agents-md: send the AGENTS.md loaded line to the debug log - #98275

Summary

TLDR: a project with AGENTS.md and no CLAUDE.md starts with no new transcript row; the loaded line goes to the debug log

The no CLAUDE.md found; AGENTS.md loaded: <paths> line is sent with { to: 'debug' }. This mirrors the change built into Claude Code 2.1.286.

Notes

• In a project that has AGENTS.md and no CLAUDE.md, the first prompt.context after the mod loads wrote a transcript row naming the files it loaded, once per project root. That is a healthy start, and a healthy start shows nothing new on screen. The same words now go to the debug log (claude --debug), once per root and again after a move to another root.
• What the model receives is unchanged: the files still join the instruction files behind claudeMd.
• /memory lists the AGENTS.md files the current context was built with, and /context all names them.
• The README's two sentences about the line now say where it goes.
• The "Mod tests" check is expected red until 2.1.286 is the public latest: the published test kit trails this folder.

Test Plan

• claude plugin test mods/agents-md against the build this mirrors: 5 of 5. "by default a project with AGENTS.md alone gets it" expects the transcript's lines to be empty and the debug log's lines to be the one line; "by default a project with a CLAUDE.md is left to the engine" expects both empty. The startedOf fixture splits a ui.log by its to.
• Revert-proof: with the old hooks/register.ts under the new test, the first case fails ("nothing new in the transcript", received the row); the other four pass.
• Driven in the built binary: a project holding only AGENTS.md shows no row in the interactive pane, the request still carries the file framed as project instructions, and the debug file has the line once; the build before the change shows the row.