v0.13.0 — Repetition Guard + RTK Token Optimization

Carries the RTK token work from 0.12.9 plus the fix below. Briefly tagged
v0.12.10 before being renumbered; same content, no npm release under that
number.

Fixed

• A reply that collapses into repeating one phrase is now cut off, not paid
  for to the last token. stepfun/step-3.5-flash, asked to build a large HTML
  page, narrated Writing the HTML structure... several hundred times, spent
  its entire 16,384-token output allowance, returned stopReason: 'limit', and
  the run ended having written nothing. It reproduced on every attempt in the
  session. Nothing in the harness noticed: text chunks were appended and printed
  regardless of what they contained, and the only backstop was the model's own
  output cap.

  agent/repetition-guard.ts watches the stream's tail for an exactly periodic
  cycle — which is what a collapsed model emits, and what ordinary prose never
  does — and trips after ~1,200 characters of it. The loop then:

  • stops reading, which returns the generator and aborts the HTTP request,
    so the provider stops generating (and billing) the remaining output. The
    openai-compatible adapter had no cleanup on early exit; it now aborts its
    controller in a finally unless the stream drained normally;
  • keeps the loop out of history — only the text from before the collapse
    survives, plus a one-line marker. A model shown even a few copies of its own
    loop carries on with it, which is why every later turn in that session
    repeated too;
  • retries with the failure named, telling the model to make the
    write_file call it was narrating instead of describing it. Twice, then it
    gives up and says plainly that this is a model failure and suggests a
    stronger --model, rather than implying the task was at fault.

  AURA_REPETITION_GUARD=0 disables it. The thresholds are set so ordinary
  output cannot reach them, but nobody should have to wait for a release to
  switch off something that truncates replies.

  Two compaction fixtures used 'y'.repeat(10_000) as filler and now trip the
  guard on purpose — a model emitting ten thousand identical characters is
  exactly this bug. They use varied prose of the same length instead; the token
  volume they depend on is unchanged.