Add fetcherKey APIs and update fetcher persistence architecture

.changeset/fetcher-key.md

@@ -0,0 +1,5 @@
+---
+"react-router-dom": minor
+---
+
+Add support for manual fetcher key specification via `useFetcher({ key: string })` so you can access the same fetcher instance from different components in your application without prop-drilling ([RFC](https://github.com/remix-run/remix/discussions/7698))

.changeset/fetcher-persistence.md

@@ -0,0 +1,15 @@
+---
+"react-router-dom": minor
+"@remix-run/router": minor
+---
+
+Fix the persistence behavior of fetchers so that they don't get cleaned up on `fetcher` unmount, but instead get cleaned up on fetcher completion (which may be after the fetcher unmounts in the UI) ([RFC](https://github.com/remix-run/remix/discussions/7698))
+
+- This is a long-standing bug fix as the `useFetchers()` API was always supposed to only reflect **in-flight** fetcher information for pending/optimistic UI
+- It was not intended to reflect fetcher data or hang onto fetchers after they returned to an `idle` state
+- To do this we've re-architected things a bit and now it's the `react-router-dom` layer that holds stateful fetcher data to expose via `useFetcher()`
+- The `router` now only knows about in-flight fetchers - they do not exist in `state.fetchers` until a `fetch()` call is made, and they are removed when it returns to `idle` (and the data is handed off to the React layer)
+- **Warning:** This has a few potential "breaking bug" side-effects for your application:
+  - `useFetchers()` longer exposes the `data` field because it now only represents in-flight fetchers, and thus it does not reflect fetchers that have completed and have data
+  - Fetchers that previously unmounted _while in-flight_ will not be immediately aborted and will instead be cleaned up once they return to an `idle` state. They will remain exposed via `useFetchers` while in-flight so you can still access pending/optimistic data after unmount.
+  - Fetchers that complete while still mounted will no longer appear in `useFetchers()` - they served effectively no purpose in there since you can access the data via `useFetcher().data`)

.changeset/fix-type-bug.md

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+---
+"@remix-run/router": patch
+---
+
+Fix `router.deleteFetcher` type definition which incorrectly specified `key` as an optional parameter

.changeset/remove-get-fetcher.md

@@ -0,0 +1,5 @@
+---
+"@remix-run/router": minor
+---
+
+Remove the internal `router.getFetcher` API

.changeset/submit-navigate-fetcherKey.md

@@ -0,0 +1,8 @@
+---
+"react-router-dom": minor
+---
+
+Add `navigate`/`fetcherKey` params/props to `useSumbit`/`Form` to support kicking off a fetcher submission under the hood with an optionally user-specified key
+
+- Invoking a fetcher in this way is ephemeral and stateless
+- If you need to access the state of one of these fetchers, you will need to leverage `useFetcher({ key })` to look it up elsewhere

package.json

@@ -113,16 +113,16 @@
       "none": "48.3 kB"
     },
     "packages/react-router/dist/react-router.production.min.js": {
-      "none": "13.9 kB"
+      "none": "13.8 kB"
     },
     "packages/react-router/dist/umd/react-router.production.min.js": {
       "none": "16.3 kB"
     },
     "packages/react-router-dom/dist/react-router-dom.production.min.js": {
-      "none": "15.9 kB"
+      "none": "16.5 kB"
     },
     "packages/react-router-dom/dist/umd/react-router-dom.production.min.js": {
-      "none": "22.1 kB"
+      "none": "22.7 kB"
     }
   }
 }