MCP feedback for agents: feature summary, warnings, check, solid_box, print tools

[jackControls]

Agents driving the MCP server got very little back from a script run: a step count, or a one-line error, and a raw scene when they asked. Everything they needed for verification (holes with positions, counts per class, an overlay on the print) had to be rebuilt outside the engine, and the mistakes that cost the most never raised an error at all. This PR moves that feedback into the host.

Script runs answer in feature terms

cad_interface script results now carry:

• summary: bodies with bounding boxes and face counts, the hole count and a tally by class (diameter, style, counterbore, thread, through or depth); detail: "full" lists every hole with position, normal, depth, face and thread. Holes come from the feature history; an imported STEP has none, so its cylinders are read back from the geometry (hole_source: "scene").
• warnings for the silent mistakes: hole_position_ignored (a positions list that leaves out position, so that point is never drilled), holes_overlap, hole_outside_body, blind_depth_exceeds_body, unused_binding.

Failing steps are more useful: a selector that matched several entries lists the candidates with the fields that tell them apart; one that matched nothing lists what each where test asked for and the values actually present at those pointers; an unknown result name lists similar earlier names.

Expected versus built

Two new cad_interface actions read the current document the same way: summary returns the feature summary, and check compares an expected feature table (bbox, holes with x, y, optional z, diameter, counterbore_diameter, through, depth) with the built model within tolerance_mm, reporting matched holes with offsets, missing holes with the nearest built one, and extras.

solid_box

A rectangular block from an origin corner and a size, as ordinary editable history: an offset construction plane when the origin is off the XY plane, a dimensioned rectangle fixed at its corner, one extrude (new_body, join, cut, intersect). The script trace records the one call, not its parts. It is a generic primitive; part-specific generators stay in plugins.

Reading scanned prints as a host service

New crate crates/print (host-neutral, png only; PDF pages render through pdftoppm) and four read-only tools: print_calibrate (plate outline by aspect ratio and line weight, skew-aware corners), print_crop (a millimetre window with a tick grid and the document's holes drawn on it, returned as MCP image content), print_probe (what is drawn at or near each model hole: symbol with centre and offset, dot, dashed, none) and print_symbols (drawn circles and dots matched against the model). holes defaults to the current document; frame: "bbox_min" shifts them to the bodies' lower-left corner.

Tool results that carry a picture now include an image content block next to the text.

Tests and docs

Script-crate tests for the diagnostics; MCP tests for the summary, warnings, check, solid_box (offset plane, cut, single trace entry) and the print tools on a synthetic sheet (no real drawings in the repository); print-crate tests on synthetic images. README section "Feedback for agents"; crate index; interface catalog groups solid/primitives and print/read.

[jeffglousher]

MCP agent feedback is coherent and on-style: script summaries/warnings, summary/check actions, solid_box as editable history (single trace), and read-only print tools with image content. Host-neutral print crate + MCP/script tests look solid. Approving while MCP acceptance/packages finish (core crates + frontend green).