Skip non-MVT content types when fetching tiles

[ibgreen]

Motivation

• Avoid attempting to parse HTML/text/JSON responses (error pages, HTML error bodies, etc.) as Mapbox Vector Tiles which causes parsing errors and wasted CPU.
• Make Content-Type handling reusable and robust by centralizing header normalization logic.

Description

• Added a Content-Type parser utility parseContentType in modules/loader-utils/src/lib/request-utils/parse-content-type.ts and exported it from modules/loader-utils/src/index.ts.
• Updated MVTTileSource.getTile (modules/mvt/src/mvt-source.ts) to call parseContentType on response.headers.get('content-type') and early-return null for known non-MVT types (e.g. text/*, application/json, application/xml) or when the header is present but not in the allowlist.
• Positive allowlist uses MVTFormat.mimeTypes and additionally accepts image/* and application/octet-stream as valid tile payloads.
• Added tests: a unit test for parseContentType (modules/loader-utils/test/lib/request-utils/parse-content-type.spec.ts) and a mvt test that simulates a text/html response to verify MVTTileSource#getTileData returns null and does not call MVTLoader.parse (modules/mvt/test/mvt-source.spec.ts).

Testing

• Added unit tests (not run in this environment):
  • modules/loader-utils/test/lib/request-utils/parse-content-type.spec.ts (verifies header normalization)
  • modules/mvt/test/mvt-source.spec.ts (new test verifies HTML responses return null and MVTLoader.parse is not invoked)
• Attempted to run formatting and tests: yarn lint fix and yarn test node — both could not be executed in this environment due to missing node_modules / install state (install required).

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Codex Task

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[chatgpt-codex-connector]

Import parseContentType as a value, not type-only

Because parseContentType is imported via a type-only import, it is erased from the JS output. When getTile executes, parseContentType is not defined and a ReferenceError is thrown before any tile parsing can happen. This will break all runtime tile fetching paths that call MVTTileSource.getTile, regardless of the response headers. Import parseContentType as a value (or add a separate non-type import) so it is available at runtime.

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