fix(desktop): WSL backend connects with Docker bridges and slow cold starts

[rehanhaider]

What Changed

• getDistroIp now prefers the default route’s source address, with hostname -I as the fallback.
• DEFAULT_BACKEND_READINESS_TIMEOUT increases from 1 to 3 minutes.

Scope: two files, 19 lines, two commits. No tests added—the changes are one shell string and one constant.

Why two commits and not one?

Both commits fix the same user-visible hang, so they ship together.

• The address bug is what [Bug]: Desktop stuck on "Connecting to WSL" — getDistroIp picks unreachable Docker bridge IP instead of eth0 #5211 reports and the address commit closes it on its own;
• the readiness budget is what kept my machine hanging afterwards.

Both causes the exact same symptoms to the user.

Happy to split if you'd rather take them separately.

Why

On Windows, the desktop can remain on “Connecting to WSL…” when Docker is running inside the distro. The backend starts, listens, and answers readiness checks, but the app targets the wrong address and times out too early. Either bug can cause the hang.

Wrong address

getDistroIp previously selected the first IPv4 address from hostname -I, which lists all bound addresses in interface order. With Docker running, a br-* or docker0 bridge can appear first, directing the renderer to an address Windows cannot route to.

This also breaks mirrored networking. isLocalHostIpv4 in DesktopBackendConfiguration maps the backend to loopback only when the reported address belongs to a Windows interface. A Docker bridge does not match, so mirrored-mode users lose the intended loopback path.

The new command asks the kernel for the default route’s source address using ip -4 route get 192.0.2.1. This avoids interface-name matching and RFC1918 heuristics without adding another spawn. The route source is printed before hostname -I, allowing the existing first-match parser and IPv4 validation to remain unchanged.

hostname -I remains the fallback, so distros without iproute2 or a default route behave as they do today. 192.0.2.1 is reserved by RFC 5737, and this is only a routing-table lookup—no packet is sent.

Readiness timed out too early

Readiness currently receives a single 60-second budget. Loading the server bundle and dependencies across /mnt/c regularly takes longer. When the probe expires, the backend process remains alive but is never marked ready, leaving the splash visible even if startup completes seconds later.

The probe polls every 100 ms and resolves immediately when the backend responds, so increasing the budget does not slow fast launches.

Verification

Verified on Windows 11 with WSL2 mirrored networking and three active Docker bridges—the topology reported in #5211:

hostname -I   ->  172.18.0.1  172.17.0.1  172.19.0.1  192.168.1.5
route source  ->  192.168.1.5

Before the timeout change, with the address fix already applied:

• Two launches abandoned readiness at exactly 60,000 ms.
• The backend was listening and answering HTTP 200 at 98 seconds.

After both changes:

• isLocalHostIpv4 matches 192.168.1.5 to the host Wi-Fi adapter.
• Readiness targets http://127.0.0.1:.
• The backend returns HTTP 200 and the desktop connects.

The address fix is evidenced by the route lookup above: hostname -I returns the bridge first, so the previous first-match selection resolves to 172.18.0.1, which Windows cannot route to. Measurements were taken against a dev build (dev:desktop), which also waits on the Vite server, so the 98s figure is not directly a packaged-build number.

Validation:

vp test run apps/desktop/src/wsl/DesktopWslEnvironment.test.ts apps/desktop/src/backend/DesktopBackendManager.test.ts

All 52 tests passed. Typecheck and lint are clean for both changed files.

Related Work

This area is active:

• fix(desktop): select the WSL route source address #5889 is a draft addressing the same IP-selection bug with two parser helpers, an octet validator, a new timeout constant, and a second sequential spawn. This PR keeps the single spawn, existing timeout, IPv4 gate, and parser; only the command changes.
• fix(desktop): verified update teardown on Windows+WSL, install integrity check, and resilient WSL readiness handshake #5998 and fix(desktop): harden Windows and WSL support #6068 also modify address selection as part of larger rewrites.
• fix(desktop): keep probing backend readiness while the process is alive #5526 replaces the one-shot readiness probe with retries.
• fix(desktop): Cache Runtime locally on WSL Filesystem, dramatically improving launch times  #5769 addresses slow startup by caching the runtime on the WSL filesystem.

There could be more robustness in the solution but I have preferred simple, tested, and workable solution instead.

Closes #5211
Refs #4535 and #5522.

Checklist

• This PR is small and focused
• I explained what changed and why
• No UI, animation, or interaction changes

Note

[!NOTE]

Fix WSL distro IP detection and extend backend readiness timeout

• Updates getDistroIpImpl in DesktopWslEnvironment.ts to prefer the IPv4 source address of the default route (ip -4 route get 192.0.2.1) before falling back to hostname -I, which is more reliable in multi-interface WSL environments.
• Increases DEFAULT_BACKEND_READINESS_TIMEOUT in DesktopBackendManager.ts from 1 minute to 3 minutes to accommodate slower WSL startup times.
• Behavioral Change: the IP returned by getDistroIpImpl may differ in environments with multiple network interfaces.

^{Macroscope summarized a702228.}

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[macroscopeapp]

Approvability

Verdict: Needs human review

This PR modifies WSL connection logic, including how the distro IP is determined. While the intent is to fix connection issues, changes to IP detection on the critical connection path warrant human verification to ensure correctness across different WSL configurations.

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