Add DECIDE LoopSpec and close loop

[rfreel]

Motivation

• Provide an explicit LoopSpec for the DECIDE PRD item so the loop contract, verification gates, budgets and stop rules are machine-checkable and auditable.

Description

• Add loop/LOOPSPEC.md documenting the minimal loop contract fields including ObjectiveMetric, DoneCondition, StateSchema, ActionsAllowed, SensorsAvailable, Precheck/Postcheck gates, EvaluatorRules, RetryPolicy, Budgets, EscalationCondition, ArtifactsRequired, AcceptanceTest, and StopRule.
• Update prd.json to add DECIDE-001 and mark it passes: true with notes referencing the new LoopSpec.
• Append a progress entry to progress.txt for DECIDE-001 and add a log entry in loop/log.txt reflecting the successful run, and replace loop/last_error.txt contents with the LLM stub output.

Testing

• Ran scripts/ralph/loop.sh which executed the radius/pre-commit checks and returned a successful output (Loop OK; consider updating prd.json/progress.txt, then commit).
• The loop run recorded [OK] pre-commit passed to loop/log.txt, indicating the pre-commit gate passed (no automated failures observed).

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Codex Task