feat(*): self-evolution stack: evolver, appworld bench, unified entry

[ethanwwwwwwww]

Summary

Port the harness self-evolution framework onto Raven and grow it into a
runnable, benchmark-pluggable stack: a budget-bounded loop that diagnoses
failing trajectories, designs candidate patches as real git commits, screens
them cheaply, confirms survivors, and promotes only what passes three
verification gates -- with a sealed test set for an honest generalisation
number.

• Evolution machinery (raven/evolver/): orchestrator state machine
  (seven-step funnel), three verification gates (infra validity, beacon
  attribution, paired significance), sealed-test runner with retention,
  git-backed candidate tree, judge, taxonomy, activation ledger.
• AppWorld bench (benchmarks/appworld/): agent_cli, batch scorer
  with trial-level resume and an infra-rerun ladder, plus the evolve glue
  (designer, diagnosis, adapter, Gate0 precheck with real-generation probing).
• Unified entry: python -m raven.evolver {check,run,status,finalize}
  drives cold start -> rounds -> terminate -> unseal as a resumable state
  machine. Config drift and unseal one-wayness are mechanized in run meta;
  benches plug in via a documented contract (docs/specs/evolve-bench-contract.md).
• Designer feedback: inert-death loop (pruned_inert status, per-WHY
  history, gentle decay) so unreachable triggers teach the next attempt.
• Launch hygiene: check runs the bench Gate0 precheck, so a dead
  subject endpoint fails at check time instead of at cold start; ephemeral
  eval/edit worktrees live under work_dir/tmp and hard-kill leftovers are
  swept on the next launch of the same run.
• Docs: SOP translation (internal details redacted), SOP-to-code map,
  bench plugin contract, and a user README with security notes and known
  limitations.

Type

• Fix
• Feature
• Docs
• CI / tooling
• Refactor
• Other

Verification

• Relevant tests pass locally
• Relevant lint / type checks pass locally
• User-facing docs or screenshots are updated when needed

Commands run:

• uv run pytest tests/test_evolver_launch.py tests/test_evolver_launch_e2e.py -q
  -> 56 passed (config, guards, trial-level idempotency, interrupt -> resume ->
  finalize with a fake bench, check precheck pass/fail, worktree sweep).
• uv run ruff check on all touched files -> no new findings versus base
  (one S607 partial-path git call matching the file's existing idiom).
• Real AppWorld end-to-end through the unified entry, from a fresh config
  written by following the README user path: check -> run --smoke (~16 min:
  cold start on 3 tasks, one full round with real diagnose/design, a real
  1-line candidate commit, focused probe + confirm, promoted with an honest
  credited=False Gate-b verdict) -> termination.
• Real check both ways: live subject endpoint -> bench precheck: OK;
  config pointed at a dead (NXDOMAIN) endpoint -> exit 1 at check time with
  an actionable subject endpoint unreachable message.
• The bench placement (repo-root benchmarks/, outside the wheel, matching
  this directory's decoupling convention) was verified with a second real
  smoke: all three phases ran against a checkout of this layout, worktree
  evals resolved python -m benchmarks.appworld.batch from the checkout,
  and the designer wrote its candidate to the new whitelist path
  (benchmarks/appworld/agent_cli.py) as a real commit.

Risk

• Security impact considered
• Backward compatibility considered
• Rollback path is clear for risky changes

Security: this system has an LLM edit and execute code. Candidate edits are
constrained to a per-bench path whitelist, an immutable kernel protects the
measurement surface (the evolver itself and the scorer), and the README
documents the threat model plus the recommendation to run evolutions in an
isolated environment. Backward compatibility: purely additive -- new packages
plus one optional BenchBundle.precheck field; nothing existing changes
behavior. Rollback: revert the branch; no migrations, no config changes to
existing features.

Related Issues

N/A

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Reviewer notes:

• Exercised at smoke scale only: a full-size run (90 tasks x K=3, multi-round,
  hours) and the sealed-test unseal/retention path on a real benchmark are
  covered by tests but not yet by a production run; the README states this
  under "Status and known limitations".
• One bench ships today (AppWorld, built-in scorer line); a framework-line
  example (external scorer) is planned as a follow-up.