PR #4918 fixed the double-/v1 bug at fresh agent init by stripping the
trailing /v1 from OpenCode base URLs when api_mode is anthropic_messages
(so the Anthropic SDK's own /v1/messages doesn't land on /v1/v1/messages).
The same logic was missing from the /model mid-session switch path.
Repro: start a session on opencode-go with GLM-5 (or any chat_completions
model), then `/model minimax-m2.7`. switch_model() correctly sets
api_mode=anthropic_messages via opencode_model_api_mode(), but base_url
passes through as https://opencode.ai/zen/go/v1. The Anthropic SDK then
POSTs to https://opencode.ai/zen/go/v1/v1/messages, which returns the
OpenCode website 404 HTML page (title 'Not Found | opencode').
Same bug affects `/model claude-sonnet-4-6` on opencode-zen.
Verified upstream: POST /v1/messages returns clean JSON 401 with x-api-key
auth (route works), while POST /v1/v1/messages returns the exact HTML 404
users reported.
Fix mirrors runtime_provider.resolve_runtime_provider:
- hermes_cli/model_switch.py::switch_model() strips /v1 after the OpenCode
api_mode override when the resolved mode is anthropic_messages.
- run_agent.py::AIAgent.switch_model() applies the same strip as
defense-in-depth, so any direct caller can't reintroduce the double-/v1.
Tests: 9 new regression tests in tests/hermes_cli/test_model_switch_opencode_anthropic.py
covering minimax on opencode-go, claude on opencode-zen, chat_completions
(GLM/Kimi/Gemini) keeping /v1 intact, codex_responses (GPT) keeping /v1
intact, trailing-slash handling, and the agent-level defense-in-depth.
