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Nic-Polumeyv · 2026-07-17T13:47:07Z

A boundary that failed during SSR hydrates via #hydrate_failed_content, which never calls onerror and passes the failed snippet a no-op reset. Both came in with #17672, whose docs say onerror "will be called upon hydration with the deserialized error object". Once hydrated as failed, the boundary can never leave that state. Downstream this is what keeps SvelteKit's +error.svelte mounted after navigating away from a server-rendered error page (sveltejs/kit#16345).

This extracts the reset/onerror machinery from #handle_error into #create_reset and uses it in the hydration path too. onerror is invoked in a microtask because it may mutate state, which is disallowed while hydrating. #handle_error already invokes it asynchronously, so the timing matches the error path.

The tests flip a recovered flag before calling reset, since the child would otherwise throw again. That is the intended retry pattern, and the same one kit uses when it resets route boundaries on navigation. Verified against kit end to end, hydrating a server-rendered error page and navigating away now tears it down with no kit changes needed.

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pkg-svelte-dev · 2026-07-17T13:47:10Z

Install the latest version of svelte from 906d82f:

pnpm add https://pkg.svelte.dev/svelte/c/906d82fc4eeb7234d929c274ee3ed7ba0eca7cd5

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/svelte/pr/18556

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This PR is from a fork. A maintainer must approve approve each commit before it can be built and installed.

changeset-bot · 2026-07-17T13:47:11Z

🦋 Changeset detected

Latest commit: 906d82f

The changes in this PR will be included in the next version bump.

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Nic-Polumeyv · 2026-07-17T13:50:00Z

One asymmetry I noticed while writing this but left alone. In #handle_error the failed snippet is rendered with effect.b = this and BOUNDARY_EFFECT, and errors thrown inside it are routed through invoke_error_boundary. The hydration path renders it in a bare branch(), so an error thrown while hydrating a failed snippet propagates differently. Unifying them would have changed behavior beyond what this PR fixes, so I kept it out. Happy to follow up here or separately if you want them aligned.

dummdidumm

thank you!

This PR was opened by the [Changesets release](https://github.com/changesets/action) GitHub action. When you're ready to do a release, you can merge this and the packages will be published to npm automatically. If you're not ready to do a release yet, that's fine, whenever you add more changesets to main, this PR will be updated. # Releases ## svelte@5.56.8 ### Patch Changes - fix: call `onerror` and provide a working `reset` when hydrating a failed boundary ([#18556](#18556)) - fix: preserve select selection when spread attributes omit value ([#18561](#18561)) Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Bumps Svelte from **5.56.7 → 5.56.8** across every workspace. ## Upstream changes Patch release, two fixes — the first lands directly on a Mochi code path, since the preprocessor auto-wraps every `mochi:hydrate*` island in a `<svelte:boundary>`: - fix: call `onerror` and provide a working `reset` when hydrating a failed boundary ([sveltejs/svelte#18556](sveltejs/svelte#18556)) - fix: preserve select selection when spread attributes omit value ([sveltejs/svelte#18561](sveltejs/svelte#18561)) ## Bump table | Workspace | Field | From | To | | --- | --- | --- | --- | | `packages/mochi` | devDependencies | `^5.56.7` | `^5.56.8` | | `packages/mochi-rsvelte` | devDependencies | `^5.56.7` | `^5.56.8` | | `packages/site` | dependencies | `^5.56.7` | `^5.56.8` | | `packages/demos` | dependencies | `^5.56.7` | `^5.56.8` | | `packages/docs` | dependencies | `^5.56.7` | `^5.56.8` | | `packages/minimal` | dependencies | `^5.56.7` | `^5.56.8` | | `packages/minimal-rsvelte` | dependencies | `^5.56.7` | `^5.56.8` | | `packages/support` | dependencies | `^5.56.7` | `^5.56.8` | ## Deliberately not changed - **`packages/mochi` `peerDependencies.svelte` stays at `^5.56.6`.** It's a floor for published consumers and already admits 5.56.8; raising it would force an upgrade for no API reason. Since published `mochi-framework` carries Svelte only as a devDependency plus this unchanged peer range, nothing consumer-visible moved — hence `chore(deps):` rather than `fix(deps):`, and no release is warranted. - Scope is Svelte only, not a full dependency sweep. Also currently outdated and left alone: `@lucide/svelte` (1.25.0 → 1.27.0), `@rsvelte/vite-plugin-svelte-native` (0.2.8 → 0.3.1), `svelte-check` (4.7.3 → 4.7.4, exact-pinned because it carries a patch keyed on the version), `typescript` (6.0.3 → 7.0.2). The `bun.lock` diff is Svelte-only; the one removed `svelte/devalue` entry is a dedupe artifact (devalue is now satisfied from the root). ## Verification - **`bun run syncpack`** — ✅ no issues; cross-workspace agreement holds, including the unchanged peer range. - **`bun run checks`** (lint:fix + format + typecheck + test) — ✅ all four stages green. Typecheck 0 errors across all workspaces; tests 142/142 mochi-framework files, 9/9 site, 2/2 support, demos/minimal/minimal-rsvelte all green, 0 failures. - **Clean reinstall + dedupe** — `rm -rf node_modules packages/*/node_modules && bun install`. `packages/*/node_modules/svelte` is empty and `node_modules/.bun` is absent, so there is exactly one hoisted `svelte@5.56.8`. (Duplicate copies mean two context maps and break `getContext` across the island boundary — invisible to CI.) - **`bun run build`** — ✅ output byte-identical to the pre-bump baseline apart from timings. No optimization skipped, no shake fallback: | | before | after | | --- | --- | --- | | `svelte-shaker` (site) | slimmed 33 of 163 | slimmed 33 of 163 | | site | 65 pages · 245 client files · 12 public · 7 image assets · 2 email templates | identical | | demos | 10 pages · 32 client files | identical | | support | 2 pages · 19 client files · 1 email template | identical | | minimal / minimal-rsvelte | 1 page · 10 client files each | identical | Per-file bundle sizes in the build listing are unchanged too. - **Browser smoke test** (`PORT=4444 bun run dev:site`, driven via chrome-devtools): - `/` — no console errors/warnings. - `/docs/queues/` — no console errors/warnings. - `/demos/error-boundaries/` — the demo most relevant to #18556. All five scenarios render their expected fallbacks (user-written boundary, `mochi:hydrate` SSR throw, `mochi:hydrate` client throw, `mochi:defer` server-island throw, healthy server island with an inner throwing `mochi:hydrate` child). All 22 requests 200, including both `/_mochi/island/*` fetches. The only console output is the demo's intentional `ThrowOnClient` failure. Debug bar reports **Svelte 5.56.8**. - `/demos/nested-islands/` — clean console, all four `/_mochi/island/*` fetches 200. - `/demos/is-hydratable/` — clean console, both island fetches 200. This is the canary for the duplicate-copy failure mode (`isHydratable()` is its first casualty), so it independently confirms the dedupe. - **`bun run cli-test`** — ✅ pass (scaffold, install, test, typecheck). `minimal` and `demos` both moved and double as `create-mochi` template sources.

##### [v5.56.8](https://github.com/sveltejs/svelte/blob/HEAD/packages/svelte/CHANGELOG.md#5568) ##### Patch Changes - fix: call `onerror` and provide a working `reset` when hydrating a failed boundary ([#18556](sveltejs/svelte#18556)) - fix: preserve select selection when spread attributes omit value ([#18561](sveltejs/svelte#18561)) ##### [v5.56.7](https://github.com/sveltejs/svelte/blob/HEAD/packages/svelte/CHANGELOG.md#5567) ##### Patch Changes - chore: provide `indent` option for `print` ([#18474](sveltejs/svelte#18474))

- `destroy_effect` cleared a boundary's component context while retained reset callbacks and queued error work could still re-enter its run path. - Reset handling is intentionally shared with hydration by [#18556](#18556), while `onerror` is deferred for safe state mutation by [#17561](#17561); neither path checked the boundary lifetime. - Make retained and deferred boundary continuations inert during destruction instead of masking null contexts in `bind:this` or `#run`, which would still let dead effects and callbacks restart. - Cover resets from `onerror` and failed snippets, cleanup ordering, delayed error transforms, DOM rendering, and hydration. Fixes #18885

fix: call onerror and provide a working reset when hydrating a fa…

4089618

…iled boundary

Merge branch 'main' into fix-hydrated-boundary-reset

906d82f

dummdidumm approved these changes Jul 23, 2026

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dummdidumm merged commit 3dde011 into sveltejs:main Jul 23, 2026
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github-actions Bot mentioned this pull request Jul 23, 2026

Version Packages #18572

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dummdidumm mentioned this pull request Jul 23, 2026

[SvelteKit 3.0.0-next.8]: In dev mode with remote functions, +error.page selects the wrong layout sveltejs/kit#16345

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github-actions Bot mentioned this pull request Jul 25, 2026

chore: upgrade Svelte submodule to 5.56.8 baseballyama/rsvelte#1785

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khromov mentioned this pull request Jul 28, 2026

chore(deps): update svelte to 5.56.8 khromov/mochi#224

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svelte-triage-bot Bot mentioned this pull request Sep 27, 2026

fix: ignore stale boundary resets after destruction #18886

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fix: call `onerror` and provide a working `reset` when hydrating a failed boundary - #18556

fix: call `onerror` and provide a working `reset` when hydrating a failed boundary#18556
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Nic-Polumeyv:fix-hydrated-boundary-reset

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Nic-Polumeyv commented Jul 17, 2026

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