Randoloot/addons/godot_mcp_toolkit/CompanionSkills/mcp-extension-creator/references/cancellation.md

Cooperative cancellation

For long-running tools (external API calls, heavy processing), opt into cooperative cancellation so the handler exits early when the caller cancels. Most tools do not need this — reach for it only when a tool does slow work that should be able to bail out mid-flight.

Enabling it

Call .mark_cancellable() on the options. This changes the handler contract: a cancellable handler takes a second argument, a MCPToolkitToolContext.

var opts := MCPToolkitExtensionOptions.new("Fetch data from an external API") \
    .with_timeout_ms(60000) \
    .mark_cancellable()
registry.add("weather.fetch", _handle_fetch, opts)

If you set mark_cancellable() but keep a one-argument handler, the dispatcher's two-argument call fails. The two must match.

Observing cancellation

The context exposes two ways to notice a cancel — use whichever fits the work:

• Reactive — connect the cancelled signal to abort an in-flight operation.
• Polling — call ctx.is_cancelled() between discrete steps.

## Fetches weather data, aborting early if the call is cancelled.
##
## Returns a success envelope with the payload, or an empty dict if cancelled
## mid-flight. [param params] carries the request; [param ctx] is the
## per-invocation cancellation context.
func _handle_fetch(params: Dictionary, ctx: MCPToolkitToolContext) -> Dictionary:
    # Reactive: abort the HTTP request the moment cancellation is requested.
    ctx.cancelled.connect(_http_request.cancel_request)

    var result = await _do_fetch(params.get("query", ""))

    # Polling: check between steps and return early.
    if ctx.is_cancelled():
        return {}

    return MCPToolkitSuccess.ok({"data": result})

Rules

• Do not store the context. It is scoped to a single invocation — the dispatcher owns it, and holding a reference past the handler's return is a bug.
• Return promptly once cancelled. A cancelled handler should stop work and return; an empty dict or an MCPToolkitError.fail("FAILED", "cancelled") are both fine — the point is to stop, not to keep computing.

C#

The context arrives as a second GodotObject and is driven by name (ctx.Connect("cancelled", …), (bool)ctx.Call("is_cancelled")). See references/csharp-extensions.md.