Fall back to disk when in-memory store is empty on client connect

storage_helpers: load_today_records() scans logs/ for all files
matching today's UTC date and VIN, merges and sorts their records.

network: _accept_loop receives an optional load_today callable;
if store_ref["current"] has no records it calls load_today() to
replay the day's history from disk before adding the client.

collect: passes a load_today lambda (None when -o is used).

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

collect.py

@@ -57,7 +57,7 @@ from pathlib import Path
 
 from server import log_config, network, we_connect
 from server.data_model import ALL_DOMAINS, collect_snapshot
-from server.storage_helpers import auto_out_path, load_store, save_store
+from server.storage_helpers import auto_out_path, load_store, load_today_records, save_store
 
 log = logging.getLogger(__name__)
 
@@ -93,10 +93,14 @@ def run(args: argparse.Namespace) -> None:
         logs_dir.mkdir(exist_ok=True)
         out = auto_out_path(logs_dir, vin)
 
-    push_clients, push_lock, push_last = network.start_push_server(args.host, args.port)
+    load_today = (lambda: load_today_records(logs_dir, vin)) if logs_dir else None
+    push_clients, push_lock, push_store_ref = network.start_push_server(
+        args.host, args.port, load_today=load_today
+    )
 
     current_day = datetime.now(timezone.utc).date()
     store = load_store(out, vin, args.interval)
+    push_store_ref["current"] = store
     log.info(
         "Collecting [%s] every %ds → %s  (Ctrl-C to stop)",
         ", ".join(domains),
@@ -111,6 +115,7 @@ def run(args: argparse.Namespace) -> None:
                 if today != current_day:
                     out = auto_out_path(logs_dir, vin)
                     store = load_store(out, vin, args.interval)
+                    push_store_ref["current"] = store
                     current_day = today
                     log.info("Midnight UTC rotation → %s", out)
 
@@ -119,7 +124,7 @@ def run(args: argparse.Namespace) -> None:
                 snapshot = collect_snapshot(vehicle, domains)
                 store["records"].append(snapshot)
                 save_store(out, store, args.max_records)
-                network.broadcast(snapshot, push_clients, push_lock, push_last)
+                network.broadcast(snapshot, push_clients, push_lock)
                 log.info("Record #%d saved at %s", len(store["records"]), snapshot["ts"])
             except KeyboardInterrupt:
                 raise

server/network.py

@@ -2,6 +2,7 @@ import json
 import logging
 import socket
 import threading
+from typing import Callable
 
 log = logging.getLogger(__name__)
 
@@ -10,30 +11,36 @@ def _accept_loop(
     server_sock: socket.socket,
     clients: list,
     lock: threading.Lock,
-    last_snapshot: dict,
+    store_ref: dict,
+    load_today: Callable | None,
 ) -> None:
     while True:
         try:
             conn, addr = server_sock.accept()
             log.info("Push client connected from %s", addr)
             with lock:
-                if last_snapshot["data"] is not None:
-                    try:
-                        line = (json.dumps(last_snapshot["data"], default=str) + "\n").encode()
-                        conn.sendall(line)
-                    except OSError:
-                        log.debug("Failed to send initial snapshot to %s", addr)
-                        conn.close()
-                        continue
+                store = store_ref["current"]
+                records = store["records"] if store else []
+                if not records and load_today is not None:
+                    log.info("In-memory store empty — loading today's records from disk")
+                    records = load_today()
+                try:
+                    for record in records:
+                        conn.sendall((json.dumps(record, default=str) + "\n").encode())
+                    if records:
+                        log.info("Sent %d record(s) to %s", len(records), addr)
+                except OSError:
+                    log.debug("Failed to send history to %s", addr)
+                    conn.close()
+                    continue
                 clients.append(conn)
         except OSError:
             break
 
 
-def broadcast(snapshot: dict, clients: list, lock: threading.Lock, last_snapshot: dict) -> None:
+def broadcast(snapshot: dict, clients: list, lock: threading.Lock) -> None:
     line = (json.dumps(snapshot, default=str) + "\n").encode()
     with lock:
-        last_snapshot["data"] = snapshot
         dead = []
         for conn in clients:
             try:
@@ -46,19 +53,23 @@ def broadcast(snapshot: dict, clients: list, lock: threading.Lock, last_snapshot
             log.info("Push client disconnected")
 
 
-def start_push_server(host: str, port: int) -> tuple:
+def start_push_server(
+    host: str,
+    port: int,
+    load_today: Callable | None = None,
+) -> tuple:
     server_sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
     server_sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
     server_sock.bind((host, port))
     server_sock.listen()
     clients: list = []
     lock = threading.Lock()
-    last_snapshot: dict = {"data": None}
+    store_ref: dict = {"current": None}
     t = threading.Thread(
         target=_accept_loop,
-        args=(server_sock, clients, lock, last_snapshot),
+        args=(server_sock, clients, lock, store_ref, load_today),
         daemon=True,
     )
     t.start()
     log.info("Push server listening on %s:%d", host, port)
-    return clients, lock, last_snapshot
+    return clients, lock, store_ref

server/storage_helpers.py

@@ -33,3 +33,19 @@ def save_store(path: Path, store: dict, max_records: int | None) -> None:
     if max_records and len(store["records"]) > max_records:
         store["records"] = store["records"][-max_records:]
     path.write_text(json.dumps(store, indent=2, default=str))
+
+
+def load_today_records(logs_dir: Path, vin: str) -> list:
+    """Load and merge all records from today's log files for this VIN."""
+    today_prefix = datetime.now(timezone.utc).strftime("%Y_%m_%d_")
+    records = []
+    for path in sorted(logs_dir.glob(f"{today_prefix}*_{vin}.json")):
+        try:
+            data = json.loads(path.read_text())
+            if isinstance(data, dict) and "records" in data:
+                records.extend(data["records"])
+                log.debug("Loaded %d records from %s", len(data["records"]), path.name)
+        except (json.JSONDecodeError, OSError):
+            log.warning("Could not load %s", path)
+    records.sort(key=lambda r: r.get("ts", ""))
+    return records