chore: refactoring and tests (#12468)

3 files changed, 194 insertions, 40 deletions

diff --git a/packages/app/src/components/session/session-context-metrics.test.ts b/packages/app/src/components/session/session-context-metrics.test.ts
new file mode 100644
index 000000000..68903a455
--- /dev/null
+++ b/packages/app/src/components/session/session-context-metrics.test.ts
@@ -0,0 +1,93 @@
+import { describe, expect, test } from "bun:test"
+import type { Message } from "@opencode-ai/sdk/v2/client"
+import { getSessionContextMetrics } from "./session-context-metrics"
+
+const assistant = (
+  id: string,
+  tokens: { input: number; output: number; reasoning: number; read: number; write: number },
+  cost: number,
+  providerID = "openai",
+  modelID = "gpt-4.1",
+) => {
+  return {
+    id,
+    role: "assistant",
+    providerID,
+    modelID,
+    cost,
+    tokens: {
+      input: tokens.input,
+      output: tokens.output,
+      reasoning: tokens.reasoning,
+      cache: {
+        read: tokens.read,
+        write: tokens.write,
+      },
+    },
+    time: { created: 1 },
+  } as unknown as Message
+}
+
+const user = (id: string) => {
+  return {
+    id,
+    role: "user",
+    cost: 0,
+    time: { created: 1 },
+  } as unknown as Message
+}
+
+describe("getSessionContextMetrics", () => {
+  test("computes totals and usage from latest assistant with tokens", () => {
+    const messages = [
+      user("u1"),
+      assistant("a1", { input: 0, output: 0, reasoning: 0, read: 0, write: 0 }, 0.5),
+      assistant("a2", { input: 300, output: 100, reasoning: 50, read: 25, write: 25 }, 1.25),
+    ]
+    const providers = [
+      {
+        id: "openai",
+        name: "OpenAI",
+        models: {
+          "gpt-4.1": {
+            name: "GPT-4.1",
+            limit: { context: 1000 },
+          },
+        },
+      },
+    ]
+
+    const metrics = getSessionContextMetrics(messages, providers)
+
+    expect(metrics.totalCost).toBe(1.75)
+    expect(metrics.context?.message.id).toBe("a2")
+    expect(metrics.context?.total).toBe(500)
+    expect(metrics.context?.usage).toBe(50)
+    expect(metrics.context?.providerLabel).toBe("OpenAI")
+    expect(metrics.context?.modelLabel).toBe("GPT-4.1")
+  })
+
+  test("preserves fallback labels and null usage when model metadata is missing", () => {
+    const messages = [assistant("a1", { input: 40, output: 10, reasoning: 0, read: 0, write: 0 }, 0.1, "p-1", "m-1")]
+    const providers = [{ id: "p-1", models: {} }]
+
+    const metrics = getSessionContextMetrics(messages, providers)
+
+    expect(metrics.context?.providerLabel).toBe("p-1")
+    expect(metrics.context?.modelLabel).toBe("m-1")
+    expect(metrics.context?.limit).toBeUndefined()
+    expect(metrics.context?.usage).toBeNull()
+  })
+
+  test("memoizes by message and provider array identity", () => {
+    const messages = [assistant("a1", { input: 10, output: 10, reasoning: 10, read: 10, write: 10 }, 0.25)]
+    const providers = [{ id: "openai", models: {} }]
+
+    const one = getSessionContextMetrics(messages, providers)
+    const two = getSessionContextMetrics(messages, providers)
+    const three = getSessionContextMetrics([...messages], providers)
+
+    expect(two).toBe(one)
+    expect(three).not.toBe(one)
+  })
+})
diff --git a/packages/app/src/components/session/session-context-metrics.ts b/packages/app/src/components/session/session-context-metrics.ts
new file mode 100644
index 000000000..2b6edbd95
--- /dev/null
+++ b/packages/app/src/components/session/session-context-metrics.ts
@@ -0,0 +1,94 @@
+import type { AssistantMessage, Message } from "@opencode-ai/sdk/v2/client"
+
+type Provider = {
+  id: string
+  name?: string
+  models: Record<string, Model | undefined>
+}
+
+type Model = {
+  name?: string
+  limit: {
+    context: number
+  }
+}
+
+type Context = {
+  message: AssistantMessage
+  provider?: Provider
+  model?: Model
+  providerLabel: string
+  modelLabel: string
+  limit: number | undefined
+  input: number
+  output: number
+  reasoning: number
+  cacheRead: number
+  cacheWrite: number
+  total: number
+  usage: number | null
+}
+
+type Metrics = {
+  totalCost: number
+  context: Context | undefined
+}
+
+const cache = new WeakMap<Message[], WeakMap<Provider[], Metrics>>()
+
+const tokenTotal = (msg: AssistantMessage) => {
+  return msg.tokens.input + msg.tokens.output + msg.tokens.reasoning + msg.tokens.cache.read + msg.tokens.cache.write
+}
+
+const lastAssistantWithTokens = (messages: Message[]) => {
+  for (let i = messages.length - 1; i >= 0; i--) {
+    const msg = messages[i]
+    if (msg.role !== "assistant") continue
+    if (tokenTotal(msg) <= 0) continue
+    return msg
+  }
+}
+
+const build = (messages: Message[], providers: Provider[]): Metrics => {
+  const totalCost = messages.reduce((sum, msg) => sum + (msg.role === "assistant" ? msg.cost : 0), 0)
+  const message = lastAssistantWithTokens(messages)
+  if (!message) return { totalCost, context: undefined }
+
+  const provider = providers.find((item) => item.id === message.providerID)
+  const model = provider?.models[message.modelID]
+  const limit = model?.limit.context
+  const total = tokenTotal(message)
+
+  return {
+    totalCost,
+    context: {
+      message,
+      provider,
+      model,
+      providerLabel: provider?.name ?? message.providerID,
+      modelLabel: model?.name ?? message.modelID,
+      limit,
+      input: message.tokens.input,
+      output: message.tokens.output,
+      reasoning: message.tokens.reasoning,
+      cacheRead: message.tokens.cache.read,
+      cacheWrite: message.tokens.cache.write,
+      total,
+      usage: limit ? Math.round((total / limit) * 100) : null,
+    },
+  }
+}
+
+export function getSessionContextMetrics(messages: Message[], providers: Provider[]) {
+  const byProvider = cache.get(messages)
+  if (byProvider) {
+    const hit = byProvider.get(providers)
+    if (hit) return hit
+  }
+
+  const value = build(messages, providers)
+  const next = byProvider ?? new WeakMap<Provider[], Metrics>()
+  next.set(providers, value)
+  if (!byProvider) cache.set(messages, next)
+  return value
+}
diff --git a/packages/app/src/components/session/session-context-tab.tsx b/packages/app/src/components/session/session-context-tab.tsx
index 37733caff..8aae44863 100644
--- a/packages/app/src/components/session/session-context-tab.tsx
+++ b/packages/app/src/components/session/session-context-tab.tsx
@@ -11,8 +11,9 @@ import { Accordion } from "@opencode-ai/ui/accordion"
 import { StickyAccordionHeader } from "@opencode-ai/ui/sticky-accordion-header"
 import { Code } from "@opencode-ai/ui/code"
 import { Markdown } from "@opencode-ai/ui/markdown"
-import type { AssistantMessage, Message, Part, UserMessage } from "@opencode-ai/sdk/v2/client"
+import type { Message, Part, UserMessage } from "@opencode-ai/sdk/v2/client"
 import { useLanguage } from "@/context/language"
+import { getSessionContextMetrics } from "./session-context-metrics"
 
 interface SessionContextTabProps {
   messages: () => Message[]
@@ -34,44 +35,11 @@ export function SessionContextTab(props: SessionContextTabProps) {
       }),
   )
 
-  const ctx = createMemo(() => {
-    const last = findLast(props.messages(), (x) => {
-      if (x.role !== "assistant") return false
-      const total = x.tokens.input + x.tokens.output + x.tokens.reasoning + x.tokens.cache.read + x.tokens.cache.write
-      return total > 0
-    }) as AssistantMessage
-    if (!last) return
-
-    const provider = sync.data.provider.all.find((x) => x.id === last.providerID)
-    const model = provider?.models[last.modelID]
-    const limit = model?.limit.context
-
-    const input = last.tokens.input
-    const output = last.tokens.output
-    const reasoning = last.tokens.reasoning
-    const cacheRead = last.tokens.cache.read
-    const cacheWrite = last.tokens.cache.write
-    const total = input + output + reasoning + cacheRead + cacheWrite
-    const usage = limit ? Math.round((total / limit) * 100) : null
-
-    return {
-      message: last,
-      provider,
-      model,
-      limit,
-      input,
-      output,
-      reasoning,
-      cacheRead,
-      cacheWrite,
-      total,
-      usage,
-    }
-  })
+  const metrics = createMemo(() => getSessionContextMetrics(props.messages(), sync.data.provider.all))
+  const ctx = createMemo(() => metrics().context)
 
   const cost = createMemo(() => {
-    const total = props.messages().reduce((sum, x) => sum + (x.role === "assistant" ? x.cost : 0), 0)
-    return usd().format(total)
+    return usd().format(metrics().totalCost)
   })
 
   const counts = createMemo(() => {
@@ -114,14 +82,13 @@ export function SessionContextTab(props: SessionContextTabProps) {
   const providerLabel = createMemo(() => {
     const c = ctx()
     if (!c) return "—"
-    return c.provider?.name ?? c.message.providerID
+    return c.providerLabel
   })
 
   const modelLabel = createMemo(() => {
     const c = ctx()
     if (!c) return "—"
-    if (c.model?.name) return c.model.name
-    return c.message.modelID
+    return c.modelLabel
   })
 
   const breakdown = createMemo(