Windows 11: fix npm install (node-pty MSB8040) and blank dev window (ERR_CONNECTION_REFUSED) - #9
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…_CONNECTION_REFUSED at npm run dev
Two bugs that break the documented dev workflow (npm install → npm run dev)
on Windows 11. Both reproduced and verified on the target machine
(Windows 11, Node v24.19.0, Visual Studio 2022 Community, Windows SDK
10.0.19041/10.0.22621). All fixes were made by Hermes Agent (Nous Research)
running on qwen3.8:27b.
1) npm install fails with MSBuild error MSB8040 (Spectre mitigation libraries
required)
Cause: postinstall runs `electron-rebuild -f -w node-pty`, which
compiles node-pty from source. node-pty hard-codes
SpectreMitigation='Spectre' in binding.gyp and deps/winpty/src/winpty.gyp,
so MSBuild (Microsoft.CppBuild.targets:504) checks for the MSVC
"Spectre-mitigated libs" VS component. On machines without that
component (common default VS installs on Windows) the build of
conpty/conpty_console_list/winpty-agent/winpty fails.
Fix: new scripts/fix-spectre.js (idempotent) flips
SpectreMitigation to 'false' in both .gyp files before the rebuild, so
the generator emits <SpectreMitigation>false</SpectreMitigation> and
MSBuild skips /Qspectre and the existence check. package.json postinstall
now runs the script first:
"postinstall": "node scripts/fix-spectre.js && electron-rebuild -f -w node-pty"
Verified: clean `rm -rf node_modules && npm install` succeeds
("Rebuild Complete", 0 vulnerabilities) and the built .node binary loads
inside Electron 42 (ABI 146).
2) npm run dev: Electron window opens blank, log says
"Failed to load URL: http://localhost:5173/ with error: ERR_CONNECTION_REFUSED"
Cause: Vite dev server binds to 'localhost', which since Node >= 17
resolves to [::1] (IPv6) first — netstat showed the listener on
[::1]:5173 only. The Electron renderer connects via 127.0.0.1 (IPv4),
where nothing listens → connection refused → blank window.
Fix: electron.vite.config.ts renderer section now pins the dev server to
the IPv4 loopback:
renderer: { server: { host: '127.0.0.1' } }
electron-vite then sets ELECTRON_RENDERER_URL to http://127.0.0.1:5173/.
Verified: dev log is error-free, netstat shows 127.0.0.1:5173 LISTENING,
and the window renders the full Kadr UI (media panel, preview,
properties, timeline V2/V1/A1).
3) Docs: README.md / README.en.md — "Windows" notes under Getting started
explaining both failure modes, the repo-side workaround, and the
alternative manual fix (install the "MSVC v143 – C++ x64/x86
Spectre-mitigated libs" component via Visual Studio Installer).
4) package-lock.json: regenerated by the clean npm install used to verify
fix 1 — npm re-resolved 104 transitive packages to their newest
versions within the ^-ranges declared in package.json (e.g. electron
42.4.0 → 42.9.2, rollup 4.61.1 → 4.62.4, esbuild 0.28.1 → 0.28.2,
@electron/rebuild 4.0.4 → 4.2.0).
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Two bugs that break the documented dev workflow (
npm install→npm run dev) on Windows 11. Both reproduced and verified on the target machine (Windows 11, Node v24.19.0, Visual Studio 2022 Community, Windows SDK 10.0.19041/10.0.22621). Fixes prepared with Hermes Agent (Nous Research) running on qwen3.8:27b.1)
npm installfails: MSBuild error MSB8040 (Spectre mitigation libraries required)Cause:
postinstallrunselectron-rebuild -f -w node-pty, which compiles node-pty from source. node-pty hard-codesSpectreMitigation='Spectre'inbinding.gypanddeps/winpty/src/winpty.gyp, so MSBuild (Microsoft.CppBuild.targets:504) checks for the MSVC Spectre-mitigated libs VS component. On machines without that component (a common default VS install) the build ofconpty/conpty_console_list/winpty-agent/winptyfails.Fix: new
scripts/fix-spectre.js(idempotent) flipsSpectreMitigationto'false'in both.gypfiles before the rebuild, so the generator emits<SpectreMitigation>false</SpectreMitigation>and MSBuild skips/Qspectreand the existence check.package.jsonpostinstall now runs it first:Verified: clean
rm -rf node_modules && npm installsucceeds ("Rebuild Complete", 0 vulnerabilities) and the built.nodebinary loads inside Electron 42 (ABI 146).2)
npm run dev: blank Electron window,ERR_CONNECTION_REFUSEDCause: the Vite dev server binds to
localhost, which since Node ≥ 17 resolves to[::1](IPv6) first —netstatshowed the listener on[::1]:5173only. The Electron renderer connects via127.0.0.1(IPv4), where nothing listens → connection refused → blank window.Fix:
electron.vite.config.tsrenderer section now pins the dev server to the IPv4 loopback:electron-vitethen setsELECTRON_RENDERER_URLtohttp://127.0.0.1:5173/.Verified: dev log is error-free,
netstatshows127.0.0.1:5173 LISTENING, and the window renders the full Kadr UI (media panel, preview, properties, timeline V2/V1/A1).3) Docs
README.md/README.en.md— "Windows" notes under Getting started explaining both failure modes, the repo-side workaround, and the alternative manual fix (install the MSVC v143 – C++ x64/x86 Spectre-mitigated libs component via Visual Studio Installer).4)
package-lock.jsonRegenerated by the clean
npm installused to verify fix 1 — npm re-resolved 104 transitive packages to their newest versions within the^-ranges already declared inpackage.json(e.g. electron 42.4.0 → 42.9.2, rollup 4.61.1 → 4.62.4, esbuild 0.28.1 → 0.28.2, @electron/rebuild 4.0.4 → 4.2.0). No version-range changes inpackage.json.Files
scripts/fix-spectre.js(new)package.json(postinstall chain)electron.vite.config.ts(IPv4 loopback bind)README.md,README.en.md(Windows notes)package-lock.json(regenerated)