fix(model): only strip /v1 from OpenCode URLs on fresh provider resolution

[aniruddhaadak80]

Summary

Fixes #14879

The /model command unconditionally strips /v1 from OpenCode base URLs when api_mode == "anthropic_messages", but this breaks models that need /v1 in the URL when the user switches models on the same provider (where the URL was already correct from a prior resolution).

Root Cause

In switch_model(), the /v1 stripping regex runs whenever:

1. api_mode == "anthropic_messages"
2. Provider is opencode-zen or opencode-go

But it didn't check whether the URL was freshly resolved or was carried over from the current session. When a user on opencode-go switches from one model to another (same provider), the base_url is already in the correct form and stripping /v1 corrupts it.

Changes

hermes_cli/model_switch.py — switch_model():

• Added (provider_changed or explicit_provider) to the /v1 strip condition
• /v1 is now only stripped when the URL was freshly resolved via resolve_runtime_provider() (i.e., the provider changed or was explicitly specified)
• When switching models on the same provider, the base_url is left as-is
• Updated the comment block to document this behavior

Testing

• Provider switch (e.g., openrouter → opencode-go): provider_changed=True → /v1 stripped as before
• Same-provider model switch (e.g., model A → model B on opencode-go): provider_changed=False, explicit_provider="" → /v1 preserved (bug fixed)
• Explicit provider (e.g., /model sonnet --provider opencode-go): explicit_provider="opencode-go" → /v1 stripped correctly
• Non-OpenCode providers: condition short-circuits at target_provider check → no change

Checklist

• Follows Conventional Commits format
• Single logical change
• No breaking changes
• Existing tests unaffected

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[teknium1]

Thanks for the investigation @aniruddhaadak80 — but I have to close this without merging.

Current main already handles this scenario correctly (fixed by PR #4508 on April 2, 22 days before #14879 was filed). E2E-verified with the exact repro from the issue:

current_provider=minimax, current_model=MiniMax-M2.7
raw_input='opencode-go glm-5.1'
→ result: base_url='https://opencode.ai/zen/go/v1', api_mode='chat_completions'  ✓

The /v1 is preserved because opencode_model_api_mode('opencode-go', 'glm-5') correctly returns chat_completions (not anthropic_messages), so the strip condition at model_switch.py:862 short-circuits.

The proposed change regresses 4 existing tests in tests/hermes_cli/test_model_switch_opencode_anthropic.py:

• test_switch_to_minimax_m27_strips_v1
• test_switch_to_minimax_m25_strips_v1
• test_trailing_slash_also_stripped
• test_switch_to_claude_sonnet_strips_v1

These guard the same-provider anthropic_messages switch case (e.g. opencode-go model-A → model-B where B is MiniMax). Gating the strip on provider_changed or explicit_provider skips the strip in exactly the case the tests assert it's required, causing the double-/v1/messages bug to return.

The underlying issue #14879 will be closed too — the user was on a version predating PR #4508.

Appreciate the detailed PR body with the three-case analysis — just happened to land against a scenario already covered.