Backward compatibility

indexnowkit/history follows SemVer and the tiers of the core's docs/bc.md. Before 1.0, minor versions may contain breaking changes, listed under "Changed" in CHANGELOG.md.

Tier	Members
Call — signatures only grow by appended, defaulted parameters	Psr16SubmissionStore, Pdo\PdoSubmissionStore (constructors, createTable()), Pdo\Schema::sql(), assertTable(), HistoryConfig (constructor, fromArray(), disabled(), loadOrDisabled(), toArray()), Check\HistoryCheck, Console\HistoryRunner, Console\StatusRunner, Console\HistoryOptions, Console\Definitions::*
Implement — methods are not added without a major version	HistoryStoreInterface
Value objects — final readonly, properties only appended with defaults	HistoryConfig
Constants — referenced, not hard-coded	HistoryConfig::OPTIONS, STORES, DEFAULT_*, Schema::DRIVERS, HistoryCheck::CODE_*
Documents — the shape only grows by optional members	docs/status.schema.json, the JSON of history --json; the table of Pdo\Schema (a column is only added, nullable or with a default)

Not covered: RecordCodec (@internal), the printed texts, anything under tests/. The cache keys of the PSR-16 store (<prefix>history.index, <prefix>history.<n>) and the batch format are implementation details: a minor may change them, and the ring buffer then starts over.