refactor(token-meter): make context occupancy durable projection state

Replace the transient `session/model-request` mux frame with ordinary durable
session state. Occupancy now rides two last-wins projection fields instead of a
non-replayable frame that needed removal tombstones and cross-stream fencing.

The frame was the only non-replayable class on the mux stream. Because host and
mux are independent SSE streams with no cross-stream order, a request emitted
before a removal could arrive after `host/session-removed`, and a legitimate
request for a new lifecycle reusing the same id could be fenced by a late
removal. Fixing that needed a lifecycle generation on every frame; the frame
itself was the problem.

Removed: the `session/model-request` frame and schema, the `agent/model-request`
core event, the ApiProxy measurement point, the client-side telemetry map and
removal tombstone, and the synthetic `cancelled` open error used to signal
reconnect through the error channel.

Added: `request/context`, a log-only session event recording the
registration-bound capacity of the route a request resolved to, appended beside
`request/header` from the lookup that already prepared the call and skipped when
the route is unchanged. Capacity stays out of `EpochHeader` because it is
adapter metadata about a route, not an input the request was built from, so it
must not join request reconstruction or header equality.

The `contextPressure` projection pairs the newest provider-reported prompt size
with the newest recorded capacity. The two are deliberately not one atomic
request observation: switching models can pair a fresh capacity with the prior
route's pressure until the next request reports usage. The figure is a
user-facing reference, and this matches how the TUI status line has always
computed occupancy.

packages/client/ui-conversation/src/client/chat/ChatView.tsx

@@ -221,9 +221,7 @@ function StreamingTail({ useSession, onGrow }: {
  * The chat view slot entry: pure component over the composed props (tool rows
  * render through the declared keyed hole's renderSlot share).
  */
-export function ChatView({
-  useProjection, useSession, useSessions, useStore, renderSlot, sessionId, openFile, loadOlder,
-}: ChatViewSlotProps) {
+export function ChatView({ useSession, useSessions, useStore, renderSlot, sessionId, openFile, loadOlder }: ChatViewSlotProps) {
   const nodes = useSession(s => s.nodes)
   // Workspace root off the session list row: path summaries display relative to it.
   const cwd = useSessions(s => s.byId[sessionId]?.cwd)
@@ -231,8 +229,7 @@ export function ChatView({
   const runningCalls = useSession(s => s.runningCalls)
   const codeDispatches = useSession(s => s.codeDispatches)
   const openState = useSession(s => s.openState)
-  const openError = useSession(s => s.openError)
-  const openErrorMessage = openError === null ? null : `${openError.message}（${openError.code}）`
+  const openErrorMessage = useSession(s => s.openError === null ? null : `${s.openError.message}（${s.openError.code}）`)
   const hasMore = useSession(s => s.hasMore)
   const loadingOlder = useSession(s => s.loadingOlder)
   const selectedCallId = useStore(s => s.selection?.callId)
@@ -356,12 +353,7 @@ export function ChatView({
       <div ref={listRef} className={css.scroll} onScroll={onScroll}>
         <div className={css.column}>
           {openState === 'loading' && <div className={css.hint}>载入历史…</div>}
-          {openState === 'error' && openError?.code === 'cancelled' && (
-            <div className={css.hint}>连接已中断，等待重连…</div>
-          )}
-          {openState === 'error' && openError?.code !== 'cancelled' && (
-            <div className={css.openError}>历史加载失败：{openErrorMessage}</div>
-          )}
+          {openState === 'error' && <div className={css.openError}>历史加载失败：{openErrorMessage}</div>}
           {hasMore && (
             <div className={css.older}>
               <button type="button" disabled={loadingOlder} onClick={loadOlderAnchored}>
@@ -397,7 +389,7 @@ export function ChatView({
           {running && <TurnDots />}
         </div>
       </div>
-      <StatsLine useSession={useSession} useProjection={useProjection} />
+      <StatsLine useSession={useSession} />
       {!atBottom && (
         <button
           type="button"

packages/client/ui-conversation/src/client/chat/StatsLine.tsx

@@ -1,12 +1,13 @@
 // Settled-node identity prevents stream-delta updates from rerendering this row.
+// Mounted on 'conversation.composer.dock' so it sticks with the composer in the
+// active conversation scrollport (see ConversationRoot data-conversation-scroll).
 
 import { memo, useMemo } from 'react'
 import type {
   ConversationSnapshot, UseProjection,
 } from '@deepseek-ai/dsh-client-runtime/client'
-import type { ModelRequestTelemetry } from '@deepseek-ai/dsh-client-connection/client'
 import type { SnapshotSelectorHook } from '@deepseek-ai/dsh-client-ui-slots'
-import type { TokenUsageProjection } from '@deepseek-ai/dsh-token-meter/client'
+import type { ContextPressureProjection, TokenUsageProjection } from '@deepseek-ai/dsh-token-meter/client'
 import css from './StatsLine.module.css'
 
 interface VisibleCounts {
@@ -57,16 +58,19 @@ export function cacheHitPercent(usage: TokenUsageProjection): number | null {
 }
 
 /**
- * Current context occupancy using the TUI's integer rounding and upper clamp.
- * @param request - one atomic request snapshot observed on this mux generation.
- * @returns occupancy percent, or null when either input is unavailable.
+ * Approximate context occupancy, using the TUI's integer rounding and upper
+ * clamp. The numerator and capacity are independent last-wins projection
+ * fields, so this is a reference figure rather than an exact request
+ * measurement (see the token-meter README).
+ * @param pressure - the session's context-pressure projection value.
+ * @returns occupancy percent, or null when no capacity is known.
  */
-export function contextPercent(request: ModelRequestTelemetry | null): number | null {
-  if (request?.contextTokens === undefined || request.contextWindow === undefined) return null
-  return Math.min(100, Math.round(request.contextTokens / request.contextWindow * 100))
+export function contextPercent(pressure: ContextPressureProjection | undefined): number | null {
+  if (pressure?.contextWindow === undefined) return null
+  return Math.min(100, Math.round(pressure.pressureTokens / pressure.contextWindow * 100))
 }
 
-/** Props: standard session hooks handed down by ChatView. */
+/** Props: the framework's session snapshot and projection hook seats. */
 export interface StatsLineProps {
   useSession: SnapshotSelectorHook<ConversationSnapshot>
   useProjection: UseProjection
@@ -74,8 +78,8 @@ export interface StatsLineProps {
 
 export const StatsLine = memo(function StatsLine({ useSession, useProjection }: StatsLineProps) {
   const nodes = useSession(s => s.nodes)
-  const modelRequest = useSession(s => s.modelRequest)
   const usage = useProjection('tokenUsage')
+  const pressure = useProjection('contextPressure')
   const counts = useMemo(() => deriveVisibleCounts(nodes), [nodes])
   const hasUsage = usage !== undefined && (
     usage.uncachedInputTokens !== 0
@@ -83,24 +87,22 @@ export const StatsLine = memo(function StatsLine({ useSession, useProjection }:
     || usage.cacheReadTokens !== 0
     || usage.cacheWriteTokens !== 0
   )
-  const context = contextPercent(modelRequest)
+  const context = contextPercent(pressure)
   if (counts.steps === 0 && !hasUsage && context === null) return null
 
   const parts: string[] = []
-  if (usage === undefined) {
-    parts.push('usage unknown')
-  } else {
+  if (usage !== undefined) {
     parts.push(`${formatMetricTokens(usage.uncachedInputTokens)} uncached input`)
     parts.push(`${formatMetricTokens(usage.outputTokens)} output`)
     parts.push(`${formatMetricTokens(usage.cacheReadTokens)} cache read`)
     const cacheHit = cacheHitPercent(usage)
     if (cacheHit !== null) parts.push(`cache hit ${cacheHit}%`)
   }
-  // contextPercent validates both fields; repeat the capacity guard so that
-  // TypeScript carries the same refinement into the formatting branch.
-  parts.push(context === null || modelRequest?.contextWindow === undefined
-    ? 'context unknown'
-    : `context ${context}% of ${formatMetricTokens(modelRequest.contextWindow)}`)
+  // Capacity absent (no token-meter, or an adapter that advertises none) omits
+  // the segment: an unknown denominator has no percentage worth a placeholder.
+  if (context !== null && pressure?.contextWindow !== undefined) {
+    parts.push(`context ${context}% of ${formatMetricTokens(pressure.contextWindow)}`)
+  }
   parts.push(`${counts.turns} turns`)
   parts.push(`${counts.steps} steps`)
   return <div className={css.root}>{parts.join(' · ')}</div>