ADR 0408 section 4 says no key of the chain is removed, a delete marker included. The Backend loses Remove and the Chain RemoveAssignment. An unassignment, and the end of a value only pulled in by another, write the value again with ended set, by compare-and-set; assigning it again writes a fresh standing value over it. A value with ended or a state is no assignment (Assignment.Stands) to the assignment lists, the joins, forgetting a module, seat holdings, the given values, the move and the assignment-changed event.
Once chain_moved records the kind, Assign, Unassign and Assigned write and read the keys <node>.<module>, and every join of the store that read assignments is made from the bucket: where a module runs, what is behind, what a machine awaits, a given value due for replacement, taking a module, and whether a module may be forgotten (refused while a standing assignment names it). An unassignment ends the key with a marker and keeps its earlier values, as it removed the row; no ended or pending mark is written yet. The generation rises with each change, and a seat held by an assignment goes with it: the foreign key from seat_holding is dropped by migration 0104 and the controller says both. The provisioner's plan is kept in the values by a pass of the tick that writes that one field by compare-and-set; the assignment-changed event is said from what the bucket holds, whoever wrote it. The start moves the rows with what each machine was last sent, keeping a plan the mirror put in a value.
Once chain_moved records the kind, RecordBuild and every build read go through the chain (reuse key and published added); before that the tables are read as before. The serving controller copies the rows at its start, holding the lease: idempotent per key, rows counted against keys, the largest value measured, a refusal (urgent condition, nothing switched) on a count that differs or a value over the bus's largest, and a re-read when the table took a row meanwhile. ForTest attaches the chain in memory with builds moved; ForTestBefore leaves it unmoved. Build requests, gates and the other kinds are still in their tables.
internal/chain holds typed Build, Rollout and Assignment and a Backend with no delete or purge, in memory and on the bus. The builds and rollouts buckets are asserted with history 64, no age and values up to just under a mebibyte; the assignments bucket gets the same, keeping its marker age because a stream cannot be made to disallow message ages. Migration 0104 makes the one-row chain_moved switch. The controller keeps no consolidated schema, so 0104 is the whole schema change. Nothing reads the buckets yet.
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