Assign an experiment

Read the current baseline and program.md, then write one complete assignment:

• a falsifiable hypothesis and mechanism;
• exact files and changes in scope;
• baseline metrics and W&B evidence;
• commands, run limits, metrics, and stopping conditions; and
• one student, one branch, and one experiment.

Fetch the configured advisor branch and record its exact remote SHA. Call create_assignment with this operation-specific payload; the runtime supplies and enforces the configured advisor branch and student allowlist:

{
  "assignment_id": "stable-assignment-id",
  "revision_id": "initial-revision-id",
  "student": "student-name",
  "expected_base_sha": "FETCHED_REMOTE_ADVISOR_SHA",
  "head_branch": "student-name/hypothesis-slug",
  "title": "Concise hypothesis title",
  "body": "Complete actionable experiment brief"
}

The tool creates an empty assignment commit without changing the advisor worktree, pushes the branch with a lease, creates or reconciles one draft PR, adds the exact routing labels, embeds the typed assignment marker, verifies the result, and rejects a second active assignment for the student.

Do not create the branch, PR, labels, or assignment marker through shell commands. If the tool reports stale state, refresh the named SHA and re-evaluate rather than bypassing the precondition.