Return the original job.accepted payload (lease, credentials) on idempotent resubmission (§7.2)

[nficano]

Category: spec-conformance Severity: major
Location: lib/arcp/runtime/session_actor.rb:265-274 (secondary: lib/arcp/runtime/job_manager.rb:79-90)
Spec: ARCP v1.1 §7.2

What

Spec §7.2: "the runtime MUST return the same job.accepted payload for any subsequent submission with the same key and identical parameters." On an idempotency hit, JobManager#submit returns a bare job_id (not the [job_id, resolved, lease, credentials] tuple). handle_submit then takes the else branch and reconstructs job.accepted with credentials: nil and re-reads the lease from the manager — so the replayed acceptance drops the credentials array that the first acceptance carried (and may differ in accepted_at, using record.created_at). A client that resubmits to recover its provisioned credentials receives none. This is distinct from #50 (which only concerns conflict detection comparing agent vs. other params).

Evidence

# lib/arcp/runtime/session_actor.rb:265-274 — idempotent replay branch
else
  job_id = result
  record = @runtime.job_manager.lookup(job_id)
  accepted = Arcp::Job::Accepted.new(
    job_id: job_id, agent: record.agent,
    accepted_at: record.created_at,
    lease: @runtime.lease_manager.get(job_id),
    credentials: nil                      # original credentials are lost
  )
end

Proposed fix

Cache the full original job.accepted payload (resolved agent, lease, credentials, accepted_at, budget) keyed by [principal, idempotency_key] at first acceptance, and return that cached payload verbatim on a hit. Alternatively have JobManager#submit always return the tuple (re-fetching the stored credentials from the registry) so handle_submit has a single code path. Add a test that submits with credentials provisioned, resubmits the same key, and asserts byte-identical job.accepted payloads.

Acceptance criteria

• An idempotent resubmission returns the same credentials array as the first acceptance.
• lease, agent, and accepted_at match the original acceptance.
• Test covers a provisioned-credentials runtime.