v2.21.42 — #375 follow-up (ค): recover Claude's lost convenience runtime-neutrally

#375 follow-up (ค). The v2.21.39 file-only SKILL_OUTPUT fix removed two conveniences from non-persist Claude runs — the same-session /cross-verify auto-populate and the visible completion line. Both are recovered on the consumer / plain-text side, not via runtime-conditional producer behavior (rejected as an ADR-024 violation).

Added

• /cross-verify session-context fallback — when no persisted block is found but the producer skills ran earlier in the same session, /cross-verify mines their PRD/design/tasks prose in context to pre-populate Q4/Q8/Q14/Q16 (marked ✓I). Runtime-neutral: reads prose, not the HTML block, so it works identically in Codex.
• Plain-text completion signal — /requirements, /design, /breakdown, /review-ai now end conversation output with a [/<skill>] complete line (canonical spec in guides/structured-output-protocol.md §"Completion signal"). Restores the visible half of the old attribution line file-only emission removed; plain text = zero Codex noise.

Full notes: CHANGELOG.md