Define an Oban worker that runs a Codex job.

A worker is a task definition; a job is one instance of it. The Codex 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-Codex 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 ObanCodex.Worker,
    queue: :review,
    max_attempts: 3,
    args: ObanCodex.Args.defaults(
      sandbox: :read_only,
      approval_policy: :never
    )

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

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

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

• :args -- a map of default Codex args, merged under each job's args (the job wins). Defaults to %{}. Build it with ObanCodex.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 Codex 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 -- sandbox, approval_policy, dangerous bypass switches, or working_dir -- which matters when job args come from an external or semi-trusted source (a webhook, an exposed enqueue API).
• :classifier -- a ObanCodex.classifier/0, the outcome -> Oban-return mapping (see ObanCodex.Outcome), forwarded to ObanCodex.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 ObanCodex.query_fun/0, the Codex entrypoint (defaults to &ObanCodex.Query.run/2), forwarded to ObanCodex.run/2; override to stub Codex in tests.

It injects a perform/1 that merges the args (pinned_args > job > args), runs ObanCodex.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 enum or incompatible session options) 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.