#913 EPIC: Highway realignment - durable-execution core on house platforms

EARS SPEC: - The Highway engine shall keep its durable-execution core, tools, and the MCP/agent surface used by highway-mcp, and shall delegate secrets, authorization, email, approvals and quotas to file/Postgres, auth, mail-api, Futex and TokenGate respectively. - If a workflow submitter requests privileged, devices, cap_add, host bind mounts, host pid/ipc, or a non-workflow-owned network, then the engine shall refuse the docker call unless a platform-admin per-tenant policy allows it. - The engine shall run on psycopg C implementation (psycopg.pq.__impl__ == 'c') with a uv.lock pinning every dependency. - The engine shall connect to PostgreSQL with sslmode=verify-full and client certificates. - The engine shall not depend on Vault, Ollama, SMTP, Jenkins, GitHub Actions or SonarQube. - While TokenGate is unreachable, metered tool calls shall fail closed and the condition shall be visible on /api/v1/health. - Every new or changed test shall be shown red against a sabotaged guard before it is accepted green. - Deployment target: docker-compose only. RunFlow migration deferred to a later stage. TECHNICAL PROBLEMS (priority order): 1. Host-escape via docker/shell tools (security P0). 2. Dependency drift and binary drivers. 3. Self-hosted cross-cutting services duplicated by house platforms. 4. Transport security and storage of persistent data (pg TLS, datashard S3). 5. API surface bloat. 6. Tests that cannot fail. SOLUTION DOMAINS: house platforms (auth, Futex, mail-api, TokenGate, datashard, migretti, resilient-circuit, bulkman), container isolation (docker security options, gVisor), mutation testing. ALTERNATIVES: recorded per child ticket. Plan of record: ~/.claude/plans/hi-we-re-back-to-fluttering-candle.md mirrored to SPECS/EPIC-realignment.md.