[AIGTWY-4877] Add MPS and MCP two-agent CUJ

[masonc08]

What did you change, and why?

Added the dedicated CUJ2 journey for a real published CodingAgentConfig: Codex uses ug_e2e.providers.openai with gpt-5-nano, Claude uses ug_e2e.providers.anthropic with claude-haiku-4-5-20251001, and both invoke system.ai.sandbox through the real agent TUIs. The runner and managed CI lane now execute the serialized workspace-backed CUJ with service-principal auth, preserve/restore any prior config, redact credentials, and install the pinned SDK through the authenticated internal Python proxy.

Skill coverage is intentionally deferred because the workspace Skill backend currently has a storage-path failure. This CUJ contains no Skill configuration, download, invocation, or assertion path.

How do you know it works?

• 60 focused runner/contract tests pass.
• Dedicated CUJ collection, Ruff/format, type checks, runner help, and diff checks pass.
• Live read-only workspace checks confirm both exact MPS targets plus system.ai.sandbox and the negative system.ai.web_search fixture.
• Full unit run: 3,170 passed and 6 skipped; four unrelated installed-agent tests fail because this developer host has machine-wide Claude/Codex policy and newer agent binaries.
• The full service-principal two-agent run is wired into the managed CI lane and will run on this PR using repository secrets.

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This PR was created with GitHub MCP.

[lilly-luo]

nit _agent_config -> expected_agent_config

[lilly-luo]

also is there a dataclass preexisting for the agent config that u can use?

[masonc08]

i can make the rename. i dont think theres any existing dataclass we can reuse for this though

[github-actions]

UG review

The PR changes Codex MCP credential forwarding and workspace discovery URL construction, and adds two-agent workspace CUJs with teardown cleanup.

Major

• Exercise Codex MCP auth forwarding — src/ucode/agents/codex.py:637: can we add a local Codex stdio MCP test verifying these variables reach the proxy? TOML snapshots and name-only listings still pass when auth forwarding fails.

Automated advisory review of f18753296923 using Lilly's UG review rubric. It does not approve or block this PR.

[david-siqi-liu]

Approving. One P1 to follow up on, not blocking:

P1

• The MPS listing, MPS get, and Anthropic models calls now build URLs from normalize_workspace_url(workspace), which only adds a scheme and strips a trailing /. ug configure --workspace stores the URL as typed, so a workspace pasted as https://<host>/?o=123 turns the listing URL into https://<host>/?o=123/api/2.1/.... Before this change, https://{hostname} dropped the query. #1004 adds workspace_origin (scheme plus netloc, keeps the recorder port), and #987 carries the same hunks verbatim. Using it here avoids three PRs editing these lines three different ways.