Fix WASM boot config ContentRoot to use IntermediateOutputPath

[lewing]

Summary

Fix a .NET 11 regression causing SRI integrity failures during incremental Blazor WASM builds. Two changes in Microsoft.NET.Sdk.WebAssembly.Browser.targets:

1. ContentRoot fix: Change the boot config's DefineStaticWebAssets ContentRoot from $(OutDir)wwwroot to $(IntermediateOutputPath)
2. Preload matching fix: Replace fragile %(FileName)%(Extension)-based scanning with direct references to the boot config output items

Regression

This is a regression in .NET 11 (works in 10.0). It was introduced by dotnet/sdk#52283, which fixed an esproj compression bug by flipping the order in AssetToCompress.TryFindInputFilePath to prefer RelatedAsset (Identity) over RelatedAssetOriginalItemSpec. That fix was correct for esproj, but exposed a latent issue in the WASM SDK targets: the boot config asset's Identity pointed to a wwwroot copy rather than the actual source file in obj/.

Before sdk#52283, OriginalItemSpec happened to point to the real file and was checked first, masking the wrong ContentRoot. After the flip, RelatedAsset (Identity) is checked first, and its stale wwwroot path is used — producing incorrect SRI hashes on incremental builds.

Reported in aspnetcore#65271.

Problem

The WASM boot config file (e.g. dotnet.js) is generated at $(IntermediateOutputPath) (the obj/ folder), but its static web asset was defined with ContentRoot="$(OutDir)wwwroot". This caused DefineStaticWebAssets to compute an Identity pointing to the wwwroot copy rather than the actual file in obj/.

During incremental builds, the compression task's RelatedAsset (which uses Identity) would point to the stale wwwroot copy, producing incorrect SRI fingerprints and causing integrity check failures at runtime.

Fix

1. ContentRoot change

Change ContentRoot to $(IntermediateOutputPath) so the asset Identity matches the real file location on disk. The CopyToOutputDirectory="PreserveNewest" attribute still ensures the file is copied to wwwroot for serving.

This follows Javier's suggestion in dotnet/sdk#52847 to "stop defining these assets with an item spec in the wwwroot folder and just define them in their original location on disk".

2. Preload matching simplification

The _AddWasmPreloadBuildProperties and _AddWasmPreloadPublishProperties targets previously scanned all @(StaticWebAsset) items by %(FileName)%(Extension) to find the boot config asset. This relied on the Identity path containing the fingerprint in the filename (e.g. dotnet.FINGERPRINT.js), which is an implementation detail of how DefineStaticWebAssets computes Identity based on ContentRoot.

With the ContentRoot change, Identity uses the physical filename (dotnet.js), so the fingerprint-in-filename matching fails and the preload filter returns all endpoints instead of just the boot config's.

The fix replaces the scanning with direct references to @(_WasmBuildBootConfigStaticWebAsset) and @(_WasmPublishBootConfigStaticWebAsset) — the output items already produced by DefineStaticWebAssets in the boot config generation targets. This is both correct and simpler: no filename decomposition, no fingerprint-dependent matching, and the same item that was defined is what gets used.

What's not changed

• WebCil ContentRoot (line ~366, ContentRoot="$(_WasmBuildOuputPath)"): WebCil candidates come from multiple source directories and don't change on incremental builds unless the assembly changes, so they don't hit the staleness issue.
• Publish boot config ContentRoot (line ~820, ContentRoot="$(PublishDir)wwwroot"): Publish builds are clean and don't have the incremental staleness problem.

Testing

• All 9 Blazor SimpleRunTests pass (build, publish, AOT, different output paths)
• Full Wasm.Build.Tests suite: 352/434 passed with workloads; remaining failures are flaky timeouts and pre-existing infrastructure issues unrelated to this change

Companion PR

SDK PR dotnet/sdk#52847 will need baseline JSON updates to reflect the changed Identity/ContentRoot paths.

Fixes dotnet/aspnetcore#65271

[Copilot]

Pull request overview

Updates the Blazor WASM SDK targets to define the build boot config static web asset from its actual on-disk generation location (obj/) to prevent stale-asset Identity selection during incremental builds (which can lead to incorrect SRI integrity values at runtime).

Changes:

• Change DefineStaticWebAssets ContentRoot for the build boot config asset from $(OutDir)wwwroot to $(IntermediateOutputPath).

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