Tool contract 3.18.0

The seam (docs/reviews/2026-09-19-INTERFACE-REVIEW.md Part 3.2, 6 and 7, Phase 5).

• elixir_timeline takes reader (a short name for this consumer's read pointer): an omitted from reads since that reader's pointer, mark_read moves it, read_to reports it, and other readers on the account and the account's own unnamed pointer are untouched. meta.timeline_pending counts admissions since the OLDEST named pointer when any reader has marked, so a consumer that names itself sees it fall to 0 after its read.
• An empty timeline window is cheap: one probe off the battle created_at index says whether the clan learned a battle in the window before the day-wide member scans run.
• Every error body carries class (retry | input | subject | server | budget; ERROR_CLASS in the contracts package): live_pending and query_timeout are retry, internal and live_unavailable are server, quota_exceeded is budget, the rest input or subject.
• The subject tools take display_name beside on_behalf_of, and an unmapped id's no_subject carries candidates[] (the clan members whose whole name matches; player_tag, name, clan_tag, role) with a hint that names the one elixir_identify call.
• elixir_feedback takes request_ids[] beside request_id.
• outputSchema declared on elixir_my_feedback, rankings_players, war_history, battles_meta_decks, battles_meta_cards, battles_levels and clans_participation (tools/list and the tool reference render them; the registry validates against them).
• A person's omitted clan_tag is the primary player's clan and nothing else: when that clan is not recorded the call is not_recorded naming it, where it used to slide to an alt's recorded clan.

Additive; migration 0136 adds timeline_reader.