fix: warn on claude-code prompt caching during setup

packages/cli/src/claude-code-prompt-caching.ts

@@ -0,0 +1,28 @@
+import type { KtxProjectLlmConfig } from '@ktx/context/project';
+
+const CLAUDE_CODE_IGNORED_PROMPT_CACHING_FIELDS = [
+  'systemTtl',
+  'toolsTtl',
+  'historyTtl',
+  'vertexFallbackTo5m',
+] as const;
+
+export function ignoredClaudeCodePromptCachingFields(config: KtxProjectLlmConfig): string[] {
+  if (config.provider.backend !== 'claude-code' || !config.promptCaching) {
+    return [];
+  }
+  return CLAUDE_CODE_IGNORED_PROMPT_CACHING_FIELDS.filter((key) => key in config.promptCaching).map(
+    (key) => `llm.promptCaching.${key}`,
+  );
+}
+
+export function formatClaudeCodePromptCachingWarning(fields: string[]): string | null {
+  if (fields.length === 0) {
+    return null;
+  }
+  return `claude-code ignores ${fields.join(', ')} because the Claude Agent SDK does not expose KTX prompt-cache TTL, tool, or history markers.`;
+}
+
+export function formatClaudeCodePromptCachingFix(): string {
+  return 'Remove those promptCaching fields or use anthropic, vertex, or gateway when those cache knobs are required.';
+}

packages/cli/src/setup-models.test.ts

@@ -209,6 +209,44 @@ describe('setup Anthropic model step', () => {
     expect(authProbe).toHaveBeenCalledWith(expect.objectContaining({ projectDir: tempDir, model: 'sonnet' }));
   });
 
+  it('warns during Claude Code setup when existing prompt-caching fields will be ignored', async () => {
+    await writeFile(
+      join(tempDir, 'ktx.yaml'),
+      [
+        'llm:',
+        '  provider:',
+        '    backend: anthropic',
+        '  models:',
+        '    default: claude-sonnet-4-6',
+        '  promptCaching:',
+        '    enabled: true',
+        '    systemTtl: 1h',
+        '    toolsTtl: 1h',
+        '    historyTtl: 5m',
+        '',
+      ].join('\n'),
+      'utf-8',
+    );
+    const io = makeIo();
+
+    const result = await runKtxSetupAnthropicModelStep(
+      {
+        projectDir: tempDir,
+        inputMode: 'disabled',
+        llmBackend: 'claude-code',
+        skipLlm: false,
+      },
+      io.io,
+      {
+        claudeCodeAuthProbe: async () => ({ ok: true as const }),
+      },
+    );
+
+    expect(result.status).toBe('ready');
+    expect(io.stderr()).toContain('claude-code ignores llm.promptCaching.systemTtl');
+    expect(io.stderr()).toContain('Claude Agent SDK does not expose KTX prompt-cache TTL, tool, or history markers');
+  });
+
   it('returns from Anthropic credential Back to provider selection', async () => {
     const prompts = makePromptAdapter({ selectValues: ['anthropic', 'back', 'back'] });
 

packages/cli/src/setup-models.ts

@@ -11,6 +11,10 @@ import {
   serializeKtxProjectConfig,
 } from '@ktx/context/project';
 import { type KtxLlmConfig, type KtxLlmHealthCheckResult, runKtxLlmHealthCheck } from '@ktx/llm';
+import {
+  formatClaudeCodePromptCachingWarning,
+  ignoredClaudeCodePromptCachingFields,
+} from './claude-code-prompt-caching.js';
 import { createClackSpinner, type KtxCliSpinner } from './clack.js';
 import type { KtxCliIo } from './cli-runtime.js';
 import { withTextInputNavigation } from './prompt-navigation.js';
@@ -946,6 +950,14 @@ export async function runKtxSetupAnthropicModelStep(
         io.stderr.write(`${health.message}\n`);
         return { status: 'failed', projectDir: args.projectDir };
       }
+      const warning = formatClaudeCodePromptCachingWarning(
+        ignoredClaudeCodePromptCachingFields(
+          buildProjectLlmConfig(project.config.llm, { backend: 'claude-code' }, model),
+        ),
+      );
+      if (warning) {
+        io.stderr.write(`${warning}\n`);
+      }
       await persistLlmConfig(args.projectDir, { backend: 'claude-code' }, model);
       io.stdout.write(`│  LLM ready: yes (${model})\n`);
       return { status: 'ready', projectDir: args.projectDir };

packages/cli/src/status-project.ts

@@ -9,6 +9,11 @@ import type {
   KtxProjectLlmConfig,
 } from '@ktx/context/project';
 import type { PostgresPgssProbeResult } from '@ktx/context/ingest';
+import {
+  formatClaudeCodePromptCachingFix,
+  formatClaudeCodePromptCachingWarning,
+  ignoredClaudeCodePromptCachingFields,
+} from './claude-code-prompt-caching.js';
 import type { DoctorCheck } from './doctor.js';
 import { KTX_NEXT_STEP_DIRECT_COMMANDS } from './next-steps.js';
 
@@ -509,13 +514,6 @@ function buildPipelineStatus(config: KtxProjectConfig): PipelineStatus {
   };
 }
 
-function ignoredClaudeCodePromptCachingFields(config: KtxProjectLlmConfig): string[] {
-  if (config.provider.backend !== 'claude-code' || !config.promptCaching) {
-    return [];
-  }
-  return Object.keys(config.promptCaching).map((key) => `llm.promptCaching.${key}`);
-}
-
 function buildStorageStatus(config: KtxProjectConfig): StorageStatus {
   return {
     state: config.storage.state,
@@ -603,11 +601,11 @@ function buildWarnings(
     });
   }
 
-  const ignored = ignoredClaudeCodePromptCachingFields(config.llm);
-  if (ignored.length > 0) {
+  const warning = formatClaudeCodePromptCachingWarning(ignoredClaudeCodePromptCachingFields(config.llm));
+  if (warning) {
     warnings.push({
-      message: `claude-code ignores ${ignored.join(', ')} because the Claude Agent SDK does not expose KTX prompt-cache TTL, tool, or history markers.`,
-      fix: 'Remove those promptCaching fields or use anthropic, vertex, or gateway when those cache knobs are required.',
+      message: warning,
+      fix: formatClaudeCodePromptCachingFix(),
     });
   }