From 6424944426165b77e6b3bc10c9c20ff4007a64fd Mon Sep 17 00:00:00 2001
From: Andrey Avtomonov <andreybavt@gmail.com>
Date: Thu, 14 May 2026 15:28:11 +0200
Subject: [PATCH] fix(llm): keep wrapSimple history breakpoint so multi-step
 agent loops cache
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Reverts the wrapSimple `messages.length > 1` guard from the prior commit.
agent-runner uses wrapSimple with a single user message, but generateText
runs a multi-step tool loop inside it — the cache marker on the first user
message is reused by every subsequent step, so it isn't waste.
The release validator (scripts/validate-llm-debug-jsonl.mjs) also requires
a `message-part` marker target in captured debug JSONL.
---
 packages/llm/src/message-builder.test.ts | 44 ------------------------
 packages/llm/src/message-builder.ts      |  7 +---
 2 files changed, 1 insertion(+), 50 deletions(-)

diff --git a/packages/llm/src/message-builder.test.ts b/packages/llm/src/message-builder.test.ts
index 7beedfbe..bc13a7e1 100644
--- a/packages/llm/src/message-builder.test.ts
+++ b/packages/llm/src/message-builder.test.ts
@@ -81,50 +81,6 @@ describe('KtxMessageBuilder.build', () => {
     expect((out.tools.z as { providerOptions?: unknown }).providerOptions).toBeUndefined();
   });
 
-  it('wrapSimple does not mark a single user message with a cache breakpoint', () => {
-    const builder = makeBuilder();
-
-    const out = builder.wrapSimple({
-      system: 'SYS',
-      messages: [{ role: 'user', content: 'one-shot prompt' }],
-      tools: {},
-      model: 'anthropic/claude-sonnet-4-6',
-    });
-
-    expect(out.messages).toHaveLength(2);
-    expect(out.messages[0]).toMatchObject({
-      role: 'system',
-      providerOptions: { anthropic: { cacheControl: { type: 'ephemeral', ttl: '1h' } } },
-    });
-    expect(out.messages[1]).toMatchObject({ role: 'user', content: 'one-shot prompt' });
-    expect((out.messages[1] as { providerOptions?: unknown }).providerOptions).toBeUndefined();
-  });
-
-  it('wrapSimple still marks the last history message when there are multiple messages', () => {
-    const builder = makeBuilder();
-
-    const out = builder.wrapSimple({
-      system: 'SYS',
-      messages: [
-        { role: 'user', content: 'turn 1' },
-        { role: 'assistant', content: 'reply 1' },
-        { role: 'user', content: 'turn 2' },
-      ],
-      tools: {},
-      model: 'anthropic/claude-sonnet-4-6',
-    });
-
-    expect(out.messages).toHaveLength(4);
-    expect(out.messages[1]).toMatchObject({ role: 'user' });
-    expect((out.messages[1] as { providerOptions?: unknown }).providerOptions).toBeUndefined();
-    expect(out.messages[2]).toMatchObject({ role: 'assistant' });
-    expect((out.messages[2] as { providerOptions?: unknown }).providerOptions).toBeUndefined();
-    const last = out.messages[3] as { content: Array<{ providerOptions?: unknown }> };
-    expect(last.content[0].providerOptions).toEqual({
-      anthropic: { cacheControl: { type: 'ephemeral', ttl: '5m' } },
-    });
-  });
-
   it('clamps every TTL to 5m for Vertex when vertexFallbackTo5m is enabled', () => {
     const provider = createKtxLlmProvider({
       backend: 'vertex',
diff --git a/packages/llm/src/message-builder.ts b/packages/llm/src/message-builder.ts
index 387d0832..a98a0375 100644
--- a/packages/llm/src/message-builder.ts
+++ b/packages/llm/src/message-builder.ts
@@ -86,13 +86,8 @@ export class KtxMessageBuilder {
     }
 
     if (input.messages) {
-      // Only mark a history breakpoint when prior turns exist. A single-message call
-      // is the current user turn — marking it writes a cache entry that can't be
-      // reused on the next (different-content) call, costing tokens for nothing.
-      const shouldMarkHistory =
-        cachingActive && this.cacheHistoryEnabled() && input.messages.length > 1;
       messages.push(
-        ...(shouldMarkHistory
+        ...(cachingActive && this.cacheHistoryEnabled()
           ? this.markLastHistoryMessage(input.messages, ttls.historyTtl, input.model)
           : input.messages),
       );