referring to #38384, which I closed

Description

Got Serena MCP properly configured (unrelated AGENTS.md issue on my end). Re-ran the same kind of prompt on the same GPT-5.6 Terra model — worked fine. GPT-5.5 works even better...

So it's not the model. The difference is that tool_search's query actually matched a real tool this time (Serena's find_referencing_symbols). In the failing case, it was searching for LSP go-to-def/find-refs, which per the docs doesn't exist — OpenCode's lsp is diagnostics-only. So tool_search had nothing to match, and whatever it does in that case produced the malformed input[N].arguments call instead of just failing cleanly.

Better guess: this is a no-match handling bug in tool_search, not a model/provider issue. Haven't confirmed on a non-OpenAI model since I'm unblocked now, but wanted to correct the record before anyone chases the model-specific angle.

So, realized that built-in lsp support does NOT do navigation. Installed Serena--works great with opencode.

But, a different bug remains: if AGENTS.md suggests using specific tools for semantic search and opencode can't find the named tools, it will attempt to use non-working tools. Probably, it should just report an error on the tool request or, better, drop back to best use of other tools. Turns, out opencode will do the latter if there is no specific instruction for searches.

I enclose the AGENTS.md

AGENTS.md

Plugins

only stock

OpenCode version

1.18.8

Steps to reproduce

1. Include an AGENTS.md that sets constraints around preferring semantic search with Serena
2. prompt something like: find all uses of SeriesColSpec in any argument list and identify the constructor overload used. requires looking across the c++ repo and specifically looking for an overloaded constructor, but it could be any overloaded function.

Screenshot and/or share link

No response

Operating System

macOS 26.5.2

Terminal

Otty