Client: Add, drop and reorder the rows a collection's payload asks for

[marcoroth]

This pull request lets a collection be edited and not only updated.

apply filled the rows both sides already agreed on and deferred every change to which rows there were, so rows could never be added, removed or moved. Two thirds of that was pessimism: removing a row and moving one need no markup at all, only the row's own range.

The third needed something to copy. Every row of a collection is the same shape by construction, so any row on the page is a template for the rest: one is cloned, emptied, given the key it is being built for, and filled from the payload like any other row. Which leaves one case that genuinely cannot be done, a collection with no rows at all, and that is what deferred now reports.

slots.reconcile(collection, ["3", "1", "2"])
// { added: [], removed: [], moved: ["3", "1"], kept: [...], unchanged: false }

So the server parks a row for a collection that rendered none, and _herb_covered_branches does the deciding exactly as it does for a branch: a collection with rows on the page marks itself covered and parks nothing, because the page already holds a better copy than the compiler could write. The parked row carries an empty key, since a row's key is an expression and has no static form, and whatever builds a row from it has to say which row it is building anyway.

Parking happens before the key marker goes in and not after, because the statics printer refuses a tree it cannot print, and an expression is exactly what it cannot print. Parking afterwards silently parked nothing at all.

Two notes on the mechanics. The rows sort by moving each one to the end in the order asked for, measured against the collection's own closing marker, which is the one node no row can be inside, and that works in a table where the parser puts the rows in a tbody and leaves the markers around them at another depth. And JavaScript sorts integer-like object keys numerically, so JSON.parse loses the order the server wrote for a collection keyed by id. Ascending is what an append wants, so it rarely shows, but a collection whose order the server decides has to be keyed by something that is not a number. There is a test saying so.

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☁️ Nx Cloud last updated this comment at 2026-08-18 03:42:23 UTC

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commit: d1e5c4b