fix: use provider context windows for transcript estimates

Desktop chat can fall back to persisted transcript estimates when live inspection context is unavailable. That path previously only used built-in model windows, so custom provider settings such as MiniMax-M3 with a 1,000,000-token window still displayed the default 200,000-token estimate. Resolve transcript context windows from the session or active provider runtime env first, then fall back to built-ins.

Constraint: Provider model context windows are stored in provider runtime env, not always in the server process env.
Rejected: Change the built-in MiniMax-M3 window to 1,000,000 | upstream preset correctly keeps MiniMax-M3 at 204,800 by default, while user overrides must remain provider-specific.
Confidence: high
Scope-risk: moderate
Directive: Keep transcript estimates aligned with session/provider runtime env before consulting built-in model defaults.
Tested: git diff --check
Tested: bun test src/server/__tests__/conversations.test.ts --test-name-pattern "active provider model context windows|Sonnet 4.6 transcript usage|low-trust media"
Tested: bun test src/server/__tests__/provider-presets.test.ts src/server/__tests__/provider-runtime-env.test.ts src/server/__tests__/providers.test.ts src/utils/__tests__/context.test.ts src/utils/__tests__/contextBudget.test.ts
Tested: bun test src/server/__tests__/conversations.test.ts src/server/__tests__/conversation-service.test.ts src/server/__tests__/providers.test.ts src/server/__tests__/provider-presets.test.ts src/server/__tests__/provider-runtime-env.test.ts src/utils/__tests__/context.test.ts src/utils/__tests__/contextBudget.test.ts
Not-tested: bun run check:server blocked before execution by expired quarantine entries: server:cron-scheduler, server:providers-real, server:tasks, server:e2e:business-flow, server:e2e:full-flow

src/server/__tests__/conversations.test.ts

@@ -530,6 +530,84 @@ describe('ConversationService', () => {
     }
   })
 
+  it('should use active provider model context windows for transcript estimates', async () => {
+    const previousConfigDir = process.env.CLAUDE_CONFIG_DIR
+    const previousNodeEnv = process.env.NODE_ENV
+    const previousModelContextWindows = process.env.CLAUDE_CODE_MODEL_CONTEXT_WINDOWS
+    const tmpConfigDir = await fs.mkdtemp(path.join(os.tmpdir(), 'claude-transcript-provider-'))
+    const workDir = await fs.mkdtemp(path.join(os.tmpdir(), 'claude-workdir-provider-'))
+    process.env.CLAUDE_CONFIG_DIR = tmpConfigDir
+    process.env.NODE_ENV = 'development'
+    delete process.env.CLAUDE_CODE_MODEL_CONTEXT_WINDOWS
+
+    try {
+      const providerService = new ProviderService()
+      const provider = await providerService.addProvider({
+        presetId: 'minimax',
+        name: 'MiniMax',
+        apiKey: 'provider-key',
+        authStrategy: 'auth_token',
+        baseUrl: 'https://api.minimaxi.com/anthropic',
+        apiFormat: 'anthropic',
+        models: {
+          main: 'MiniMax-M3',
+          haiku: 'MiniMax-M3',
+          sonnet: 'MiniMax-M3',
+          opus: 'MiniMax-M3',
+        },
+        modelContextWindows: {
+          'MiniMax-M3': 1_000_000,
+        },
+      })
+      await providerService.activateProvider(provider.id)
+
+      const svc = new SessionService()
+      const { sessionId } = await svc.createSession(workDir)
+      const found = await svc.findSessionFile(sessionId)
+      expect(found).not.toBeNull()
+
+      await fs.appendFile(found!.filePath, JSON.stringify({
+        type: 'assistant',
+        uuid: crypto.randomUUID(),
+        timestamp: '2026-04-27T12:00:00.000Z',
+        cwd: workDir,
+        version: '999.0.0-test',
+        message: {
+          role: 'assistant',
+          model: 'MiniMax-M3',
+          content: [{ type: 'text', text: 'hello' }],
+          usage: {
+            input_tokens: 100,
+            output_tokens: 20,
+          },
+        },
+      }) + '\n')
+
+      const contextEstimate = await svc.getTranscriptContextEstimate(sessionId)
+
+      expect(contextEstimate?.model).toBe('MiniMax-M3')
+      expect(contextEstimate?.rawMaxTokens).toBe(1_000_000)
+    } finally {
+      if (previousConfigDir === undefined) {
+        delete process.env.CLAUDE_CONFIG_DIR
+      } else {
+        process.env.CLAUDE_CONFIG_DIR = previousConfigDir
+      }
+      if (previousNodeEnv === undefined) {
+        delete process.env.NODE_ENV
+      } else {
+        process.env.NODE_ENV = previousNodeEnv
+      }
+      if (previousModelContextWindows === undefined) {
+        delete process.env.CLAUDE_CODE_MODEL_CONTEXT_WINDOWS
+      } else {
+        process.env.CLAUDE_CODE_MODEL_CONTEXT_WINDOWS = previousModelContextWindows
+      }
+      await fs.rm(tmpConfigDir, { recursive: true, force: true })
+      await fs.rm(workDir, { recursive: true, force: true })
+    }
+  })
+
   it('should not report transcript context as full for low-trust media usage spikes', async () => {
     const previousConfigDir = process.env.CLAUDE_CONFIG_DIR
     const previousNodeEnv = process.env.NODE_ENV

src/server/services/sessionService.ts

@@ -19,7 +19,12 @@ import {
   MODEL_CONTEXT_WINDOW_DEFAULT,
   getContextWindowForModel,
   getModelMaxOutputTokens,
+  is1mContextDisabled,
 } from '../../utils/context.js'
+import {
+  MODEL_CONTEXT_WINDOWS_ENV_KEY,
+  getModelContextWindowFromEnvValue,
+} from '../../utils/model/modelContextWindows.js'
 import {
   calculateContextBudget,
   getProviderUsageTrust,
@@ -36,6 +41,7 @@ import { registerFilesystemAccessRoot } from './filesystemAccessRoots.js'
 import { normalizeDriveRootPathForPlatform } from './windowsDrivePath.js'
 import { cleanSessionTitleSource } from '../../utils/sessionTitleText.js'
 import { roughTokenCountEstimationForMessages } from '../../services/tokenEstimation.js'
+import { ProviderService } from './providerService.js'
 
 // ============================================================================
 // Types
@@ -269,6 +275,8 @@ const TASK_NOTIFICATION_BLOCK_RE = /<task-notification>\s*[\s\S]*?<\/task-notifi
 // ============================================================================
 
 export class SessionService {
+  private providerService = new ProviderService()
+
   private readonly sessionListCacheTtlMs = 5_000
   private readonly sessionListCache = new Map<string, {
     expiresAt: number
@@ -1288,7 +1296,43 @@ export class SessionService {
     return `$${cost > 0.5 ? (Math.round(cost * 100) / 100).toFixed(2) : cost.toFixed(4)}`
   }
 
-  private getTranscriptContextWindow(model: string): number {
+  private async getProviderContextWindowForSession(
+    sessionId: string,
+    model: string,
+  ): Promise<number | undefined> {
+    const launchInfo = await this.getSessionLaunchInfo(sessionId).catch(() => null)
+    const providerIds: string[] = []
+
+    if (typeof launchInfo?.runtimeProviderId === 'string') {
+      providerIds.push(launchInfo.runtimeProviderId)
+    } else if (launchInfo?.runtimeProviderId !== null) {
+      const { activeId } = await this.providerService.listProviders().catch(() => ({ activeId: null }))
+      if (activeId) providerIds.push(activeId)
+    }
+
+    for (const providerId of providerIds) {
+      const env = await this.providerService.getProviderRuntimeEnv(providerId).catch(() => null)
+      const contextWindow = getModelContextWindowFromEnvValue(
+        model,
+        env?.[MODEL_CONTEXT_WINDOWS_ENV_KEY],
+      )
+      if (contextWindow !== undefined) {
+        if (contextWindow > MODEL_CONTEXT_WINDOW_DEFAULT && is1mContextDisabled()) {
+          return MODEL_CONTEXT_WINDOW_DEFAULT
+        }
+        return contextWindow
+      }
+    }
+
+    return undefined
+  }
+
+  private async getTranscriptContextWindow(sessionId: string, model: string): Promise<number> {
+    const providerContextWindow = await this.getProviderContextWindowForSession(sessionId, model)
+    if (providerContextWindow !== undefined) {
+      return providerContextWindow
+    }
+
     try {
       return getContextWindowForModel(model)
     } catch (err) {
@@ -1362,7 +1406,7 @@ export class SessionService {
 
     if (!latest) return null
 
-    const rawMaxTokens = this.getTranscriptContextWindow(latest.model)
+    const rawMaxTokens = await this.getTranscriptContextWindow(sessionId, latest.model)
     const promptTokens = latest.inputTokens + latest.cacheReadInputTokens + latest.cacheCreationInputTokens
     const transcriptMessages = entries.filter(entry =>
       entry.type === 'user' || entry.type === 'assistant' || entry.type === 'attachment',
@@ -1502,7 +1546,7 @@ export class SessionService {
           webSearchRequests: 0,
           costUSD: 0,
           costDisplay: '$0.0000',
-          contextWindow: this.getTranscriptContextWindow(model),
+          contextWindow: await this.getTranscriptContextWindow(sessionId, model),
           maxOutputTokens: getModelMaxOutputTokens(model).default,
         }
         models.set(model, modelUsage)

src/utils/model/modelContextWindows.ts

@@ -61,33 +61,25 @@ function normalizeWindow(value: unknown): number | undefined {
   return value
 }
 
-function parseConfiguredContextWindows(): Record<string, number> {
-  const raw = process.env[MODEL_CONTEXT_WINDOWS_ENV_KEY]
-  if (!raw?.trim()) {
+function normalizeConfiguredContextWindows(parsed: unknown): Record<string, number> {
+  if (!parsed || typeof parsed !== 'object' || Array.isArray(parsed)) {
     return {}
   }
 
-  try {
-    const parsed = JSON.parse(raw) as Record<string, unknown>
-    if (!parsed || typeof parsed !== 'object' || Array.isArray(parsed)) {
-      return {}
+  const windows: Record<string, number> = {}
+  for (const [model, value] of Object.entries(parsed)) {
+    const normalized = normalizeWindow(value)
+    if (normalized !== undefined) {
+      windows[normalizeModelContextKey(model)] = normalized
     }
-
-    const windows: Record<string, number> = {}
-    for (const [model, value] of Object.entries(parsed)) {
-      const normalized = normalizeWindow(value)
-      if (normalized !== undefined) {
-        windows[normalizeModelContextKey(model)] = normalized
-      }
-    }
-    return windows
-  } catch {
-    return {}
   }
+  return windows
 }
 
-function getConfiguredModelContextWindow(model: string): number | undefined {
-  const configured = parseConfiguredContextWindows()
+function findConfiguredModelContextWindow(
+  model: string,
+  configured: Record<string, number>,
+): number | undefined {
   const normalizedModel = normalizeModelContextKey(model)
   const exact = configured[normalizedModel]
   if (exact !== undefined) {
@@ -105,6 +97,42 @@ function getConfiguredModelContextWindow(model: string): number | undefined {
   return undefined
 }
 
+export function getModelContextWindowFromEnvValue(
+  model: string,
+  raw: string | undefined,
+): number | undefined {
+  if (!raw?.trim()) {
+    return undefined
+  }
+
+  try {
+    const parsed = JSON.parse(raw) as Record<string, unknown>
+    return findConfiguredModelContextWindow(
+      model,
+      normalizeConfiguredContextWindows(parsed),
+    )
+  } catch {
+    return undefined
+  }
+}
+
+function parseConfiguredContextWindows(): Record<string, number> {
+  const raw = process.env[MODEL_CONTEXT_WINDOWS_ENV_KEY]
+  if (!raw?.trim()) {
+    return {}
+  }
+
+  try {
+    return normalizeConfiguredContextWindows(JSON.parse(raw) as Record<string, unknown>)
+  } catch {
+    return {}
+  }
+}
+
+function getConfiguredModelContextWindow(model: string): number | undefined {
+  return findConfiguredModelContextWindow(model, parseConfiguredContextWindows())
+}
+
 function getBuiltInModelContextWindow(model: string): number | undefined {
   const normalizedModel = normalizeModelContextKey(model)
   const exact = DIRECT_MODEL_CONTEXT_WINDOWS[normalizedModel]