Initial commit: scan_web integrated recording UI

FastAPI backend + vanilla JS frontend for LiDAR/camera startup, camera
settings, and rosbag recording, unifying the previous scan_gui/scan_gui_dual/
scan_gui_triple desktop tools into one web app.

backend/routers/recording.py

@@ -0,0 +1,119 @@
+from __future__ import annotations
+
+import os
+import time
+from pathlib import Path
+
+from fastapi import APIRouter, HTTPException, Request
+from pydantic import BaseModel
+
+import bag_metadata
+import config
+
+router = APIRouter(tags=["recording"])
+
+# Directory browsing/recording is restricted to the user's home tree — the
+# browser has no server-filesystem access, so /api/fs/browse is a small
+# custom endpoint standing in for a native folder picker.
+BROWSE_ROOT = Path.home()
+
+
+def _safe_path(raw: str) -> Path:
+    p = (BROWSE_ROOT / raw).resolve() if not os.path.isabs(raw) else Path(raw).resolve()
+    try:
+        p.relative_to(BROWSE_ROOT.resolve())
+    except ValueError:
+        raise HTTPException(400, f"path must be under {BROWSE_ROOT}")
+    return p
+
+
+@router.get("/fs/browse")
+async def browse(path: str = str(BROWSE_ROOT)):
+    p = _safe_path(path)
+    if not p.exists() or not p.is_dir():
+        raise HTTPException(404, "not a directory")
+    entries = []
+    for child in sorted(p.iterdir()):
+        if child.is_dir():
+            entries.append({"name": child.name, "path": str(child)})
+    return {"path": str(p), "parent": str(p.parent) if p != BROWSE_ROOT.resolve() else None, "dirs": entries}
+
+
+@router.get("/bags")
+async def list_bags(save_dir: str = config.DEFAULT_SAVE_DIR, limit: int = 10):
+    d = Path(save_dir)
+    if not d.exists():
+        return {"bags": []}
+    bags = []
+    children = sorted(d.iterdir(), key=lambda p: p.stat().st_mtime, reverse=True)
+    for child in children:
+        if not child.is_dir():
+            continue
+        if len(bags) >= limit:
+            break
+        meta = bag_metadata.read_bag_metadata(child)
+        bags.append({
+            "name": child.name,
+            "path": str(child),
+            "mtime": child.stat().st_mtime,
+            "duration_s": meta["duration_s"] if meta else None,
+            "message_count": meta["message_count"] if meta else None,
+            "topics": meta["topics"] if meta else [],
+            "size_bytes": meta["size_bytes"] if meta else bag_metadata.dir_size_bytes(child),
+            "complete": meta is not None,  # False = still recording, or was killed before flush
+        })
+    return {"bags": bags}
+
+
+@router.get("/fs/disk-usage")
+async def disk_usage(path: str = config.DEFAULT_SAVE_DIR):
+    return {"free_gb": round(config.disk_free_gb(path), 2)}
+
+
+class RecordingStartIn(BaseModel):
+    filename: str
+    save_dir: str = config.DEFAULT_SAVE_DIR
+
+
+@router.post("/recording/start")
+async def recording_start(body: RecordingStartIn, request: Request):
+    session = request.app.state.session
+    pm = request.app.state.pm
+
+    if not pm.is_running("lidar") or not pm.is_running("camera"):
+        raise HTTPException(409, "start lidar+camera before recording")
+    if session.recording:
+        raise HTTPException(409, "already recording")
+    if not body.filename.strip():
+        raise HTTPException(400, "filename required")
+
+    save_dir = body.save_dir.strip() or config.DEFAULT_SAVE_DIR
+    os.makedirs(save_dir, exist_ok=True)
+    bag_path = os.path.join(save_dir, body.filename.strip())
+    topics = config.base_record_topics(session.camera_count)
+
+    # FAST-LIO tracks the scan (LiDAR+IMU-only mapping) for exactly the
+    # recording's lifetime — started alongside the bag, stopped alongside it.
+    # It only needs /livox/lidar + /livox/imu, both already live since
+    # lidar+camera are required (checked above) before recording can start.
+    request.app.state.ros.pointcloud.reset()  # fresh map for this recording, not last one's leftovers
+    pm.start("fastlio", config.FASTLIO_LAUNCH_CMD, log_path=config.FASTLIO_LOG_PATH, env=config.fastlio_env())
+
+    cmd = f"{config.ROSBAG_SOURCE} && stdbuf -oL -eL ros2 bag record -o {bag_path} {topics}"
+    pm.start("recording", cmd, log_path=config.RECORDING_LOG_PATH)
+    session.recording = True
+    session.recording_path = bag_path
+    session.recording_started_at = time.monotonic()
+    return {"ok": True, "path": bag_path}
+
+
+@router.post("/recording/stop")
+async def recording_stop(request: Request):
+    session = request.app.state.session
+    pm = request.app.state.pm
+    pm.stop("recording")
+    pm.stop("fastlio")
+    session.recording = False
+    session.recording_path = None
+    session.recording_started_at = None
+    return {"ok": True}