feat(alpha): gate MCTS on immutable CEX baselines

[proerror77]

Change contract

Require an immutable, content-bound, replay-verified, passing Ridge/CART Gate before the shared MCTS fan-in, then fail closed until the Factor-Bank subset adapter in #601 exists.

Issue relationship

Refs #600

Out of scope

Factor-Bank add/remove/swap MCTS (#601), sealed-holdout evaluation, ACK/OSS execution, and Paper/Shadow/Live.

Dependencies and merge order

Stacked on #664, #668, #663, and #662. Merge last. After the stack lands and this PR is retargeted to main, update the issue relationship to the final completion form.

Focused validation

• cargo test -p alpha-harness --locked (131 passed)
• cargo clippy -p alpha-harness --locked -- -D warnings
• cargo fmt -p alpha-harness -- --check
• Missing, mismatched, failed, wrong-parent, or replay-invalid Gate evidence rejects before MCTS construction.

Rollout and rollback

Research control-plane admission only. No MCTS search is enabled, and no ACK, OSS, collector, or trading runtime is touched. Roll back independently from producer persistence.

Scope exception

None.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Bind the decoded gate to the frozen revision ID

When a registry row is stored under mission.baseline_artifact_id but contains another valid gate payload, this check accepts it because get_registry_revision(gate_id) already looked up that same key, making gate_revision.revision_id != gate_id ineffective. Since the subsequently decoded gate.gate_id is never compared with the frozen mission ID, validation follows the payload's dependencies and treats the mismatched gate as valid; explicitly require gate.gate_id == gate_id before accepting its evidence.

AGENTS.md reference: AGENTS.md:L38-L41

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[chatgpt-codex-connector]

Bind the Factor Bank lineage to its source mission

When a valid Factor Bank shares the runtime dataset and partition but was produced under a different search lineage or GP/screening policy, this validation still accepts it: factor_bank.validate() only checks the bank internally, while control_mission.validate() and the baseline artifact bindings never compare factor_bank.search_lineage_id, gp_policy, screening_policy, or evaluation_policy with the source mission's frozen fields. This allows the fan-in gate to admit factors generated outside the claimed source mission contract; validate those bank-to-mission relationships before accepting the gate.

AGENTS.md reference: AGENTS.md:L40-L41

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