Admins can now give each EXTERNAL MCP server a free-text instruction ("how/
when to use this server's tools") that the agent receives in its SYSTEM
PROMPT next to the tool descriptions — porting the built-in SERVER_INSTRUCTIONS
idea to admin-configured servers. Trusted, admin-authored text (like a system
prompt); NON-secret, so unlike headersEnc it IS returned in views/forms.
- Migration: nullable `instructions text` on ai_mcp_servers (old rows = null =
no guidance). Table type + repo insert/update (blank/whitespace -> null via
blankToNull). DTO `@MaxLength(4000)`. Service threads it through
McpServerView/toView.
- mcp-clients: `McpServerInstruction { serverName, toolPrefix, instructions }`
threaded through the toolset/cache/lease. Guidance is built ONLY for a server
that actually connected AND contributed >=1 callable tool (the allowlist may
filter all of them out) AND has non-blank text — so a guide never appears for
tools the agent cannot call. Cached with the toolset, so an edit is picked up
next turn via the existing CRUD cache invalidation.
- System prompt: `buildMcpToolingBlock` renders an <mcp_tooling> block INSIDE
the safety sandwich (after context, before the trailing SAFETY_FRAMEWORK) so
it informs tool choice but cannot override the rules; each section is headed
by the server's `prefix_*` namespace. Empty/blank -> block omitted. The
caller (ai-chat.service) now builds the external toolset BEFORE the prompt and
passes external.instructions; client-handle lifecycle (close-once) unchanged.
- Client: instructions field in types + a Textarea (autosize, maxLength 4000)
in the MCP-server form with a namespace-prefix hint; i18n (en/ru).
Tests across every layer (prompt block placement + both SAFETY copies; view
blank->null; buildEntry includes guidance only for connected+>=1-tool+non-blank;
DTO MaxLength; repo + integration round-trip; service wiring). Delegated impl
reviewed (APPROVE); applied the import-type follow-up.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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