feat(api): /api/work_plane/{fit,save,get,delete} endpoints

POST /fit returns a candidate WorkPlane + a downsampled CV-frame cloud
preview, without writing to disk. POST /save persists the plane. GET
returns the current saved plane (or null). DELETE clears it.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/presa_mano/api/work_plane_routes.py

@@ -0,0 +1,123 @@
+"""Work-plane calibration endpoints: fit (preview), save, get, delete."""
+from __future__ import annotations
+
+import time
+from dataclasses import asdict
+from typing import Any
+
+import numpy as np
+from fastapi import APIRouter, HTTPException
+from pydantic import BaseModel, Field
+
+from ..perception import filter_outliers, nuwa_to_cv_frame
+from ..perception.work_plane import (
+    WorkPlane,
+    WorkPlaneError,
+    fit_plane_svd,
+    get_work_plane,
+    set_work_plane,
+)
+from ..timing import Stopwatch
+from . import _deps
+
+router = APIRouter()
+
+
+class FitReq(BaseModel):
+    u_min: int = Field(..., ge=0)
+    v_min: int = Field(..., ge=0)
+    u_max: int = Field(..., gt=0)
+    v_max: int = Field(..., gt=0)
+    offset_mm: float = Field(5.0, ge=0.0, le=200.0)
+    max_preview_points: int = Field(5000, ge=100, le=20000)
+
+
+class SaveReq(BaseModel):
+    plane: dict[str, Any]   # accept a serialised WorkPlane
+
+
+@router.post("/fit")
+def fit(req: FitReq) -> dict[str, Any]:
+    """Compute a candidate work plane from a rectangle on the RGB image.
+
+    Does NOT persist. Returns the plane + a downsampled CV-frame cloud for
+    the GUI 3D preview.
+    """
+    sw = Stopwatch()
+    nuwa = _deps.nuwa()
+    try:
+        with sw.step("pointcloud_roi"):
+            pc, _meta = nuwa.pointcloud_roi(
+                req.u_min, req.v_min, req.u_max, req.v_max,
+                step=1, max_depth_mm=4000,
+            )
+    except Exception as e:
+        raise HTTPException(status_code=502, detail=f"Nuwa pointcloud_roi failed: {e}")
+    if len(pc) < 10:
+        raise HTTPException(
+            status_code=422,
+            detail=f"too few depth points in ROI: {len(pc)}",
+        )
+    pts_cv = nuwa_to_cv_frame(pc[:, :3])
+    with sw.step("filter_outliers"):
+        pts_cv = filter_outliers(pts_cv, n_std=2.0)
+    if len(pts_cv) < 10:
+        raise HTTPException(
+            status_code=422,
+            detail=f"too few inliers after outlier filter: {len(pts_cv)}",
+        )
+    try:
+        with sw.step("fit_plane_svd"):
+            normal, offset, centroid, rms_mm = fit_plane_svd(pts_cv)
+    except WorkPlaneError as e:
+        raise HTTPException(status_code=422, detail=str(e))
+
+    wp = WorkPlane(
+        normal=[float(x) for x in normal],
+        offset=float(offset),
+        centroid=[float(x) for x in centroid],
+        n_inliers=int(len(pts_cv)),
+        fit_rms_mm=float(rms_mm),
+        roi=[int(req.u_min), int(req.v_min), int(req.u_max), int(req.v_max)],
+        offset_mm=float(req.offset_mm),
+        created_at=time.time(),
+    )
+
+    # Downsample for preview.
+    if len(pts_cv) > req.max_preview_points:
+        idx = np.random.choice(len(pts_cv), req.max_preview_points, replace=False)
+        preview = pts_cv[idx]
+    else:
+        preview = pts_cv
+
+    return {
+        "plane": asdict(wp),
+        "preview": True,
+        "points_camera": preview.tolist(),
+        "timings_ms": sw.as_dict(),
+    }
+
+
+@router.post("/save")
+def save(req: SaveReq) -> dict[str, Any]:
+    """Persist a previously-fitted work plane to disk."""
+    try:
+        d = dict(req.plane)
+        d.setdefault("offset_mm", 5.0)
+        wp = WorkPlane(**d)
+    except Exception as e:
+        raise HTTPException(status_code=422, detail=f"invalid plane payload: {e}")
+    set_work_plane(wp)
+    return {"ok": True, "plane": asdict(wp), "saved": True}
+
+
+@router.get("")
+def get_current() -> dict[str, Any]:
+    wp = get_work_plane()
+    return {"plane": asdict(wp) if wp is not None else None}
+
+
+@router.delete("")
+def delete_current() -> dict[str, Any]:
+    set_work_plane(None)
+    return {"ok": True, "plane": None}