feat(metrics): consume contextSize — current context-usage readout

Backend context-size handoff: re-pin [email protected] / [email protected]
(+ re-mirror .dispatch reference snapshots). Thread the optional contextSize
through core/metrics (done fold + durable + selectCurrentContextSize: latest
turn's defined value, undefined=>unknown never 0, durable-wins-over-live).
Chat store exposes currentContextSize; ContextSizeBadge renders
"N tokens in context" / "context size unknown" above the composer.
GLOSSARY: add context size / context window. 533 tests green.

2 files changed, 44 insertions, 5 deletions

diff --git a/.dispatch/transport-contract.reference.md b/.dispatch/transport-contract.reference.md
index c2e2076..40ced1e 100644
--- a/.dispatch/transport-contract.reference.md
+++ b/.dispatch/transport-contract.reference.md
@@ -5,9 +5,16 @@
 > hangs on a permission prompt). Your CODE still imports `@dispatch/transport-contract` normally —
 > this file is for READING only.
 >
-> **Orchestrator:** SNAPSHOT of `[email protected]` (committed, backend `6db12ff`; the metrics
-> endpoint shipped + version-bumped + LIVE-VERIFIED). Depends on `@dispatch/[email protected]` (see
-> `wire.reference.md`) + `@dispatch/ui-contract` (see `ui-contract.reference.md`).
+> **Orchestrator:** SNAPSHOT of `[email protected]` (the metrics endpoint shipped +
+> version-bumped + LIVE-VERIFIED). Depends on `@dispatch/[email protected]` (see `wire.reference.md`) +
+> `@dispatch/[email protected]` (see `ui-contract.reference.md`).
+>
+> **2026-06-12 delta (context-size handoff — package bumped `0.5.0` → `0.6.0`, depends on
+> `[email protected]`):** no NEW transport shape — the optional `contextSize?: number` rides the
+> re-exported `TurnMetrics` (so `ConversationMetricsResponse.turns[].contextSize`) and, live, the
+> `TurnDoneEvent.contextSize` on the `done` AgentEvent (`chat.delta` WS / `/chat` NDJSON). On
+> (re)hydrate take the LAST `turns[]` element with a defined `contextSize`; live, update on `done`.
+> See the `wire.reference.md` context-size delta for the definition.
 >
 > **2026-06 delta (cache-warming handoff, additive — package still `0.4.0`):** adds
 > `POST /chat/warm` (`WarmRequest` → `WarmResponse`) for an on-demand prompt-cache warm, and the
diff --git a/.dispatch/wire.reference.md b/.dispatch/wire.reference.md
index ee5488c..cf1410a 100644
--- a/.dispatch/wire.reference.md
+++ b/.dispatch/wire.reference.md
@@ -4,8 +4,15 @@
 > types WITHOUT following the `file:` dep symlink out of this repo (which hangs on a permission
 > prompt). Your CODE still imports `@dispatch/wire` normally — this file is for READING only.
 >
-> **Orchestrator:** SNAPSHOT of `[email protected]` (committed, backend `6db12ff`; the metrics types below
-> shipped + version-bumped). Regenerate whenever `@dispatch/wire` changes.
+> **Orchestrator:** SNAPSHOT of `[email protected]` (the metrics types below shipped + version-bumped).
+> Regenerate whenever `@dispatch/wire` changes.
+>
+> **2026-06-12 delta (context-size handoff — package bumped `0.4.0` → `0.5.0`):** adds an OPTIONAL
+> `contextSize?: number` to BOTH `TurnDoneEvent` (live `done`) and `TurnMetrics` (persisted) — the
+> turn's FINAL step `inputTokens + outputTokens` (current context occupancy), NOT the aggregate
+> `usage` (which overcounts multi-step turns). The two carriers are equal for the same turn. Current
+> value = the LATEST turn's `contextSize`; `undefined` ⇒ render "unknown", never `0`. See the field
+> doc-comments on `TurnMetrics`/`TurnDoneEvent` below.
 >
 > **0.3.0 changes (token + timing metrics):**
 > - **Live per-step/per-turn telemetry on the event stream** (transient — NOT persisted):
@@ -221,6 +228,16 @@ export interface TurnMetrics {
 	readonly durationMs?: number;
 	/** Per-step metrics in step order. */
 	readonly steps: readonly StepMetrics[];
+	/**
+	 * **Context size** — tokens the conversation occupies as of this turn: the
+	 * turn's FINAL step `inputTokens + outputTokens` (the last entry of `steps`),
+	 * NOT the aggregate `usage` (which sums per-step prompts and overcounts a
+	 * multi-step turn). The persisted, replayable counterpart of
+	 * `TurnDoneEvent.contextSize` and equal to it for the same turn. A client
+	 * reopening a past conversation reads the LAST turn's `contextSize` as the
+	 * current context usage. Optional: absent when no per-step usage was available.
+	 */
+	readonly contextSize?: number;
 }
 
 // ─── Outward events ─────────────────────────────────────────────────────────
@@ -393,6 +410,21 @@ export interface TurnDoneEvent {
 	 * provider reported no usage).
 	 */
 	readonly usage?: Usage;
+	/**
+	 * **Context size** — tokens the conversation occupies right now: the turn's
+	 * FINAL step `inputTokens + outputTokens` (the prompt sent into the last LLM
+	 * round-trip plus that round-trip's output). This is the "tokens in context"
+	 * figure a client renders as the chat's current context usage, and a client
+	 * treats the LATEST turn's value as the live total.
+	 *
+	 * Deliberately NOT the aggregate `usage` above: `usage` SUMS each step's
+	 * `inputTokens`, which overcounts a multi-step / tool-calling turn because every
+	 * step re-prefills the growing prompt — the final step's input already includes
+	 * all prior context, so its input+output is the true occupancy. Optional: absent
+	 * when no per-step usage was observed this turn (mirrors `usage`). A later field
+	 * will carry the model's max context-window LIMIT; this is only the current size.
+	 */
+	readonly contextSize?: number;
 }
 
 /**