refactor(helpers): extract duplicated setFormDataHeaders into a shared helper - #11062

Summary

lib/helpers/resolveConfig.js and lib/adapters/http.js each carry their own copy of setFormDataHeaders (plus the FORM_DATA_CONTENT_HEADERS list). The two copies are identical except that the resolveConfig.js one guards against a missing headers object (formHeaders || {}).

This PR moves the function to lib/helpers/setFormDataHeaders.js (one helper per file, matching the rest of lib/helpers) and imports it from both call sites, keeping the defensive variant — so the http adapter now also tolerates a FormData implementation whose getHeaders() returns undefined.

No other behavior change: both call sites already invoke it with the same (headers, data.getHeaders(), formDataHeaderPolicy) shape.

Testing

• npm run lint clean
• vitest run --project unit: 946 passed — including all 89 form-data-related tests that exercise both touched call paths. (The two failures on my machine — fetch failed error as an AxiosError with ERR_NETWORK and the DNS should handle errors case — fail identically on an unmodified checkout; they are environment/DNS-dependent, not related to this change.)

Found with an automated near-duplicate-helper detector I'm building (QodeX); the consolidation itself was reviewed and applied by hand.

Summary by cubic

Centralized FormData header handling by extracting setFormDataHeaders into lib/core/setFormDataHeaders.js and using it in both resolveConfig and the Node HTTP adapter. Behavior is unchanged; the adapter now also tolerates FormData#getHeaders() returning undefined when formDataHeaderPolicy: 'content-only'.

Description

• Summary of changes
  • Added lib/core/setFormDataHeaders.js and imported it in lib/helpers/resolveConfig.js and lib/adapters/http.js.
  • Preserved content-only policy behavior and the guard for missing formHeaders.
• Reasoning
  • Removed duplicate logic and kept axios-specific behavior in core rather than expanding generic helpers.
• Additional context
  • Both call sites already call it as (headers, data.getHeaders(), formDataHeaderPolicy). Pre-release changelog notes the Node robustness fix.

Docs

• No user-facing changes. Optionally add a short note in /docs/form-data.md confirming both environments honor formDataHeaderPolicy and tolerate missing form-data headers.

Testing

• Added a Node HTTP regression test to ignore undefined getHeaders() results with content-only policy.
• Existing unit tests continue to cover both paths.

Semantic version impact

• Patch: internal refactor with no API changes; minor robustness improvement only.

^{Written for commit 14c01a0. Summary will update on new commits.}