diff --git a/src/agents/pi-embedded-helpers.validate-turns.test.ts b/src/agents/pi-embedded-helpers.validate-turns.test.ts
index 9e20ad0d48f..3847d5322dd 100644
--- a/src/agents/pi-embedded-helpers.validate-turns.test.ts
+++ b/src/agents/pi-embedded-helpers.validate-turns.test.ts
@@ -357,6 +357,26 @@ describe("mergeConsecutiveUserTurns", () => {
     expect(merged.timestamp).toBe(2000);
   });
 
+  it("preserves string content while merging content", () => {
+    const previous = {
+      role: "user",
+      content: "before",
+      timestamp: 1000,
+    } as Extract<AgentMessage, { role: "user" }>;
+    const current = {
+      role: "user",
+      content: "after",
+      timestamp: 2000,
+    } as Extract<AgentMessage, { role: "user" }>;
+
+    const merged = mergeConsecutiveUserTurns(previous, current);
+
+    expect(merged.content).toEqual([
+      { type: "text", text: "before" },
+      { type: "text", text: "after" },
+    ]);
+  });
+
   it("backfills timestamp from earlier message when missing", () => {
     const previous = {
       role: "user",
diff --git a/src/agents/pi-embedded-helpers/turns.ts b/src/agents/pi-embedded-helpers/turns.ts
index c64efbe4ff9..5c3871f4984 100644
--- a/src/agents/pi-embedded-helpers/turns.ts
+++ b/src/agents/pi-embedded-helpers/turns.ts
@@ -10,6 +10,10 @@ type AnthropicContentBlock = {
   toolUseId?: string;
   toolCallId?: string;
 };
+type UserContentBlock = Extract<
+  Extract<AgentMessage, { role: "user" }>["content"],
+  readonly unknown[]
+>[number];
 
 function isToolCallBlock(block: AnthropicContentBlock): boolean {
   return block.type === "toolUse" || block.type === "toolCall" || block.type === "functionCall";
@@ -350,8 +354,8 @@ export function mergeConsecutiveUserTurns(
   current: Extract<AgentMessage, { role: "user" }>,
 ): Extract<AgentMessage, { role: "user" }> {
   const mergedContent = [
-    ...(Array.isArray(previous.content) ? previous.content : []),
-    ...(Array.isArray(current.content) ? current.content : []),
+    ...normalizeUserContentForMerge(previous.content),
+    ...normalizeUserContentForMerge(current.content),
   ];
 
   return {
@@ -361,6 +365,16 @@ export function mergeConsecutiveUserTurns(
   };
 }
 
+function normalizeUserContentForMerge(content: unknown): UserContentBlock[] {
+  if (Array.isArray(content)) {
+    return content as UserContentBlock[];
+  }
+  if (typeof content === "string") {
+    return [{ type: "text", text: content }];
+  }
+  return [];
+}
+
 /**
  * Validates and fixes conversation turn sequences for Anthropic API.
  * Anthropic requires strict alternating user→assistant pattern.
diff --git a/src/agents/pi-embedded-runner.sanitize-session-history.test.ts b/src/agents/pi-embedded-runner.sanitize-session-history.test.ts
index 85d8a6e3309..1e0c6653360 100644
--- a/src/agents/pi-embedded-runner.sanitize-session-history.test.ts
+++ b/src/agents/pi-embedded-runner.sanitize-session-history.test.ts
@@ -1141,17 +1141,9 @@ describe("sanitizeSessionHistory", () => {
       "```",
     ].join("\n");
     const messages = castAgentMessages([
-      {
-        role: "user",
-        content: [{ type: "text", text: "First" }],
-        timestamp: nextTimestamp(),
-      },
+      makeUserMessage("First"),
       makeAssistantMessage([{ type: "text", text: metadataOnlyText }]),
-      {
-        role: "user",
-        content: [{ type: "text", text: "Second" }],
-        timestamp: nextTimestamp(),
-      },
+      makeUserMessage("Second"),
     ]);
 
     const sanitized = await sanitizeSessionHistory({