### Motivation

Motivation

• Provide production-grade authority and receipt proofs (Ed25519) and durable, crash-recoverable admission evidence to move the IOC vertical-slice forward.
• Replace test-only, in-memory-only receipt persistence with a content-addressed, fsync-backed ledger so admissions survive process restart and can be lineage-verified.

Description

• Add strict Ed25519 adapters: Ed25519Verifier and LocalEd25519Signer in admission_gate.py to verify and emit Ed25519-signed authority envelopes and receipts.
• Introduce FileDecisionLedger in admission_gate.py, a content-addressed append-only receipt store that writes canonical JSON, verifies receipt hashes before publish, fsyncs both the file and containing directory, atomically publishes without overwriting existing receipts, and rejects malformed or tampered receipts on reload.
• Keep existing Secp256k1 support and in-memory ledger for tests while exposing the new durable ledger for IOC-focused flows.
• Add integration tests in tests/test_admission_gate.py that exercise an Ed25519-authenticated, context-bound admission decision, verify the receipt survives restart via FileDecisionLedger, and assert that post-write tampering is detected and rejected.

Testing

• Ran the full test suite with python -m pytest -q, all tests passed (411 passed).
• Verified bytecode/compilation with python -m compileall -q admission_gate.py tests/test_admission_gate.py.
• Performed repository checks (git diff --check) and local status validation after the change with no outstanding check failures.

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Codex Task

Originally posted by @TrueAlpha-spiral in https://github.com/Sovereign-Data-Foundation/truealphaspiral-ethent/pull/48