5. Slot catalog

This section lists every slot a plugin can occupy or declare, plus the pane kinds, tab kinds, route contributions, client command ids, and pin targets that sit beside the slot tree. The mechanism (register options, owner props, arbitration) is §4. Status per row: built = exists in kernel-ui or in the Stage 2 slice (stage-2/03 §2); spec = 08 only; deleted = RECONCILIATION. Where 08 and stage-2/03 disagree, the row carries the stage-2/03 name and the 08 name sits in a note. Occupants marked "(spec)" inside a built row are 08's Stage 3 occupants; the slot exists, they do not yet.

Key grammars (08 §0; one rule for every keyed slot). <kind> is a core row kind, snake_case (command, file_change). <pluginId>/<kind> is an extension kind or a plugin-defined request (secrets/request). <providerId>:<kind> is a provider-scoped override of a core kind (rows only; the only place a provider id appears in a key). approval:<subject> is an interaction key over the closed set command | file_change | permission_grant | plan (R27, snake_case); question is the core question; a provider's tool-use prompt is the open kind <providerId>/tool_use, not a fifth subject. tool-ui:<pluginId>/<renderer> names a tool result's self-declared UI; tool:<name> names one tool. * is the fallback key. No globs, no reserved provider ids.

The timeline.row ladder has five rungs, passed as keys in this order (09 §2.6; stage-2/03 §2.5): tool-ui:<pluginId>/<renderer> (only kind === 'tool' with payload.result.ui) → tool:<payload.name> (only tool) → <providerId>:<kind> → <kind> (<pluginId>/<kind> for extension kinds) → * (the ui-default-rows painter). Original follows the same order. 07 §5.2's three-rung example is superseded.

Scopes: root (one instance), thread (per thread id), pane (per pane id); composer children are instanced per owner mount (composerId). Kinds: single, list, keyed, chain. A dash in "Key grammar" means the slot is not keyed.

5.1 Root and shell (08 A.1; stage-2/03 §2.1)

5.2 Sidebar (08 A.2; stage-2/03 §2.2) — ui-sidebar, occupies shell.sidebar:app

5.3 Thread list (08 A.3; stage-2/03 §2.3) — ui-thread-list, occupies sidebar.body

ThreadRowOwner = { thread: ThreadListEntry; isActive; compact; depth }. Sort modes are the ui-thread-list/sort registry (A.14), not a slot.

5.4 Thread page (08 A.4; stage-2/03 §2.4) — ui-thread-page, pane kind thread

The thread.* slots are children of the thread pane kind (panes.register({ children }), built), not of a slot.

ThreadOwner = { threadId; projectId; thread: Thread }, where Thread is the threads/threads.show result (stage-2/03 §2.4; 08 A.4 writes ThreadHead). There is no thread.chat slot: ThreadChat is a component exported by ui-thread-page that renders thread.timeline + thread.composer (09 §2.11).

5.5 Compose page and homepage (08 A.5; stage-2/03 §2.4) — ui-compose-page, pane kind compose

Fork drafts, initialPrompt, reuseEnvironmentId, sectionId, and thread handoff arrive as the intent of navigation.open({ kind: 'compose' }, { intent }), never as location.state (08 A.5).

5.6 Plugin pages (08 A.6) — ui-shell PluginPageFrame, pane kind page

The page pane kind and its route are built (stage-2/03 §2.4). ui-shell/pages has no registrants in the slice, and the two header slots are 08 only.

5.7 Panel shell (08 A.7) — ui-panel-shell, occupies pane.dock

There is no panel.tab slot: the kernel mounts TabKind.Component per tab; a tab kind is replaced through kind arbitration and the tab:<kind> pin (08 A.7). In-panel splits are deleted (Q21).

5.8 Timeline (08 A.8; 09 §2; stage-2/03 §2.5) — ui-timeline-view, occupies thread.timeline

One interaction.renderer slot serves the composer body chain (view: 'takeover') and the row body (view: 'row'). Per-kind policy (expandable, bundling concept, summary verbs, auto-expand, hidden, text) is data on ui-timeline-view/kinds, not a slot (stage-2/03 §2.5). ui-markdown/render is a service key, not a slot (stage-2/04 D16).

5.9 Composer (08 A.9 names; 09 §3.5 order; stage-2/03 §2.6) — ui-composer, occupies thread.composer and compose.composer

Sixteen slots are children of ui-composer's two occupant registrations; composer.pickerFooter is declared by ui-execution-picker. All are scope pane, instanced per owner mount (composerId).

ComposerOwner = { composerId; mode: 'newThread' | 'followUp' | 'queuedEdit' | 'sentEdit' | 'embedded'; scope: DraftScope; threadId | null; projectId | null; draft; selection: ExecutionSelection; submitMode: 'ready' | 'queue' | 'blocked'; disabledReason: { reason; code } | null; layout: 'regular' | 'compact' | 'zen'; compactCollapsed }.

composer.submit chain by order (09 §3.8; stage-2/03 §2.6, frozen): 100 attachmentsReady (ui-composer) · 200 blockedReasonGate (ui-composer) · 250 archivedReadOnly (threads; disabled → { reason: 'This thread is archived', code: 'archived' }) · 300 runTargetValid (ui-run-target) · 400 providerReady (ui-execution-picker) · 500 provider middlewares (when: ctx.selection.providerId === ownId; plan-mode entry/exit lives here) · 600 serialize · 700 dispatch · 800 drafts · 900 navigate (ui-composer). The primary action's disabled reason is the first non-null disabled(ctx) in this order. Verb → command: send → thread.send {mode: 'queue'}, steer → thread.send {mode: 'steer'}, queue → thread.queue.create, sendQueueHead → thread.queue.sendHead, stop → thread.stop, create → thread.create. The composer never sends mode: 'auto'.

Takeover: while view.takeover !== null, composer.stack renders only cards with showDuringTakeover: true and the interaction renders as the last stack item; the editor stays mounted hidden so the draft survives. The archived / environment-gone banners stay in thread.banner, not in the stack (08 A.4).

5.10 Settings (08 A.10) — ui-settings, pane kind settings, shell.sidebar:settings

5.11 Extensions hub (08 A.11) — ui-extensions, pane kind extensions, shell.sidebar:extensions

5.12 Dialogs, toasts, attention, overlays (08 A.12; stage-2/03 §3)

One slot (shell.overlay, A.1) and three services. Listed so the catalog is complete; the service shapes are stage-2/03 §3.

5.13 File openers and open targets (08 A.13) — panel-files

FileRef = { source: 'workspace' | 'host' | 'thread-storage'; path; hostId | null; environmentId | null; threadId | null }.

5.14 Registries and chains that are not slots (08 A.14; stage-2/03 §3)

Service-container registries and data-carrying list slots. "Kind" names the mechanism; they appear in bb ui catalog under "registries".

app.contentScript is named only in 13 D.1 (contentScripts.register → "kernel-ui, keep"); it is in neither 08 nor kernel-ui and is not listed above.

5.15 Pane kinds (07 §4.2; 08 A.1; stage-2/03 §2.4)

panes.register(PaneKindInput) — not a slot. As built (kernel-ui/src/layout/layout-store.ts): { kind; schema; priority; Component; title(s); icon; threadId(s); dock: { default(s); allowedTabKinds } | null; equals; intents; children }. The collector fills priority 0, icon null, equals deepEqual, intents null. children declares the pane component's child slots (how ui-thread-page declares thread.*). Several plugins may register one kind; the kernel orders them with the pane:<kind> pin and the winner receives Original. An unknown kind renders the kernel MissingKindPane and the node is kept. threadId(state) sets the thread:<id> scope key for the pane's subtree.

"Settings replaces the workspace" is not a pane-kind flag: the settings and extensions panes write the tab-scope preference ui-settings/lastAppPath and their back arrow calls navigation.openPath(lastAppPath) (08 A.1).

5.16 Tab kinds (07 §4.2; 08 A.7)

tabs.register(TabKindInput). As built: { kind; schema; priority; Component; label(s); icon (required); singleton; persist: 'thread' | 'tab' | (s) => …; launcher: { label; order; create() } | null; closable }; the collector fills priority 0, singleton false, launcher null, closable true and records persist: 'dynamic' for the function form. Hosting is the pane kind's dock.allowedTabKinds, not a field on the tab. persist: 'thread' tabs live in the kernel-ui/dock.tabs thread annotation (CAS through kernel/preferences.set expectedUpdatedAt, #29); persist: 'tab' tabs live in the tab-scoped tree. No tab kind is registered in the slice: the thread pane's default thread-info tab renders MissingKindPane inside the empty PlainDockList (stage-2/03 §2.4, accepted).

The legacy side-chat tab kind is dropped; side-chat registers a plugin-panel action. file replaces today's three preview kinds with one discriminated schema (08 A.7).

5.17 Route contributions (07 §3.1; stage-2/03 §1)

routes.register(RouteContribution). As built (kernel-ui/src/router/router.ts): { id: '<pluginId>/<name>'; path; pane: { kind; toState(params, url); toPath(state) }; title(state) }. path takes :name segments and a trailing *. Two contributions with the same path are a RouteCollision for the later plugin by sorted id; there is no route priority (a fork uses replaces, which removes the original's routes). The kernel has no routes of its own; an unmatched URL renders the kernel NoRoutePage. One URL shape per pane kind; the personal project is an ordinary project id (no /threads/:id shortcut). url.hash reaches toState and PaneProps.hash; location.state is not used (one-shot payloads are intent). Legacy redirects are dropped.

5.18 Client command ids (07 §4.7, §6.1; 08 A.14; kernel-ui/src/layout/layout-commands.ts)

Id grammar. Ids are flat, open, and today's ids verbatim (thread.new, panel.toggle, composer.focus); there is no ui.<surface> prefix and no manifest claim. A family is <noun>.<verb>.* with family: { count }, expanded to .1 … .<count>; the handler receives index. Uniqueness is per (side, id): the first registration in composition order owns a local id, and a second registration of the same id is conflict for the later plugin (degraded). pane is not a reserved noun on the client side. bindable: false hides an id from Settings › Keyboard. One executor per id; further handle calls are before interceptors by priority desc.

Kernel-owned (registerLayoutCommands, built). Every row: when: { all: ['splitActive'], none: ['modalOpen'] } (07 §4.7 writes none: []; built wins), bindable, web and desktop, no menu entry, registered before any plugin runs.

Kernel context keys (07 §6.1): modalOpen (from ModalPresence, not a DOM selector), editableFocus, layoutCompact, webSurface, desktopSurface, mobileSurface, macPlatform, splitActive (bound to "more than one pane"). Plugins define the rest with commands.context.define.

Plugin-owned ids (08 A.14; R10):

Bindings are the profile preference ui-keyboard/keybindings (ui-keyboard; bb keybindings list|set|reset). No command palette in v1 (Q2).

5.19 Pin targets (02 §3.4; 07 §5.4; 08 B.3; kernel-core/src/names.ts)

kernel/pins is one profile-scope map. Its key is the pin target and is identical to the CLI argument: bb composition pin <target> <pluginId>. As built: PinTarget = service:<id> | slot:<name>[:<key>] | pane:<kind> | tab:<kind>. There is no kernel.pin. prefix (09 §2.6's kernel.pin.slot:… spelling is superseded by 08 B.3 and the built key) and no provider:<id> target (RECONCILIATION #28; the default provider is the preference providers/default). Arbitration is replaces → pin → priority → sorted plugin id; a pin on a multi-contract service may name an instance (service:kernel/secrets.backend os-keychain).

Base-layer winners (08 B.3): slot:root, slot:shell.titleBar, slot:shell.main → ui-shell; slot:sidebar.body, slot:sidebar.search → ui-thread-list; slot:thread.timeline, slot:timeline.view → ui-timeline-view; slot:thread.composer, slot:compose.composer → ui-composer; slot:composer.editor → ui-editor-tiptap; slot:pane.dock, slot:layout.dropZones → ui-panel-shell (spec; ui-shell fallback in the slice); slot:timeline.row:task → workflows (spec; ui-default-rows in the slice); slot:files.opener:md → docs, slot:files.opener:pdf → pdf-preview (spec); slot:diff.renderer, slot:source.renderer → ui-diff; pane:<kind> and tab:<kind> → their owners. A crashed winner falls back to the next candidate and shows one toast.

5.20 Names that do not exist