DSH plugin client slots: cardinality, scope and props

DSH plugin Web UI extension is not "export a component and let others import it"; it is a typed composition system where SlotMap declares slots at compile time and feature plugins contribute through ctx.slots.register(), with components never importing each other. Two consequences follow directly: props are derived from declarations, so do not re-copy members, and registration and declaration follow the effect lifecycle, so contributions collapse recursively when the owner unloads. Those two rules prevent the three most common problems: missing session values, duplicate registration errors and leftover UI after unload.

DSH plugin slot declarations and lifecycle

Bottom line: declaring a child does three things at once, and each declaration allows exactly one live owner.

1. Three effects: the child key activates, the parent entry is authorized to call renderSlot/renderSlotChain, and the runtime dispatch spec is recorded.
2. Single owner: registering into an undeclared slot, or re-declaring a child another entry owns, fails at plugin activation.
3. root is special: the only built-in declaration and the only key rendered by the Cordis service itself; all descendants render through props.
4. Effect lifecycle: destroying an entry removes its contributions and recursively collapses the child slots it declared.
5. Cross-package contribution: use ctx.slots.inject(key, callback); the callback runs per declaration lifecycle and re-runs when the owner remounts.

DSH plugin cardinalities: count and addressing

Bottom line: single picks a winner, list lays out by id, keyed matches by key, chain competes through select.

1. Do not treat single as a list: declare a child slot for side-by-side content.
2. Priority semantics: shadowing priority for single/list/keyed, election order for chain; smaller runs first.
3. Add with new ids: use a new list id or keyed key; reusing an existing cell replaces it intentionally.
4. Chain fallback: the owner's fallback renders when everything declines.

DSH plugin scopes: whether a session binding is required

Bottom line: root has one instance, session requires a definite session, session-maybe tolerates absence.

1. root: one root-scoped component and store instance.
2. session: requires a resolvable outer Provider binding and receives a definite Session value.
3. session-maybe: inherits the outer binding but renders without one, with an optional session value.
4. Subtree override: declaring session or session-maybe children provides SessionProvider; omitting it inherits, while passing a reference or undefined overrides only that subtree.
5. Remount rules: strict session entries remount when the binding generation changes; blank session-maybe entries do not remount on first acceptance, only on later generation changes or returning to missing.

DSH plugin component props: derive, do not copy

Bottom line: six input classes each have a declarer; components derive props from types while service objects stay in the closure.

1. No ctx: components never receive the context object.
2. Parent values via owner: values known at render time arrive through renderSlot's owner argument.
3. Services stay hidden: service and model objects remain in the apply closure, projecting callbacks or observable sources.
4. Localize through the namespace: do not hardcode copy.

DSH plugin slot troubleshooting

Bottom line: separate undeclared, registration conflict and missing values.

1. Registration errors — confirm the target slot is declared and the child is not owned elsewhere.
2. Duplicate registration — the same id registered twice.
3. Missing session — check whether the scope is session or session-maybe and whether a binding exists.
4. Leftover UI after unload — registration is not on an effect, or inject was bypassed.
5. Wrong list order — check order, then registration order.
6. Repair status, stated honestly: declaration effects, cardinalities, scopes and input classes follow the official Web Client Slots page; confirm slot keys and types against the official package and your version.

Sources: Web Client Slots, dsh-client-ui-slots README, Client resources.