[AspireE2E] This project cannot be opened automatically in the browser when running the Aspire 13.4 project with `dotnet watch`

[EmilyFeng97]

REGRESSION INFO: Work well in Aspire.ProjectTemplates 13.3.5

INSTALL STEPS

1. Clean machine: Win11 x64 25h2 ENU
2. Install SDK 10.0.300
3. Add feed
4. Install Aspire.ProjectTemplates 13.4.0:

dotnet new install Aspire.ProjectTemplates::13.4.0 --force

REPRO STEPS

1. Open CMD and create an Aspire Starter App (ASP.NET Core/Blazor) project

    dotnet new aspire-starter -o aspire01
    cd aspire01/aspire01.AppHost
   

2. Run dotnet watch

ACTUAL
This project cannot be opened automatically in the browser.

Error Logs
dotnetwatch.txt

[joperezr]

🤖 Aspire triage pass — 2026-05-28 09:50 UTC

Area: area-orchestrator
Kind: regression
Repro: yes-minimal — see steps in body (dotnet new aspire-starter then dotnet watch)
Affected version(s): 13.4.0 — reporter confirms 13.3.5 worked (latest: 13.4.0)
Severity: S2 — dotnet watch no longer auto-opens the browser to the dashboard; workaround is to use aspire run or open the dashboard URL manually

Urgency: 🟡 vNext — recommend milestone 13.5
Reason: regression in dotnet watch integration path (AspireServerService / Microsoft.DotNet.Watch.AspireServiceFactory) but a workaround exists (aspire run and/or manual browser launch). Per conservative rules near the 13.4 snap, recommending 13.5 and flagging for human re-escalation since the regressing PR has not been identified yet.

Suggested owner(s): @karolz-ms (score 11), backup @danegsta (score 9)
Evidence:

• @karolz-ms closed ~11 issues as completed in area-orchestrator in the last 180d (e.g. Starting Dashboard failing after update to 13.3.3 #16866, [Container Tunnel] OtlpEndpointReferenceGatherer hangs forever for containers with OtlpExporterAnnotation when no containers are tunnel-dependent #15041, Failing test: ContainerTunnelWorksWithYarp #14325, Env vars are missing from the dashboard #14269, [main] Final logs for containers that exit quickly are missing #14262, Network Tunnel build failure shouldn't be a debug message #13892, Failing test: Aspire.Hosting.Tests.DistributedApplicationTests.AllocatedPortsAssignedAfterHookRuns #13833, Container considered FailedToStart if it starts then immediately exists #13760, No Logs if container fails to start due to bad bind mount #13756, Dashboard doesn't load if Docker not running and ASPIRE_ENABLE_CONTAINER_TUNNEL #12998, [13.0] Container Tunnel fails to start. #12842)
• @danegsta closed ~9 issues as completed in area-orchestrator in the last 180d (e.g. WithOtlpExporter() breaks ContainerLifetime.Persistent, lifecycle key mismatch on every run #17191, [13.3] Container Tunnel fails to start without internet connectivity #16615, CosmosDB Preview Emulator Regression from 13.1.2 to 13.2.0 - ContainerLifetime.Persistent does not keep the same container #15626, Failing test: DistributedApplicationTests.VerifyContainerSucceedsWithCreateFileContinueOnError #15195, [AspireE2E][Linux]Create Aspire Starter App ~ 10.0, run the project, open link for webfrontend, then navigate to "Weather", the browser always show "Loading...",an exception of type 'System.Net.Http.HttpRequestException' occurred #13563, [AspireE2E][Linux] The start time in the dashboard Resources page is incorrect #13455, Failure to create certs directory and other permissions issues on MacOS #13138, Certificates that the X509Store and X509Certificate2 consider valid can result in errors when loaded in OpenSSL #12693)
• CODEOWNERS lists @JamesNK @karolz-ms @danegsta @mitchdenny @davidfowl for /src/Aspire.Hosting (where AppHost ⇄ dotnet watch IPC lives)

Confidence: medium
Needs human?: yes — regression baseline is clear (13.3.5 → 13.4.0) but no suspected regressing PR has been identified; a human should decide whether this clears the 13.4 release-blocking bar given a workaround exists

Dry-run mode — no labels or milestone applied. Reply /triage apply to promote, or edit and reapply.

[joperezr]

@karolz-ms can you please take a look?

[karolz-ms]

#17206 changed how the dashboard connectivity information is presented. Unfortunately, dotnet watch is looking for very specific string, namely

Login to the dashboard at <URL>

to determine whether the application is serving HTTP traffic and thus when it should open a browser: https://github.com/dotnet/sdk/blob/main/src/Dotnet.Watch/Watch/Process/WebServerProcessStateObserver.cs.

@JamesNK FYI