[dvkam]

Fixes #647

Preserve built _headers files when uploading Worker versions that keep active secrets. Forward authored and generated files through the supported asset metadata format, without rewriting their contents.

Keep reserved metadata files out of downloadable assets even when custom ignore rules try to include them. Clarify how framework apps configure headers on native Cloudflare deployments.

Validation:

• Verified a real TanStack build and preview, then both upload paths against a local provider server.
• Verified that the forwarded text produces the configured CSS and JavaScript headers locally.
• Rebased onto main at f184a2f. All 170 focused tests and 33 workspace type-check tasks pass. Scoped formatting, lint and diff checks pass.
• Full suite after rebase: 15,409 passed, 19 failed. Eighteen failures are in the initializer/Nitro test files that also failed during the original local verification. The additional Cloudflare-plugin timeout passes in isolation, all 7 tests. Four preview suites initially lacked generated output; all four pass after rebuilding.

No live Cloudflare deployment was performed.