Shim server instructions: lead with MCP-only, drop the transport wording, shorten 14 tool descriptions

SHIPPED 2026-09-23 as shim 2.61.15, commit d0fa422, audit-general-cc PASS. Filed retroactively - see REF COLLISION below. The server 'instructions' opener read 'llmmsg-srv v2: HTTP-polled chat hub', which names the TRANSPORT rather than the interface. Replaced with an opener that leads 'THESE TOOLS ARE THE ONLY INTERFACE TO IT' and prohibits curl/raw HTTP/hub SQLite/another MCP client, repeated in register's description because instructions are read at session start but a tool description is read at the moment an agent picks a call. 14 tool descriptions shortened by moving rationale into // comments with every binding fact kept in the string. Advertised surface 16453 -> 13474 chars. Verified by t432.mjs: control = pre-change shim, patched = new, stdio initialize + tools/list with LLMMSG_SKIP_REGISTER=1 against a dead port. 41 checks, control RED on 4. SHIPPED ON ITS OWN MERITS, NOT AS THE FIX FOR THE INCIDENT THAT PROMPTED IT. The directive's stated cause - 'the HTTP-polled wording makes curl look equivalent' - did not survive asking audit-mba-l-ca what it actually did: it had never read that paragraph before choosing a CLI, because in Codex the MCP tools are DEFERRED and absent from the visible tool list. Shim text cannot reach an agent that has not found the tools. The real fix was a rule in ~/.codex/AGENTS.md on all three hosts. REF COLLISION, recorded so nobody is misled: commit d0fa422 and the // comments in hub/llmmsg-srv-mcp.mjs cite this work as 'MSG-432'. That ref was used in the commit message but the row was never filed, and MSG-432 has since been minted for an unrelated item (One identity file per agent folder). Git history is immutable and will not be rewritten. The authoritative ref for THIS work is this row. Same defect applies to the follow-up commit 9588c00, which cites 'MSG-433'.