Environment remediation

fuse up runs the same load diagnosis as fuse doctor, then classifies each downgraded project's failure against a knowledge base of known environment problems and names the remedy that would address it. The catalog below is that knowledge base. Repository-code failures (a compile error in the repository's own source) are named as not fixable by fuse up, never edited: the hard rule is that fuse up never edits files inside the repository, so every remedy is environment- or overlay-scoped.

By default fuse up is report-only: it names what it would do. Add --apply to apply the install-free remedy (the NU1507 overlay NuGet config) and re-attempt the load: fuse up writes the overlay to a temp file, runs dotnet restore --configfile <overlay> (never editing the repository), then re-runs the load diagnosis and prints the new per-project tiers. The consent-gated remedies (the SDK and workload installs) are never run without --allow-install; without it they are reported, not applied. The apply path is bounded to a single remediation round.

fuse up .
fuse up . --apply

The report-only command reads local project and SDK state. --apply can contact the repository's configured NuGet feeds because it runs dotnet restore. --allow-install can download an SDK or workload and changes the machine or isolated SDK directory, so review the printed plan before granting that flag. Fuse does not send source code to a Fuse-hosted service.

A Downgrade Is Still Usable

An imperfect repository does not make every Fuse operation unavailable. If MSBuild cannot load all projects, indexing reports partial or syntax and continues with source structure, exact lookup, and lexical task localization. Operations that require compiler truth either use the loaded subset or report that the graph claim is unavailable.

fuse_check has a separate verification fallback. Without a resident or build-captured compilation, it mirrors the owning project to a temporary directory and runs a scoped real dotnet build; the result is labeled build grade. The CLI fuse check --delta is only the ambient on-disk edit delta from a running host. It does not accept proposed file content.

Recognized Failures

NU1507

Central Package Management needs a single package source or a source mapping. Multiple package sources are defined without a source mapping under Central Package Management. Remedy: an overlay NuGet.config with a packageSourceMapping passed to restore explicitly, never written into the repository. No consent required.

NETSDK1045

The installed .NET SDK does not support the targeted version. The project targets an SDK band the machine does not have. Remedy: install the pinned SDK from global.json behind --allow-install; consent-gated because it changes the machine.

SDK_NOT_FOUND

The SDK band pinned in global.json is not installed. The .NET host cannot select an SDK and fails before the build begins (distinct from NETSDK1045, which fires when a present SDK is too old for the target framework). Remedy: install the pinned band from global.json via the dotnet-install script into an isolated directory behind --allow-install; consent-gated because it changes the machine.

MSB4018

An MSBuild task failed to load or execute. Often a missing workload or SDK-band task assembly, which a workload install can fix (consent-gated). It can also be a repository-custom task, in which case Fuse classifies rather than remediates.

CS0104

Ambiguous type reference in repository code. A compile error in the repository's own source. Fuse never edits repository files, so this is reported with its reason, not remediated.

CS2007

Unrecognized compiler option in repository code. A legacy or repository-specific compiler option the current toolchain rejects. Fuse never edits repository files, so this is reported with its reason, not remediated.

Rollback and Reset

The report-only command needs no rollback. The NU1507 remedy uses a temporary overlay NuGet configuration and does not modify the repository's NuGet.config; remove any temporary file named in the command output if the operating system has not already cleaned it.

SDK or workload installation is an external dotnet machine change. Remove it with the same .NET installation mechanism named in the remediation plan; Fuse does not silently remove shared SDKs or workloads.

Remediation can change the compiler tier recorded in the derived index. Stop the MCP client or host, then delete .fuse/ at the repository root for a full reset. The next Fuse read rebuilds .fuse/fuse.db from source. Deleting it does not remove source, packages, SDKs, MCP configuration, or AI-client rules.