fix: gracefully handle well-known provider being down

[optix2000]

Issue for this PR

Closes #10930

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Fixes issue where opencode crashes if a previously authed .well-known/opencode endpoint becomes unavailable.

Actually adds error handling and caching so transient errors, or downtime doesn't brick your opencode.

How did you verify your code works?

1. Run a localhost/.well-known/opencode stub server,
2. Run opencode auth login http://localhost
3. Stop stub server
4. opencode no longer crashes

Screenshots / recordings

# Server running
% opencode auth login http://localhost:3456

┌  Add credential
│
●  Running `echo stub-token`
│
◆  Logged into http://localhost:3456
│
└  Done

# Server stopped (old behavior)
% opencode
{
  "name": "UnknownError",
  "data": {
    "message": "Error: Unable to connect. Is the computer able to access the url?"
  }
}

% opencode run 'immediately return'
Error: Unexpected error, check log file at /Users/./.local/share/opencode/log/2026-02-21T052204.log for more details

Unable to connect. Is the computer able to access the url?

% bun run --cwd packages/opencode dev run 'immediately return'
$ bun run --conditions=browser ./src/index.ts run "immediately return"

> build · Claude Opus 4.6

Could you clarify what you mean? Are you referring to something in the codebase, a code pattern, or something else?

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

If you do not follow this template your PR will be automatically rejected.

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[alexyaroshuk]

can try/catch be avoided? See: https://github.com/anomalyco/opencode/blob/dev/CONTRIBUTING.md#style-preferences