fix: work around DevFlow.Blazor packaging bug breaking Windows build

[PureWeen]

Summary

• The Microsoft.Maui.DevFlow.Blazor preview NuGet package has a packaging bug: its PRI file references chobitsu.js and Microsoft.Maui.DevFlow.Blazor.lib.module.js under lib/.../wwwroot/, but the files only exist under staticwebassets/
• This causes MSB3030 copy errors on Windows builds, completely blocking relaunch.ps1 and any Windows debug builds
• Adds a build target (_FixDevFlowBlazorWwwroot) that copies the missing files from staticwebassets/ to the expected wwwroot/ location before the content copy step runs

Test plan

• dotnet build PolyPilot.csproj -f net10.0-windows10.0.19041.0 -c Debug succeeds with 0 errors
• relaunch.ps1 completes build + launch cycle successfully
• Remove the workaround target once an updated DevFlow.Blazor package ships the fix upstream

[PureWeen]

Update: This PR was briefly closed as superseded by #532, but reopened because #532 only fixes Release builds (DevFlow is now Debug-only). This PR is still needed for local Windows Debug builds where the DevFlow.Blazor packaging bug causes MSB3030 errors. Rebased on latest main with source-existence guards added.

[PureWeen]

🔍 Multi-Model Code Review — PR #484

PR: fix: work around DevFlow.Blazor packaging bug breaking Windows build
Branch: fix/devflow-blazor-wwwroot-build → main
Changes: +25 / -0 across 1 file (PolyPilot.csproj)
CI Status: ⚠️ No CI checks reported on this branch
Prior Reviews: None (author comment clarifies this is still needed for Windows Debug builds alongside #532)

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🟡 MODERATE — Hardcoded package version creates silent maintenance trap

File: PolyPilot/PolyPilot.csproj — _FixDevFlowBlazorWwwroot target
Flagged by: 3/3 reviewers

The version 0.1.0-preview.4.26202.3 is hardcoded in the _DevFlowPkgRoot path, duplicating the version on the PackageReference (lines 86-87). When someone bumps the DevFlow package, the Exists() guards silently make the target a no-op — the original MSB3030 error resurfaces with zero indication the workaround exists and needs updating.

The comment says this is by design ("no-op when the package version changes"), but this conflates two scenarios: (a) upstream bug fixed (desired no-op), and (b) version bumped but bug persists (silent breakage). Both look identical.

The hardcoded TFM path lib\net10.0-windows10.0.19041\... in _DevFlowWwwrootDest has the same fragility — a TFM change silently breaks the workaround.

Suggested fix: Add GeneratePathProperty="true" to the DevFlow.Blazor PackageReference (already used in PolyPilot.Gtk.csproj:60 for precedent), then replace _DevFlowPkgRoot with $(PkgMicrosoft_Maui_DevFlow_Blazor). This auto-tracks version bumps while the Exists() guard still makes it a no-op when the upstream fix ships.

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🟡 MODERATE — Target mutates the global NuGet package cache

File: PolyPilot/PolyPilot.csproj — MakeDir and Copy tasks
Flagged by: 3/3 reviewers

The target writes files into $(NuGetPackageRoot), which is the shared, global NuGet cache (~/.nuget/packages/). Concerns:

1. Cross-project pollution — other projects referencing the same DevFlow.Blazor version will see the injected files
2. CI read-only caches — restored NuGet caches may have read-only attributes, causing UnauthorizedAccessException with no diagnostic (no ContinueOnError)
3. Concurrent build races — the !Exists() guards are non-atomic with the file operations (low practical impact since SkipUnchangedFiles provides idempotency)

Suggested fix: For a temporary workaround, this is pragmatically acceptable — but add ContinueOnError="WarnAndContinue" to the MakeDir and Copy tasks with a <Warning> explaining the fallback, so permission failures on CI don't produce opaque errors. If the workaround is expected to live longer, consider copying into $(IntermediateOutputPath) instead.

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✅ What looks good

• Condition logic — Debug + windows platform correctly scopes the fix to where the bug manifests
• Source-existence guards — all three tasks have Exists() conditions preventing errors when the package layout changes
• Idempotency — SkipUnchangedFiles="true" + destination existence checks prevent repeated work
• Path separators — \ is fine since the target only runs on Windows
• Comment documentation — clearly explains the bug, scope, and expected removal conditions

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🏁 Recommendation: ⚠️ Request Changes

1. 🟡 MODERATE: Use GeneratePathProperty="true" on the PackageReference to avoid hardcoded version/TFM — single source of truth for the package path
2. 🟡 MODERATE: Add ContinueOnError="WarnAndContinue" to MakeDir/Copy tasks for CI resilience