Document CLOUDFLARE_CF_FETCH_ENABLED and CLOUDFLARE_CF_FETCH_PATH environment variables

Add documentation for two new environment variables that control cf.json
fetching behavior in Miniflare:

- CLOUDFLARE_CF_FETCH_ENABLED: disable cf.json fetching entirely
- CLOUDFLARE_CF_FETCH_PATH: use a custom cache location for cf.json

Updates both the system environment variables reference page and the
Miniflare get-started guide.

Related: cloudflare/workers-sdk#12469
Co-Authored-By: pbacondarwin@cloudflare.com <pete@bacondarwin.com>

Author: devin-ai-integration[bot]

src/content/docs/workers/testing/miniflare/get-started.mdx

@@ -193,7 +193,7 @@ console.log("Listening on :5000");
 #### `Request#cf` Object
 
 By default, Miniflare will fetch the `Request#cf` object from a trusted
-Cloudflare endpoint. You can disable this behaviour, using the `cf` option:
+Cloudflare endpoint and cache it to `node_modules/.mf/cf.json`. You can disable this behaviour, using the `cf` option:
 
 ```js
 const mf = new Miniflare({
@@ -209,6 +209,20 @@ const mf = new Miniflare({
 });
 ```
 
+You can also control this behaviour using [system environment variables](/workers/wrangler/system-environment-variables/), which is useful when you are not using the Miniflare API directly (for example, when running `wrangler dev`):
+
+```sh
+# Disable cf fetching entirely (uses fallback data)
+export CLOUDFLARE_CF_FETCH_ENABLED=false
+npx wrangler dev
+
+# Use a custom cache location for cf.json
+export CLOUDFLARE_CF_FETCH_PATH=/tmp/.cf-cache.json
+npx wrangler dev
+```
+
+The explicit `cf` option in the Miniflare API takes precedence over both environment variables.
+
 ### HTTPS Server
 
 To start an HTTPS server instead, set the `https` option. To use the [default shared self-signed certificate](https://github.com/cloudflare/workers-sdk/tree/main/packages/miniflare/src/http/cert.ts), set `https` to `true`:

src/content/docs/workers/wrangler/system-environment-variables.mdx

@@ -90,6 +90,13 @@ Wrangler supports the following environment variables:
 
 * `WRANGLER_R2_SQL_AUTH_TOKEN` <Type text="string" /> <MetaInfo text="optional" />
   - API token used for executing queries with [R2 SQL](/r2-sql).
+
+- `CLOUDFLARE_CF_FETCH_ENABLED` <Type text="string" /> <MetaInfo text="optional" />
+  - Controls whether [Miniflare](/workers/testing/miniflare/) fetches the `cf.json` file containing [`Request.cf`](/workers/runtime-apis/request/#the-cf-property-requestinitcfproperties) properties from Cloudflare during local development. Set to `"false"` or `"0"` to disable fetching entirely and use fallback data. No `node_modules/.mf/cf.json` file will be created when disabled. Defaults to `"true"`. This is particularly useful for non-JavaScript projects (such as Rust or Go Workers) that do not want a `node_modules` directory created automatically. The explicit `cf` option in the [Miniflare API](/workers/testing/miniflare/get-started/#requestcf-object) takes precedence over this environment variable.
+
+- `CLOUDFLARE_CF_FETCH_PATH` <Type text="string" /> <MetaInfo text="optional" />
+  - Specifies a custom path for caching the `cf.json` file, overriding the default `node_modules/.mf/cf.json` location. This is useful for multi-project setups where you want a shared cache location, or for projects that want to store the cache outside of `node_modules`. The explicit `cf` option in the [Miniflare API](/workers/testing/miniflare/get-started/#requestcf-object) takes precedence over this environment variable, and `CLOUDFLARE_CF_FETCH_ENABLED=false` takes precedence over this variable.
+
 ## Example `.env` file
 
 The following is an example `.env` file:
@@ -103,6 +110,7 @@ CLOUDFLARE_API_BASE_URL=https://api.cloudflare.com/client/v4
 WRANGLER_LOG=debug
 WRANGLER_LOG_PATH=../Desktop/my-logs/my-log-file.log
 WRANGLER_R2_SQL_AUTH_TOKEN=<YOUR_R2_API_TOKEN_VALUE>
+CLOUDFLARE_CF_FETCH_ENABLED=true
 ```
 
 ## Deprecated global variables