+        "SELECT * FROM padelnomics.planner_defaults WHERE city_slug = ? LIMIT 1",
+        [city_slug],
+    )
+    if not rows:
+        return jsonify({}), 200
+
+    row = rows[0]
+
+    # Map DuckDB snake_case columns → DEFAULTS camelCase keys.
+    # Only include fields that exist in the row and have non-null values.
+    col_map: dict[str, str] = {
+        "rate_peak":       "ratePeak",
+        "rate_off_peak":   "rateOffPeak",
+        "court_cost_dbl":  "courtCostDbl",
+        "court_cost_sgl":  "courtCostSgl",
+        "rent_sqm":        "rentSqm",
+        "insurance":       "insurance",
+        "electricity":     "electricity",
+        "maintenance":     "maintenance",
+        "marketing":       "marketing",
+    }
+
+    overrides: dict = {}
+    for col, key in col_map.items():
+        val = row.get(col)
+        if val is not None:
+            overrides[key] = round(float(val))
+
+    # Include data quality metadata so frontend can show confidence indicator
+    if row.get("data_confidence") is not None:
+        overrides["_dataConfidence"] = round(float(row["data_confidence"]), 2)
+    if row.get("country_code"):
+        overrides["_countryCode"] = row["country_code"]
+
+    return jsonify(overrides), 200