feat(mcpgen,mcpserver): @mcpToolArg for tool-only arguments#35
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Shortcut tools that need an argument-driven selection (e.g. signals
time-series where each {name, agg} pair becomes a sub-field) currently
require that argument to exist on the GraphQL field itself — which
forces a schema change on queries that have been stable for years.
Add a repeatable @mcpToolArg directive that declares arguments belonging
only to the MCP tool. They feed SelectionTemplate via the same args map,
and mcpserver strips them from the variables map before the GraphQL
executor is called, so the underlying field never sees them.
Usage:
signals(tokenId: Int!, interval: String!, from: Time!, to: Time!, filter: SignalFilter): [SignalAggregations!]
@mcptool(
name: "get_signals_time_series"
description: "..."
selection: "timestamp{{range .signalRequests}} {{.name}}(agg: {{.agg}}){{end}}"
)
@mcpToolArg(
name: "signalRequests"
type: "[SignalAggregationRequest!]!"
description: "..."
)
The GraphQL field keeps its existing arguments and return type. The MCP
tool gets `signalRequests` as a required input. At call time the
template renders it into the selection, and `signalRequests` is dropped
from the variables map before executing.
ArgDefinition gets a `ToolOnly bool` field; mcpgen emits it alongside
the other ArgDefinition fields and reuses the existing JSON-schema
mapping via a small ad-hoc type-string parser so the `type:` argument
of the directive can name any loaded GraphQL type (e.g.
"[SignalAggregationRequest!]!", "[String!]!", "Int").
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Summary
Why
Builds on the templated selections from #34 (v0.2.0). That release exposed a new problem: to feed the template, the arg had to live on the GraphQL field, which means every repo adopting this pattern has to modify long-standing query signatures. For telemetry-api's `signals` / `signalsLatest`, that's a non-starter. `@mcpToolArg` keeps the change at the MCP layer where it belongs.
Example
```graphql
signals(tokenId: Int!, interval: String!, from: Time!, to: Time!, filter: SignalFilter): [SignalAggregations!]
@mcptool(
name: "get_signals_time_series"
description: "..."
selection: "timestamp{{range .signalRequests}} {{.name}}(agg: {{.agg}}){{end}}"
)
@mcpToolArg(
name: "signalRequests"
type: "[SignalAggregationRequest!]!"
description: "..."
)
```
The GraphQL field and its arguments are unchanged. The MCP tool gets `signalRequests` as a required input. On each call the template expands it into a per-signal selection set; `signalRequests` is dropped before the GraphQL executor runs.
Changes
Test plan