v0.58.1 — Recaps keep their history; sensors nudge toward AST

The recap stops forgetting the last three sessions (§5.6)

• A topic-upsert recap now archives the outgoing session into a bounded per-session history instead
  of overwriting it. The field report could not tell what the previous three sessions did, because
  each mem_session_end overwrote the last (revision_count: 12, history gone). The newest recap
  still sits at the top — so the briefing head keeps surfacing only the latest goal + next steps
  (v0.58.0) — with each prior session kept as one compact dated entry beneath a ## Session history
  heading, capped at 6. The full record is one mem_get <id> away. Applied to both the MCP and CLI
  session-end writers via the pure buildRecapWithHistory.

propose_sensor points at AST for parseable languages (§3.1)

• The kind guidance now recommends ast for a parseable language when the engine is available.
  A structural AST match can never false-positive on a comment or a string; regex (still the default,
  since it needs no extra engine) now strips comments before matching but deliberately keeps string
  literals so it can still target a bad literal. The default is unchanged — flipping it to AST would
  break sensor creation everywhere the optional @ast-grep/napi engine is not installed — but the
  nudge is now explicit rather than buried.