fix: resolve e2e cloud host from region, not a hardcoded default

[AlexLiu190625]

The e2e cloud suite still encoded an invalid host and a key-only flow that now fails fast: running it without XAGENT_BASE_URL routed runtime traffic to a dead host, and the bad-key probe raised ValueError in the constructor before it could reach the unauthorized path.

Changes

• Resolve the cloud host from XAGENT_REGION (au/sg) or XAGENT_BASE_URL. There is no default host: the service is per-region and a key only authenticates against the region that minted it.
• The bad-key probe and the full-flow runtime client take the resolved host via a cloud_base_url fixture, so an empty host can no longer raise ValueError before the unauthorized path runs.
• Drop the docstrings describing a key-only workflow and a hosted default that no longer exist.

Verification

ruff + mypy --strict clean, pytest 215 passed, the e2e suite collects cleanly (skipped by default; not run in CI).

[gemini-code-assist]

Code Review

This pull request updates the end-to-end tests to support per-region cloud hosts by introducing a cloud_base_url fixture and helper functions in conftest.py that resolve the host using XAGENT_BASE_URL or XAGENT_REGION. The smoke tests are refactored to consume this new fixture. The feedback suggests normalizing the XAGENT_REGION environment variable to lowercase before passing it to the Region enum to avoid potential case-sensitivity issues.

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[rogercloud]

Design verdict: sound ✅

This is the follow-up to the PR #6 review, and it resolves all three findings cleanly. The fix mirrors the library's own host-resolution contract inside the e2e test surface: a single _cloud_base_url() resolver (explicit XAGENT_BASE_URL wins → else XAGENT_REGION via the Region enum → else None/skip), exposed through a shared cloud_base_url fixture. No hardcoded host, no guessing — consistent with the per-region model the library now enforces.

Resolution of prior findings

• #1 [Major] — Fixed. _runtime_base_url() and its hardcoded https://cloud.xagent.run are gone; test_workspace_full_flow now drives the runtime AgentClient off the resolved cloud_base_url.
• #2 [Minor] — Fixed. test_bad_workspace_key_unauthorized now takes cloud_base_url, so it reaches the InvalidAPIKey assertion instead of raising ValueError from the constructor when XAGENT_BASE_URL was unset.
• #3 [Minor] — Fixed. Stale "defaults to the hosted endpoint" docstrings in python/tests/e2e/conftest.py and python/tests/e2e/test_cloud_smoke.py are corrected to the XAGENT_REGION / XAGENT_BASE_URL story.

The earlier case-sensitivity suggestion is also handled — Region(region.strip().lower()) normalizes " SG ", AU, etc.

Verification

• ruff check and mypy --strict both clean.
• e2e suite collects and skips cleanly with no env set (0 errors).
• Resolution paths exercised: none→None, " SG "→sg host, AU→au host, explicit base_url wins, invalid region → clear ValueError.

Minor observation (non-blocking)

An invalid XAGENT_REGION raises ValueError during fixture setup rather than pytest.skip. This is defensible fail-fast behavior — a typo'd region should be loud rather than silently skipped — so no change needed.

LGTM.