agentic-stack v0.19.1

agentic-stack v0.19.1

Patch release. Four correctness fixes in memory retrieval, project upgrade, and
file I/O. No contract, CLI, or on-disk format changes.

Fixes

• Recall returned superseded lessons (#60). Supersession appends a new id
  and never edits the old row, so retrieval kept surfacing retired guidance
  beside its replacement. superseded_by_map() now lives in
  render_lessons.py and is shared with recall.py, so rendering and
  retrieval can't disagree about what is retired. Provisional supersessions
  still do not retire the old lesson.
• upgrade copied new loop skills to a doubled path (#63). A missing
  loop-* skill landed at .agent/skills/skills/loop-x/ instead of
  .agent/skills/loop-x/, in both --dry-run reports and real copies.
• Locale-dependent encoding in learn.py (#61). stdout/stderr forced to
  UTF-8 and candidate JSON written with an explicit encoding, so non-ASCII
  claims survive on hosts whose default codepage isn't UTF-8.
• Leaked file handle (#62). _lesson_already_appended() reads through a
  context manager instead of relying on refcounting.

Upgrade

agentic-stack upgrade --dry-run
agentic-stack upgrade --yes

Optional — nothing breaks on 0.19.0. Projects that previously upgraded into
.agent/skills/skills/ can delete that stray directory; the correctly-placed
skills are copied on the next upgrade.

Verification

• python3 -m pytest: 180 passed (175 on 0.19.0 plus 5 new regression
  tests covering supersession filtering and the loop-skill copy path).
• Each fix ships with a test that fails on the pre-fix code.

Loop usage, safety boundaries, and the sandbox caveat are unchanged from
v0.19.0.