fix: Throw if Snap not installed

[FrederikBolding]

When invoking Snaps directly, e.g. from within MetaMask, we were currently not validating that Snaps were installed. This means that misleading errors would be thrown about permissions when the Snap was not installed in the first place.

Also removes this check from one RPC method, since it is now unnecessary. We leave the RPC method around in invokeKeyring to not change the error handling behavior.

Closes #3658

---

Note

Adds an installation check to SnapController.handleRequest, removes redundant snap-installed checks from invokeSnap, aligns error messages, and updates tests and coverage thresholds.

• SnapController:
  • Validate Snap exists in handleRequest and throw a clear error if not installed.
  • Refactor subsequent checks to use local snap (enabled/status).
• RPC Methods:
  • invokeSnap: Remove getSnap hook and installed check; rely on controller for validation.
  • invokeKeyring: Align "not installed" error message with controller.
• Tests:
  • Add test for non-installed Snap in SnapController.handleRequest.
  • Update invokeSnap tests to drop getSnap usage and non-installed error case.
  • Update invokeKeyring tests to match new error message.
• Config:
  • Slightly adjust Jest coverage thresholds in snaps-rpc-methods.

^{Written by Cursor Bugbot for commit 303b2b9. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.29%. Comparing base (5d19c66) to head (303b2b9).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3666   +/-   ##
=======================================
  Coverage   98.29%   98.29%           
=======================================
  Files         417      417           
  Lines       11924    11924           
  Branches     1852     1851    -1     
=======================================
  Hits        11721    11721           
  Misses        203      203           

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