opencode_env: keep the upstream base path in the interception proxy

[jayzuccarelli]

Summary

The interception proxy builds the upstream URL by appending /v1/chat/completions to any base_url that doesn't end in /v1. For OpenAI-compatible providers with a different prefix (Gemini .../v1beta/openai, z.ai .../api/paas/v4) that produces .../v1beta/openai/v1/chat/completions, while opencode in black_box mode calls .../v1beta/openai/chat/completions with the same base_url. So the same config works in black_box and not in transparent_proxy.

This applies the rule #1237 settled on for OpenAIClient: add /v1 only when the URL has no path, otherwise use it as-is. The proxy runs standalone in the sandbox, so the check is inlined rather than imported from openenv.core. /v1 and pathless bases resolve exactly as before.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation
• New environment
• Refactoring

Alignment Checklist

Before submitting, verify:

• I have read .claude/docs/PRINCIPLES.md and this PR aligns with our principles
• I have checked .claude/docs/INVARIANTS.md and no invariants are violated
• I have run /pre-submit-pr (or bash .claude/hooks/lint.sh and tests) and addressed all issues

RFC Status

• Not required (bug fix, docs, minor refactoring)
• RFC exists: #___
• RFC needed (will create before merge)

Test Plan

PYTHONPATH=src:envs uv run pytest tests/envs/test_opencode_*.py -q: 48 passed, 1 skipped. The new test fails on main. Also ran the proxy against a local stub mounted at /api/paas/v4: main forwards to /api/paas/v4/v1/chat/completions, this branch to /api/paas/v4/chat/completions.

Claude Code Review

N/A

🤖 Generated with Claude Code

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Note

Low Risk
Localized URL-building bugfix in the sandbox proxy with unit tests; pathless bases behave as before.

Overview
Fixes transparent proxy upstream URL construction so it matches opencode black_box behavior for non-OpenAI path prefixes.

_resolve_upstream_url no longer treats “doesn’t end with /v1” as “needs /v1 inserted.” It uses urlsplit: if the base URL already has a path (/v1, /v1beta/openai, /api/paas/v4, etc.), it only appends /chat/completions; pathless hosts still get /v1/chat/completions. That stops broken URLs like .../v1beta/openai/v1/chat/completions for Gemini-style bases.

Adds test_interception_keeps_upstream_base_path covering OpenAI /v1, localhost, Gemini, and z.ai-style bases.

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