feat(page-tree): show a node only when its row says so

[mostafasadeghidev]

The gap

A list whose items are not uniform cannot be built today.

Two nodes sit in one card — a video player and a "Coming soon" caption — and exactly one belongs on any given row, decided by whether that row's video field is filled. The card is authored once, so every row gets a blank player or every row gets the caption. Visual CMSs generally call this conditional visibility and content sites lean on it heavily; Instatic has only hidden, which is the same on every render.

The change

visibleWhen on a node names a source, a field and a test:

{ source: 'currentEntry', field: 'video', test: 'isSet' }

• source — the set the prop bindings already use, so currentEntry inside a base.loop is that iteration's row. Dotted paths work (author.name).
• test — isSet / isNotSet only. Comparisons against a value need an operand and a type model; every case met so far is "does this row have one".

Set from the Properties panel's Attributes view, or with the setNodeVisibleWhen store action.

Three decisions worth reviewing

The publisher hides; the editor canvas does not. Everywhere else the two surfaces are kept identical, and this is the one place they differ on purpose: the canvas is where the node gets edited, and one hidden because the preview row happens to have no video is one the author cannot click. The panel states the rule in words instead.

A malformed condition parses to undefined and the node stays visible — the only safe direction, since the alternative is silently erasing content that was rendering fine.

Dynamic detection gains rule 2c. A condition reading a request-dependent source makes the node a Layer C hole. This is a stronger dependency than rule 2: a request-dependent binding changes what a node says, a request-dependent condition changes whether it is there at all, and baking it would freeze one visitor's answer into the artefact for everyone.

Impact

Additive and optional. A node without visibleWhen behaves exactly as before; no persisted data changes shape; no migration.

setNodeVisibleWhen lives in a new page-tree/nodeVisibility.ts rather than mutations.ts, which the module-size gate records as grandfathered debt that may only shrink.

Verification

bun run build          # tsc -b && vite build — clean
bun test src/core/templates/__tests__/visibilityCondition.test.ts   # 11 pass
bun test src/__tests__/architecture                                 # same failures as main, none new
bun run lint           # clean

Architecture gates were compared against a clean main checkout commit-by-commit: identical failure set, nothing added.