docs(plans): trim s6-overlay plan to a post-implementation reference

PR #30136 review item O7: the plan doc was 3,191 lines — 5x the
size of any other plan in docs/plans/ and the largest reference
document in the repo. With the implementation shipped, most of
that content is either:

* The phase-by-phase TDD walkthrough (~2,800 lines): now canonical
  in the PR commit log (`git log a957ef083..a6f7171a5`).
* The v2/v3 re-validation preambles: artifacts of the planning
  process, no longer load-bearing.
* The full Open Questions deliberations with options A/B/C laid
  out: collapsed into the Decision Log.
* The Rollout Plan and Estimated Timeline: history.

Trim to ~430 lines covering what readers actually need going
forward: the goal, architecture, scope, key design decisions
(D1–D9), risk register (now including the three risks surfaced
in PR review — `_s6_running` detection, svscanctl FIFO perms,
supervise control FIFO perms), the decision log including the
post-merge additions, and the verification checklist (now all
boxes ticked).

Header now reads 'Status: shipped' and points at the PR. The git
history preserves the full v3 plan for anyone who needs it.
This commit is contained in:
Ben 2026-05-23 16:24:33 +10:00 committed by teknium1
parent cd5b2c4123
commit 6c49bdc4f4
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