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Renzo Beux
41de91668b
The security control for plugin MCP tools, landed on its own so it is
reviewable as one diff. Pure and Nest-free: no container, no DB, no
running plugin needed to test it.
The threat is not a plugin crashing. A tool name, title and description
are a persistent, admin-invisible write into every user's assistant
context, and .meta() puts the JSON Schema there verbatim. TREK's own code
proves the channel is obeyed: the static-token deprecation notice is
delivered in a tool result precisely because that is what an assistant
reliably surfaces.
sanitiseAssistantText is a sibling of stripEmoji, not a change to it.
stripEmoji preserves newlines on purpose (PDF paragraphs) and ~15 render
call sites depend on that. The new one collapses every whitespace run to
a single space, so a description cannot forge "## System" as a heading
that reads to the model like host text, and strips more than the brief
asked for: the bidi overrides and isolates and U+2028/9 are neither C0
controls nor \n, so they defeat both halves of the stated rule.
The schema is advertised rather than converted. z.looseObject({}).meta()
passes the plugin's own schema through byte for byte, keeping pattern,
oneOf and format, which a hand-rolled converter flattens to unknown. The
.check() keeps required enforced, so the handler cannot receive a call
missing arguments its own schema declared mandatory.
That only works with a normaliser in front, since .meta() is a
passthrough. It rejects a root type that is not object (which would
advertise a non-object inputSchema while the runtime still passes an
object), rejects $ref/$defs/definitions at any depth, and caps bytes,
properties and nesting. It strips a top-level id, which vanishes from the
advertisement and lands in z.globalRegistry._idmap, a strong Map unlike
the WeakMap holding the rest.
Sanitising recurses into every nested description, title and string enum
member. That is the part a top-level cap misses, and where a property
named trek_session_token with a plausible description would live.
Annotations are clamped asymmetrically. readOnlyHint gates client
auto-approval, so a plugin may lower its danger level and never raise it;
openWorldHint goes the other way, since egress makes a tool open-world
whether it admits it or not. db:own is deliberately not a side effect:
counting the plugin's private SQLite would make nearly every plugin
non-read-only and kill auto-approval for legitimate read tools.
MCPSCHEMA-001 to MCPSCHEMA-030.