feat(oauth): use asExternalUrl to get the correct callback

[JonZeolla]

Description

This replaces the hardcoded localhost from #6800 with using asExternalUrl to support configuration in more complex environments

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Checklist

• I've read the contributing guide
• The relevant docs, if any, have been updated or created
• The relevant tests, if any, have been updated or created

Screen recording or screenshot

asExternalUrl.mov

Tests

Updated core/context/mcp/MCPOauth.vitest.ts to ensure use of getExternalUri when available, and fallback to the old localhost:3000 when it isn't, and some (limited) concurrency tests.

➜ npx vitest run context/mcp/MCPOauth.vitest.ts

 RUN  v3.1.4 /Users/jonzeolla/src/jonzeolla/continue/core

(node:73219) [DEP0147] DeprecationWarning: In future versions of Node.js, fs.rmdir(path, { recursive: true }) will be removed. Use fs.rm(path, { recursive: true }) instead
(Use `node --trace-deprecation ...` to show where the warning was created)
stderr | context/mcp/MCPOauth.vitest.ts > MCPOauth > redirect URL handling > should handle getExternalUri errors gracefully
Failed to initialize redirect URL: Error: Network error
    at Object.<anonymous> (/Users/jonzeolla/src/jonzeolla/continue/core/context/mcp/MCPOauth.vitest.ts:218:52)
    at Object.mockCall (file:///Users/jonzeolla/src/jonzeolla/continue/core/node_modules/@vitest/spy/dist/index.js:66:15)
    at Object.spy [as getExternalUri] (file:///Users/jonzeolla/src/jonzeolla/continue/core/node_modules/tinyspy/dist/index.js:45:80)
    at MCPConnectionOauthProvider._initializeRedirectUrl (/Users/jonzeolla/src/jonzeolla/continue/core/context/mcp/MCPOauth.ts:89:44)
    at new MCPConnectionOauthProvider (/Users/jonzeolla/src/jonzeolla/continue/core/context/mcp/MCPOauth.ts:81:41)
    at Module.performAuth (/Users/jonzeolla/src/jonzeolla/continue/core/context/mcp/MCPOauth.ts:241:24)
    at /Users/jonzeolla/src/jonzeolla/continue/core/context/mcp/MCPOauth.vitest.ts:226:13
    at processTicksAndRejections (node:internal/process/task_queues:105:5)
    at file:///Users/jonzeolla/src/jonzeolla/continue/core/node_modules/@vitest/runner/dist/index.js:596:20

 ✓ context/mcp/MCPOauth.vitest.ts (12 tests) 10ms
   ✓ MCPOauth > getOauthToken > should return undefined when no tokens are stored 1ms
   ✓ MCPOauth > getOauthToken > should return access token when tokens are stored 1ms
   ✓ MCPOauth > getOauthToken > should handle different server URLs independently 0ms
   ✓ MCPOauth > performAuth > should call auth with correct parameters and return auth result 2ms
   ✓ MCPOauth > removeMCPAuth > should clear oauth storage for the server 0ms
   ✓ MCPOauth > removeMCPAuth > should handle non-existent server gracefully 0ms
   ✓ MCPOauth > redirect URL handling > should use getExternalUri when available for VS Code 0ms
   ✓ MCPOauth > redirect URL handling > should fallback to localhost when getExternalUri is not available 0ms
   ✓ MCPOauth > redirect URL handling > should handle getExternalUri errors gracefully 3ms
   ✓ MCPOauth > concurrent authentication > should handle multiple concurrent auth flows 0ms
   ✓ MCPOauth > error handling > should clean up context on auth failure 1ms
   ✓ MCPOauth > error handling > should handle missing server URL 0ms

 Test Files  1 passed (1)
      Tests  12 passed (12)
   Start at  07:25:48
   Duration  224ms (transform 56ms, setup 11ms, collect 80ms, tests 10ms, environment 0ms, prepare 27ms)

---

Summary by cubic

Switch OAuth redirects to use IDE external URLs (VS Code asExternalUri) instead of hardcoded localhost, so callbacks work in local, remote, and web environments. Adds state-based concurrency and safer server handling.

• New Features

  • Use ide.getExternalUri for the redirect URL; fallback to http://localhost:3000.
  • Add OAuth state to support multiple concurrent auth flows.
  • Start the local callback server only when using localhost; close it after completion.
  • Extend IDE interface with getExternalUri and implement it in the VS Code extension.

• Bug Fixes

  • Fix broken OAuth in remote/web VS Code where localhost callbacks failed.
  • Better error handling and toasts; clean up auth context on failure.
  • Add tests for redirect URL behavior, fallbacks, and concurrent auth flows.

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[JonZeolla]

I have read the CLA Document and I hereby sign the CLA

[JonZeolla]

This is the main thing I'm addressing in this PR. I don't fully understand the question about hub URLs; should I leave a comment behind somewhere like there was before?

[RomneyDa]

@JonZeolla the files changed appears to be in an odd state where it's showing a bunch of extraneous added spaces, formatting changes, etc. Could you take a look and whittle down to only the relevant changes?

[JonZeolla]

@RomneyDa that came from prettier, following the contributing guide. I can undo it though