fix(alpha): isolate blocking prediction pipelines

[proerror77]

Change contract

Run prediction execute and prediction snapshot on Tokio blocking workers so their synchronous HTTP, filesystem, archive, and subprocess pipelines cannot block or create/drop blocking runtimes on the async dispatcher thread, while preserving inner error chains.

Out of scope

• Mission execution dispatch, which merged independently in fix(alpha): isolate blocking mission execution #88.
• Prediction research semantics, snapshot contents, cost modeling, live execution, collectors, or broader async refactors.
• New runtime configuration or dependencies; this only enables the already-installed Tokio sync feature for test serialization.

Dependency or merge order

#88 merged first to avoid an overlapping cli.rs rebase. This PR is now based directly on current main and has no remaining behavioral or stacked dependency.

Focused validation

• cargo +1.91 fmt --manifest-path rust_hft/Cargo.toml --package alpha-harness -- --check
• CARGO_BUILD_JOBS=2 cargo +1.91 test --manifest-path rust_hft/Cargo.toml --locked -p alpha-harness (74 passed)
• CARGO_BUILD_JOBS=2 cargo +1.91 clippy --manifest-path rust_hft/Cargo.toml --locked -p alpha-harness --all-targets -- -D warnings
• Targeted counterexamples run both prediction commands under a current-thread Tokio runtime. Execute preserves the missing-source error; snapshot reaches the blocking HTTP client then preserves the occupied immutable-result error.
• Scope: 2 files, 125 additions, 3 deletions.

Rollout / rollback impact

Research CLI scheduling only. Prediction artifacts, validation, immutable publication, and fail-closed behavior are unchanged. Roll back by reverting this PR; no schema, data, deployment, or live-execution migration is involved.

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: cab3a88c-a532-495a-85fa-bd7e94c126b9

📥 Commits

Reviewing files that changed from the base of the PR and between 04d548c and 0c1cde4.

📒 Files selected for processing (2)

• rust_hft/alpha-harness/app/Cargo.toml
• rust_hft/alpha-harness/app/src/cli.rs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/prediction-blocking-runner

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