Define an Oban worker that runs a claude job.

A worker is a task definition; a job is one instance of it. The claude args are a merge of worker-level defaults (:args) and the per-job args, the job winning on conflicts -- except worker-level :pinned_args, which win over the job (a guardrail for keys a job must not override). That spans a spectrum from one mechanism:

• no defaults -> the job carries everything (a bare Oban-to-claude passthrough)
• fixed config in the worker, the variable input in the job (the common case)
• everything in the worker, an empty job -> a routine, e.g. scheduled with Oban.Plugins.Cron

Example

defmodule MyApp.PrReview do
  use ObanClaude.Worker,
    queue: :review,
    max_attempts: 3,
    args: ObanClaude.Args.defaults(model: "sonnet", system_prompt: "Review the pull request.")

  @impl ObanClaude.Worker
  def handle_result(result, _job) do
    case ObanClaude.outcome(result) do
      "blocked" -> {:cancel, :blocked}
      _ -> :ok
    end
  end
end

# the job is just the instance:
MyApp.PrReview.new(ObanClaude.Args.new(prompt: "PR #4321: " <> diff))
|> Oban.insert()

use ObanClaude.Worker accepts every Oban.Worker option (:queue, :max_attempts, :unique, :priority, ...) plus:

• :args -- a map of default claude args, merged under each job's args (the job wins). Defaults to %{}. Build it with ObanClaude.Args.defaults/1 (prompt-optional; evaluates at compile time) or write the string map directly. It may reference module attributes defined before use. Keys must be strings (atom keys raise at compile time -- they would otherwise be silently dropped by the string-keyed merge).
• :pinned_args -- a map of claude args merged over each job's args, so these keys are worker-invariant (they win even when a job supplies the same key). Defaults to %{}; same build/key rules as :args. Precedence is pinned_args > job args > args. Use it to pin security-relevant keys a job must not override -- permission_mode, mcp_config, max_budget_usd, tool allow/deny lists -- which matters when job args come from an external or semi-trusted source (a webhook, an exposed enqueue API).
• :classifier -- a ObanClaude.classifier/0, the outcome -> Oban-return mapping (see ObanClaude.Outcome), forwarded to ObanClaude.run/2. It must return the {oban_return, payload} envelope (e.g. {{:cancel, :blocked}, error}), not a flat verdict like {:cancel, :blocked} -- run/2 raises on the latter, which Oban would otherwise treat as success.
• :query_fun -- a ObanClaude.query_fun/0, the claude entrypoint (defaults to &ClaudeWrapper.query/2), forwarded to ObanClaude.run/2; override to stub claude in tests.

It injects a perform/1 that merges the args (pinned_args > job > args), runs ObanClaude.run/2, calls handle_result/2 on success, and routes every non-:ok verdict ({:error,...} / {:cancel,...} / {:snooze,...}) through handle_error/3 with the run's payload (default: pass the verdict straight to Oban). A deterministic args fault (a missing prompt, an unknown permission_mode) becomes {:cancel, {:invalid_args, message}} rather than a raise, so a malformed stored job dead-letters at once instead of retrying to exhaustion (the message omits the arg values). perform/1, handle_result/2, and handle_error/3 are all overridable.