Summary

crates/zeph-core/src/agent/provider_cmd.rs (203 lines) and build_provider_for_switch() have zero unit test coverage.

What to Test

• /provider with multiple configured providers — list output, active highlighted
• /provider <name> valid switch — state reset verified (cached_prompt_tokens, compaction, ACP override)
• /provider <unknown> — clear error returned, no panic
• /provider status — correct provider/model/cost output
• ProviderConfigSnapshot construction from ProviderEntry

Pattern

Use MockProvider and MockChannel per existing test patterns in crates/zeph-core/src/agent/.

Discovered during tester review of PR #2150.