Problem

On the Node adapter, NodeRequestHeaders.get() / has() / getSetCookie() had a fast path that read Node's collapsed req.headers object before _headers was materialized. For headers Node treats as single-value (authorization, content-type, …), Node keeps only the first occurrence, whereas the rawHeaders-materialized _headers appends all occurrences, matching WHATWG Headers.

As a result, get('authorization') returned a different value depending on whether the Headers object had been iterated first:

get('authorization') BEFORE iteration = "Bearer AAA"              <- fast path, first only
get('authorization') AFTER  iteration = "Bearer AAA, Bearer BBB"  <- via rebuilt _headers
native Headers.get()                  = "Bearer AAA, Bearer BBB"  <- WHATWG (correct)

This is a spec divergence and a header-confusion primitive: two layers reading the same header can disagree if one reads before iteration and the other after. Reproduced end-to-end against a live Node server over a raw socket (duplicate Authorization / Content-Type lines — a normal fetch client can't send these).

Fix

Route get() / has() / getSetCookie() through the rawHeaders-materialized _headers consistently, dropping the if (this.#headers) fast branches. The result no longer depends on prior iteration order and matches native Headers.

Node adapter only — other adapters (Deno/Bun/Cloudflare/Bunny/generic/AWS-Lambda) use native Request/Headers and are unaffected.

Tests

• Added a regression test in test/node-headers.test.ts sending duplicate authorization / content-type headers and asserting the joined value both before and after iteration.
• Full node suite passes (144 passed, 6 skipped); typecheck and lint clean.
• Post-fix raw-socket repro confirms before and after both return the joined value and match native Headers.

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