PathOutlineLayer / PathMarkerLayer: incomplete v9 port, example non-functional

[charlieforward9]

Summary

PathOutlineLayer and PathMarkerLayer in @deck.gl-community/layers were never fully ported from deck.gl/luma.gl v8 to v9. The path-marker-outline example (added in #403) renders plain colored paths with no visible outlines and no directional arrow markers.

#403 added the example, docs, and partial parameter updates, but was generated by Codex and only verified with lint/vitest — never visually tested. It also removed a dummyTexture workaround from an earlier incomplete v9 migration attempt, introducing a WebGL feedback loop.

Broken APIs (pre-existing, predate #403)

These v8 patterns were present before #403 and have never worked with v9:

• model.updateModuleSettings() — removed in luma.gl v9 (replaced by model.shaderInputs.setProps())
• model.draw({uniforms, parameters, framebuffer}) — v8 API; v9 requires model.draw(renderPass)
• GL.UNSIGNED_BYTE for attribute type — v9 expects string types like uint8
• this.state.attributeManager — deprecated, should be this.getAttributeManager()
• Shader: texture2DProj — GLSL ES 1.0; must be textureProj in ES 3.0
• Shader: #version 300 es in module code — should not be in shader modules
• Shader: duplicate out vec4 fragColor — declared in outline module and main shader
• Shader: vec4(color.rgb * 0.5, color.a) — creates value but never assigns it; outline darken effect was always a no-op
• Arrow2DGeometry — texCoords array has 3 components per vertex but declares size 2, causing vertex count mismatch
• depthTest: false in PathMarkerLayer — not a valid luma.gl v9 parameter

Introduced by #403

• Removed the dummyTexture from state and bound shadowmapTexture as both sampler input and framebuffer render target, causing a WebGL feedback loop

Questions

1. Should these layers be deprecated? The outline effect uses custom multi-pass rendering with a shadowmap, which is fragile against luma.gl API changes. The arrow markers could be achieved with simpler approaches (e.g. IconLayer placed along paths).
2. If kept, they need a proper v9 rewrite — the draw method needs render pass management, shader modules need updating to v9 patterns, and the example needs visual verification.

[charlieforward9]

@georgioskarnas Ib made me aware that you made these layers work beautifully in the nebula days - do you have any bandwidth these days to try to restore them?