Keep night lights and one atmosphere on Enhanced Earth

[Protonmatter]

Outcome

Same head as pull request 116. Night-side Enhanced Earth clouds no longer cover Black Marble, and a close view no longer stacks illustrative cloud haze on the physical atmosphere shell.

Specification and traceability

• Requirements: SOL-VIS-009
• RFC: docs/rfcs/0008-enhanced-earth.md
• ADR: Not required: display compositing only
• Governing specification: docs/SPEC.md
• Non-goals: browser qualification, volumetric clouds, changing source images

Correctness and risk

• Inputs, outputs, and failure behavior: cloud alpha is clouds.a * smoothstep(0.05, 0.22, max(N·L, 0)). When the physical atmosphere shell is queued, the cloud pass uploads zero haze tau.
• Compatibility or migration: Enhanced Earth stays off by default.
• Scientific/accuracy/provenance impact: illustrative display only.
• Privacy/security/dependency impact: none.
• Release risk, monitoring, and rollback: uncheck Enhanced Earth. This branch is also codex/enhanced-earth; do not merge this draft separately from Add optional Enhanced Earth oceans, raised clouds and shadows #116.

UI and UX

• Primary task and disclosure-level impact: night lights remain visible through the unlit cloud shell.
• Keyboard, focus, touch/pointer, responsive, and reduced-motion evidence: unchanged.
• Loading, empty, success, degraded, unavailable, and error states: unchanged.
• 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/enhancedEarth.test.mjs
  14 passed, 0 failed.

Documentation

• RFC 0008 and the enhanced-earth validation note describe the night falloff and the single close-up atmosphere.

  

[Protonmatter]

Closing this duplicate PR under the owner's approved consolidation plan. PR #116 remains the canonical Enhanced Earth change. Both PR heads were verified at 0cf75a30b90c283860158f63091ecdbad9548322 with the same master base; no unique discussion/review comments were returned for #118. The compositing rationale and validation notes remain preserved in this PR description. No branch is deleted, no commits are discarded, and this closure does not merge or accept the Earth rendering. The newer approved Earth candidate remains unrecovered; continue that recovery separately in #116.