[tmm]

Writes in a Swift mutator now look like JS: all four tx.mutate.<table> calls are typed.

try tx.mutate.issue.insert(.init(id: id, title: "Crash", ...))
try tx.mutate.issue.update(.init(id: id, title: "New title"))   // only title changes
try tx.mutate.issue.update(.init(id: id, assigneeID: .null))    // unassigns
try tx.mutate.issueLabel.delete(.init(labelID: l, issueID: i))  // compound key

var change = Issue.Update(id: id)                               // or build it first
change.title = title
try tx.mutate.issue.update(change)

Before, tx.mutate.issue was the untyped TableMutator (dynamic member lookup): update and delete took dictionaries, and only insert/upsert had a typed form, without the table name.

What changes

• zero-swift codegen emits, per table, a tx.mutate.<table> member returning TypedTableMutator<Row>, and nested Row.Update (like JS's UpdateValue) and Row.Key (DeleteID). Rows conform to ZeroTable.
• In an Update, a column left nil keeps its value, as an undefined one does in JS. An optional column is a ColumnUpdate (.unchanged by default, .null, .set(x), or a literal), so leaving it differs from setting it to null.
• upsert takes the whole row, so it writes every column; JS keeps a column the value leaves out. Documented.
• The untyped API stays as tx.mutate.table("issue").
• zbugs-swift writes through the typed calls; its issue.update no longer round-trips its arguments through JSON.

Breaking (minor): passing a dictionary to tx.mutate.<table> no longer compiles. Regenerate, and use the typed calls or tx.mutate.table(...).

Known limit: two generated schemas in one module with the same table name clash on the tx.mutate member, a compile error in the generated file. Nothing does this today.

Verification

• Swift suite: 220 tests pass on Linux, including the end-to-end tests against zero-cache. A new test covers leaving a column, setting null, setting a value, and deleting by a compound key; it fails if .unchanged writes null.
• zbugs drift tests pass (they compare the Swift mutators with the TS ones, including issue.update with an assignee set, null, and left out).
• Codegen sweep: every hostile schema compiles, plus two new ones (tables named table/insert/tx; columns named Update/Key/row/value with optional enums, nullable JSON, and a compound key).
• Lint, tsc, oxfmt clean; DocC builds with no warnings. macOS and iOS run in CI only.