Stack the Venus atmosphere on the Magellan ground

[Protonmatter]

Outcome

Same head as pull request 115. The seven illustrative maps stay. Default Venus keeps its Magellan source row. Illustrative maps decode once before lighting on both sphere programs. With Magellan radar and Illustrative look both on, the registered radar mosaic stays the ground and textures/illustrative/venus_atmosphere.jpg is drawn as a translucent shell above it. Lifecycle tests lock texture identity, terrain, that composite, and context-loss deletion.

Specification and traceability

• Requirements: SOL-VIS-008
• RFC: docs/rfcs/0007-illustrative-planet-looks.md (remains Draft)
• ADR: Not required: presentation and resource lifetime only
• Governing specification: docs/SPEC.md
• Non-goals: accepting the RFC, GPU qualification, deduplicating the pinned JPEGs, a qualified Venus optical profile

Correctness and risk

• Inputs, outputs, and failure behavior: u_illustrativeLinear is 1 only on a draw that binds an artistic map. displayLinear skips a second decode. The registered surface row hides only when textures are off or Illustrative look replaces the surface. Venus radar does not replace the artistic atmosphere; mode 4 on the base sphere program samples that JPEG, derives coverage (translucent disk, thicker limb, no night veil), and blends it over the Magellan pass. The physical sphere program does not contain mode 4. The procedural limb is skipped while the shell is drawn.
• Compatibility or migration: Source-qualified stays the default. Without radar, Illustrative look still replaces Venus with the opaque artistic cloud deck.
• Scientific/accuracy/provenance impact: artistic maps stay out of the registered inventory. The shell is a display composite, not a measured cloud top or co-registered opacity. Mars terrain stays suspended whenever the look is selected.
• Privacy/security/dependency impact: none. Leaving the view deletes ready illustrative textures.
• Release risk, monitoring, and rollback: switch back to Source-qualified. This branch is also codex/planet-look-presets; do not merge this draft separately from Add optional illustrative looks for seven planets #115.

UI and UX

• Primary task and disclosure-level impact: Magellan citation stays on the Venus card when radar is on, and the card says the artistic atmosphere is drawn above that ground. Help text matches that stack.
• Keyboard, focus, touch/pointer, responsive, and reduced-motion evidence: existing controls.
• Loading, empty, success, degraded, unavailable, and error states: a focused body evicted from the two-map cache is no longer told to focus or zoom. If the Venus atmosphere map is not retained, the note says it is not drawn and the Magellan ground remains.
• Manual usability/accessibility checks: not run.

Validation evidence

• Unit tests cover positive, boundary, and negative cases where applicable.
• Contract/integration tests cover producer-consumer boundaries where applicable.
• Browser end-to-end and visual assertions cover user-visible rendering where applicable.
• Deterministic generation/accuracy checks pass where applicable.
• Rust, Python, Node, and whole-web coverage gates remain at least 90%.
• Locally unavailable checks are named and left to required CI.

Commands and results:

node --experimental-vm-modules --test tests/web/illustrativeAppearance.test.mjs tests/web/orreryIllustrativeLifecycle.test.mjs tests/web/detailCoverage.test.mjs tests/web/orreryScatteringShaders.test.mjs tests/web/venusCloudDeck.test.mjs
  43 passed, 0 failed.

The Venus lifecycle test checks two passes. Before the mosaic finishes loading, the ground does not bind the artistic texture. After that image loads, the ground pass is texMode 3 on the Magellan texture, and the shell pass still binds the artistic map at mode 4, with a 40 km display lift, straight alpha, depth test without depth write, and backface culling. A rasterized screenshot of that composite was not captured; this worktree has no built wasm package, so the page was not opened in a browser.

Documentation

• SPEC, RFC 0007, and the plan match the renderer. RFC 0007 stays Draft.