The audit page that hardened the foundation
Issue #103 started as a simple evaluation: does the IoT bridge audit page need a richer viewer? The 30-line pages-ui DSL table we’d shipped worked fine for flat scanning — event type, device ID, timestamp, CSV export. But the BridgeMessage payload (seven sealed variants carrying state changes, commands, provider status transitions) was invisible. A STATE_CHANGE row told you something changed. It didn’t tell you what.
The original issue listed three options: a generic blocks-event-trail component, an IoT-specific viewer, or incremental DSL enhancement. All three were wrong. While exploring the pages-ui-components package, I found pages-event-trail — a platform component that already had expandable row details, chip filtering, entity selection, and date ranges. It had configure() for hostPanel integration. It was exactly what we needed.
Except it wasn’t.
The configure() gap
The design review caught something I’d missed. PagesEventTrail.configure() explicitly handles eight properties — data, columnDefs, columnConfig, chipField, chipValues, entityField, entityLabel, showDateRange. Properties not in that list are silently dropped. getRowDetail, getRowKey, columnRenderers — the three properties the audit trail viewer depends on — all vanish without error.
The @property() decorator creates the illusion of automatic binding. In normal Lit usage it works. But configure() is a custom integration point, not part of Lit’s property system. The hostPanel runtime delivers the properties correctly — the receiving component just never reads them.
CellValue destruction
The second gap was deeper. The pages-data pipeline converts raw entries to TypedRow via fromRows(). TypedRow cells support five scalar types: TEXT, NUMBER, DATE, LABEL, NULL. A polymorphic BridgeMessage object — a command with target device, action, parameters, dispatched-by — gets converted to "[object Object]" via String(). Gone. No warning, no error.
We fixed this with a WeakMap<TypedRow, unknown> that preserves the mapping between each row and its raw entry. The detail renderer receives the original object as an optional second parameter. WeakMap (not Map) so filtered-out rows can be garbage collected. The second parameter is optional so existing consumers work unchanged.
Upstream, not around
The instinct was to work around it — build a thin IoT-local wrapper around pages-data-table, bypass pages-event-trail entirely. It would have been faster. But the whole point of the app tier is to exercise foundation components under real load. Every gap we work around is a gap that bites the next consumer. The configure() fix was three lines. The recordsPath extraction was ten. The csvExport passthrough was two. Fifteen lines of upstream code that harden the component for every future hostPanel consumer.
What shipped
A tab-toggled audit page. The “Table” tab keeps the original DSL table — fast scanning, CSV export, dropdown filters. The “Trail” tab hosts pages-event-trail via hostPanel() with tailored detail rendering for all eight BridgeAuditEventType values. STATE_CHANGE shows a capability diff table (brightness: 50 → 100). COMMAND_SENT shows target device, action, parameters. AGENT_CONNECTED shows a lifecycle badge. Expanding a row with a correlationId fires a server-side query and renders the full correlation chain — command sent, state changed, response received — inline.
The TypeScript type model uses a discriminated union mirroring the Java sealed interface. The exhaustive switch catches missing variants at compile time. AGENT_CONNECTED and AGENT_DISCONNECTED have null payloads (no BridgeMessage) — the renderer branches on eventType first, then on @type for message-bearing events.
The shared filter adapter (syncing page-level filters across tabs) was deferred. It needs understanding of the pages-runtime ContextManager filter event model that we haven’t explored yet. Each tab has its own filter UI for now — the Table uses DSL dropdown selectors, the Trail uses built-in chips and entity selection. Both have the same filter capabilities, just not shared state.
The totalCount bug in getBridgeAudit — returning events.size() instead of the actual total count — was caught by the spec review and filed separately. It doesn’t block the viewer but it’ll matter when pagination arrives.