fix(msg): busy window reads activity only; --busy-only (fixes #341, fixes #256)

releases#341 + releases#256 (SEAMLESS-UPDATES W10), operator-ruled
2026-09-24: instance state selects WHICH INSTANCE a bare id resolves to and
may require a wake; it NEVER gates a delivery window.

- The AND is DELETED, not relaxed. Both hook drains (api poll's poll_drain,
  api worker-poll) narrowed an include-deferred poll by
  resting::deferred_held (Dormant|Suspended): an activity-axis flag gated on
  the control-axis rest record, whose events carry no activity input.
  deferred_held had exactly those two callers and is removed with its unit.
  A dormant (unwatched, possibly working) endpoint now drains its
  busy-window rows on its own poll. So the away notice reaches the agent
  WHILE it is away, and the return notice can only follow it. A suspended
  endpoint gets them on its first poll after waking.
- --active-only is now --busy-only. --active-only and --deferred keep
  parsing as HIDDEN aliases, and neither is in help or reference.md.
  `api poll --include-deferred` and the deferred=1 column keep their
  spelling (adapter-facing / storage) and are documented as the busy
  window. NO_PERCH now says "(busy-only stays local-only)".
- REQ-INST-6 AMENDED IN PLACE (doyle ruling): its title was the deleted
  rule word for word. It now owns the rest RECORD and its remote drive and
  points at REQ-DELIVERY-WINDOW-IS-ACTIVITY-AXIS-ONLY for the window. The
  D5a comment half is rewritten, D5b kept. wansend's remote-rest int keeps
  its wire legs and drops the hold asserts.
- CONTEXT.md: the deferred-message gate clause is replaced by the positive
  statement, the active-window/active-only prose is swept, and dormant's
  two arms are named. Public docs: messaging, instances, and lifecycle
  (which carried the same hold claim). CHANGELOG Fixed + Changed.
  reference.md and changelog.md regenerated.
- Tests: the drain units are rewritten on the new REQ (dormant: away ->
  peer in order, then return alone; suspended -> wake: first poll, exactly
  once). New flag unit (primary + two hidden aliases, help hides both).
  New int busy_window_axis_e2e drives the real away/return producer and
  the real binary and asserts ORDER: the away notice drains on a poll
  taken before the return notice exists. It stops the daemon its calls
  start via a guard that carries no session identity. The
  broker-stop guard rightly refuses one that does, and the first version
  leaked a daemon pair holding target/debug/spt.exe.
  active_only_never_relay_e2e's three text asserts moved with the NO_PERCH
  text (the negative one too, so it cannot pass vacuously).

Negative control: re-adding the AND reds the int at its tagged assertion
(busy_window_axis_e2e.rs:170, left 0 right 2) and the drain unit
(delivery.rs:1507, left []).

Co-authored by: todlando
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014j8UXzGXXsDsTJBYYUSCTC