Keep game-owned scoring evidence distinct from sampled tokens

[relh]

Consolidated into #248 at 87c40eaa18229a3497ac68c15cc83345747e6e57 on current master. All21combined serializer contracts pass, including scoring/generation exclusion and private-player injection rejection. Source branch and frozen historical evidence remain preserved.

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Change

Add game-owned DecisionAttempt.actionEvidence to authoritative native JSONL as action_evidence. Private player evidence cannot inject it.

A scoring attempt must use candidate inference mode, retain a null generation response, and omit sampled tokens and behavior log-probabilities. Recording snapshots scoring evidence before later mutation. Rejected attempts and engine-selected action joins remain intact.

This is a generic serializer prerequisite for Parley legal-choice ranking. The game producer and Python typed reader validate the detailed scoring protocol. This PR implements neither a scorer backend nor model routing.

Verification

• Host Nim 2.2.10, macOS arm64: tests/test_decision_trajectory.nim passes 18 tests in 2.53 seconds.
• Three new tests cover rejected/selected scoring retention, generation/sampling exclusion, and private-player injection rejection.
• Removing the candidate-only guard makes the retained exclusion test fail. Exact source was restored.
• git diff --check passes.

Host packages are not a proof of the pinned Linux image or full dependency lock. No model, scorer, game comparison, GPU, or paid-resource calls occurred.

Integration

Based on current master at a69e563, preserving existing response-provenance and lifecycle changes. The older 23e8eb8 pinned-source prototype and its controls remain separate retained evidence.

Owner8 retains native serialization and Parley producer work. Owner9 retains Python typed reader and explicit SFT export exclusion. Root07 and owner61 retain consumer and provider audit. Sole44’s frozen ce2a/6ea3 pair is unchanged at 0/2 completed. This draft does not authorize a new runtime or replace frozen source/image pins.