## MODIFIED Requirements

### Requirement: Task submission enqueues a scheduled task
The system SHALL allow a caller to submit a task (a goal string, or a
reference to a `WorkflowDefinition`, plus optional device constraints:
`driver_type`, required capability tags, and an explicit Host/Device target)
and SHALL enqueue it as a `ScheduledTask` with status `queued`, returning a
stable task id the caller can poll. A Device target MUST name its owning Host;
an explicit target remains attached to the task for its entire lifecycle.

#### Scenario: Successful submission
- **WHEN** a caller submits a task with a goal and no constraints
- **THEN** the scheduler creates a `ScheduledTask` with status `queued`,
  assigns it a unique id, and returns that id to the caller without blocking
  for a device to become available

#### Scenario: Targeted submission
- **WHEN** a caller submits a valid task targeted to a Host and one of its
  Devices
- **THEN** the queued task retains that Host/Device target until it is assigned
  or reaches a terminal lifecycle state

#### Scenario: Queue depth limit reached
- **WHEN** a caller submits a task while the queue already holds
  `config.max_queue_depth` queued tasks
- **THEN** the scheduler rejects the submission with a clear error rather than
  accepting an unbounded backlog

### Requirement: Assignment matches a queued task to an idle, constraint-matching device
The system SHALL assign a queued `ScheduledTask` to an idle `PooledDevice`
(as reported by the `device-pool` capability) whose explicit target, if any,
`driver_type`, and capability tags satisfy the task's constraints, using a
named, registrable `AssignmentStrategy`.

#### Scenario: Matching idle device available
- **WHEN** `assign()` runs and at least one idle `PooledDevice` matches the
  head-of-queue task's constraints
- **THEN** the scheduler selects one such device via the configured
  `AssignmentStrategy`, transitions the task to status `assigned`, and records
  the chosen `device_id`/`host_id`

#### Scenario: Targeted Device is unavailable
- **WHEN** `assign()` runs and the only explicitly targeted Device is busy,
  stale, absent, or otherwise ineligible
- **THEN** the task remains `queued` and the scheduler does not assign a
  different Device or Host

#### Scenario: No matching device available
- **WHEN** `assign()` runs and no idle `PooledDevice` matches the head-of-queue
  task's constraints
- **THEN** the task remains `queued` (not failed), and `assign()` returns
  without error, ready to be retried on a later call

#### Scenario: Unknown assignment strategy configured
- **WHEN** `TaskScheduler` is configured with an `AssignmentStrategy` name
  that is not registered
- **THEN** the scheduler raises a clear configuration error at startup/first-
  assign rather than silently falling back to a default strategy