Calypso cutaway + export angles

name: Calypso cutaway angles overview: Clean up headless PNG clutter with stable overwrite names, replace the interior-only near-eye “cutaway” with a real world-space slicing plane that culls the camera-side half-space (orbit + interior), and expand the tour with warship/fan-style exterior angles including a longitudinal cutaway. todos:

• id: export-cleanup

content: Stable PNG overwrite names + purge legacy -headless- clutter on headless run status: completed

• id: slice-plane

content: World-space cutaway plane; cull camera-side half-space in orbit + interior; cut-face cue status: completed

• id: orbit-presets

content: Warship-style orbit presets + headless tour (bow/broadside/stern/cutaway); trim wire from default tour status: completed

• id: verify-readme

content: Re-export headless + update README tour checklist status: completed isProject: false

Problem

• Exports under %LocalAppData%\Novolis\CalypsoCad\generated\exports\ accumulate timestamped duplicates (*-headless-yyyyMMdd-…png).
• CutawayPartial only runs in Interior, and `GetCutPlane` places a plane 1.1 m in front of the eye along look — near-clip style, not a shipyard slice.
• Headless tour is mostly plan + one orbit + room solids; missing classic warship / fan-render exterior angles and a readable cutaway shot.

Approach (locked)

Slicing plane: one world plane (cutPt, cutN). Cull any draw whose representative point satisfies Dot(p - cutPt, cutN) > 0 when cutN points toward the camera (camera-side half-space discarded). Geometry on/behind the far side of the plane stays. Enable this in Orbit and Interior when WireMeshMode == CutawayPartial.

Default orbit cut: longitudinal centerline (cutPt = ship mid, cutN = ±UnitX chosen so camera sits on the culled side). Interior cut: vertical plane through selected-space center, normal toward eye (architectural section through the room).

Exports: stable basenames overwrite; delete leftover *-headless-*.png at start of each headless run.

flowchart LR
  presets["Named camera presets"] --> orbit["Orbit / section shots"]
  plane["World cutPt + cutN"] --> cull["Cull camera-side half-space"]
  cull --> draw["Walls spaces boxes openings"]
  orbit --> png["Stable PNG overwrite"]
  draw --> png

Phase 1 — Export cleanup

In `HeadlessPngExporter.cs` and `ViewportPngExporter.AllocatePath`:

• Write {kind}.png (no timestamp), overwrite in place.
• At headless start: delete *-headless-*.png in the exports dir (legacy clutter only).
• Keep UI single-frame export as {kind}-{timestamp}.png only when user hits Export PNG (E) so manual snaps do not collide with the tour set.

Phase 2 — Real slicing-plane cutaway

In `CalypsoRenderer.cs` + `CalypsoSession.cs`:

1. Add session fields (or renderer state): CutPlaneOrigin, CutPlaneNormal, CutawayEnabled (driven by WireMeshMode.CutawayPartial).
2. Replace GetCutPlane:

• Orbit: origin at hull mid (0, midY, 0); normal = ±UnitX (pick sign so Dot(eye - origin, normal) > 0); optional beam cut preset uses ±UnitZ.
• Interior: origin = selected space center; normal = horizontal toward eye (Y=0), so the near half of the room (camera side) is removed.

1. Enable cutaway culling for orbit (today gated && interior in DrawSpace / DrawWall). Apply the same half-space test to spaces, walls, boxes, openings, props.
2. Draw a thin cut-face cue: vertical line grid / edge strip on the plane (few DrawLines along LOA or beam) so the slice reads in PNGs.
3. Fix cull semantics once: rename helper to CulledByCutPlane = camera-side of plane; use consistently everywhere BehindCut is used today.

No Raylib DrawTriangle3D / stencil — AABB/line cull only (same constraint as detail pass).

Phase 3 — Warship / fan-render angle presets

Add ApplyOrbitPreset(string id) on the renderer (sets _orbit yaw/pitch/distance/target). Headless tour captures these stable names:

Interior wire variants leave the default tour (still available via UI W).

Preset numbers (approximate, tune after one export pass):

• Bow quarter: yaw ~0.9, pitch ~0.45, distance ~95, target mid-forward
• Broadside: yaw ~0 / π, pitch ~0.22, distance ~100
• Stern quarter: yaw ~2.4, pitch ~0.35, distance ~90
• Cutaway: yaw such that eye is on +X (or −X), pitch ~0.3, distance ~85; enable CutawayPartial

Phase 4 — Verify + README

• Run --headless; confirm exports dir is a small stable set (no timestamp pile-up).
• Spot-check: plan-deck-0.png still clean; orbit-cutaway-long.png shows half-hull with interior partitions; bow/broadside/stern read as intentional gallery shots.
• Update `README.md` tour checklist to the new filenames + one sentence on cutaway = world slicing plane (camera-side culled).

Explicitly not in this pass

• Engineering arrangement / WT / vestibule generator work (calypso_engineering_finish) — separate track.
• GPU clip planes / stencil / DrawTriangle3D.
• OBJ furniture import.