Say "tariff" below the type level too: the tier and rate synonyms survive in locals, prose, one public method and a broken api.php example

Problem

The tariff rename settled the vocabulary and reached the types. Entity types, classes and services carry no "tier": TierLookup is SlotTariffLookup, SingleTierPerRate is UniqueSlotTariff, groupTiers() is tariffsByClass(). Below the type level nothing moved, and reading the module now means holding three words for one thing.

Counted at c6103a3:

The production locals cluster in seven files: PlaceSelectionController (23), SlotBookingForm (14), then ConstraintPolicyResolver, SlotTariffLookup, BookingCart, GenerateSlotsForm and BookingCartInterface. "rate" is never used in any other sense anywhere: no tax rate, no rate limit, no exchange rate. It always means a tariff.

Four things in there are more than untidiness:

• hook_yoyaku_summary_alter() documents a key that does not exist. yoyaku.api.php says each ticket offers a tier_key, "the line's price tier id, or '' when untiered", and its worked example calls $ticket['tier_key']. TransactionSummary has never built that key: a ticket carries tariff and tariff_id. Anybody who copied the example got an undefined array key and a NULL price, silently, because an unpriced ticket is a legal answer.
• policiesForTier() is a public method whose parameter is already typed BookingSlotTariffInterface, so its name is the last thing calling it a tier.
• Six orphaned strings in the French translation carry @rate and %tier placeholders that no code emits: the "take one place at @rate" family and "The @count %tier places could not be found next to each other". They are the leftovers of a UI that has since been rebuilt, and they are what a translator sees.
• Five live interface strings say "rate", including a field description a site builder reads on every booking and the seating strategy's own description in the plugin list.

The three tariff scopes are the reason this matters more than a synonym usually would. yoyaku_tariff is the definition in a preset, yoyaku_resource_tariff is what one production offers, yoyaku_slot_tariff is one session's override. A variable called $tier says which of the three it holds only by luck, and $rate says even less.

Proposed resolution

One sweep, by hand, naming each thing after what it actually holds rather than substituting one word for another:

• $tier or $rate holding a BookingResourceTariffInterface becomes $tariff; one holding a BookingSlotTariffInterface becomes $slot_tariff. That distinction is the point, and it is why a search and replace is the wrong tool: the two are spelled the same today.
• Prose says "tariff", and says which scope where the sentence depends on it.
• policiesForTier() becomes policiesForSlotTariff(), matching its parameter type.
• yoyaku.api.php documents the keys a ticket actually carries, and its example becomes code that runs.
• The six orphaned French entries go. The five live strings are reworded, and translations/yoyaku.fr.po is updated in the same commit, since French already uses tarif everywhere else.
• Test method names and test locals follow, including the untiered family, which becomes "offers no tariff" rather than a coined word.

No entity type, field name, config key, route, service id or plugin id changes, so nothing on a site moves and there is no migration. The only signature that changes is policiesForTier(), whose callers are all in this module.

Remaining tasks

• The seven production files carrying locals, then the prose across the remaining files.
• policiesForTier() and its callers.
• yoyaku.api.php: the documented keys, and an example that would run.
• The five interface strings, the six orphaned entries, and fr.po, in the same commit.
• Test method names and locals. The suite passing unchanged is the proof, so no test's assertions may change: a renamed test that also changes what it asserts hides a behavior change inside a sweep.
• docs/, about 65 hits across 12 files, 18 of them in docs/seating.md, whose prose calls a tariff a rate throughout.
• Re-run every linter afterwards. A rewrap after a rename is where a docblock loses its closing line, so the prose gets read back rather than trusted to a script.

User interface changes

Five strings say "tariff" where they said "rate", and their French follows. Nothing moves and nothing is renamed that a site stores.