The FROZEN conversational-tip predicate — the single contract implementation of conversational?/1 and tip/2.

Frozen contract. A resume locates its point by a backward scan under this predicate. Raxol.Agent.Journal.Records.Checkpoint.FileBackend validates a stamped tip_offset against the same predicate, with its own copy of the whitelist.

The predicate

conversational?(record) :=
  record.kind == "event"
  ∧ record.family == "loop"
  ∧ record.type ∈ CONVERSATIONAL

tip(journal, branch := "main") :=
  the record with the HIGHEST offset satisfying
  (record.branch_id == branch ∧ conversational?(record))
  (undefined on an empty/no-conversational branch → :no_tip)

Frozen decisions this module encodes

• The grandfather clause. A record with no "kind" reads as "event"; a record with no "branch_id" reads as "main". Every journal written before those keys existed therefore keeps its historical tip byte-for-byte.
• The closure rule. CONVERSATIONAL is a whitelist and the ONLY door: every future record kind and every future family: "loop" type is tip-excluded unless explicitly added here. Nothing becomes a tip by default.
• The exclusions. state_change, idle, every family: "meta" event, every non-"event" kind, and — deliberately, though it is family: "loop" — woken are excluded. A trailing checkpoint / meta event / idle marker / woken must never be selected as the tip.
• approval_requested IS included — a pending approval is exactly where a resumed conversation must land (emitted family: "loop", not :meta).

This module is pure and reader-side only: it never touches the journal, the bus, or a writer. It reads decoded journal records (string-keyed maps) as produced by the tolerant Reader or by an independent raw decoder.