[process-manager PM-35] Per-host multi-instance / clustering (template units + reusePort)

[rickylabs]

Summary

Per-host multi-instance / clustering (OF-5 — owner-ratified to Backlog, 2026-07-06): systemd template units + SO_REUSEPORT sketch from D1. Until this lands, concurrencyEnvVar self-fan-out ships in M1 and instances > 1 hard-errors with a pointer here (E9). Converges with the re-scoped #345 (cross-host HA composes with this per-host primitive).

Scope

• Archetype / area: engine + deploy-core (template-unit rendering)
• Part of Epic: NetScript Process Manager — bare-metal supervisor + admin console (pup/pm2 done right) #510
• Depends on: [process-manager PM-6] Supervisor loop + composable start policies (autostart/cron/watch) #517, [process-manager PM-20] Extract packages/deploy-core (@netscript/deploy-core) + promote F-DEPLOY gates #531 · Cross-epic: re-scoped [Deploy-S9] Bare-metal enterprise hardening (stable): cross-host HA + external secret store + signing #345 depends on this slice

Design source

• research/design/d1-supervision-engine-core.md (clustering sketch) · plan.md §4 PM-35, E9, OF-5

Acceptance criteria

• gate: instances: N renders N template-unit instances with port-sharing semantics defined
• gate: E9's hard error replaced by the real implementation + migration note
• gate: scoped check/lint/fmt wrappers green (--ext ts,tsx)

Non-scope

• Cross-host HA (re-scoped [Deploy-S9] Bare-metal enterprise hardening (stable): cross-host HA + external secret store + signing #345 owns it).

Drift / Debt

• none