fix(research): preserve checkpoint float identity

[proerror77]

Change contract: Enable exact f64 JSON roundtrips for ploy-research checkpoint state and atomically refresh the governed policy identity and BTC/SOL mission pins so a freshly written checkpoint survives typed readback.

Out of scope: Checkpoint schema, evaluator semantics, cohort or projection logic, collector/runtime, hft-search-kernel, CEX, alpha-harness, and the #325 E2E fixture.

Dependency / merge order: This is the sole predecessor to #325. Merge #428 first; only then rebase and promote #325.

Focused validation:

• cargo test --locked -p ploy-research prediction_mcts_run::tests --lib (19 passed)
• cargo test --locked -p ploy-research prediction_policy_identity --lib (3 passed)
• cargo test --locked -p ploy-research checked_in_btc_and_sol_templates --lib (1 passed)
• cargo clippy --locked -p ploy-research --no-deps -- -D warnings -A clippy::type_complexity
• rustfmt check and git diff --check
• Two independent read-only committed-range reviews: no findings

TDD note: A PRD is unnecessary because this is a small, already-specified defect. The counterexample proves that -1.9089014592447406 changed one ULP under the prior serde_json feature graph and now preserves exact to_bits identity.

Rollout / rollback impact: Dependency-feature-only research correctness change. Rollback restores the known false corruption rejection for valid checkpoint metrics and requires reverting the refreshed policy graph and mission pins atomically.

Closes #428

Summary by CodeRabbit

• Configuration

  • Updated Bitcoin and Solana short-term research mission configurations to use refreshed search policy snapshots.

• Reliability

  • Improved consistency when handling floating-point research data.

• Tests

  • Updated training evidence values and expanded validation for checkpoint rewards, including precise serialization and round-trip checks.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 91d1316d-85eb-4fe8-8d5c-4248f0ea7998

📥 Commits

Reviewing files that changed from the base of the PR and between 82b8f7e and 5eeac4d.

📒 Files selected for processing (6)

• rust_hft/prediction-markets/config/research_missions/polymarket-btc-5m.example.json
• rust_hft/prediction-markets/config/research_missions/polymarket-sol-5m.example.json
• rust_hft/prediction-markets/crates/ploy-research/Cargo.toml
• rust_hft/prediction-markets/crates/ploy-research/prediction-policy-dependencies.linux.sha256
• rust_hft/prediction-markets/crates/ploy-research/prediction-policy-dependencies.linux.txt
• rust_hft/prediction-markets/crates/ploy-research/src/prediction_mcts_run.rs

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📝 Walkthrough

Walkthrough

The PR enables exact serde_json floating-point round-tripping for MCTS checkpoint data, updates dependency metadata and test evidence, and replaces the pinned search-policy snapshot identifiers for the BTC and SOL five-minute missions.

Changes

Prediction policy and checkpoint precision

Layer / File(s)	Summary
Exact checkpoint float round-trip rust_hft/prediction-markets/crates/ploy-research/Cargo.toml, rust_hft/prediction-markets/crates/ploy-research/prediction-policy-dependencies.linux.*, rust_hft/prediction-markets/crates/ploy-research/src/prediction_mcts_run.rs	Enables the serde_json float_roundtrip feature, updates recorded dependency metadata, changes training metrics, and verifies exact checkpoint_reward preservation through JSON round-tripping.
Mission snapshot pin updates rust_hft/prediction-markets/config/research_missions/polymarket-*-5m.example.json	Replaces the search_policy_snapshot_id values for the BTC and SOL five-minute research missions.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• proerror77/monday#412: Both changes update prediction MCTS selection-evidence tests and checkpoint-related behavior.
• proerror77/monday#76: Both update pinned prediction-policy artifacts and mission snapshot references.
• proerror77/monday#425: Both update the BTC and SOL five-minute mission snapshot identifiers.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise and accurately summarizes the float roundtrip fix in ploy-research.
Description check	✅ Passed	The description covers the contract, scope, dependencies, validation, and rollback, with only the optional scope-exception section omitted.
Linked Issues check	✅ Passed	The changes match #428 by enabling exact f64 JSON roundtrips, updating checkpoint readback assertions, and keeping the scope limited to dependency behavior.
Out of Scope Changes check	✅ Passed	The mission pin and policy identity refreshes are part of the stated contract, and no unrelated subsystem changes are present.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/mcts-checkpoint-float-roundtrip-428

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