feat(using-tasks): session_break marker [v1.2.0]

Add a session_break marker so a task author can mark a task's
completion as a natural session boundary. After the task closes 🟢,
before tasks_claim_next, an autonomous agent prints the verbatim
SESSION BOUNDARY line and stops instead of chaining the next task.
Absent -> behaviour unchanged.

- STATUS.md format: optional **Session break:** field + new
  "### session_break marker" subsection (type bool|string, examples).
- Task completion step 6: after close, before claim-next, check the
  closed task's session_break; print boundary line + stop if present.
- Rules bullet "Honour session_break".
- Wiki concept page concepts/using-tasks-session-break.md + index + log.

MINOR bump: new optional capability, no existing behaviour changed.
Closes [session-break-using-tasks].

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.wiki/log.md

@@ -67,3 +67,4 @@ Parseable: `grep "^## \[" .wiki/log.md | tail -20`.
 ## [2026-05-25] decision | install-cross-platform extended to build scripts — `build.{ps1,sh}` get the symmetric `--prune` / `-Prune` flag (removes `dist/<name>.skill` where `<name>` is not in `skills/`). Bash delegation to `powershell.exe -File build.ps1` does NOT forward the flag — bash runs prune itself against the shared `dist/`. Both paths smoke-tested with fake stale .skill files against real dist/. Closes `[install-ps1-build-prune-followup]`.
 
 ## [2026-06-09] decision | delegate-task-negative-trigger-fp — `delegate-task` 0.2.0→0.2.1 (PATCH): fixed 5/5-consistent false-positive on «создать задачу себе». Root cause: self-task phrase shares stem «создать задачу» with the «создать задачу на агента» positive trigger; the abstract "Does NOT apply when doing the work yourself" carve-out can't beat a literal stem-match under the 1%-rule. Fix: made the negative literal + routed («создать задачу себе» / «task for myself» / «поставить себе задачу» → using-tasks) in description + body disambiguator («на агента»/«агенту» = delegate; «себе» = own board). Re-verified via fresh-context subagent trigger run: positives 5/5 (no regression), negative 4/5 → using-tasks (was 0/5); the 1 residual miss was an eval-harness artifact (forced skill-name-before-reasoning), not description ambiguity. Concept page written; reusable principle = put the exact colliding negative phrase with an explicit →sibling route, literal beats abstract.
+## [2026-06-09] decision | using-tasks-session-break — `using-tasks` 1.1.0→1.2.0 (MINOR): added the `session_break` marker. Task author sets `session_break: true | "<hint>"` in task frontmatter (mirrored as `**Session break:**` on the local board); after the task closes 🟢, before `tasks_claim_next`, an autonomous agent prints the verbatim line `🔚 SESSION BOUNDARY — [slug] закрыта. Рекомендую завершить текущую сессию. Следующий трек: [value | "см. STATUS.md"]` and stops instead of chaining the next task. Absent → behaviour unchanged. Enforced in Task completion step 6 + Rules bullet + format docs. Marker not heuristic: the stop-point is an authoring choice, not a runner guess.