feat(web): add durable session metrics (round 1)

packages/client/ui-conversation/README.md

@@ -18,6 +18,8 @@ Per-session UI state for selection and the active view lives in the declared cha
 
 The composer bar declares session-scoped single seats for `'conversation.input.plan'` and `'conversation.input.model'`, plus list slots for overlay, dock, left, and right input extensions. InputBar renders the model seat immediately before its pending indicator and send/stop button. Feature packages own each control and its state; ui-conversation supplies placement, the `locked` owner prop, and the standard slot shares. The resident no-session shell uses `DisabledInputBar` and therefore dispatches no session-scoped control seats.
 
+The chat stats line reads durable token counters and current-context pressure only from `ConversationSnapshot.metrics`; visible nodes supply only the existing turn/step counts. It renders uncached input, output, and cache reads as separate compact values, computes cache hit as `cacheRead / (uncachedInput + cacheRead)` without cache writes, and shows context occupancy against the selected route's exact capacity. Missing host data is labeled unknown, never reconstructed from a paged window.
+
 `src/client/` is organized for the future package split: `contract/` is the sole inter-domain shared face (`slots.ts` slot declarations + composed slot props including the tool-row contract, `views.ts` shared primitives, `tool-call-model.ts`); the `skeleton/`, `chat/`, and `toolviews/` (sample registrants) domain directories import contract files and never each other; `apply.ts` is the only assembly point allowed to import all three domains. The `/client` export surface is the contract only — `apply`/`inject`, the two service classes, and the `contract/` type families; implementation components (skeleton, chat rows) and the store factory stay internal and reach the page exclusively through apply's slot registrations (tests take them via the `./src/*` subpath).
 
 ## Model Experience