Expose the current HarnessToolCall id to tool handlers (public accessor)

Component

hyperforge.harness_sdk (AgentHarness._execute_tool_call, HarnessTool.execute)

Summary

When the Harness executes a tool call, the call's id is emitted in the TOOL_REQUESTED event and then the handler is invoked with only the harness and the validated input (HarnessTool.execute → await self.handler(harness, value)). The handler has no public way to learn which tool call it is executing:

• AgentHarness._execute_tool_call emits TOOL_REQUESTED with call.id, then calls tool.execute(self, call.arguments).
• harness.turn_id is a public property, but there is no public accessor for the active HarnessToolCall (the only call-related attributes on AgentHarness are the private _execute_tool_call/_execute_tool_calls methods).

Impact

Handlers that fan out nested work and emit their own lifecycle events cannot correlate those events with the parent tool call. Concrete example from an embedding application: a scoped "Code Mode" tool that runs restricted Python in a remote sandbox and exposes a fixed set of nested capabilities must emit TOOL_REQUESTED/TOOL_COMPLETED/TOOL_FAILED for each nested capability call; without the outer call id, those events cannot be parented to the harness's own tool-call event, and downstream consumers cannot reconstruct the hierarchy. The only workaround today is reading private harness state, which public-API consumers must not do.

Verified on hyperforge==1.0.0.post310.

Proposal (non-breaking)

Expose a read-only property, set and cleared around execution:

@property
def current_tool_call(self) -> HarnessToolCall | None:
    return self._current_tool_call

# in _execute_tool_call:
self._current_tool_call = call
try:
    ...
finally:
    self._current_tool_call = None

An alternative is passing a context object to handlers, but that changes the handler signature and belongs to a major-version design discussion; the property unblocks event correlation now without touching the handler contract.

Acceptance criteria

• During a tool execution, harness.current_tool_call.id equals the call.id emitted in the corresponding TOOL_REQUESTED event.
• Outside of an execution (including after exceptions/cancellation), current_tool_call is None.

Start in hyperforge.harness_sdk at AgentHarness._execute_tool_call and HarnessTool.execute, tracing when the TOOL_REQUESTED event is emitted and when the handler runs. Add the public current_tool_call behavior described in the proposal, then verify the accessor exposes the matching call id during execution and is None after normal completion, exceptions, and cancellation.