diff --git a/packages/agent/src/harness/agent-harness.ts b/packages/agent/src/harness/agent-harness.ts
index 1d09b054..1ce57b14 100644
--- a/packages/agent/src/harness/agent-harness.ts
+++ b/packages/agent/src/harness/agent-harness.ts
@@ -1,4 +1,11 @@
-import type { AssistantMessage, ImageContent, Model, Models, UserMessage } from "@earendil-works/pi-ai";
+import {
+	type AssistantMessage,
+	contentText,
+	type ImageContent,
+	type Model,
+	type Models,
+	type UserMessage,
+} from "@earendil-works/pi-ai";
 import { runAgentLoop } from "../agent-loop.ts";
 import type {
 	AgentContext,
@@ -781,23 +788,10 @@ export class AgentHarness<
 			let newLeafId: string | null;
 			if (targetEntry.type === "message" && targetEntry.message.role === "user") {
 				newLeafId = targetEntry.parentId;
-				const content = targetEntry.message.content;
-				editorText =
-					typeof content === "string"
-						? content
-						: content
-								.filter((c): c is { readonly type: "text"; readonly text: string } => c.type === "text")
-								.map((c) => c.text)
-								.join("");
+				editorText = contentText(targetEntry.message.content, "");
 			} else if (targetEntry.type === "custom_message") {
 				newLeafId = targetEntry.parentId;
-				editorText =
-					typeof targetEntry.content === "string"
-						? targetEntry.content
-						: targetEntry.content
-								.filter((c): c is { readonly type: "text"; readonly text: string } => c.type === "text")
-								.map((c) => c.text)
-								.join("");
+				editorText = contentText(targetEntry.content, "");
 			} else {
 				newLeafId = targetId;
 			}
diff --git a/packages/agent/src/harness/compaction/branch-summarization.ts b/packages/agent/src/harness/compaction/branch-summarization.ts
index fdf1df49..a8d68673 100644
--- a/packages/agent/src/harness/compaction/branch-summarization.ts
+++ b/packages/agent/src/harness/compaction/branch-summarization.ts
@@ -1,4 +1,4 @@
-import type { Model, Models } from "@earendil-works/pi-ai";
+import { contentText, type Model, type Models } from "@earendil-works/pi-ai";
 
 import type { AgentMessage } from "../../types.ts";
 import {
@@ -245,10 +245,7 @@ export async function generateBranchSummary(
 		);
 	}
 
-	let summary = response.content
-		.filter((c): c is { type: "text"; text: string } => c.type === "text")
-		.map((c) => c.text)
-		.join("\n");
+	let summary = contentText(response.content);
 	summary = BRANCH_SUMMARY_PREAMBLE + summary;
 	const { readFiles, modifiedFiles } = computeFileLists(fileOps);
 	summary += formatFileOperations(readFiles, modifiedFiles);
diff --git a/packages/agent/src/harness/compaction/compaction.ts b/packages/agent/src/harness/compaction/compaction.ts
index 4132e3dd..a7f8ebc0 100644
--- a/packages/agent/src/harness/compaction/compaction.ts
+++ b/packages/agent/src/harness/compaction/compaction.ts
@@ -1,4 +1,12 @@
-import type { AssistantMessage, ImageContent, Model, Models, TextContent, Usage } from "@earendil-works/pi-ai";
+import {
+	type AssistantMessage,
+	contentText,
+	type ImageContent,
+	type Model,
+	type Models,
+	type TextContent,
+	type Usage,
+} from "@earendil-works/pi-ai";
 import type { AgentMessage, ThinkingLevel } from "../../types.ts";
 import {
 	convertToLlm,
@@ -513,10 +521,7 @@ export async function generateSummary(
 		);
 	}
 
-	const textContent = response.content
-		.filter((c): c is { type: "text"; text: string } => c.type === "text")
-		.map((c) => c.text)
-		.join("\n");
+	const textContent = contentText(response.content);
 
 	return ok(textContent);
 }
@@ -744,10 +749,5 @@ async function generateTurnPrefixSummary(
 		);
 	}
 
-	return ok(
-		response.content
-			.filter((c): c is { type: "text"; text: string } => c.type === "text")
-			.map((c) => c.text)
-			.join("\n"),
-	);
+	return ok(contentText(response.content));
 }
diff --git a/packages/agent/src/harness/compaction/utils.ts b/packages/agent/src/harness/compaction/utils.ts
index 07535b79..7fd3aac0 100644
--- a/packages/agent/src/harness/compaction/utils.ts
+++ b/packages/agent/src/harness/compaction/utils.ts
@@ -1,4 +1,4 @@
-import type { Message } from "@earendil-works/pi-ai";
+import { contentText, type Message } from "@earendil-works/pi-ai";
 import type { AgentMessage } from "../../types.ts";
 
 /** File paths touched by a session branch or compaction range. */
@@ -93,23 +93,14 @@ export function serializeConversation(messages: Message[]): string {
 
 	for (const msg of messages) {
 		if (msg.role === "user") {
-			const content =
-				typeof msg.content === "string"
-					? msg.content
-					: msg.content
-							.filter((c): c is { type: "text"; text: string } => c.type === "text")
-							.map((c) => c.text)
-							.join("");
+			const content = contentText(msg.content, "");
 			if (content) parts.push(`[User]: ${content}`);
 		} else if (msg.role === "assistant") {
-			const textParts: string[] = [];
 			const thinkingParts: string[] = [];
 			const toolCalls: string[] = [];
 
 			for (const block of msg.content) {
-				if (block.type === "text") {
-					textParts.push(block.text);
-				} else if (block.type === "thinking") {
+				if (block.type === "thinking") {
 					thinkingParts.push(block.thinking);
 				} else if (block.type === "toolCall") {
 					const args = block.arguments as Record<string, unknown>;
@@ -123,17 +114,14 @@ export function serializeConversation(messages: Message[]): string {
 			if (thinkingParts.length > 0) {
 				parts.push(`[Assistant thinking]: ${thinkingParts.join("\n")}`);
 			}
-			if (textParts.length > 0) {
-				parts.push(`[Assistant]: ${textParts.join("\n")}`);
+			if (msg.content.some((block) => block.type === "text")) {
+				parts.push(`[Assistant]: ${contentText(msg.content)}`);
 			}
 			if (toolCalls.length > 0) {
 				parts.push(`[Assistant tool calls]: ${toolCalls.join("; ")}`);
 			}
 		} else if (msg.role === "toolResult") {
-			const content = msg.content
-				.filter((c): c is { type: "text"; text: string } => c.type === "text")
-				.map((c) => c.text)
-				.join("");
+			const content = contentText(msg.content, "");
 			if (content) {
 				parts.push(`[Tool result]: ${truncateForSummary(content, TOOL_RESULT_MAX_CHARS)}`);
 			}
diff --git a/packages/ai/CHANGELOG.md b/packages/ai/CHANGELOG.md
index 7f9388ac..ed86ca72 100644
--- a/packages/ai/CHANGELOG.md
+++ b/packages/ai/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 ### Added
 
+- Added `contentText` for extracting joined text from message content.
 - Added a shared `uuidv7` utility for time-ordered identifiers.
 
 ### Fixed
diff --git a/packages/ai/src/index.ts b/packages/ai/src/index.ts
index 1ba45811..4ff67810 100644
--- a/packages/ai/src/index.ts
+++ b/packages/ai/src/index.ts
@@ -41,6 +41,7 @@ export * from "./utils/event-stream.ts";
 export * from "./utils/json-parse.ts";
 export * from "./utils/overflow.ts";
 export * from "./utils/retry.ts";
+export { contentText } from "./utils/text.ts";
 export * from "./utils/typebox-helpers.ts";
 export { uuidv7 } from "./utils/uuid.ts";
 export * from "./utils/validation.ts";
diff --git a/packages/ai/src/utils/text.ts b/packages/ai/src/utils/text.ts
new file mode 100644
index 00000000..66f5b9c5
--- /dev/null
+++ b/packages/ai/src/utils/text.ts
@@ -0,0 +1,12 @@
+import type { ImageContent, TextContent, ThinkingContent, ToolCall } from "../types.ts";
+
+type Content = TextContent | ImageContent | ThinkingContent | ToolCall;
+
+/** Extract and join text from message content. */
+export function contentText(content: string | readonly Content[], separator = "\n"): string {
+	if (typeof content === "string") return content;
+	return content
+		.filter((block) => block.type === "text")
+		.map((block) => block.text)
+		.join(separator);
+}
diff --git a/packages/ai/test/text.test.ts b/packages/ai/test/text.test.ts
new file mode 100644
index 00000000..43dc21c8
--- /dev/null
+++ b/packages/ai/test/text.test.ts
@@ -0,0 +1,33 @@
+import { describe, expect, it } from "vitest";
+import { type AssistantMessage, contentText, type ToolResultMessage } from "../src/index.ts";
+
+const content: AssistantMessage["content"] = [
+	{ type: "thinking", thinking: "reasoning" },
+	{ type: "text", text: "first" },
+	{ type: "toolCall", id: "1", name: "read", arguments: {} },
+	{ type: "text", text: "second" },
+];
+
+describe("contentText", () => {
+	it("extracts assistant text blocks", () => {
+		expect(contentText(content)).toBe("first\nsecond");
+	});
+
+	it("supports custom separators", () => {
+		expect(contentText(content, "")).toBe("firstsecond");
+	});
+
+	it("passes string content through", () => {
+		expect(contentText("hello")).toBe("hello");
+	});
+
+	it("extracts text from tool-result content", () => {
+		const toolResultContent: ToolResultMessage["content"] = [
+			{ type: "text", text: "first" },
+			{ type: "image", data: "...", mimeType: "image/png" },
+			{ type: "text", text: "second" },
+		];
+
+		expect(contentText(toolResultContent, "")).toBe("firstsecond");
+	});
+});
diff --git a/packages/coding-agent/src/core/agent-session.ts b/packages/coding-agent/src/core/agent-session.ts
index 36e542e5..c4afb9b1 100644
--- a/packages/coding-agent/src/core/agent-session.ts
+++ b/packages/coding-agent/src/core/agent-session.ts
@@ -24,11 +24,11 @@ import type {
 	PrepareNextTurnContext,
 	ThinkingLevel,
 } from "@earendil-works/pi-agent-core";
+import { contentText } from "@earendil-works/pi-ai";
 import type {
 	AssistantMessage,
 	AuthResult,
 	ImageContent,
-	Message,
 	Model,
 	ProviderHeaders,
 	TextContent,
@@ -576,7 +576,7 @@ export class AgentSession {
 		// This ensures the UI sees the updated queue state
 		if (event.type === "message_start" && event.message.role === "user") {
 			this._overflowRecoveryAttempted = false;
-			const messageText = this._getUserMessageText(event.message);
+			const messageText = contentText(event.message.content, "");
 			if (messageText) {
 				// Check steering queue first
 				const steeringIndex = this._steeringMessages.indexOf(messageText);
@@ -659,15 +659,6 @@ export class AgentSession {
 		return false;
 	}
 
-	/** Extract text content from a message */
-	private _getUserMessageText(message: Message): string {
-		if (message.role !== "user") return "";
-		const content = message.content;
-		if (typeof content === "string") return content;
-		const textBlocks = content.filter((c) => c.type === "text");
-		return textBlocks.map((c) => (c as TextContent).text).join("");
-	}
-
 	/** Find the last assistant message in agent state (including aborted ones) */
 	private _findLastAssistantMessage(): AssistantMessage | undefined {
 		const messages = this.agent.state.messages;
@@ -2954,17 +2945,11 @@ export class AgentSession {
 			if (targetEntry.type === "message" && targetEntry.message.role === "user") {
 				// User message: leaf = parent (null if root), text goes to editor
 				newLeafId = targetEntry.parentId;
-				editorText = this._extractUserMessageText(targetEntry.message.content);
+				editorText = contentText(targetEntry.message.content, "");
 			} else if (targetEntry.type === "custom_message") {
 				// Custom message: leaf = parent (null if root), text goes to editor
 				newLeafId = targetEntry.parentId;
-				editorText =
-					typeof targetEntry.content === "string"
-						? targetEntry.content
-						: targetEntry.content
-								.filter((c): c is { type: "text"; text: string } => c.type === "text")
-								.map((c) => c.text)
-								.join("");
+				editorText = contentText(targetEntry.content, "");
 			} else {
 				// Non-user message: leaf = selected node
 				newLeafId = targetId;
@@ -3032,7 +3017,7 @@ export class AgentSession {
 			if (entry.type !== "message") continue;
 			if (entry.message.role !== "user") continue;
 
-			const text = this._extractUserMessageText(entry.message.content);
+			const text = contentText(entry.message.content, "");
 			if (text) {
 				result.push({ entryId: entry.id, text });
 			}
@@ -3041,17 +3026,6 @@ export class AgentSession {
 		return result;
 	}
 
-	private _extractUserMessageText(content: string | Array<{ type: string; text?: string }>): string {
-		if (typeof content === "string") return content;
-		if (Array.isArray(content)) {
-			return content
-				.filter((c): c is { type: "text"; text: string } => c.type === "text")
-				.map((c) => c.text)
-				.join("");
-		}
-		return "";
-	}
-
 	/**
 	 * Get session statistics. Aggregates over ALL session entries (including
 	 * history that was compacted away), so token/cost totals reflect what was
diff --git a/packages/coding-agent/src/core/compaction/branch-summarization.ts b/packages/coding-agent/src/core/compaction/branch-summarization.ts
index a96bb202..f2e06876 100644
--- a/packages/coding-agent/src/core/compaction/branch-summarization.ts
+++ b/packages/coding-agent/src/core/compaction/branch-summarization.ts
@@ -6,6 +6,7 @@
  */
 
 import type { AgentMessage, StreamFn } from "@earendil-works/pi-agent-core";
+import { contentText } from "@earendil-works/pi-ai";
 import type { Model, SimpleStreamOptions } from "@earendil-works/pi-ai/compat";
 import { completeSimple } from "@earendil-works/pi-ai/compat";
 import {
@@ -351,10 +352,7 @@ export async function generateBranchSummary(
 		return { error: response.errorMessage || "Summarization failed" };
 	}
 
-	let summary = response.content
-		.filter((c): c is { type: "text"; text: string } => c.type === "text")
-		.map((c) => c.text)
-		.join("\n");
+	let summary = contentText(response.content);
 
 	// Prepend preamble to provide context about the branch summary
 	summary = BRANCH_SUMMARY_PREAMBLE + summary;
diff --git a/packages/coding-agent/src/core/compaction/compaction.ts b/packages/coding-agent/src/core/compaction/compaction.ts
index 39b1042d..5c71c74d 100644
--- a/packages/coding-agent/src/core/compaction/compaction.ts
+++ b/packages/coding-agent/src/core/compaction/compaction.ts
@@ -6,6 +6,7 @@
  */
 
 import type { AgentMessage, StreamFn, ThinkingLevel } from "@earendil-works/pi-agent-core";
+import { contentText } from "@earendil-works/pi-ai";
 import type { AssistantMessage, Context, Model, SimpleStreamOptions, Usage } from "@earendil-works/pi-ai/compat";
 import { completeSimple } from "@earendil-works/pi-ai/compat";
 import { convertToLlm } from "../messages.ts";
@@ -600,10 +601,7 @@ export async function generateSummary(
 		throw new Error(`Summarization failed: ${response.errorMessage || "Unknown error"}`);
 	}
 
-	const textContent = response.content
-		.filter((c): c is { type: "text"; text: string } => c.type === "text")
-		.map((c) => c.text)
-		.join("\n");
+	const textContent = contentText(response.content);
 
 	return textContent;
 }
@@ -865,8 +863,5 @@ async function generateTurnPrefixSummary(
 		throw new Error(`Turn prefix summarization failed: ${response.errorMessage || "Unknown error"}`);
 	}
 
-	return response.content
-		.filter((c): c is { type: "text"; text: string } => c.type === "text")
-		.map((c) => c.text)
-		.join("\n");
+	return contentText(response.content);
 }
diff --git a/packages/coding-agent/src/core/compaction/utils.ts b/packages/coding-agent/src/core/compaction/utils.ts
index 6cfc1622..35d1a29b 100644
--- a/packages/coding-agent/src/core/compaction/utils.ts
+++ b/packages/coding-agent/src/core/compaction/utils.ts
@@ -3,7 +3,7 @@
  */
 
 import type { AgentMessage } from "@earendil-works/pi-agent-core";
-import type { Message } from "@earendil-works/pi-ai";
+import { contentText, type Message } from "@earendil-works/pi-ai";
 
 // ============================================================================
 // File Operation Tracking
@@ -111,23 +111,14 @@ export function serializeConversation(messages: Message[]): string {
 
 	for (const msg of messages) {
 		if (msg.role === "user") {
-			const content =
-				typeof msg.content === "string"
-					? msg.content
-					: msg.content
-							.filter((c): c is { type: "text"; text: string } => c.type === "text")
-							.map((c) => c.text)
-							.join("");
+			const content = contentText(msg.content, "");
 			if (content) parts.push(`[User]: ${content}`);
 		} else if (msg.role === "assistant") {
-			const textParts: string[] = [];
 			const thinkingParts: string[] = [];
 			const toolCalls: string[] = [];
 
 			for (const block of msg.content) {
-				if (block.type === "text") {
-					textParts.push(block.text);
-				} else if (block.type === "thinking") {
+				if (block.type === "thinking") {
 					thinkingParts.push(block.thinking);
 				} else if (block.type === "toolCall") {
 					const args = block.arguments as Record<string, unknown>;
@@ -141,17 +132,14 @@ export function serializeConversation(messages: Message[]): string {
 			if (thinkingParts.length > 0) {
 				parts.push(`[Assistant thinking]: ${thinkingParts.join("\n")}`);
 			}
-			if (textParts.length > 0) {
-				parts.push(`[Assistant]: ${textParts.join("\n")}`);
+			if (msg.content.some((block) => block.type === "text")) {
+				parts.push(`[Assistant]: ${contentText(msg.content)}`);
 			}
 			if (toolCalls.length > 0) {
 				parts.push(`[Assistant tool calls]: ${toolCalls.join("; ")}`);
 			}
 		} else if (msg.role === "toolResult") {
-			const content = msg.content
-				.filter((c): c is { type: "text"; text: string } => c.type === "text")
-				.map((c) => c.text)
-				.join("");
+			const content = contentText(msg.content, "");
 			if (content) {
 				parts.push(`[Tool result]: ${truncateForSummary(content, TOOL_RESULT_MAX_CHARS)}`);
 			}