test: add comprehensive tests for hub error re-throwing

[continue-development-app]

Summary

Adds extensive test coverage for the new error handling logic introduced in PR #9270.

New Test Coverage

Hub Error Re-throwing

• ✅ Test re-throwing of 404 errors for non-existent hub slugs
• ✅ Test re-throwing of network timeout errors
• ✅ Test re-throwing of authentication (401) errors
• ✅ Verify hub errors are preserved instead of generic "Not a markdown file" message

Hub Slug vs File Path Distinction

• ✅ Test hub slug priority for two-part paths without extensions
• ✅ Test file fallback for markdown paths when hub fails
• ✅ Test NO file fallback for non-markdown paths when hub fails
• ✅ Test hub slugs with hyphens (e.g., continue-dev/cloud-agent)
• ✅ Test hub slugs with numbers (e.g., owner123/agent456)
• ✅ Test rejection of paths with dots (e.g., owner.com/agent)

Markdown Extension Detection

• ✅ Test recognition of .md extension
• ✅ Test recognition of .markdown extension
• ✅ Test rejection of non-markdown files (e.g., .txt)
• ✅ Test case sensitivity for extensions
• ✅ Test markdown extension handling in two-part hub-like paths

Test Plan

• All new tests follow existing patterns
• Tests cover edge cases and error scenarios
• Tests verify both positive and negative cases

Related Issues

• Improves test coverage for PR fix: re-throw hub error for non-markdown hub slugs #9270

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This agent session was co-authored by peter-parker and Continue.

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Summary by cubic

Add comprehensive tests for AgentFileService error handling. Ensures hub errors are re-thrown, correct hub-vs-file resolution, and strict markdown detection.

• New Tests
  • Re-throw hub errors (404, network timeout, 401) and keep original messages.
  • Prioritize hub for two-part paths; fall back to file only when the path has a markdown extension.
  • Validate slug formats: support hyphens/numbers; reject parts containing dots.
  • Detect .md and .markdown extensions; enforce case sensitivity; handle two-part paths with .md by trying hub then file.

^{Written for commit 550e480. Summary will update automatically on new commits.}

[cubic-dev-ai]

No issues found across 1 file

[continue]

No documentation updates needed for this PR.

This PR adds test coverage for the error handling improvements in #9270. Since these changes are:

• Internal test improvements
• Bug fixes that improve error messages (no new user-facing behavior)
• Already covered by existing documentation on agent referencing

The current documentation accurately describes how agents work and how to reference them. ✅