Input trigger pipeline plugin: / and @ detection under the caret (word-boundary + guard-tier rules), the grouped candidate menu, and pick routing to registered sources. ctx.slash owns the source roster and resolves one SlashController per session scope (sessionOf); the conversation wiring layer drives track/arbitrate/onSpace/adjudicate on the controller. Sources receive a ClientSessionContext projection per call — sessions are always agent-backed, so the projection is the session identity alone. A source is warmed in every session controller it can reach: the roster present at scope birth warms during controller construction, and a source registered later is warmed into every live controller by the registration itself. Sources whose lexicon roll changes after warm implement subscribeLexicon(session, listener); the controller re-polls on each notification and publishes the aggregation through its lexicon snapshot store. The pipeline is command-agnostic: space/enter adjudication polls the optional matchSpace/matchEnter hooks in registration order and the first non-undefined answer wins.

Layering: src/core/ (T2) is the pure core — detectTrigger, menuReduce/seedGroups/MENU_CLOSED, exactMatch, zero React/DOM/cordis; src/client/service.ts is the shell wiring the core to the menu snapshot store, the per-hit candidate fetch (generation-gated, AbortSignal-superseded, failed sources drop silently with a console record), and the three pick paths. src/types.ts and the two contract.ts files are the frozen cross-package contract (design v4 §5.1); changes require main-thread arbitration.

MenuView renders the menu store into the conversation.input.overlay slot (list kind, session scope) and renders null while closed. Groups sort by the optional SlashSource.order (lower first, default 0, ties keep registration order) under title rows localized through the slash.menu locale namespace (an unknown source shows its raw name); the list height clamps to the space above the composer, and a pointer down outside both the menu and the surrounding composer card dismisses it. The slot is owned by ui-conversation's composer entry (anchor, children declaration, lifecycle); its SlotMap type merge lives in this package's src/client/slots.ts because the dependency direction (ui-conversation → ui-slash) admits no reverse type import. Combobox pattern: focus stays in the textarea, rows pick on mousedown, the highlight rides aria-activedescendant.

The /client export surface is the plugin body (apply/inject), SlashService, MenuViewInjected, and the contract types. MenuView itself is internal — the slot registration closes over it.

Model Experience

None, as the trigger pipeline is browser presentation only — picks produce CommandClaim/ReferenceInsert data whose model-visible consequences (host command execution; inserted reference text riding an ordinary prompt) are owned by the consuming host and input-machine packages.

KV Cache effect

None; this package neither assembles nor sends a provider request.

Known Limitations and Deferred Work

Global source layer only — session-scope source registration (per-session shadowing, ScopedLayers-alike) is designed but not enabled; the ledger tracks the trigger condition (a real per-session source need).
SlashCandidate.icon renders as text — MenuView drops the string into the icon slot verbatim; wiring to the design-system icon enum (iconFile five-variant family) lands when that enum ships.
Overlay SlotMap merge home is split from slot ownership — the conversation.input.overlay merge lives here (sole copy) while the slot's owner semantics (anchor, children declaration, lifecycle) stay with ui-conversation; the dependency direction (ui-conversation → ui-slash) forces the split, so a future dependency reshuffle should revisit it.