feat(metrics): per-turn + per-step token/timing metrics bubbles

Consume [email protected] / [email protected] metrics: usage.stepId,
step-complete (ttft/decode/genTotal), done.durationMs/usage, and the
durable GET /conversations/:id/metrics endpoint.

- core/metrics: pure live-fold + durable-merge reducer; decode-rate TPS;
  head-aligned, stable placement; progressive per-step rows (each shown as
  its step ends) with the turn-total row gated on the done event.
- features/chat: store folds metric events + hydrates durable TurnMetrics;
  ChatView renders inline step bubbles + a turn-total bubble.
- app: MetricsSync HTTP effect (tolerates 404) injected into chat stores.
- scripts/live-probe: drives the metrics path; live-verified 17/17 vs bin/up.
- docs: regenerate .dispatch wire/transport mirrors to 0.4.0; glossary terms
  (turn/step metrics, TTFT, decode time, TPS, metrics bubble); trim handoff.

1 files changed, 16 insertions, 76 deletions

diff --git a/backend-handoff.md b/backend-handoff.md
index b0b0494..df6a618 100644
--- a/backend-handoff.md
+++ b/backend-handoff.md
@@ -5,93 +5,33 @@
 > **From:** dispatch-web orchestrator · **To:** arch-rewrite orchestrator · **Courier:** the user.
 > `lsp` does NOT span the repos (ORCHESTRATOR §5) — every cross-repo ask flows through here.
 
-_Last updated: 2026-06-06 — Slice 3 (tabs + model selector + DaisyUI) FE-complete; no new backend asks._
+_Last updated: 2026-06-10 — metrics display slice FE-complete + live-verified (probe 17/17). No open backend asks._
 
 ---
 
-## 1. Current FE status
+## 1. Pinned backend contracts (consumed by the FE)
 
-| Slice | State |
-|---|---|
-| **Slice 1** — surface system + WS + composition root | ✅ DONE, committed, green. |
-| **Slice 2** — conversation transcript: cache + delta streaming (design §6) | ✅ DONE + **LIVE-VERIFIED** — live e2e probe **9/9** against `bin/up` (see §6). |
-| **Slice 3** — tabs (multi-conversation) + model selector + DaisyUI/dracula | ✅ FE-COMPLETE — svelte-check 0/0, **281 vitest**, biome clean, build ok. Per-tab chat stores, one WS routed by `conversationId`, local-forget on tab close, tabs persisted to localStorage. No backend change needed. |
-
-**Slice 2 units built** (all pure-core / injected-shell, single-owner): `core/chunks` (the one
-transcript reducer) · `core/wire` (contract-conformance drift guard) · `adapters/ws` (now multiplexes
-`chat.send`/`chat.delta` on the one socket) · `features/conversation-cache` (pure reconcile/evict +
-`ConversationChunkStore` port) · `adapters/idb` (IndexedDB impl) · `features/chat` (runes view-model
-+ `ChatView`/`Composer`) · `app` (one socket for surface+chat, host-relative HTTP `:24203` history
-sync, IndexedDB cache, renders the chat). Consumes ONLY the pinned `@0.1.0` contracts — no backend
-change was needed.
-
-## 2. Pinned backend contracts (consumed by the FE)
-
-All three pinned as `file:` deps at **`@0.1.0`** and live-verified consumable (import smoke-test passes):
+Pinned as `file:` deps: **`[email protected]`; `[email protected]`; `[email protected]`**.
 
 | Package | Used for |
 |---|---|
-| `@dispatch/ui-contract` | surfaces + surface WS protocol (Slice 1) |
-| `@dispatch/wire` | chat wire types: `Chunk`/`StoredChunk`(+`seq`)/`ChatMessage`/`AgentEvent`/`TurnSealedEvent`/`Usage` |
-| `@dispatch/transport-contract` | HTTP endpoints + `ChatRequest`/`ModelsResponse`/`ConversationHistoryResponse` + WS chat ops + unified `WsClientMessage`/`WsServerMessage` |
-
-Backend endpoints in use (port **24203** HTTP, **24205** WS, CORS wildcard `*` — all confirmed live):
-`POST /chat` (NDJSON), `GET /models`, `GET /conversations/:id?sinceSeq=<n>`, WS `chat.send`→`chat.delta`.
-Confirmed invariants C1–C4 (raw seq-ordered history slice · one path-agnostic WS multiplexing surface+chat · `turn-sealed` fires post-persist = cache-commit · live deltas carry no `seq`).
-
-Mirrored in-repo for headless agents: `.dispatch/ui-contract.reference.md`, `.dispatch/wire.reference.md`,
-`.dispatch/transport-contract.reference.md` (regenerated on any contract bump).
-
-## 3. Open items FOR THE BACKEND
+| `@dispatch/ui-contract` | surfaces + surface WS protocol |
+| `@dispatch/wire` | `Chunk`/`StoredChunk`(+`seq`)/`ChatMessage`/`AgentEvent`/`TurnSealedEvent`/`Usage`/`StepId` + metrics: `StepMetrics`/`TurnMetrics`, `usage.stepId`, `step-complete`, `done.durationMs`/`done.usage`, `tool-result.durationMs` |
+| `@dispatch/transport-contract` | `ChatRequest`/`ModelsResponse`/`ConversationHistoryResponse`/`ConversationMetricsResponse` + WS chat ops + `WsClientMessage`/`WsServerMessage` |
 
-### 3.1 Resolved / answered
-- ✅ Wire-types split, per-chunk `seq`, history endpoint, WS chat multiplexing, CORS — all delivered
-  (backend commit `812621c`).
+Endpoints in use (HTTP **24203**, WS **24205**, CORS `*`):
+`POST /chat` (NDJSON) · `GET /models` · `GET /conversations/:id?sinceSeq=<n>` ·
+`GET /conversations/:id/metrics` · WS `chat.send`→`chat.delta`.
 
-### 3.2a Finding — model is NOT persisted/exposed per conversation (FE handled it)
-`model` is a per-turn `ChatRequest` field only; `session-orchestrator` resolves it per `handleMessage`
-and never stores it, and `conversation-store`/`ConversationHistoryResponse` carry no model. So the FE
-**persists the selected model per tab** (localStorage). No action needed. OPTIONAL future nicety: if
-you ever persist + expose a per-conversation "last model" (e.g. on the `GET /conversations` list when
-it lands), the FE could seed a reopened tab's model from the server instead of localStorage.
+Mirrored in-repo for headless agents: `.dispatch/{ui-contract,wire,transport-contract}.reference.md`
+(regenerate on any contract bump).
 
-### 3.2 FYI — non-blocking gotcha (no action required unless you publish externally)
-- **`workspace:*` breaks external `file:` consumption under bun.** `transport-contract`'s deps are
-  `@dispatch/ui-contract`/`@dispatch/wire` at `workspace:*`; `bun install` from dispatch-web could not
-  resolve them ("Workspace dependency not found"). **Worked around FE-side** with a `package.json`
-  `overrides` block mapping both to their `file:` paths — no backend change needed now. If you ever
-  publish these to a registry, prefer real semver ranges over `workspace:*` for out-of-monorepo
-  consumers.
+## 2. Open asks FOR THE BACKEND
 
-### 3.3 Pending asks / roadblocks
-- _(none open)_ — Slice 2 needed no backend change. One coordination item below (§6).
+- _(none open)_
 
-## 6. LIVE end-to-end probe — DONE ✅ (9/9, against `bin/up`)
+## 3. Likely NEXT backend asks (heads-up, not yet requested)
 
-Ran `bun scripts/live-probe.ts` (drives the FE's REAL network-facing stack — `adapters/ws` socket,
-`core/chunks` reducer, `conversation-cache` + `adapters/idb`, and the HTTP history endpoint — against
-the running backend). **All 9 checks passed:**
-- one WS (`:24205`) delivered the surface `catalog` AND the chat stream;
-- `chat.send` → ~33 `chat.delta` events (incl. `text-delta`) → folded to the expected assistant text
-  → `turn-sealed`;
-- post-seal `GET :24203/conversations/:id?sinceSeq=0` → 3 seq-monotonic `StoredChunk`s
-  (`latestSeq=3`); `applyHistory` superseded the provisional turn (`sealedTurnId` cleared);
-- IndexedDB cache persisted the sealed turn; committed transcript shows the assistant text.
-
-**No backend mismatch found — every confirmed invariant (C1–C4) held live.** One FE-internal note
-(not a backend matter): the idb adapter relies on the global `IDBKeyRange` (fine in a browser; the
-probe needed `fake-indexeddb/auto` to supply it under Bun).
-
-Also caught + fixed during browser bring-up (FE-only bug, not backend): a BLANK page on plain-HTTP
-non-localhost origins (`http://arch-razer:24204`) because `crypto.randomUUID()` is secure-context-only
-— now replaced with a `getRandomValues`-based fallback.
-
-## 4. (history) Slice 2 unit map — delivered, see §1.
-
-## 5. Likely NEXT backend asks (heads-up, not yet requested)
-
-These belong to **later** FE slices (design §7 "later slice") — flagged early so they're on your radar:
-- `GET /conversations` — conversation list / sidebar (FE history explorer / conversation switcher).
+- `GET /conversations` — conversation list / sidebar (history explorer / switcher); could also expose a
+  per-conversation "last model" so a reopened tab seeds its model from the server instead of localStorage.
 - `POST /conversations/:id/cancel` — "stop generating".
-
-When the FE reaches those slices, the concrete request will be filed here in §3.3.