Restrict SCML player protocol

[Muhtasham]

Summary

• replace native SCML OneShotAgent submissions with a restricted decide(observation) policy function
• keep SCML world objects, trusted wrapper agents, offer/response validation, scoring, and result-file handling inside the arena runtime
• run submitted policies in isolated worker processes with startup handshakes, per-decision timeouts, and max_policy_errors fallback disabling
• switch SCML worlds to a two-process setup so submitted policies actually participate in buy/sell negotiations
• update starter code, docs, example config, validation, and tests for the restricted protocol

Design Choice For Review

This intentionally makes SCML more CodeClash-controlled than a native simulator-agent submission.

Instead of letting submitted code subclass SCML OneShotAgent directly, the arena exposes only a plain policy callback:

def decide(observation):
    return {}

The trusted runtime owns the actual SCML agents and converts policy decisions into validated negotiation intents:

• proposal: {"offer": [quantity, time, unit_price]}
• response: {"response": "accept" | "reject" | "end"}
• {} or None: use the trusted greedy fallback

The tradeoff is deliberate:

• pro: simulator ownership, scoring, offer validation, timeouts, and fallback behavior stay in trusted arena code
• pro: submitted code cannot directly mutate the scored SCML agent/world objects
• con: policies cannot use the full native SCML agent API directly, so this is less expressive than native OneShotAgent submissions

@john-b-yang could you sanity-check whether this restricted policy interface is the right CodeClash-compatible shape for SCML, or whether you would rather expose native SCML agent classes for more expressivity?

Verification

• uv run ruff check codeclash/arenas/scml/scml.py codeclash/arenas/scml/runtime/run_scml.py tests/arenas/test_scml.py
• uv run pytest -q tests/arenas/test_scml.py -> 10 passed
• uv run pytest -q tests/arenas -> 190 passed
• uv run pre-commit run --files codeclash/arenas/scml/scml.py codeclash/arenas/scml/runtime/README.md codeclash/arenas/scml/runtime/scml_agent.py codeclash/arenas/scml/runtime/run_scml.py configs/examples/SCML__dummy__r1__s2.yaml docs/reference/arenas/scml.md tests/arenas/test_scml.py
• docker build -t codeclash/scml -f codeclash/arenas/scml/SCML.Dockerfile .
• direct Docker starter smoke: two sims completed; all details had nonzero decisions, zero policy_errors, zero invalid_decisions, and zero disabled_policies
• direct Docker invalid-output smoke: invalid offers/responses were rejected, logged as invalid_decisions, and the world completed using trusted fallback behavior
• direct Docker infinite-loop smoke: looping policies hit per-decision timeout, were disabled after max_policy_errors, and the world completed using trusted fallback behavior
• uv run python main.py configs/examples/SCML__dummy__r1__s2.yaml -o /private/tmp/codeclash-scml-protocol.sFesGl -> two launcher rounds completed, both players validated, details had active policy decisions and zero policy errors
• after adding worker startup handshakes: rebuilt codeclash/scml and reran configs/examples/SCML__dummy__r1__s2.yaml; both launcher rounds completed with policy_errors_total: 0 and invalid_decisions_total: 0
• uv run pytest -q -> 192 passed