diff --git a/pyproject.toml b/pyproject.toml
index be84cf3..1bd64dc 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -10,7 +10,7 @@ readme = "README.md"
 requires-python = ">=3.11"
 dependencies = [
     "pyyaml",
-    "jfjoch-client",
+    "jfjoch-client>=1.0.0rc166",
     "pydantic",
     "numpy",
     "scipy",
diff --git a/src/aarecommon/math/jfjoch_gridscan_union.py b/src/aarecommon/math/jfjoch_gridscan_union.py
index 1dfadc4..7019ccc 100644
--- a/src/aarecommon/math/jfjoch_gridscan_union.py
+++ b/src/aarecommon/math/jfjoch_gridscan_union.py
@@ -199,6 +199,12 @@ class GridScanResult(BaseModel):
     warnings: list[str] = Field(
         default_factory=list, description="Reasons to distrust a found=True result"
     )
+    contour_cells: Optional[list[tuple[int, int]]] = Field(
+        None,
+        description="(nx, ny) of every collected cell inside the chosen 50 % "
+        "blob -- the decision's own footprint, for drawing it over the sample "
+        "image without recomputing the map",
+    )
     jpeg: Optional[bytes] = Field(
         None,
         exclude=True,
@@ -610,6 +616,9 @@ def analyse(
         if keep.shape == inside.shape:
             inside = inside & keep
     counts.n_fragments = n_frag
+    if cell.any():
+        yy_c, xx_c = np.nonzero(cell)
+        out.contour_cells = [(int(x), int(y)) for y, x in zip(yy_c, xx_c)]
 
     if line:
         # One position wide: the 50 % crossings either side of the peak. The outer
diff --git a/src/aarecommon/models/gridscan_decision.py b/src/aarecommon/models/gridscan_decision.py
new file mode 100644
index 0000000..e4e23c9
--- /dev/null
+++ b/src/aarecommon/models/gridscan_decision.py
@@ -0,0 +1,36 @@
+"""The grid-scan centring decision, as taken at the beamline.
+
+The DAQ runs the analysis (``aarecommon.math.jfjoch_gridscan_union``) to pick
+the collection position; this wraps its result verbatim with provenance and
+rides on ``RasterPayloadModel.decision`` into AareDB, whose Results viewer
+displays THE decision instead of recomputing one -- two implementations of the
+same analysis drifting apart is how a UI ends up contradicting the beamline.
+
+The pictures are excluded from the result's serialization by the model itself;
+the DAQ ships them through the ordinary image pipeline.
+"""
+
+from typing import Any, Optional
+
+from pydantic import BaseModel, Field
+
+from aarecommon.math.jfjoch_gridscan_union import GridScanResult
+
+GRIDSCAN_DECISION_CONTRACT = 1
+
+
+class GridScanDecision(BaseModel):
+    contract: int = GRIDSCAN_DECISION_CONTRACT
+    algorithm: str = Field(
+        description="Which analysis took the decision, e.g. a "
+        "GridscanAnalysisMode value such as 'jfjoch_gridscan_union'"
+    )
+    algorithm_version: Optional[str] = Field(
+        None, description="aarecommon version (or commit) the DAQ ran"
+    )
+    thresholds: Optional[dict[str, Any]] = Field(
+        None,
+        description="Thresholds.model_dump() used at decision time, so a "
+        "stored decision states its own tuning",
+    )
+    result: GridScanResult
diff --git a/src/aarecommon/models/raster_grid.py b/src/aarecommon/models/raster_grid.py
index ed9a1b0..db37e4a 100644
--- a/src/aarecommon/models/raster_grid.py
+++ b/src/aarecommon/models/raster_grid.py
@@ -6,6 +6,7 @@ from pydantic import AfterValidator, BaseModel, Field
 
 from aarecommon.math.coordinate import Coordinate, SmargonCoordinate, positive_coords
 from aarecommon.math.sample_geometry import SampleGeometryModel
+from aarecommon.models.gridscan_decision import GridScanDecision
 
 
 class RasterGridRequest(BaseModel):
@@ -92,3 +93,6 @@ class RasterPayloadModel(BaseModel):
     cell_size_pxl: Annotated[Coordinate, AfterValidator(positive_coords)]
     beam_mark_pxl: tuple[float, float]
     beam_size_mm: Annotated[Coordinate, AfterValidator(positive_coords)]
+    # The centring decision as taken at the beamline (None from DAQs that
+    # have not adopted it yet); AareDB stores and displays it verbatim.
+    decision: GridScanDecision | None = None
diff --git a/tests/test_gridscan_decision.py b/tests/test_gridscan_decision.py
new file mode 100644
index 0000000..41866a8
--- /dev/null
+++ b/tests/test_gridscan_decision.py
@@ -0,0 +1,68 @@
+"""GridScanDecision wire contract: wraps the analysis result verbatim."""
+
+import json
+
+import numpy as np
+
+from aarecommon.math.jfjoch_gridscan_union import Thresholds, analyse
+from aarecommon.models.gridscan_decision import GridScanDecision
+from aarecommon.models.raster_grid import RasterPayloadModel
+
+
+def _synthetic_scan(ny_n=20, nx_n=20):
+    """A gaussian protein blob on a flat loop, as plain dicts (jfjoch-free)."""
+    rng = np.random.default_rng(0)
+    yy, xx = np.mgrid[0:ny_n, 0:nx_n]
+    blob = 80 * np.exp(-(((xx - 7) ** 2 + (yy - 12) ** 2) / 8.0))
+    images = [
+        {
+            "number": int(y * nx_n + x),
+            "nx": int(x),
+            "ny": int(y),
+            "spots": int(blob[y, x] + 10 + rng.integers(0, 3)),
+            "spots_low_res": int(4 + rng.integers(0, 2)),
+            "spots_ice": 0,
+            "bkg": float(30 + 40 * np.exp(-(((x - 9) ** 2 + (y - 10) ** 2) / 90.0))),
+            "res": 2.0,
+        }
+        for y in range(ny_n)
+        for x in range(nx_n)
+    ]
+    return {"file_prefix": "decision-test", "images": images}
+
+
+def test_decision_round_trips_without_pictures():
+    th = Thresholds()
+    r = analyse(_synthetic_scan(), {"step_x_um": 10.0, "step_y_um": 10.0}, thresholds=th)
+    assert r.found
+    assert r.contour_cells, "the chosen 50 % blob must ship its cells"
+    assert all(
+        0 <= x < r.n_fast and 0 <= y < r.n_slow for x, y in r.contour_cells
+    )
+    # the centre lies within the contour's bounding box
+    xs = [x for x, _ in r.contour_cells]
+    ys = [y for _, y in r.contour_cells]
+    assert min(xs) - 1 <= r.centre.nx <= max(xs) + 1
+    assert min(ys) - 1 <= r.centre.ny <= max(ys) + 1
+
+    d = GridScanDecision(
+        algorithm="jfjoch_gridscan_union",
+        algorithm_version="test",
+        thresholds=th.model_dump(),
+        result=r,
+    )
+    wire = json.loads(d.model_dump_json())
+    assert wire["contract"] == 1
+    assert "jpeg" not in wire["result"], "pictures never ride the JSON"
+    assert wire["result"]["centre"]["image_number"] == r.centre.image_number
+    assert wire["thresholds"]["object_union_spots"] is True
+
+    back = GridScanDecision.model_validate(wire)
+    assert back.result.centre.nx == r.centre.nx
+    assert [tuple(c) for c in back.result.contour_cells] == r.contour_cells
+
+
+def test_payload_decision_is_optional():
+    fields = RasterPayloadModel.model_fields
+    assert "decision" in fields
+    assert fields["decision"].default is None