Fix channel NyxID credential routing

[louis4li]

Summary

• Keep registration AgentKey authority for merchant-owned channel inventory, skill loading, and operation execution even when sender binding exists.
• Use client credentials only for recommended skill ref ensure/provisioning in registration AgentKey mode.
• Include the target NyxID service in connected-service invocation visibility failures so users know which service permission to add.

Test plan

• dotnet test test/Aevatar.GAgents.ChannelRuntime.Tests/Aevatar.GAgents.ChannelRuntime.Tests.csproj --nologo --filter FullyQualifiedName~ChannelNyxIdConnectedServiceInventoryToolSourceTests
• bash tools/ci/test_stability_guards.sh
• Local relay smoke: registration revision 147 included aevatar-local-tunnel; nyxid_invoke_operation no longer returned operation_not_visible and the LLM completed with finish=stop.

🤖 Generated with Claude Code

[chatgpt-codex-connector]

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-01T03:57:50.515034Z	4572efd	PR opened

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Reviewed commit: 4572efd639

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