refactor(core): retire context_budget_exhausted at the decode boundary

Nothing has produced this outcome since the runtime stopped issuing local
termination verdicts: whether a request fits is the provider's answer, and a
rejection is recovered from by compacting and retrying. What remained was a
read-only chain nine files long — a `CompleteEvent.stopReason` member no backend
can emit, a six-value detail enum with no writer, its predicate, the mapper's
stateDelta pass-through, the Host protocol allowlist and decoder, the canonical
snapshot field, the session projector's `details`, and two desktop presentation
branches with their locale copy.

Old sessions still carry the name, so the durable ledger's own read boundary
folds it to `context_overflow` — the outcome every downstream consumer already
treated it as. That is the only place that now knows two names for it.

The summarizer's malformed-summary taxonomy, which derived its type from the
retired enum, was already moved into the history-compaction domain.

The host fixture's provider stub now reports input tokens that grow with the
request. Its flat 11 made the anchored turn-start estimate meaningless, which is
exactly the number that test's compaction assertions depend on.

Author: Astro-Han

apps/desktop/src/main/__tests__/session-error-presentation.test.ts

@@ -37,20 +37,3 @@ describe('provider capacity presentation', () => {
   });
 });
 
-describe('context compaction failure presentation', () => {
-  it('shows actionable malformed-summary guidance', () => {
-    const message = sessionEventErrorMessage({
-      type: 'error',
-      id: 'error-1',
-      turnId: 'turn-1',
-      ts: 1,
-      recoverable: false,
-      reason: 'context_budget_exhausted',
-      message: 'Turn failed: context_budget_exhausted',
-      details: { contextBudgetExhaustedDetail: 'malformed_summary_missing_section' },
-    });
-
-    assert.match(message, /上下文压缩/);
-    assert.match(message, /上下文窗口设置|切换模型|开启新任务/);
-  });
-});

apps/desktop/src/renderer/locales/conversation-copy.ts

@@ -342,8 +342,6 @@ export interface DesktopConversationCopy {
   turnError: {
     unknown: string;
     contextOverflow: string;
-    contextBudgetExhausted: string;
-    malformedSummary: string;
     timeout: string;
     auth: string;
     providerBilling: string;
@@ -658,7 +656,7 @@ const COPY = {
       reauth: { label: '上次连接测试鉴权失败', tooltip: '最近一次连接测试返回鉴权失败（401 / 403），密钥可能已过期或被吊销。这不会拦截发送，但若发送失败请到 设置 · 模型 重新登录。' },
       testError: { label: '上次连接测试失败', tooltip: '最近一次连接测试因网络 / 超时 / 5xx 失败。这不会拦截发送，但若问题持续请到 设置 · 模型 检查 Base URL / 代理。' },
     },
-    turnError: { unknown: '出错了，原因不明。重新发消息重试。', contextOverflow: '上下文超出模型窗口限制，减少附件或开启新任务。', contextBudgetExhausted: '上下文已达上限，这个任务无法继续。换模型或开启新任务。', malformedSummary: '上下文压缩未能生成有效摘要。请检查模型的上下文窗口设置、切换模型，或开启新任务。', timeout: '模型请求超时，重新发消息重试。', auth: '模型鉴权失败，请到设置里重新连接或登录。', providerBilling: '模型服务计费受限，请检查账号余额或订阅状态。', providerCapacity: '模型服务暂时满载，等几分钟重试，或换一个模型。', rateLimit: '模型请求太频繁被限流了，等一会儿再发消息重试。', network: '网络连接失败，检查网络后重新发消息。', provider: '模型服务返回错误，稍后重试或换一个模型。', stepCap: '达到工具调用步数上限，任务可能没做完。发消息让它继续。', tool: '工具调用失败，看一下上面的工具结果再决定要不要重试。', permission: '这一轮在等权限确认时结束了，重新发消息会再问一次。', restarted: '本地应用重启，上一轮没有完成', sandboxBoundaryClosed: '本地应用重启时，等待确认的「允许访问工作区以外的内容」请求已按拒绝关闭。重新发消息可以再决定一次。', executionState: { erroredTool: '这一轮有工具执行出错，先看它的结果，再决定要不要重发。', toolRan: '这一轮已经执行过工具，可能已经产生实际改动，重发前先看工具结果。', partialOutput: '这一轮已经产生了部分回答，重发前可以先看看。' } },
+    turnError: { unknown: '出错了，原因不明。重新发消息重试。', contextOverflow: '上下文超出模型窗口限制，减少附件或开启新任务。', timeout: '模型请求超时，重新发消息重试。', auth: '模型鉴权失败，请到设置里重新连接或登录。', providerBilling: '模型服务计费受限，请检查账号余额或订阅状态。', providerCapacity: '模型服务暂时满载，等几分钟重试，或换一个模型。', rateLimit: '模型请求太频繁被限流了，等一会儿再发消息重试。', network: '网络连接失败，检查网络后重新发消息。', provider: '模型服务返回错误，稍后重试或换一个模型。', stepCap: '达到工具调用步数上限，任务可能没做完。发消息让它继续。', tool: '工具调用失败，看一下上面的工具结果再决定要不要重试。', permission: '这一轮在等权限确认时结束了，重新发消息会再问一次。', restarted: '本地应用重启，上一轮没有完成', sandboxBoundaryClosed: '本地应用重启时，等待确认的「允许访问工作区以外的内容」请求已按拒绝关闭。重新发消息可以再决定一次。', executionState: { erroredTool: '这一轮有工具执行出错，先看它的结果，再决定要不要重发。', toolRan: '这一轮已经执行过工具，可能已经产生实际改动，重发前先看工具结果。', partialOutput: '这一轮已经产生了部分回答，重发前可以先看看。' } },
   },
   en: {
     actions: { stopFailedTitle: 'Failed to stop', stopFailedFallback: 'The task action failed. Try again later.', refreshSessionsFailedTitle: 'Failed to refresh tasks', refreshSessionsFailedFallback: 'The task list could not be refreshed. Try again later.', conversationErrorTitle: 'Task error', conversationErrorFallback: 'The task run failed. Try again later.', regenerateStartedTitle: 'Regeneration started', regenerateStartedDescription: 'Generating a new response', branchCreatedTitle: 'Branch created', branchCreatedDescription: (name) => `New task: ${name}`, revisionStartedTitle: 'Edit draft ready', revisionStartedDescription: 'The original task is kept; sending creates a new version', revisionReadyTitle: 'Ready to edit and resend', revisionReadyDescription: 'Rewound to before that message; edit and send when ready', revisionUnavailableTitle: 'This message cannot be edited yet', revisionAttachmentsUnsupported: 'Edit & resend does not yet support historical attachments. Copy the text into a new message instead.', revisionTransformedTextUnsupported: 'Edit & resend does not yet support messages sent with an explicit skill. Copy the text and select the skill again instead.', revisionDraftAttachmentConflict: 'The composer already has pending attachments. Send or remove them before editing a sent message.', revisionCommandUnsupported: 'You cannot run /compact, /side, or orchestration commands while editing a sent message. Cancel the edit first.', revisionAlreadyActive: 'Another message is already being edited. Send or cancel that edit first.', revisionCancelLabel: 'Cancel', revisionBannerTitle: 'Editing sent message', revisionBannerDetail: '· New version on send', revisionUnchanged: 'Nothing changed. Use Regenerate if you only want a new answer.', operationFailedTitle: 'Action failed', operationFailedFallback: 'The task action failed. Try again later.', attachmentFailedTitle: 'Failed to add attachment', imageAttachmentNotDirectTitle: 'Image added as an attachment', imageAttachmentNotDirectDescription: 'The current model does not receive images directly. The image has been provided as an attachment.', tryAgain: 'Try again later.', modelReboundTitle: 'Switched to an available model', modelReboundDescription: (modelId) => `The previous connection is unavailable${modelId ? ` · ${modelId}` : ''}`, messageReadFailedTitle: 'Failed to load task', partialHistoryTitle: 'Viewing earlier messages', returnLatest: 'Return to latest', scrollMainToBottom: 'Scroll main conversation to bottom' },
@@ -894,7 +892,7 @@ const COPY = {
       reauth: { label: 'Last connection test failed authentication', tooltip: 'The latest test returned 401 / 403. Sending is not blocked, but sign in again under Settings · Models if it fails.' },
       testError: { label: 'Last connection test failed', tooltip: 'The latest test failed because of a network, timeout, or 5xx error. Sending is not blocked; check Base URL or proxy settings if it persists.' },
     },
-    turnError: { unknown: 'Something went wrong, cause unknown. Send a message to retry.', contextOverflow: 'Context exceeded the model window. Reduce attachments or start a new task.', contextBudgetExhausted: 'The context limit was reached and this task cannot continue. Switch models or start a new task.', malformedSummary: 'Context compaction could not produce a valid summary. Check the model context-window setting, switch models, or start a new task.', timeout: 'The model request timed out. Send a message to retry.', auth: 'Model authentication failed. Reconnect or sign in again from Settings.', providerBilling: 'Model billing is restricted. Check the account balance or subscription.', providerCapacity: 'The model service is temporarily at capacity. Wait a few minutes, or switch models.', rateLimit: 'Requests were rate-limited. Wait a moment, then send a message to retry.', network: 'The network connection failed. Check the network, then send a message again.', provider: 'The model service returned an error. Retry later, or switch models.', stepCap: 'The tool-step limit was reached, so the task may be incomplete. Send a message to continue.', tool: 'A tool call failed. Check the tool result above before deciding whether to retry.', permission: 'This turn ended while waiting for permission. Send a message and it will ask again.', restarted: 'The app restarted before the previous turn completed', sandboxBoundaryClosed: 'The app restarted, so the pending request to reach outside the workspace was closed as denied. Send a message to decide again.', executionState: { erroredTool: 'A tool errored during this turn. Read its result before deciding whether to send another message.', toolRan: 'Tools already ran during this turn and may have made real changes. Read their results before sending another message.', partialOutput: 'This turn produced part of an answer. Worth reading before you send another message.' } },
+    turnError: { unknown: 'Something went wrong, cause unknown. Send a message to retry.', contextOverflow: 'Context exceeded the model window. Reduce attachments or start a new task.', timeout: 'The model request timed out. Send a message to retry.', auth: 'Model authentication failed. Reconnect or sign in again from Settings.', providerBilling: 'Model billing is restricted. Check the account balance or subscription.', providerCapacity: 'The model service is temporarily at capacity. Wait a few minutes, or switch models.', rateLimit: 'Requests were rate-limited. Wait a moment, then send a message to retry.', network: 'The network connection failed. Check the network, then send a message again.', provider: 'The model service returned an error. Retry later, or switch models.', stepCap: 'The tool-step limit was reached, so the task may be incomplete. Send a message to continue.', tool: 'A tool call failed. Check the tool result above before deciding whether to retry.', permission: 'This turn ended while waiting for permission. Send a message and it will ask again.', restarted: 'The app restarted before the previous turn completed', sandboxBoundaryClosed: 'The app restarted, so the pending request to reach outside the workspace was closed as denied. Send a message to decide again.', executionState: { erroredTool: 'A tool errored during this turn. Read its result before deciding whether to send another message.', toolRan: 'Tools already ran during this turn and may have made real changes. Read their results before sending another message.', partialOutput: 'This turn produced part of an answer. Worth reading before you send another message.' } },
   },
 } satisfies UiCatalog<DesktopConversationCopy>;
 

apps/desktop/src/renderer/model-connection-errors.ts

@@ -60,13 +60,6 @@ export function sessionEventErrorMessage(
   if (isNoRealConnectionEvent(event)) {
     return noRealConnectionSetupDescription(noRealConnectionReasonFromEvent(event), locale);
   }
-  const contextBudgetDetail =
-    event.details && !Array.isArray(event.details)
-      ? event.details.contextBudgetExhaustedDetail
-      : undefined;
-  if (typeof contextBudgetDetail === 'string' && contextBudgetDetail.startsWith('malformed_summary_')) {
-    return getDesktopConversationCopy(locale).turnError.malformedSummary;
-  }
   const reasonDescription = describeSessionErrorReason(event.reason, locale);
   if (reasonDescription) return reasonDescription;
   const fallback = getDesktopConversationCopy(locale).actions.conversationErrorFallback;

apps/desktop/src/renderer/session-error-presentation.ts

@@ -30,8 +30,6 @@ export function describeSessionErrorReason(reason: string | undefined, locale: U
   switch (reason?.toLowerCase()) {
     case 'context_overflow':
       return copy.contextOverflow;
-    case 'context_budget_exhausted':
-      return copy.contextBudgetExhausted;
     case 'timeout':
       return copy.timeout;
     case 'model_after_tool_timeout':

packages/cli/src/__tests__/runtime-host-run-command.test.ts

@@ -500,15 +500,6 @@ describe('Runtime Host maka run adapter', () => {
     assert.equal(durable.failure?.class, 'tool_step_cap_reached');
   });
 
-  test('classifies a standalone context-budget completion as failed', async () => {
-    const outcome = await observeFixtureOutcome({
-      turnEvents: completionEvents('turn-1', 'context_budget_exhausted'),
-    });
-
-    assert.equal(outcome.status, 'failed');
-    assert.equal(outcome.failure?.class, 'context_budget_exhausted');
-  });
-
   test('uses the latest durable terminal state for a Graph Turn', async () => {
     const outcome = await observeFixtureOutcome({
       graph: true,

packages/core/src/events.ts

@@ -1247,14 +1247,7 @@ export interface CompleteEvent extends BaseEvent {
     | 'graph_yield'
     | 'permission_handoff'
     | 'step_limit'
-    | 'max_tokens'
-    | 'context_budget_exhausted';
-  /**
-   * Detail for `stopReason: 'context_budget_exhausted'` — the runtime could not
-   * produce a provider-safe request even after mid-turn compaction. A first-class
-   * outcome, not a provider context-length error.
-   */
-  contextBudgetExhaustedDetail?: ContextBudgetExhaustedDetail;
+    | 'max_tokens';
   /** Durable result of an explicit context-compaction execution. */
   contextCompactionOutcome?: ContextCompactionOutcome;
 }
@@ -1264,32 +1257,14 @@ export type ContextCompactionOutcome =
   | { kind: 'unchanged'; reason: string }
   | { kind: 'failed'; reason: string };
 
-export const CONTEXT_BUDGET_EXHAUSTED_DETAILS = [
-  'no_safe_completed_span',
-  'summarizer_failed',
-  'malformed_summary_missing_section',
-  'malformed_summary_truncated',
-  'malformed_summary_too_small_for_fold',
-  'head_anchor_exceeds_capacity',
-] as const;
-
-export type ContextBudgetExhaustedDetail = (typeof CONTEXT_BUDGET_EXHAUSTED_DETAILS)[number];
-
-export function isContextBudgetExhaustedDetail(
-  value: unknown,
-): value is ContextBudgetExhaustedDetail {
-  return CONTEXT_BUDGET_EXHAUSTED_DETAILS.includes(value as ContextBudgetExhaustedDetail);
-}
-
 export type CompleteStopReason = CompleteEvent['stopReason'];
 
 /** Stable failure taxonomy for complete events that did not finish the turn. */
 export function failureClassFromCompleteStopReason(
   reason: CompleteStopReason,
-): 'runtime_error' | 'tool_step_cap_reached' | 'context_budget_exhausted' | undefined {
+): 'runtime_error' | 'tool_step_cap_reached' | undefined {
   if (reason === 'error') return 'runtime_error';
   if (reason === 'step_limit') return 'tool_step_cap_reached';
-  if (reason === 'context_budget_exhausted') return 'context_budget_exhausted';
   return undefined;
 }
 

packages/runtime-host/src/__tests__/canonical-session-projection.test.ts

@@ -335,12 +335,6 @@ test('preflights the worst-case failed Turn before accepting more queued content
     );
     const worstCaseFailedTurn = worstCaseFailedTurnSnapshot(capacityCanonical.rootTurn!);
     assert.equal(worstCaseFailedTurn.status, 'failed');
-    if (worstCaseFailedTurn.status === 'failed') {
-      assert.equal(
-        worstCaseFailedTurn.contextBudgetExhaustedDetail,
-        'malformed_summary_too_small_for_fold',
-      );
-    }
     assert.throws(() =>
       createSessionContinuitySnapshot(
         {
@@ -429,7 +423,7 @@ test('projects a failed Turn message from the canonical terminal event', async (
   });
 });
 
-test('projects context-budget exhaustion detail from the canonical terminal event', async () => {
+test('a legacy context_budget_exhausted terminal event still projects, as a context overflow', async () => {
   await withStores(async (root, stores) => {
     const { sessionId, rootAdmissions } = await createRunningRoot(root, stores);
     const context = {
@@ -450,18 +444,30 @@ test('projects context-budget exhaustion detail from the canonical terminal even
       newId: () => 'unused',
       now: () => 12,
     } as const;
-    const terminalEvent = mapSessionEventToRuntimeEvent(
+    // Exactly what a session written before this outcome was retired holds: the
+    // runtime can no longer emit it, so the durable shape is rebuilt here.
+    const mapped = mapSessionEventToRuntimeEvent(
       {
         type: 'complete',
         id: 'terminal-context-budget-1',
         turnId: 'turn-1',
         ts: 13,
-        stopReason: 'context_budget_exhausted',
-        contextBudgetExhaustedDetail: 'malformed_summary_missing_section',
+        stopReason: 'error',
       },
       context,
       createSessionEventMapMemory(),
     );
+    const terminalEvent = {
+      ...mapped,
+      actions: {
+        ...mapped.actions,
+        stateDelta: {
+          stopReason: 'context_budget_exhausted',
+          failureClass: 'context_budget_exhausted',
+          contextBudgetExhaustedDetail: 'malformed_summary_missing_section',
+        },
+      },
+    };
     await stores.runtimeEventStore.appendRuntimeEvent(sessionId, 'run-1', terminalEvent);
     await stores.agentRunStore.updateRun(sessionId, 'run-1', {
       status: 'failed',
@@ -480,10 +486,7 @@ test('projects context-budget exhaustion detail from the canonical terminal even
     const canonical = await reader.read(sessionId);
     assert.equal(canonical?.rootTurn?.status, 'failed');
     if (canonical?.rootTurn?.status === 'failed') {
-      assert.equal(
-        canonical.rootTurn.contextBudgetExhaustedDetail,
-        'malformed_summary_missing_section',
-      );
+      assert.equal(canonical.rootTurn.failureClass, 'context_overflow');
     }
   });
 });