Runtime context

Harn exposes logical runtime identity through runtime_context(). This is the task/thread abstraction Harn code should use for observability and debugging; raw OS thread IDs are not part of the stable language surface.

task_current() is an alias for runtime_context().

let ctx = runtime_context()
log(ctx.task_id)
log(ctx.parent_task_id)
log(ctx.root_task_id)

Stable fields

These fields are stable API and always present. Unavailable values are nil.

Field	Description
task_id	Current logical task id
parent_task_id	Parent logical task id, or nil for the root task
root_task_id	Root logical task id for this execution tree
task_name	Runtime label such as root, spawn, parallel, parallel each, or parallel settle
task_group_id	Shared id for siblings created by one parallel operation
scope_id	Optional host/runtime scope id
workflow_id, run_id, stage_id, worker_id	Workflow and delegated-worker identity when available
agent_session_id, parent_agent_session_id, root_agent_session_id, agent_name	Agent-loop session identity when available
trigger_id, trigger_event_id, binding_key, tenant_id, provider	Trigger-dispatch identity when available
trace_id, span_id	Current tracing identity when available
scheduler_key, runner, capacity_class	Scheduler/runtime hints when available
context_values	Task-local values for the current logical task
cancelled	Whether the current task has observed cancellation

Context values

Task-local values are stored on the current logical task. Children created by spawn, parallel, parallel each, and parallel settle inherit a snapshot of the parent values. Later child writes do not mutate the parent, and later parent writes do not affect already-created children.

runtime_context_set("tenant", "acme")

let result = parallel each ["a", "b"] { item ->
  runtime_context_get("tenant")
}

assert_eq(result, ["acme", "acme"])

Function	Description
runtime_context_values()	Return the current task-local values as a dict
runtime_context_get(key, default?)	Return a task-local value, default, or nil
runtime_context_set(key, value)	Set a task-local value and return the previous value or nil
runtime_context_clear(key)	Clear a task-local value and return the previous value or nil

Copying vs sharing

spawn, parallel, parallel each, and parallel settle create isolated interpreter instances. Normal bindings, lists, dicts, structs, and task-local context values are copied into the child at creation time. Later assignment in one task does not mutate another task's binding.

Explicit handle values are shared by design:

Handle	Shared behavior
channel(...)	Message transport shared by every task that receives the handle
atomic(...)	Shared integer cell
sync_*_acquire(...)	Shared named synchronization runtime
shared_cell(...) / shared_map(...)	Scoped process-local shared state
mailbox_open(...)	Targeted actor-style inbox

agent_loop calls do not share transcript internals with tasks. A named session_id shares durable transcript history through the agent session store. spawn_agent workers get their own worker/session lineage; use explicit mailboxes, shared state handles, agent_state_*, or host storage when a parent and worker need data exchange outside the transcript.

Debug fields

runtime_context().debug contains best-effort introspection for tools: active_task_ids, waiting_reason, cancelled, and held_synchronization. These fields are intended for diagnostics and may grow as the scheduler gains more structured-concurrency and synchronization primitives.