fix(client): count the system prompt on legacy contextHeaders wire values

The context browser read the system row's item count from
`header.systemTokens`, a field only the post-#37 metadata wire shape
carries — but a host still running the pre-#37 view (a stale watch
build, an app not restarted since the upgrade) delivers content-bearing
epochs where the system TEXT rides the value instead. The row then read
0 项 while the ≈tokens figure still rendered, because the two come from
independent projections. Diagnosed against a real session: the cached
projection row was pre-#37 shaped, holding a 6261-char system string
(≈1570 tokens shown, count 0).

`headersOf` now normalizes both generations: unpriced legacy entries get
the meter's own heuristic, priced entries and new-shape values keep the
zero-copy pass-through. The heuristic (ceil(chars/4) + 4) moves to
shared/estimate.ts so the host fold and the client boundary price
identically. Regression tests cover the boundary matrix and the browser
row through the real call path; the #37 slimming itself is untouched.

src/client/services.ts

@@ -11,6 +11,7 @@
  */
 
 import type { Context } from '@deepseek-ai/cordis'
+import { estimateSystemTokens } from '../shared/estimate'
 import type { ContextBreakdown, ContextHeaders, ContextPressure, ContextTimeline, HeaderEpochContent, TimingTotals, TokenUsage, ToolTimingTotals } from '../shared/types'
 
 export interface LocaleService {
@@ -417,6 +418,13 @@ export function timingOf(value: unknown): TimingTotals | null {
  * browser's tools/sections reads, so the WHOLE projection degrades to null
  * and the card falls back to its metadata-only note. The epoch CONTENT is
  * not part of this value — the browser fetches it per epoch on demand.
+ *
+ * The pre-#37 wire generation carries the system TEXT instead of its token
+ * price (a host still running the old view — stale watch build, an app not
+ * restarted since the upgrade — serves it from its cache verbatim), so the
+ * two generations are normalized to the metadata shape here: unpriced legacy
+ * entries get the shared meter heuristic applied, priced ones and
+ * new-shape values pass through untouched.
  */
 export function headersOf(value: unknown): ContextHeaders | null {
   const headers = asRecord(value)
@@ -427,7 +435,20 @@ export function headersOf(value: unknown): ContextHeaders | null {
     if (!Array.isArray(entry.tools)) return null
     if (entry.systemTokens !== undefined && (typeof entry.systemTokens !== 'number' || !Number.isFinite(entry.systemTokens))) return null
   }
-  return headers as unknown as ContextHeaders
+  let legacy = false
+  for (const entry of headers.headers as { systemTokens?: unknown; system?: unknown }[]) {
+    if (entry.systemTokens === undefined && typeof entry.system === 'string' && entry.system !== '') {
+      legacy = true
+      break
+    }
+  }
+  if (!legacy) return headers as unknown as ContextHeaders
+  return {
+    headers: (headers.headers as { systemTokens?: number; system?: unknown }[]).map((entry) => {
+      if (entry.systemTokens !== undefined) return entry
+      return { ...entry, systemTokens: estimateSystemTokens(entry.system) || undefined }
+    }),
+  } as unknown as ContextHeaders
 }
 
 export interface TriggerCandidate {

src/host/fold.ts

@@ -20,10 +20,10 @@
  */
 
 import type { Category, ContextEventRecord, CostFamilyUsage, RequestRecord, SessionCostUsage, Snapshot, SurfaceNode, TimingTotals, ToolTimingTotals } from '../shared/types'
+import { estimateSystemTokens } from '../shared/estimate'
 import type { FoldBounds } from './config'
 import {
   estimateMessage,
-  estimateSystem,
   estimateToolsTotal,
   firstText,
   imageCountOf,
@@ -588,7 +588,7 @@ export function applyTimeline(state: TimelineState, event: TimelineEvent, bounds
         const s = ensure()
         // Tools TOTAL = dsh's whole-array price (one JSON string of every schema).
         s.toolsTokens = estimateToolsTotal(tools)
-        s.systemTokens = estimateSystem(header.system)
+        s.systemTokens = estimateSystemTokens(header.system)
         // Current route/model: the durable request envelope is the source of
         // truth (request/context is only route/capacity metadata, appended
         // AFTER request/header per request — see agent-loop `buildRequest`).

src/host/headers.ts

@@ -37,7 +37,8 @@ import { z } from 'zod'
 import type { SessionEvent } from '@deepseek-ai/dsh-session'
 import type { ProjectionDefinition } from './compat'
 import type { ContextHeaders, HeaderRecord, HeaderTool } from '../shared/types'
-import { estimateSystem, estimateToolSchema } from './pricing'
+import { estimateToolSchema } from './pricing'
+import { estimateSystemTokens } from '../shared/estimate'
 
 /** Retention cap on header epochs (metadata only; changes are rare; 50 is generous). */
 const HEADERS_MAX = 50
@@ -137,7 +138,7 @@ function recordOf(event: SessionEvent): StoredHeaderRecord | null {
     }),
   }
   if (typeof header.system === 'string' && header.system.length > 0) {
-    record.systemTokens = estimateSystem(header.system)
+    record.systemTokens = estimateSystemTokens(header.system)
   }
   return record
 }
@@ -169,7 +170,7 @@ export function createContextHeadersDefinition(
         }),
       }
       const systemTokens = h.systemTokens
-        ?? (typeof h.system === 'string' && h.system !== '' ? estimateSystem(h.system) : undefined)
+        ?? (typeof h.system === 'string' && h.system !== '' ? estimateSystemTokens(h.system) : undefined)
       if (systemTokens !== undefined) record.systemTokens = systemTokens
       return record
     }),

src/host/pricing.ts

@@ -92,11 +92,7 @@ export function estimateMessage(message: { content?: ContentBlock[] } | undefine
   return estimateBlocks(message?.content) + ROLE_OVERHEAD
 }
 
-export function estimateSystem(text: unknown): number {
-  if (typeof text !== 'string' || text.length === 0) return 0
-  return Math.ceil(text.length / CHARS_PER_TOKEN) + ROLE_OVERHEAD
-}
-
+/** The shared meter heuristic over rendered system-prompt text (shared/estimate.ts). */
 /** Per-tool price for the top-tools display (the total uses dsh's whole-array price). */
 export function estimateToolSchema(tool: unknown): number {
   return Math.ceil(JSON.stringify(tool).length / CHARS_PER_TOKEN) + BLOCK_OVERHEAD

src/shared/estimate.ts

@@ -0,0 +1,16 @@
+/**
+ * Token heuristics shared by the host fold and the client boundary — the
+ * harness token-meter's own fixed-density figure (dsh-token-meter/estimate.ts:
+ * ~4 chars ≈ 1 token, +4 role framing). Priced identically on both sides so a
+ * legacy value normalized at the client boundary matches what the host view
+ * would have served.
+ */
+
+const CHARS_PER_TOKEN = 4
+const ROLE_OVERHEAD = 4
+
+/** Price rendered system-prompt text; 0 for absent/empty/non-string input. */
+export function estimateSystemTokens(text: unknown): number {
+  if (typeof text !== 'string' || text.length === 0) return 0
+  return Math.ceil(text.length / CHARS_PER_TOKEN) + ROLE_OVERHEAD
+}

tests/client/components/browser.spec.ts

@@ -10,7 +10,7 @@ import { h } from '../../../src/client/react'
 import { makeContextBrowser, type ContextBrowserProps } from '../../../src/client/components/browser'
 import { makeStackedBar } from '../../../src/client/components/stackedBar'
 import { UNKNOWN_TOOL_SOURCE, type ContextHeaders, type ContextTimeline, type HeaderEpochContent, type RequestRecord, type SurfaceNode } from '../../../src/shared/types'
-import type { ConversationNodeLike, ImageLoader } from '../../../src/client/services'
+import { headersOf, type ConversationNodeLike, type ImageLoader } from '../../../src/client/services'
 import { click, flush, hover, makeKit, mount, query, queryAll, text, unhover, type Mounted } from '../helpers/kit'
 
 const kit = makeKit()
@@ -486,6 +486,25 @@ describe('ContextBrowser header epochs', () => {
     await m.unmount()
   })
 
+  test('a legacy content-bearing epoch (pre-#37 wire) still counts the system prompt', async () => {
+    // The value shape a host running the pre-#37 view serves: the system TEXT
+    // rides the epoch and no systemTokens price exists (the real cached row
+    // that read 0 项 while the breakdown still showed ≈1.6k). Routed through
+    // headersOf — the boundary the real callers sanitize the projection with.
+    const legacy = {
+      headers: [{
+        seq: 12,
+        time: 1_000,
+        system: 'You are an AI agent.\n',
+        tools: [{ name: 'bash', tokens: 815, description: 'run', schema: { type: 'object' } }],
+      }],
+    } as unknown as ContextHeaders
+    const data = tl({ current: { system: 9, tools: 815, user: 0, inject: 0, assistant: 0, tool: 0, total: 824 } })
+    const m = await mount(h(Browser, props({ data, headers: headersOf(legacy) })))
+    assert.ok(text(catRow(m, 'system')).includes(kit.t('browser.items', { n: 1 })))
+    await m.unmount()
+  })
+
   test('a fetched epoch without a system prompt explains its absence', async () => {
     const headers: ContextHeaders = { headers: [{ seq: 3, time: 3, systemTokens: 0, tools: [] }] }
     const data = tl({ current: { system: 0, tools: 0, user: 0, inject: 0, assistant: 0, tool: 0, total: 0 } })

tests/client/services.spec.ts

@@ -396,6 +396,36 @@ describe('headersOf', () => {
     }
     assert.equal(headersOf(value), value)
   })
+
+  test('a legacy content-bearing epoch (pre-#37 wire) normalizes to the metadata shape', () => {
+    // 16 chars → ceil(16/4) + 4 = 8, the harness meter's own heuristic.
+    const legacy = { headers: [{ seq: 12, time: 1000, system: 'x'.repeat(16), tools: [{ name: 'bash', tokens: 815 }] }] }
+    const out = headersOf(legacy)
+    assert.equal(out?.headers[0]?.systemTokens, 8)
+    // The content fields ride along untouched — the browser never reads them
+    // from the delivered value (content fetches per epoch on demand).
+    assert.equal((out?.headers[0] as { system?: string }).system, 'x'.repeat(16))
+  })
+
+  test('mixed generations price only the unpriced legacy entries', () => {
+    const value = {
+      headers: [
+        { seq: 1, time: 1000, system: 'prompt', tools: [] },
+        { seq: 2, time: 2000, system: 'kept', systemTokens: 55, tools: [] },
+        { seq: 3, time: 3000, tools: [] },
+      ],
+    }
+    const out = headersOf(value)
+    assert.equal(out?.headers[0]?.systemTokens, Math.ceil(6 / 4) + 4)
+    assert.equal(out?.headers[1]?.systemTokens, 55)
+    assert.equal(out?.headers[2]?.systemTokens, undefined)
+  })
+
+  test('a legacy entry whose system is not a non-empty string stays unpriced', () => {
+    const out = headersOf({ headers: [{ seq: 1, time: 1, system: '', tools: [] }, { seq: 2, time: 2, system: 7, tools: [] }] })
+    assert.equal(out?.headers[0]?.systemTokens, undefined)
+    assert.equal(out?.headers[1]?.systemTokens, undefined)
+  })
 })
 
 describe('workspaceOf', () => {

tests/host/headers.spec.ts

@@ -5,7 +5,7 @@
 
 import assert from 'node:assert/strict'
 import { describe, test } from 'vitest'
-import { estimateSystem } from '../../src/host/pricing'
+import { estimateSystemTokens } from '../../src/shared/estimate'
 import { createContextHeadersDefinition } from '../../src/host/headers'
 import type { HeadersState } from '../../src/host/headers'
 import { header, foreign } from './helpers/events'
@@ -42,7 +42,7 @@ describe('createContextHeadersDefinition', () => {
     assertPlainJson(state)
     assert.equal(state.headers.length, 1)
     assert.equal(state.headers[0].seq, 1)
-    assert.equal(state.headers[0].systemTokens, estimateSystem('You are an agent.'))
+    assert.equal(state.headers[0].systemTokens, estimateSystemTokens('You are an agent.'))
     assert.equal(state.headers[0].tools.length, 1)
     assert.equal(state.headers[0].tools[0].name, 'bash')
 
@@ -105,7 +105,7 @@ describe('createContextHeadersDefinition', () => {
     ]))
     assert.ok(!('systemTokens' in view.headers[0]))
     assert.ok(!('systemTokens' in view.headers[1]))
-    assert.equal(view.headers[2].systemTokens, estimateSystem('sys'))
+    assert.equal(view.headers[2].systemTokens, estimateSystemTokens('sys'))
   })
 
   test('the same epoch seq twice in a row returns the same state reference', () => {
@@ -265,7 +265,7 @@ describe('read-compat over v1 rows', () => {
     assert.deepEqual(def.stateSchema.parse(structuredClone(v1State())), v1State())
     const view = def.wire.view(v1State())
     assert.equal(def.wire.viewSchema.safeParse(view).success, true, 'normalized view passes the strict wire schema')
-    assert.equal(view.headers[0].systemTokens, estimateSystem('You are an agent.'), 'legacy system text priced at view time')
+    assert.equal(view.headers[0].systemTokens, estimateSystemTokens('You are an agent.'), 'legacy system text priced at view time')
     assert.ok(!('system' in view.headers[0]), 'system text stripped from the wire')
     assert.deepEqual(view.headers[0].tools, [
       { name: 'bash', tokens: 12 },
@@ -289,7 +289,7 @@ describe('read-compat over v1 rows', () => {
     assert.equal(state.headers.length, 3)
     const view = def.wire.view(state)
     assert.equal(def.wire.viewSchema.safeParse(view).success, true)
-    assert.equal(view.headers[2].systemTokens, estimateSystem('next'))
+    assert.equal(view.headers[2].systemTokens, estimateSystemTokens('next'))
     assert.ok(!('system' in state.headers[2]), 'new folds stay metadata-only in state')
     assert.ok('system' in state.headers[0], 'seeded legacy epochs keep their state shape until they age out')
 

tests/host/pricing.spec.ts

@@ -6,7 +6,6 @@ import assert from 'node:assert/strict'
 import { describe, test } from 'vitest'
 import {
   estimateMessage,
-  estimateSystem,
   estimateToolSchema,
   estimateToolsTotal,
   firstText,
@@ -15,6 +14,7 @@ import {
   isInjection,
   toolCallNames,
 } from '../../src/host/pricing'
+import { estimateSystemTokens } from '../../src/shared/estimate'
 import type { ContentBlock } from '../../src/host/pricing'
 
 describe('estimateToolsTotal', () => {
@@ -115,14 +115,14 @@ describe('estimateMessage', () => {
 
 describe('estimateSystem', () => {
   test('non-strings and the empty string price zero', () => {
-    assert.equal(estimateSystem(undefined), 0)
-    assert.equal(estimateSystem(null), 0)
-    assert.equal(estimateSystem(42), 0)
-    assert.equal(estimateSystem(''), 0)
+    assert.equal(estimateSystemTokens(undefined), 0)
+    assert.equal(estimateSystemTokens(null), 0)
+    assert.equal(estimateSystemTokens(42), 0)
+    assert.equal(estimateSystemTokens(''), 0)
   })
 
   test('text prices chars/4 plus role framing', () => {
-    assert.equal(estimateSystem('abcd'), 5)
+    assert.equal(estimateSystemTokens('abcd'), 5)
   })
 })