fix(mcp): report zero packing demand accurately

OpenNest.FrontEnd.Tests/McpMixReportingTests.cs

@@ -77,6 +77,18 @@ public class McpMixReportingTests
         Assert.Empty(session.GetPlate(0).Parts);
     }
 
+    [Fact]
+    public void ZeroDemandHasZeroRemainingAndNegativeDemandIsRejected()
+    {
+        var session = Session();
+        var tools = new NestingTools(session);
+        var text = tools.PackPlate(0, "A", "0");
+        Assert.Contains("A: requested=0, placed=0, remaining=0", text);
+        Assert.Contains("zero progress", text);
+        Assert.Contains("negative", tools.PackPlate(0, "A", "-1"), StringComparison.OrdinalIgnoreCase);
+        Assert.Empty(session.GetPlate(0).Parts);
+    }
+
     private sealed class Stub : INestingEngine
     {
         public NestJobResult Solve(NestJob job, IProgress<NestJobProgress>? progress = null,

OpenNest.Mcp/Tools/NestingTools.cs

@@ -346,7 +346,7 @@ namespace OpenNest.Mcp.Tools
             {
                 var item = items[i];
                 placed[i] = counts.GetValueOrDefault(item.Drawing);
-                var remaining = item.Quantity > 0 ? (item.Quantity - placed[i]).ToString() : "unlimited";
+                var remaining = item.Quantity - placed[i];
                 sb.AppendLine($"    [{i}] {item.Drawing.Name}: requested={item.Quantity}, placed={placed[i]}, remaining={remaining}");
             }
 
@@ -405,6 +405,8 @@ namespace OpenNest.Mcp.Tools
             {
                 if (!int.TryParse(qtyStrings[i], out qtys[i]))
                     return (null, $"Error: '{qtyStrings[i]}' is not a valid quantity");
+                if (qtys[i] < 0)
+                    return (null, $"Error: negative quantity '{qtys[i]}' is not supported");
             }
 
             if (names.Length != qtys.Length)

docs/automatic-nesting.md

@@ -48,7 +48,7 @@ Invalid output is printed and rejected with exit code 2 without saving or postin
 
 MCP `autonest_plate` requires an empty target. The stdio server serializes all tool calls sharing its mutable session, so another request cannot change drawings or occupy a target during a solve. `allow_invalid` defaults to false. It reports violations and makes no changes on rejection, including with an override when the output is unrepresentable or contains multiple sheets. `engine` defaults to Default, and its description lists the built-in engines with what each suits. Fill tools (`fill_plate`, `fill_area`, `fill_remnants`, `pack_plate`) remain separate and default to the Fill strategy. Console and MCP load jobs plug-ins from `Engines/` beside their executable.
 
-MCP `pack_plate` and `autonest_plate` report each requested drawing's newly placed count and remaining ceiling, indexed by request; a skewed positive-demand mix gets an explicit `ratio not met` warning. This is reporting, not proportional packing: both tools still choose the same density-first layout. Duplicate request tokens and ambiguous drawing names are refused before placement. A zero-quantity pack request remains unlimited and has no meaningful ratio. A partially placed balanced mix can still leave demand unfilled. Strict per-sheet ratio enforcement is not available yet.
+MCP `pack_plate` and `autonest_plate` report each requested drawing's newly placed count and remaining ceiling, indexed by request; a skewed positive-demand mix gets an explicit `ratio not met` warning. This is reporting, not proportional packing: both tools still choose the same density-first layout. Duplicate request tokens and ambiguous drawing names are refused before placement. A zero-quantity pack request places zero parts for that drawing; negative quantities are rejected, and neither has a meaningful proportional mix. A partially placed balanced mix can still leave demand unfilled. Strict per-sheet ratio enforcement is not available yet.
 
 MCP `delete_plate(plateIndex)` removes only a sheet with no parts and no cutoff definitions, from either loaded or newly created session plates. Occupied, cutoff-bearing and invalid indices are refused without changing the session. After deletion every later index shifts down by one; inspect `get_plate_info` before further edits. This is session cleanup, not a data purge or a save-time option. `save_nest` lists all session plates in its response, but the existing `.nest` writer omits empty cutoff-free plates from the serialized file; reloading may therefore have fewer plates than the response says. There is no opt-in switch to preserve empty plates in the file.