Fixed #8735.

The glTF KHR_materials_specular specularFactor (and specularColorFactor) were silently dropped from the shader when their corresponding texture was set on the same material, producing renders that didn't match the spec or other engines (three.js, Babylon, Khronos sample viewer).

Root cause

StandardMaterialOptionsBuilder only emitted STD_SPECULAR_CONSTANT / STD_SPECULARITYFACTOR_CONSTANT when the corresponding map was absent, unless the user explicitly set specularTint / specularityFactorTint. The glTF parser sets material.specularTint = true (which masked the color-factor case in practice), but not material.specularityFactorTint, so the scalar specularFactor was silently dropped whenever specularTexture was present.

Fix

Auto-include the constant whenever its value differs from the multiplicative identity (white for color, 1 for the scalar factor), mirroring how metalness is already handled in the same file. The public specularTint / specularityFactorTint flags remain as explicit overrides.

Changes:

• standard-material-options-builder.js: gate specularTint / specularityFactorTint on the value differing from identity, not on map absence.
• standard-material.js: match the gating in the uniform-upload path; update JSDoc on the two flags to describe the new auto-behaviour.
• Add a hidden test example `test/specular` that loads the Khronos SpecularTest grid as visual regression coverage.

API Changes:

• `StandardMaterial.specularTint` and `StandardMaterial.specularityFactorTint` remain public boolean flags, but are now effectively redundant overrides: the constant is auto-applied whenever it isn't the identity value. Setting them to `true` explicitly still works. JSDoc updated to reflect this.

Examples:

• New `examples/src/examples/test/specular.example.mjs` (hidden in production) loading the Khronos `SpecularTest.glb` grid for visual verification of `KHR_materials_specular`.