feat(react-router-serve): add DISABLE_COMPRESSION environment variable

[kklem0]

Problem

react-router-serve unconditionally applies the compression middleware (for non-RSC builds). When the app server runs behind a CDN / edge cache that also compresses — in our case Azure Front Door — origin-side compression breaks edge caching: the origin's compressed response is chunked with no Content-Length, and when Front Door caches it, it re-serves the compressed body stamped with the uncompressed Content-Length. Clients receive a truncated body and hang waiting for the rest (we hit ~91 s stalls in production). With the origin serving identity responses, the edge compresses and caches correctly.

Today the only escape hatch is the documented one: "migrate to @react-router/express". In practice that means maintaining a full re-implementation of cli.ts in order to remove a single middleware line — a copy that silently drifts as react-router-serve evolves (ours already lagged behind the RSC handling and the absolute-base publicPath fix that landed upstream since we forked it).

Proposal

Support a DISABLE_COMPRESSION environment variable (true or 1) that skips the compression() middleware:

DISABLE_COMPRESSION=true react-router-serve build/server/index.js

Why an env var, and why this doesn't conflict with the "no customization options by design" policy:

• Env vars are already the configuration surface of react-router-serve — HOST and PORT work exactly this way. This is deployment-environment adaptation, not server customization: the middleware itself cannot detect that a compressing cache sits in front of it.
• react-router-serve already treats compression as conditional: RSC builds run with compression fully disabled (disable compression for RSC responses for now #14381).
• The alternative (fully ejecting to Express) forces users to fork ~200 lines of server for a one-line toggle, which seems worse for the ecosystem than one narrowly-scoped env var.

Changes

• packages/react-router-serve/cli.ts — skip compression() when DISABLE_COMPRESSION is true/1
• docs/api/other-api/serve.md — document the new env var alongside HOST/PORT
• packages/react-router-serve/.changes/minor.disable-compression-env-var.md — change file
• integration/react-router-serve-test.ts — tests asserting the default response is compressed and the DISABLE_COMPRESSION=true response is identity-encoded, against the real spawned server
• integration/helpers/create-fixture.ts — allow passing extra env vars to the spawned react-router-serve process (additive optional param)

Testing

• pnpm build, then playwright test --config ./integration/playwright.config.ts react-router-serve-test — all pass, including the two new compression tests (verified across chromium/firefox/webkit/msedge projects).
• tsc for the serve package and prettier --check on all touched files pass.

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Type	Change
minor	Add support for a DISABLE_COMPRESSION environment variable that disables the built-in compression middleware, for deployments where a proxy or CDN in front of the app server handles compression instead