Add registry format converters and support for the Official MCP Registry

[rdimitrov]

The following PR:

• Adds converter functions for going back and forth between the 2 formats (toolhive's current format and the upstream one). This is temporary as those should live under toolhive-registry and not toolhive.
• Implements the registry provider interface by adding support for using upstream API compliant registries. This allows users to discover and run servers they already published upstream (or in another compliant registry)
• Fixes a few issues discovered while implementing this, i.e. we were not reseting the default registry when the config was changed.

Notes:

• The size is big because we are copying the whole converters package from https://github.com/stacklok/toolhive-registry/tree/main/pkg/registry/converters to here.

To test it:

1. Build it

task build

2. Set the registry

./bin/thv config set-registry-api https://registry.example.com

3. Confirm it's set

./bin/thv config get-registry

4. Search for a server

./bin/thv search io.github.github/github-mcp-server

5. Run a server

./bin/thv run io.github.github/github-mcp-server -e GITHUB_PERSONAL_ACCESS_TOKEN=test123

[codecov]

Codecov Report

❌ Patch coverage is 43.94231% with 583 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.17%. Comparing base (cd66940) to head (f37a2fa).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/registry/provider_cached.go	0.00%	175 Missing ⚠️
pkg/registry/api/client.go	0.00%	146 Missing ⚠️
pkg/registry/provider_api.go	0.00%	99 Missing ⚠️
pkg/config/registry.go	2.85%	33 Missing and 1 partial ⚠️
pkg/registry/converters/upstream_to_toolhive.go	85.46%	23 Missing and 10 partials ⚠️
pkg/api/v1/registry.go	44.44%	23 Missing and 7 partials ⚠️
pkg/auth/remote/config.go	0.00%	14 Missing ⚠️
pkg/registry/converters/toolhive_to_upstream.go	94.52%	4 Missing and 4 partials ⚠️
pkg/registry/provider_base.go	38.46%	8 Missing ⚠️
pkg/runner/retriever/retriever.go	46.15%	7 Missing ⚠️
... and 11 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2469      +/-   ##
==========================================
- Coverage   55.80%   55.17%   -0.64%     
==========================================
  Files         299      305       +6     
  Lines       28341    29218     +877     
==========================================
+ Hits        15816    16120     +304     
- Misses      11097    11667     +570     
- Partials     1428     1431       +3     

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[dmartinol]

LGMT, what else is missing to un-draft it?

[rdimitrov]

LGMT, what else is missing to un-draft it?

I just added a change for setting the User Agent when we reach out a registry server but nothing else major I think, it was mostly the changes on the operator side (which we've agreed are out of scope).

The things I'd like to get covered before merging are:

• More people testing this locally and starting servers from the upstream registry. I'll update the description above how to configure the upstream one.
• Ensure this works well with Studio
• Should we cache the results from querying the registry? In general yes, but I think we can do that as a follow up as the value is to confirm the conversion works now.