[process-manager PM-7] Log multiplexer + persistent sink (rotation)

[rickylabs]

Summary

Log multiplexer over runner output streams + persistent sink with rotation; journald/Servy interplay documented (who owns persistence per mode).

Scope

• Archetype / area: packages/plugin-process-manager-core engine
• Part of Epic: NetScript Process Manager — bare-metal supervisor + admin console (pup/pm2 done right) #510
• Depends on: [process-manager PM-5] Process runner: Deno.Command-native spawn + descendant-tree kill #516 · Blocks: PM-13 (follow-logs source)

Design source

• research/design/d1-supervision-engine-core.md (D1-S8) · plan.md §4 PM-7

Acceptance criteria

• gate: rotation policy tested (size/count bounds); no unbounded growth
• gate: docs state the journald/Servy interplay per mode (dev vs OS-supervised)
• gate: scoped check/lint/fmt wrappers green (--ext ts,tsx)

Non-scope

• Log streaming over the wire (PM-13).

Drift / Debt

• none