Go extractor does not support build-mode: none, preventing overlay/incremental analysis on PRs

Start with the Go extractor's build-mode handling and the buildless option referenced in the issue; inspect codeql-extractor.yml for declared options, including trap.cache.*. Reproduce with build-mode: none and compare extraction behavior with the existing workaround. Done means Go accepts the mode and overlay or incremental extraction works without those environment variables.

Problem

The Go extractor (CodeQL CLI 2.25.1) does not support build-mode: none:

A fatal error occurred: Go does not support the none build mode.
Please try using one of the following build modes instead: autobuild, manual.

This means Go cannot benefit from overlay/incremental analysis on pull requests. JavaScript gets this automatically — in our monorepo we see Overlay filter removed 4311 out of 4312 files from extraction on JS PRs, reducing a full extraction to just the changed files. Go still does a full extraction of every package on every PR (~2.5 min for autobuild + ~1.5 min for analysis in a large monorepo).

Current workaround

We use legacy env var hacks to skip the actual go build:

env:
  CODEQL_EXTRACTOR_GO_FAST_PACKAGE_INFO: y
  CODEQL_EXTRACTOR_GO_BUILD_COMMAND: false

This avoids compilation but still runs full type extraction for every Go package on every PR.

Expected behavior

Setting build-mode: none should work for Go, enabling overlay/incremental analysis on PRs (as it already does for JavaScript/TypeScript). The Go extractor already has a buildless/standalone extraction path (DEPRECATED: Use --build-mode none instead appears in the extractor options for the buildless flag), so the extraction capability exists — it just isn't wired up to accept build-mode: none.

Additional context

• We also noticed that Go's extractor does not declare trap.cache.* options in codeql-extractor.yml, so TRAP caching is also unavailable for Go.
• The v3→v4 action upgrade enabled overlay for JS automatically, but there's no path to get the same benefit for Go.
• codeql-action v4.35.1, CodeQL CLI 2.25.1