Serve the MCP-Apps shell from static assets on Workers hosts - #1502
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The deployed cloud Worker has no filesystem, so loadMcpAppsShellHtml's fs.readFile always failed and the ui://executor/shell.html resource silently served a 'Shell not built' placeholder — an inert document that never starts the MCP-Apps handshake, so every artifact widget in every MCP client spun on its loading state forever with no error anywhere. - Workers hosts (cloud, host-cloudflare) now fetch the built shell through the ASSETS binding: mcpAppsShellAsset emits a stable-named copy alongside the content-hashed one, and makeAssetsShellHtmlLoader (new @executor-js/mcp-apps-shell/worker entry) reads and verifies it. Under vite dev the document travels inline via a dev-only virtual module, since no assets are emitted yet. - The shell document carries an identity marker the loaders verify, so an SPA not-found fallback (index.html with a 200) can never be served as the shell. - The self-host image reads the same emitted asset from its SPA dist; the runtime image has no packages/ tree for the old candidates. - The silent placeholder is gone: a host that cannot produce the shell fails the resource read with an actionable error. - App builds now fail when the shell asset is missing or wrong (apps/cloud scripts/build.mjs, assert-shell-asset.mjs on both hosts).
Deploying with
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| Status | Name | Latest Commit | Updated (UTC) |
|---|---|---|---|
| ❌ Deployment failed View logs |
executor-cloud | 1e50ff3 | Jul 30 2026, 01:39 AM |
Deploying with
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| Status | Name | Latest Commit | Preview URL | Updated (UTC) |
|---|---|---|---|---|
| ✅ Deployment successful! View logs |
executor-marketing | 1e50ff3 | Commit Preview URL Branch Preview URL |
Jul 30 2026, 01:38 AM |
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Cloudflare previewTorn down — the PR is closed. |
@executor-js/cli
@executor-js/config
@executor-js/execution
@executor-js/sdk
@executor-js/codemode-core
@executor-js/runtime-quickjs
@executor-js/plugin-file-secrets
@executor-js/plugin-graphql
@executor-js/plugin-keychain
@executor-js/plugin-mcp
@executor-js/plugin-onepassword
@executor-js/plugin-openapi
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RhysSullivan
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July 30, 2026 01:57
This was referenced Jul 30, 2026
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* Deliver MCP responses larger than the DO storage value cap The DO transport persisted every outbound message for reconnect replay BEFORE writing the live SSE frame, and storage.put of a value over the 128 KiB DO cap throws — so an oversize response (the ~5MB ui://executor/shell.html resource) was neither stored nor delivered and the client hung on keepalives forever. Found live in prod after #1502 made the shell resource actually serve its bytes. - storeEvent skips persistence for messages over a 120 KiB guard, logging mcp_event_store_skipped_oversize and returning undefined; the caller delivers the live frame without a replay id. - sendOnStream treats any storeEvent failure as best-effort: log, then still write the live SSE frame. - New e2e (cloud/mcp-oversize-response.test.ts) drives resources/read of the shell over real workerd and fails on a hang. - Event-store unit tests updated for the skip contract. * Fix e2e typecheck: Effect.die instead of the unavailable dieMessage
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Problem
The cloud MCP host served a
Shell not builtplaceholder as theui://executor/shell.htmlresource:loadMcpAppsShellHtmlreads the built shell withfs.readFile, which can never succeed on a deployed Worker, and the loader silently fell back to an inert placeholder (and cached it for the isolate's lifetime). The placeholder never starts the MCP-Apps handshake, so every artifact widget in every remote MCP client hung on its loading state with no error anywhere in the chain. Confirmed against production with a directresources/read.The self-host image had the same failure by a different path: its runtime bundle carries no
packages/tree, so every read candidate missed there too.Fix
mcpAppsShellAssetnow emits a second, stable-named copy of the built shell (/assets/executor-mcp-apps-shell-stable.html) alongside the content-hashed one.@executor-js/mcp-apps-shell/workerentry:makeAssetsShellHtmlLoaderfetches that asset through theASSETSbinding (same pattern as the worker-bundler artifact, Serve the worker-bundler artifact from static assets #1378). cloud and host-cloudflare DOs use it; host-cloudflare gains theASSETSbinding in wrangler.jsonc. Undervite devthe document travels inline through a dev-only virtual module, built on first use.<meta>marker that loaders verify, so an SPA not-found fallback (index.html with a 200) can never be served as the shell.apps/cloud/scripts/build.mjsandassert-shell-asset.mjson both self-host targets fail the build if the stable asset is missing or is not the shell document; the shell build itself fails if the marker is lost.Verification
packages/hosts/mcp-apps-shellfull suite (82 tests, incl. the Chromium browser suite) green; new unit tests for the assets loader (404, SPA-fallback 200, dev thunk, caching).packages/hosts/mcpsuite green (167 tests).undefinedas intended.scenarios/artifacts.test.tsagainst the cloud target: 4/4 passed.