fix(ssr): stop a pending seed reading the registry after a failed render

.changeset/failed-render-seed.md

@@ -0,0 +1,5 @@
+---
+"effect-atom-svelte": patch
+---
+
+A server render that fails while a serializable atom's result is still being prepared for the browser no longer reports an unhandled rejection ("registry is disposed"). The provider disposes of its registry when the failed render ends, and the pending result now stops there instead of reading from it.

packages/effect-atom-svelte/src/Hooks.svelte.ts

@@ -15,6 +15,7 @@ import {
   decodeSeed,
   encodeSeed,
   isWaiting,
+  noSeed,
   revalidatesOnHydrate,
 } from "./internal/hydration.ts";
 import { onRenderEnd } from "./internal/renderEnd.ts";
@@ -1054,7 +1055,13 @@ const seedOnServer = (
 ): Promise<void> => {
   // Mounted until the render ends, so the settled node is what the render reads.
   const release = serverMount(registry, atom);
-  onRenderEnd(release);
+  // A render ends before its seeds settle only when it fails, as when a later reader throws during
+  // setup. The provider has disposed of the registry by then, so the seed reads nothing from it.
+  let ended = false;
+  onRenderEnd(() => {
+    ended = true;
+    release();
+  });
   // hydratable hands every later reader of a key the first reader's value, but Svelte's dev build
   // also runs each later reader's callback and throws hydratable_clobbering if what it encodes
   // differs. Reading the atom again there would encode whatever it holds by then, so a later
@@ -1064,6 +1071,9 @@ const seedOnServer = (
   const encoded = hydratable(key, () => {
     claim.own = (async () => {
       await undefined;
+      if (ended) {
+        return noSeed;
+      }
       if (claim.first !== claim.own) {
         return await claim.first;
       }
@@ -1079,6 +1089,9 @@ const seedOnServer = (
           await awaitResult(registry, atom, { suspendOnWaiting: settled });
         }
       }
+      if (ended) {
+        return noSeed;
+      }
       return encodeSeed(key, encode, serverGet(registry, atom));
     })();
     return claim.own;

packages/effect-atom-svelte/src/internal/hydration.ts

@@ -24,7 +24,7 @@ export const revalidatesOnHydrate = (option: boolean | undefined): boolean =>
  * What the server sends for a result it doesn't pass on, so the browser computes the atom itself.
  * An encoded `AsyncResult` is an object, never `null`.
  */
-const noSeed = null;
+export const noSeed = null;
 
 /**
  * Encodes the server's result for the page, or returns the no-seed marker for a result that must