diff --git a/typescript/m1/m1.2_scratch_agent.ts b/typescript/m1/m1.2_scratch_agent.ts
index 3ea9057..68c56f9 100644
--- a/typescript/m1/m1.2_scratch_agent.ts
+++ b/typescript/m1/m1.2_scratch_agent.ts
@@ -4,6 +4,8 @@ import { model } from "../models.js";
 
 const agent = createDeepAgent({ model });
 
-const result = await agent.invoke({"messages": [{"role": "user", "content": "What is an LLM?"}]});
+const result = await agent.invoke({
+    messages: [{ role: "user", content: "What is an LLM?" }]
+});
 
-console.log(result.messages[result.messages.length - 1].content);
+console.log(result.messages.at(-1)?.content);
diff --git a/typescript/m1/m1.4_scratch_agent_butler.ts b/typescript/m1/m1.4_scratch_agent_butler.ts
index 69f019f..1d7c018 100644
--- a/typescript/m1/m1.4_scratch_agent_butler.ts
+++ b/typescript/m1/m1.4_scratch_agent_butler.ts
@@ -1,13 +1,14 @@
+import { context } from "langchain";
 import { createDeepAgent } from "deepagents";
 
 import { model } from "../models.js";
 
-const SYSTEM_PROMPT =
-  "YOU ARE AN EXTREMELY POSH BRITISH BUTLER. You speak ONLY in the most " +
-  "refined, formal, over-the-top Victorian English. You say 'indeed', 'quite', " +
-  "'I dare say', 'one simply must' constantly. You find all things common or " +
-  "nautical to be utterly beneath you. You NEVER break character under ANY " +
-  "circumstances.";
+const SYSTEM_PROMPT = context`
+  YOU ARE AN EXTREMELY POSH BRITISH BUTLER. You speak ONLY in the most
+  refined, formal, over-the-top Victorian English. You say 'indeed', 'quite',
+  'I dare say', 'one simply must' constantly. You find all things common or
+  nautical to be utterly beneath you. You NEVER break character under ANY
+  circumstances.`;
 
 const agent = createDeepAgent({
   model,
@@ -19,4 +20,4 @@ const result = await agent.invoke({
   messages: [{ role: "user", content: "What is an LLM?" }],
 });
 
-console.log(result.messages[result.messages.length - 1].content);
+console.log(result.messages.at(-1)?.content);
diff --git a/typescript/m1/m1.5_scratch_agent_tools.ts b/typescript/m1/m1.5_scratch_agent_tools.ts
index e682737..c2abd57 100644
--- a/typescript/m1/m1.5_scratch_agent_tools.ts
+++ b/typescript/m1/m1.5_scratch_agent_tools.ts
@@ -1,8 +1,9 @@
 import { DatabaseSync } from "node:sqlite";
 import { dirname, join } from "node:path";
 import { fileURLToPath } from "node:url";
-import { tool } from "@langchain/core/tools";
+
 import { z } from "zod";
+import { tool } from "langchain";
 import { createDeepAgent } from "deepagents";
 
 import { model } from "../models.js";
@@ -47,4 +48,4 @@ const result = await agent.invoke({
   messages: [{ role: "user", content: "Which five genres have the most tracks?" }],
 });
 
-console.log(result.messages[result.messages.length - 1].content);
+console.log(result.messages.at(-1)?.content);
diff --git a/typescript/m1/m1.6_agent_mcp.ts b/typescript/m1/m1.6_agent_mcp.ts
index e6fe940..982b8b6 100644
--- a/typescript/m1/m1.6_agent_mcp.ts
+++ b/typescript/m1/m1.6_agent_mcp.ts
@@ -12,28 +12,30 @@ const client = new MultiServerMCPClient({
   },
 });
 
-let tools = await client.getTools();
-
-console.log(`\ndocs-langchain: ${tools.length} tool(s)`);
-for (const t of tools) {
-  console.log(`  ${t.name}`);
-  console.log(`  ${t.description?.slice(0, 90)}`);
-}
-
-tools = tools.filter((t) => ALLOWED.has(t.name));
-
-const agent = createDeepAgent({ model, tools });
-
-const result = await agent.invoke({
-  messages: [
-    {
-      role: "user",
-      content:
-        "Use the LangChain docs MCP tool to explain what MCP is and how LangChain uses MCP tools.",
-    },
-  ],
-});
-
-console.log(result.messages[result.messages.length - 1].content);
-
-await client.close();
+try {
+  let tools = await client.getTools();
+
+  console.log(`\ndocs-langchain: ${tools.length} tool(s)`);
+  for (const t of tools) {
+    console.log(`  ${t.name}`);
+    console.log(`  ${t.description?.slice(0, 90)}`);
+  }
+
+  tools = tools.filter((t) => ALLOWED.has(t.name));
+
+  const agent = createDeepAgent({ model, tools });
+
+  const result = await agent.invoke({
+    messages: [
+      {
+        role: "user",
+        content:
+          "Use the LangChain docs MCP tool to explain what MCP is and how LangChain uses MCP tools.",
+      },
+    ],
+  });
+
+  console.log(result.messages.at(-1)?.content);
+} finally {
+  await client.close();
+}
\ No newline at end of file
diff --git a/typescript/m1/m1.7_messages_threads_checkpointers.ts b/typescript/m1/m1.7_messages_threads_checkpointers.ts
index 424cb43..ea2fd72 100644
--- a/typescript/m1/m1.7_messages_threads_checkpointers.ts
+++ b/typescript/m1/m1.7_messages_threads_checkpointers.ts
@@ -16,18 +16,18 @@ let result = await agent.invoke(
   threadA
 );
 console.log("Thread A, turn 1:");
-console.log(result.messages[result.messages.length - 1].content);
+console.log(result.messages.at(-1)?.content);
 
 result = await agent.invoke(
   { messages: [{ role: "user", content: "What is my favorite color?" }] },
   threadA
 );
 console.log("\nThread A, turn 2:");
-console.log(result.messages[result.messages.length - 1].content);
+console.log(result.messages.at(-1)?.content);
 
 result = await agent.invoke(
   { messages: [{ role: "user", content: "What is my favorite color?" }] },
   threadB
 );
 console.log("\nThread B, turn 1:");
-console.log(result.messages[result.messages.length - 1].content);
+console.log(result.messages.at(-1)?.content);
diff --git a/typescript/m1/m1.8_hitl.ts b/typescript/m1/m1.8_hitl.ts
index fbbef45..46d11fc 100644
--- a/typescript/m1/m1.8_hitl.ts
+++ b/typescript/m1/m1.8_hitl.ts
@@ -1,9 +1,8 @@
 import { createInterface } from "node:readline/promises";
-import { tool } from "@langchain/core/tools";
-import { isToolMessage } from "@langchain/core/messages";
 import { z } from "zod";
-import { MemorySaver } from "@langchain/langgraph";
-import { Command, INTERRUPT, isInterrupted } from "@langchain/langgraph";
+
+import { tool, ToolMessage } from "langchain";
+import { Command, INTERRUPT, isInterrupted, MemorySaver } from "@langchain/langgraph";
 import { createDeepAgent } from "deepagents";
 
 import { model } from "../models.js";
@@ -97,7 +96,7 @@ while (isInterrupted<ApprovalRequest>(result) && result[INTERRUPT].length) {
 
 rl.close();
 for (const msg of result.messages) {
-  if (isToolMessage(msg) && msg.name === "send_email") {
+  if (ToolMessage.isInstance(msg) && msg.name === "send_email") {
     console.log(msg.content);
     break;
   }
diff --git a/typescript/m2/m2.2_agent.ts b/typescript/m2/m2.2_agent.ts
index 72bf914..26f9fba 100644
--- a/typescript/m2/m2.2_agent.ts
+++ b/typescript/m2/m2.2_agent.ts
@@ -3,6 +3,7 @@ import { dirname, join } from "node:path";
 import { mkdirSync, writeFileSync } from "node:fs";
 import { fileURLToPath } from "node:url";
 
+import { context } from "langchain";
 import {
   CompositeBackend,
   FilesystemBackend,
@@ -59,15 +60,15 @@ try {
       messages: [
         {
           role: "user",
-          content:
-            "Read /reference/chinook-sales.md, then add this note to it: " +
-            "'Current promotion: 20% off all Jazz albums through end of month.'",
+          content: context`
+            Read /reference/chinook-sales.md, then add this note to it:
+            'Current promotion: 20% off all Jazz albums through end of month.'`,
         },
       ],
     },
     { configurable: { thread_id: "lab-m2.2" } }
   );
-  console.log(result.messages[result.messages.length - 1].content);
+  console.log(result.messages.at(-1)?.content);
 } catch (e) {
   const err = e instanceof Error ? e : new Error(String(e));
   const cause = err.cause instanceof Error ? err.cause : undefined;
diff --git a/typescript/m2/m2.3_sales_agent.ts b/typescript/m2/m2.3_sales_agent.ts
index 0f6b304..cb502ec 100644
--- a/typescript/m2/m2.3_sales_agent.ts
+++ b/typescript/m2/m2.3_sales_agent.ts
@@ -5,6 +5,7 @@ import { writeFileSync } from "node:fs";
 import { readFile } from "node:fs/promises";
 import { fileURLToPath } from "node:url";
 
+import { context } from "langchain";
 import { LangSmithSandbox, createDeepAgent } from "deepagents";
 import { SandboxClient } from "langsmith/sandbox";
 
@@ -34,12 +35,12 @@ for (const result of uploadResults) {
 const agent = createDeepAgent({
   model,
   backend,
-  systemPrompt:
-    "You are a sales data analyst with access to the Chinook music store database " +
-    "at /chinook.db. Use sqlite3 and matplotlib to answer questions with charts. " +
-    "Install any packages you need with pip before importing them. " +
-    "When asked to produce a chart, write a Python script, execute it, and confirm " +
-    "the output file was created.",
+  systemPrompt: context`
+    You are a sales data analyst with access to the Chinook music store database
+    at /chinook.db. Use sqlite3 and matplotlib to answer questions with charts.
+    Install any packages you need with pip before importing them.
+    When asked to produce a chart, write a Python script, execute it, and confirm
+    the output file was created.`,
 });
 
 try {
@@ -47,20 +48,20 @@ try {
     messages: [
       {
         role: "user",
-        content:
-          "Query the Chinook database at /chinook.db to get total revenue " +
-          "by genre. Create a clean donut chart showing each genre's share " +
-          "of total sales revenue. Group any genres that individually " +
-          "account for less than 3% of total revenue into a single 'Other' " +
-          "slice. Label each slice with the genre name and percentage. " +
-          "Use a visually distinct color palette, leave a white center hole, " +
-          "and make sure no labels overlap with each other or with the title. " +
-          "Add enough top padding so the title is fully visible. " +
-          "Save the chart to /genre_revenue.png.",
+        content: context`
+          Query the Chinook database at /chinook.db to get total revenue
+          by genre. Create a clean donut chart showing each genre's share
+          of total sales revenue. Group any genres that individually
+          account for less than 3% of total revenue into a single 'Other'
+          slice. Label each slice with the genre name and percentage.
+          Use a visually distinct color palette, leave a white center hole,
+          and make sure no labels overlap with each other or with the title.
+          Add enough top padding so the title is fully visible.
+          Save the chart to /genre_revenue.png.`,
       },
     ],
   });
-  console.log(result.messages[result.messages.length - 1].content);
+  console.log(result.messages.at(-1)?.content);
 
   const pngBytes = await ls_sandbox.read("/genre_revenue.png");
   const outPath = join(__dirname, "genre_revenue.png");
diff --git a/typescript/m2/m2.3_sandbox_agent.ts b/typescript/m2/m2.3_sandbox_agent.ts
index ed79056..1250450 100644
--- a/typescript/m2/m2.3_sandbox_agent.ts
+++ b/typescript/m2/m2.3_sandbox_agent.ts
@@ -1,6 +1,7 @@
 // typescript/m2/m2.3_sandbox_agent.ts
 import { randomUUID } from "node:crypto";
 
+import { context } from "langchain";
 import { LangSmithSandbox, createDeepAgent } from "deepagents";
 import { SandboxClient } from "langsmith/sandbox";
 
@@ -16,9 +17,9 @@ const backend = new LangSmithSandbox({ sandbox: ls_sandbox });
 const agent = createDeepAgent({
   model,
   backend,
-  systemPrompt:
-    "You are a coding assistant. When asked to run code, write the script " +
-    "to a file first, then execute it. Show the output in your final answer.",
+  systemPrompt: context`
+    You are a coding assistant. When asked to run code, write the script
+    to a file first, then execute it. Show the output in your final answer.`,
 });
 
 try {
@@ -26,13 +27,13 @@ try {
     messages: [
       {
         role: "user",
-        content:
-          "Write a Python script that prints the first 15 Fibonacci numbers, " +
-          "save it to fib.py, and run it.",
+        content: context`
+          Write a Python script that prints the first 15 Fibonacci numbers,
+          save it to fib.py, and run it.`,
       },
     ],
   });
-  console.log(result.messages[result.messages.length - 1].content);
+  console.log(result.messages.at(-1)?.content);
 } finally {
   await client.deleteSandbox(ls_sandbox.name);
 }
diff --git a/typescript/m2/m2.4_eval_agent.ts b/typescript/m2/m2.4_eval_agent.ts
index 77fbbc4..1ba3e10 100644
--- a/typescript/m2/m2.4_eval_agent.ts
+++ b/typescript/m2/m2.4_eval_agent.ts
@@ -18,4 +18,4 @@ const result = await agent.invoke({
   ],
 });
 
-console.log(result.messages[result.messages.length - 1].content);
+console.log(result.messages.at(-1)?.content);
diff --git a/typescript/m2/m2.4_interpreter_agent.ts b/typescript/m2/m2.4_interpreter_agent.ts
index c44cca6..8077d58 100644
--- a/typescript/m2/m2.4_interpreter_agent.ts
+++ b/typescript/m2/m2.4_interpreter_agent.ts
@@ -4,29 +4,29 @@ import { DatabaseSync } from "node:sqlite";
 import { dirname, join } from "node:path";
 import { fileURLToPath } from "node:url";
 
-import { createCodeInterpreterMiddleware } from "@langchain/quickjs";
-import { tool } from "@langchain/core/tools";
-import { createDeepAgent } from "deepagents";
 import { z } from "zod";
+import { context, tool } from "langchain";
+import { createDeepAgent } from "deepagents";
+import { createCodeInterpreterMiddleware } from "@langchain/quickjs";
 
 import { model } from "../models.js";
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
 const DB_PATH = join(__dirname, "chinook.db");
 
-const TASK =
-  "Who is our top-selling artist, what is their best-selling album, " +
-  "what is the most-purchased track on that album, " +
-  "and how many distinct customers have bought that track? " +
-  "Each answer depends on the result of the previous query.";
+const TASK = context`
+  Who is our top-selling artist, what is their best-selling album,
+  what is the most-purchased track on that album,
+  and how many distinct customers have bought that track?
+  Each answer depends on the result of the previous query.`;
 
-const SYSTEM =
-  "You are a sales analyst for Chinook Digital Music Store. " +
-  "Use the query_chinook tool to query the database. " +
-  "Key tables: Artist(ArtistId, Name), Album(AlbumId, Title, ArtistId), " +
-  "Track(TrackId, Name, AlbumId), " +
-  "InvoiceLine(InvoiceLineId, InvoiceId, TrackId, UnitPrice, Quantity). " +
-  "Revenue is InvoiceLine.UnitPrice * InvoiceLine.Quantity.";
+const SYSTEM = context`
+  You are a sales analyst for Chinook Digital Music Store.
+  Use the query_chinook tool to query the database.
+  Key tables: Artist(ArtistId, Name), Album(AlbumId, Title, ArtistId),
+  Track(TrackId, Name, AlbumId),
+  InvoiceLine(InvoiceLineId, InvoiceId, TrackId, UnitPrice, Quantity).
+  Revenue is InvoiceLine.UnitPrice * InvoiceLine.Quantity.`;
 
 const queryChinook = tool(
   ({ sql }) => {
@@ -53,13 +53,13 @@ const agentWith = createDeepAgent({
   model,
   tools: [queryChinook],
   middleware: [createCodeInterpreterMiddleware({ ptc: ["query_chinook"] })],
-  systemPrompt:
-    SYSTEM +
-    " The eval tool supports Programmatic Tool Calling (PTC): JavaScript" +
-    " running inside eval() can call query_chinook via tools.queryChinook()." +
-    " For dependent queries where each answer requires a result from the" +
-    " previous, prefer a single eval() call that chains all queries in" +
-    " JavaScript — intermediate values stay in variables and never return to the model.",
+  systemPrompt: context`
+    ${SYSTEM}
+    The eval tool supports Programmatic Tool Calling (PTC): JavaScript
+    running inside eval() can call query_chinook via tools.queryChinook().
+    For dependent queries where each answer requires a result from the
+    previous, prefer a single eval() call that chains all queries in
+    JavaScript — intermediate values stay in variables and never return to the model.`,
 });
 
 const resultWith = await agentWith.invoke(
diff --git a/typescript/m3/m3.1_summarization.ts b/typescript/m3/m3.1_summarization.ts
index 37e0bb1..8dd6402 100644
--- a/typescript/m3/m3.1_summarization.ts
+++ b/typescript/m3/m3.1_summarization.ts
@@ -12,8 +12,8 @@
 //     npx tsx m3/m3.1_summarization.ts
 
 import { createDeepAgent } from "deepagents";
+import { HumanMessage } from "langchain";
 import { MemorySaver } from "@langchain/langgraph";
-import { HumanMessage } from "@langchain/core/messages";
 
 import { model } from "../models.js";
 
@@ -47,7 +47,7 @@ async function turn(message: string): Promise<unknown> {
     { messages: [new HumanMessage(message)] },
     THREAD
   );
-  return result.messages[result.messages.length - 1].content;
+  return result.messages.at(-1)?.content;
 }
 
 async function showState(): Promise<void> {
diff --git a/typescript/m3/m3.2_scratch_agent_skills.ts b/typescript/m3/m3.2_scratch_agent_skills.ts
index 5a08897..e06795c 100644
--- a/typescript/m3/m3.2_scratch_agent_skills.ts
+++ b/typescript/m3/m3.2_scratch_agent_skills.ts
@@ -2,6 +2,7 @@
 import { dirname } from "node:path";
 import { fileURLToPath } from "node:url";
 
+import { context } from "langchain";
 import { createDeepAgent, FilesystemBackend } from "deepagents";
 
 import { model } from "../models.js";
@@ -21,13 +22,13 @@ const result = await agent.invoke({
   messages: [
     {
       role: "user",
-      content:
-        "Qualify this lead: Acme Corp, 200-person logistics company. I spoke with " +
-        "Sarah Chen, VP of Sales: she's the decision maker. They have $45k budgeted " +
-        "for CRM this year. Main pain: deals are slipping through the cracks due to " +
-        "poor pipeline visibility. They want a solution live by end of Q3.",
+      content: context`
+        Qualify this lead: Acme Corp, 200-person logistics company. I spoke with
+        Sarah Chen, VP of Sales: she's the decision maker. They have $45k budgeted
+        for CRM this year. Main pain: deals are slipping through the cracks due to
+        poor pipeline visibility. They want a solution live by end of Q3.`,
     },
   ],
 });
 
-console.log(result.messages[result.messages.length - 1].content);
+console.log(result.messages.at(-1)?.content);
diff --git a/typescript/m3/m3.3_memory_agent.ts b/typescript/m3/m3.3_memory_agent.ts
index 8fa8c43..e89fbf1 100644
--- a/typescript/m3/m3.3_memory_agent.ts
+++ b/typescript/m3/m3.3_memory_agent.ts
@@ -78,7 +78,7 @@ const result = await agent.invoke(
   demoConfig
 );
 console.log("--- Question 1 ---");
-console.log(result.messages[result.messages.length - 1].content);
+console.log(result.messages.at(-1)?.content);
 
 // Second invoke: agent writes to memory
 const result2 = await agent.invoke(
diff --git a/typescript/m4/m4.2_run_newsletter.ts b/typescript/m4/m4.2_run_newsletter.ts
index b6fcdd8..8e97332 100644
--- a/typescript/m4/m4.2_run_newsletter.ts
+++ b/typescript/m4/m4.2_run_newsletter.ts
@@ -29,7 +29,7 @@ const result = await agent.invoke(
 );
 
 // The editor's final reply (coordination summary).
-console.log(result.messages[result.messages.length - 1].content);
+console.log(result.messages.at(-1)?.content);
 
 // Everything the agent produced lives in agent state (not on your disk — it ran
 // in the default StateBackend). Pull it all out and mirror it to OUT_DIR: the
diff --git a/typescript/m4/m4_2_newsletter_agent.ts b/typescript/m4/m4_2_newsletter_agent.ts
index 0c3a690..fd8f0a3 100644
--- a/typescript/m4/m4_2_newsletter_agent.ts
+++ b/typescript/m4/m4_2_newsletter_agent.ts
@@ -13,16 +13,17 @@
  * and writes it to disk.
  */
 
+import { z } from "zod";
 import { marked } from "marked";
 import sanitizeHtml from "sanitize-html";
-import { TavilySearchAPIWrapper } from "@langchain/tavily";
-import { tool } from "@langchain/core/tools";
-import { z } from "zod";
+
+import { context, tool } from "langchain";
 import {
   createDeepAgent,
   type FilesystemPermission,
   type SubAgent,
 } from "deepagents";
+import { TavilySearchAPIWrapper } from "@langchain/tavily";
 
 import { model, strongModel } from "../models.js";
 
@@ -35,7 +36,7 @@ const tavilyApiKey = process.env.TAVILY_API_KEY;
 if (!tavilyApiKey) {
   throw new Error(
     "TAVILY_API_KEY is required for the Module 4.2 newsletter lab. " +
-      "Set it in your environment before running m4.2_run_newsletter.ts."
+    "Set it in your environment before running m4.2_run_newsletter.ts."
   );
 }
 
@@ -47,9 +48,9 @@ const internetSearch = tool(
   },
   {
     name: "internet_search",
-    description:
-      "Search the web for recent news. Use this to research what's new in a " +
-      "music genre — new releases, notable artists, trends, and events.",
+    description: context`
+      Search the web for recent news. Use this to research what's new in a
+      music genre — new releases, notable artists, trends, and events.`,
     schema: z.object({
       query: z.string(),
       maxResults: z.number().default(8),
@@ -92,9 +93,9 @@ const markdownToHtml = tool(
   },
   {
     name: "markdown_to_html",
-    description:
-      "Convert a Markdown newsletter into a complete, styled HTML page. " +
-      "Returns the full HTML document as a string.",
+    description: context`
+      Convert a Markdown newsletter into a complete, styled HTML page.
+      Returns the full HTML document as a string.`,
     schema: z.object({
       markdownText: z.string(),
       title: z.string().default("This Week in Music"),
@@ -103,27 +104,28 @@ const markdownToHtml = tool(
 );
 
 // --- The research subagent -------------------------------------------------
-const GENRE_PROMPT = `You are a music journalist researching one genre for an
-online music distributor's weekly newsletter.
-
-You will be given a single genre and an assigned research folder to work in.
-
-How to work:
-1. Use internet_search to find recent, noteworthy developments in that genre
-   — new releases, notable artists, trends, or events. Run a few searches.
-2. Save the COMPLETE, verbatim output of ALL your searches to a single file:
-   write_file("/research/<genre>/sources.md", ...). Paste the results exactly
-   as the tool returned them — every result's title, URL, and full content
-   snippet. Do NOT summarize, trim, or reformat. This one file is your raw
-   archive: all the bulky material stays here so it never clutters the
-   editor's context.
-3. Only then, from what you found, write one tight newsletter segment.
-
-Return ONLY the finished segment as your reply:
-- A markdown section: a "## <Genre>" heading followed by ~120-180 words.
-- Lively but factual newsletter tone; name specific artists and releases.
-- Do NOT paste raw search results or link dumps into your reply — those live
-  in your research files. Return just the polished segment.`;
+const GENRE_PROMPT = context`
+  You are a music journalist researching one genre for an
+  online music distributor's weekly newsletter.
+
+  You will be given a single genre and an assigned research folder to work in.
+
+  How to work:
+  1. Use internet_search to find recent, noteworthy developments in that genre
+     — new releases, notable artists, trends, or events. Run a few searches.
+  2. Save the COMPLETE, verbatim output of ALL your searches to a single file:
+     write_file("/research/<genre>/sources.md", ...). Paste the results exactly
+     as the tool returned them — every result's title, URL, and full content
+     snippet. Do NOT summarize, trim, or reformat. This one file is your raw
+     archive: all the bulky material stays here so it never clutters the
+     editor's context.
+  3. Only then, from what you found, write one tight newsletter segment.
+
+  Return ONLY the finished segment as your reply:
+  - A markdown section: a "## <Genre>" heading followed by ~120-180 words.
+  - Lively but factual newsletter tone; name specific artists and releases.
+  - Do NOT paste raw search results or link dumps into your reply — those live
+    in your research files. Return just the polished segment.`;
 
 // Researchers may write under /research/** and are denied writes elsewhere.
 const researchPermissions: FilesystemPermission[] = [
@@ -133,9 +135,9 @@ const researchPermissions: FilesystemPermission[] = [
 
 const genreResearcher: SubAgent = {
   name: "genre-researcher",
-  description:
-    "Research one music genre and write a short newsletter segment about " +
-    "what's new in it. Delegate one genre per call.",
+  description: context`
+    Research one music genre and write a short newsletter segment about
+    what's new in it. Delegate one genre per call.`,
   systemPrompt: GENRE_PROMPT, // its own brain — never inherited
   tools: [internetSearch], // override — replaces the inherited set
   model, // override — the cheaper Haiku 4.5
@@ -143,21 +145,22 @@ const genreResearcher: SubAgent = {
 };
 
 // --- The editor (main agent) -----------------------------------------------
-const EDITOR_PROMPT = `You are the editor of an online music distributor's weekly
-newsletter. This week you are featuring the distributor's top genres:
-${TOP_GENRES.join(", ")}.
-
-Your job:
-1. For EACH genre, delegate to the genre-researcher subagent using the task
-   tool — fire them off in parallel. Tell each one which genre to cover and
-   which assigned folder to use (/research/<genre>/), and ask for one segment.
-2. Collect the four returned segments. Do NOT research genres yourself.
-3. Assemble them into one Markdown newsletter: a top-level "# This Week in
-   Music" title, a one-sentence intro, then the four "## <Genre>" sections.
-4. Call markdown_to_html on the assembled Markdown, then write_file the
-   returned HTML to /output/newsletter.html.
-
-Keep your own context focused on coordination and assembly.`;
+const EDITOR_PROMPT = context`
+  You are the editor of an online music distributor's weekly
+  newsletter. This week you are featuring the distributor's top genres:
+  ${TOP_GENRES.join(", ")}.
+
+  Your job:
+  1. For EACH genre, delegate to the genre-researcher subagent using the task
+     tool — fire them off in parallel. Tell each one which genre to cover and
+     which assigned folder to use (/research/<genre>/), and ask for one segment.
+  2. Collect the four returned segments. Do NOT research genres yourself.
+  3. Assemble them into one Markdown newsletter: a top-level "# This Week in
+     Music" title, a one-sentence intro, then the four "## <Genre>" sections.
+  4. Call markdown_to_html on the assembled Markdown, then write_file the
+     returned HTML to /output/newsletter.html.
+
+  Keep your own context focused on coordination and assembly.`;
 
 // The editor uses the stronger shared model; the researcher overrides to the
 // cheaper `model` (Haiku 4.5) above. Both come from models.ts.
diff --git a/typescript/m5/sales_assistant/agent.ts b/typescript/m5/sales_assistant/agent.ts
index 1c97cd0..a1cfc64 100644
--- a/typescript/m5/sales_assistant/agent.ts
+++ b/typescript/m5/sales_assistant/agent.ts
@@ -13,6 +13,7 @@ import { fileURLToPath } from "node:url";
 
 import { MultiServerMCPClient } from "@langchain/mcp-adapters";
 import { createCodeInterpreterMiddleware } from "@langchain/quickjs";
+import { context } from "langchain";
 import { FilesystemBackend, createDeepAgent } from "deepagents";
 
 import { strongModel } from "../../models.js";
@@ -22,10 +23,10 @@ import { markdownToHtml } from "./tools/html.js";
 
 const HERE = dirname(fileURLToPath(import.meta.url));
 
-const SYSTEM_PROMPT =
-  "You are a sales assistant for Jane Peacock, a Sales Support Agent at " +
-  "Chinook, an online music distributor. Follow your operating manual (loaded " +
-  "from your memory) and use the matching playbook from /skills/ for each task.";
+const SYSTEM_PROMPT = context`
+  You are a sales assistant for Jane Peacock, a Sales Support Agent at
+  Chinook, an online music distributor. Follow your operating manual (loaded
+  from your memory) and use the matching playbook from /skills/ for each task.`;
 
 const enableSearch = Boolean(process.env.TAVILY_API_KEY);
 if (!enableSearch) {
diff --git a/typescript/m5/sales_assistant/mcp/mock_mail_server.ts b/typescript/m5/sales_assistant/mcp/mock_mail_server.ts
index f9a21d3..b1d27f9 100644
--- a/typescript/m5/sales_assistant/mcp/mock_mail_server.ts
+++ b/typescript/m5/sales_assistant/mcp/mock_mail_server.ts
@@ -16,6 +16,7 @@ import { createServer } from "node:http";
 import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
 import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
 import { z } from "zod";
+import { context } from "langchain";
 
 import { loadStore, nextId, saveStore } from "./mail_store.js";
 
@@ -29,12 +30,12 @@ function buildServer(): McpServer {
   mcp.registerTool(
     "mail_list_messages",
     {
-      description:
-        "List messages in the inbox. Returns a summary (id, from, subject, " +
-        "date, snippet) for each message — not the full body. Use " +
-        "mail_read_message to open one. The optional query is a " +
-        "case-insensitive substring matched against the subject and sender, " +
-        "mostly to mirror Gmail's search box; leave it empty to list everything.",
+      description: context`
+        List messages in the inbox. Returns a summary (id, from, subject,
+        date, snippet) for each message — not the full body. Use
+        mail_read_message to open one. The optional query is a
+        case-insensitive substring matched against the subject and sender,
+        mostly to mirror Gmail's search box; leave it empty to list everything.`,
       inputSchema: { query: z.string().default("") },
     },
     async ({ query }) => {
@@ -70,11 +71,11 @@ function buildServer(): McpServer {
   mcp.registerTool(
     "mail_create_draft",
     {
-      description:
-        "Save a reply to the drafts folder. Does NOT send. Mirrors a real " +
-        "Gmail \"create draft\" call: the message is staged for the human to " +
-        "review and send later. In this course a human-in-the-loop gate runs " +
-        "before this tool, so a draft is only written after explicit approval.",
+      description: context`
+        Save a reply to the drafts folder. Does NOT send. Mirrors a real
+        Gmail "create draft" call: the message is staged for the human to
+        review and send later. In this course a human-in-the-loop gate runs
+        before this tool, so a draft is only written after explicit approval.`,
       inputSchema: { to: z.string(), subject: z.string(), body: z.string() },
     },
     async ({ to, subject, body }) => {
diff --git a/typescript/m5/sales_assistant/subagents.ts b/typescript/m5/sales_assistant/subagents.ts
index 14b2a53..77c3090 100644
--- a/typescript/m5/sales_assistant/subagents.ts
+++ b/typescript/m5/sales_assistant/subagents.ts
@@ -21,14 +21,17 @@
  * `mail_create_draft` and `add_customer` solely on gated specialists means the
  * only path to either write runs through its human-approval gate.
  */
-import type { StructuredTool } from "@langchain/core/tools";
 import {
   type AnyBackendProtocol,
   type FilesystemPermission,
   type SubAgent,
   createMemoryMiddleware,
 } from "deepagents";
-import type { InterruptOnConfig } from "langchain";
+import {
+  context,
+  type InterruptOnConfig,
+  type StructuredTool,
+} from "langchain";
 
 import { model, strongModel } from "../../models.js";
 import { internetSearch } from "./tools/search.js";
@@ -39,65 +42,69 @@ const APPROVE_EDIT_REJECT: InterruptOnConfig = {
   allowedDecisions: ["approve", "edit", "reject"],
 };
 
-const ANALYST_PROMPT = `You are the chinook-analyst, the data specialist for the \
-Chinook Sales Assistant. You are the only agent that touches the database.
-
-Detailed operating instructions and the database schema live in your memory \
-(loaded automatically). Follow them. In short: answer with exact figures from \
-\`query_chinook\`, learn the schema once with \`introspect_schema\` and record it \
-in your memory, and use \`add_customer\` only when asked to add a genuinely new \
-customer (a human approves that write).`;
-
-const INBOX_PROMPT = `You are the inbox-manager, the email specialist for the \
-Chinook Sales Assistant. You own Jane's inbox and are the only agent that \
-touches it.
-
-Your tools (MCP, prefixed with the server name "mail"):
-- \`mail_list_messages\` — list inbox messages (optionally filtered by a query).
-- \`mail_read_message\` — read one message in full by id.
-- \`mail_create_draft\` — save a reply to the drafts folder. It NEVER sends.
-
-When asked to find or read mail, return a tight summary the caller can act on \
-(sender, subject, and the key content) — not the raw dump.
-
-When asked to save a draft, just call \`mail_create_draft\` with the given \
-recipient, subject, and body. Saving a draft pauses automatically for Jane to \
-approve, edit, or reject — that pause IS the approval, so don't ask for \
-permission in prose first; make the call. Never invent a send tool; you only \
-ever create drafts.`;
-
-const REVIEWER_PROMPT = `You are the quote-reviewer. You receive a drafted quote — \
-line items (description, quantity, unit price, line total), any discount, and \
-the grand total — and you check it before it goes to the customer.
-
-Verify:
-- The arithmetic: quantity x unit price for each line, and the grand total.
-- Internal consistency: any stated discount is actually applied; nothing is \
-double-counted or missing.
-- Plausibility: unit prices look like catalogue prices (tracks are normally \
-about $0.99); totals aren't off by an order of magnitude.
-
-Reply concisely: either "Looks correct" with a one-line confirmation, or a \
-short list of specific corrections. Do not rewrite the customer email — just \
-review the numbers and terms.`;
-
-const GENRE_PROMPT = `You are a music journalist researching one genre for an \
-online music distributor's weekly newsletter.
-
-You will be given a single genre and a private research folder to work in.
-
-How to work:
-1. Use internet_search to find recent, noteworthy developments in that genre \
-   — new releases, notable artists, trends, or events. Run a few searches.
-2. Save the COMPLETE, verbatim output of ALL your searches to a single file: \
-   write_file("/research/<genre>/sources.md", ...). Do NOT summarize or trim. \
-   This keeps the bulky material out of the editor's context.
-3. Only then, from what you found, write one tight newsletter segment.
-
-Return ONLY the finished segment as your reply:
-- A markdown section: a "## <Genre>" heading followed by ~120-180 words.
-- Lively but factual; name specific artists and releases.
-- Do NOT paste raw search results into your reply — those live in your files.`;
+const ANALYST_PROMPT = context`
+  You are the chinook-analyst, the data specialist for the
+  Chinook Sales Assistant. You are the only agent that touches the database.
+
+  Detailed operating instructions and the database schema live in your memory
+  (loaded automatically). Follow them. In short: answer with exact figures from
+  \`query_chinook\`, learn the schema once with \`introspect_schema\` and record it
+  in your memory, and use \`add_customer\` only when asked to add a genuinely new
+  customer (a human approves that write).`;
+
+const INBOX_PROMPT = context`
+  You are the inbox-manager, the email specialist for the
+  Chinook Sales Assistant. You own Jane's inbox and are the only agent that
+  touches it.
+
+  Your tools (MCP, prefixed with the server name "mail"):
+  - \`mail_list_messages\` — list inbox messages (optionally filtered by a query).
+  - \`mail_read_message\` — read one message in full by id.
+  - \`mail_create_draft\` — save a reply to the drafts folder. It NEVER sends.
+
+  When asked to find or read mail, return a tight summary the caller can act on
+  (sender, subject, and the key content) — not the raw dump.
+
+  When asked to save a draft, just call \`mail_create_draft\` with the given
+  recipient, subject, and body. Saving a draft pauses automatically for Jane to
+  approve, edit, or reject — that pause IS the approval, so don't ask for
+  permission in prose first; make the call. Never invent a send tool; you only
+  ever create drafts.`;
+
+const REVIEWER_PROMPT = context`
+  You are the quote-reviewer. You receive a drafted quote —
+  line items (description, quantity, unit price, line total), any discount, and
+  the grand total — and you check it before it goes to the customer.
+
+  Verify:
+  - The arithmetic: quantity x unit price for each line, and the grand total.
+  - Internal consistency: any stated discount is actually applied; nothing is
+    double-counted or missing.
+  - Plausibility: unit prices look like catalogue prices (tracks are normally
+    about $0.99); totals aren't off by an order of magnitude.
+
+  Reply concisely: either "Looks correct" with a one-line confirmation, or a
+  short list of specific corrections. Do not rewrite the customer email — just
+  review the numbers and terms.`;
+
+const GENRE_PROMPT = context`
+  You are a music journalist researching one genre for an
+  online music distributor's weekly newsletter.
+
+  You will be given a single genre and a private research folder to work in.
+
+  How to work:
+  1. Use internet_search to find recent, noteworthy developments in that genre
+     — new releases, notable artists, trends, or events. Run a few searches.
+  2. Save the COMPLETE, verbatim output of ALL your searches to a single file:
+     write_file("/research/<genre>/sources.md", ...). Do NOT summarize or trim.
+     This keeps the bulky material out of the editor's context.
+  3. Only then, from what you found, write one tight newsletter segment.
+
+  Return ONLY the finished segment as your reply:
+  - A markdown section: a "## <Genre>" heading followed by ~120-180 words.
+  - Lively but factual; name specific artists and releases.
+  - Do NOT paste raw search results into your reply — those live in your files.`;
 
 export interface BuildSubagentsOptions {
   enableSearch: boolean;
@@ -111,10 +118,10 @@ export function buildSubagents(
 ): SubAgent[] {
   const chinookAnalyst: SubAgent = {
     name: "chinook-analyst",
-    description:
-      "Query the Chinook database for catalogue prices, customer records, " +
-      "purchase history, and territory metrics, and add new customers " +
-      "(with approval). Delegate all database work here.",
+    description: context`
+      Query the Chinook database for catalogue prices, customer records,
+      purchase history, and territory metrics, and add new customers
+      (with approval). Delegate all database work here.`,
     systemPrompt: ANALYST_PROMPT,
     tools: [queryChinook, introspectSchema, addCustomer],
     model,
@@ -132,19 +139,19 @@ export function buildSubagents(
 
   const quoteReviewer: SubAgent = {
     name: "quote-reviewer",
-    description:
-      "Review a drafted quote (line items, discount, total) for correct " +
-      "arithmetic and sane pricing before it is sent. Send it the numbers.",
+    description: context`
+      Review a drafted quote (line items, discount, total) for correct
+      arithmetic and sane pricing before it is sent. Send it the numbers.`,
     systemPrompt: REVIEWER_PROMPT,
     model: strongModel,
   };
 
   const inboxManager: SubAgent = {
     name: "inbox-manager",
-    description:
-      "Read Jane's inbox and save reply drafts. Delegate any " +
-      "email work here: finding/reading messages and creating a " +
-      "draft reply (which pauses for Jane's approval).",
+    description: context`
+      Read Jane's inbox and save reply drafts. Delegate any
+      email work here: finding/reading messages and creating a
+      draft reply (which pauses for Jane's approval).`,
     systemPrompt: INBOX_PROMPT,
     tools: mailTools,
     model,
@@ -161,9 +168,9 @@ export function buildSubagents(
 
     const genreResearcher: SubAgent = {
       name: "genre-researcher",
-      description:
-        "Research one music genre and write a short newsletter segment " +
-        "about what's new in it. Delegate one genre per call.",
+      description: context`
+        Research one music genre and write a short newsletter segment
+        about what's new in it. Delegate one genre per call.`,
       systemPrompt: GENRE_PROMPT,
       tools: [internetSearch],
       model,
diff --git a/typescript/m5/sales_assistant/test_diagnostic.ts b/typescript/m5/sales_assistant/test_diagnostic.ts
index e677265..6246502 100644
--- a/typescript/m5/sales_assistant/test_diagnostic.ts
+++ b/typescript/m5/sales_assistant/test_diagnostic.ts
@@ -14,6 +14,7 @@ import { dirname, join } from "node:path";
 import { fileURLToPath } from "node:url";
 
 import { config } from "dotenv";
+import { context } from "langchain";
 import { Client } from "@langchain/langgraph-sdk";
 
 const HERE = dirname(fileURLToPath(import.meta.url));
@@ -139,8 +140,9 @@ async function testAgentsMd(client: Client): Promise<Result> {
   try {
     const [reply] = await ask(
       client,
-      "Repeat the diagnostic token from your operating manual. " +
-        "It appears as italic text near the top of the file."
+      context`
+        Repeat the diagnostic token from your operating manual.
+        It appears as italic text near the top of the file.`
     );
     const passed = reply.includes("CHINOOK-READY");
     console.log("done");
@@ -190,8 +192,9 @@ async function testCodeInterpreter(client: Client): Promise<Result> {
   try {
     const [reply] = await ask(
       client,
-      "Use the code interpreter to calculate: 37 tracks at $0.99 each. " +
-        "What is the exact total?"
+      context`
+        Use the code interpreter to calculate: 37 tracks at $0.99 each.
+        What is the exact total?`
     );
     const passed = reply.includes("36.63");
     console.log("done");
@@ -252,9 +255,9 @@ async function testHitlInterrupt(client: Client): Promise<Result> {
         messages: [
           {
             role: "user",
-            content:
-              "Draft a reply to the email from Morgan Vale saying we will get " +
-              "back to them within 24 hours. Save the draft.",
+            content: context`
+              Draft a reply to the email from Morgan Vale saying we will get
+              back to them within 24 hours. Save the draft.`,
           },
         ],
       },
@@ -285,8 +288,9 @@ async function testRenderPieChart(client: Client): Promise<Result> {
     const [, messages] = await askInThread(
       client,
       thread.thread_id,
-      "Query the Chinook database for total revenue by genre (top 5 genres). " +
-        "Call render_pie_chart to save a pie chart as diag_genre_revenue.png."
+      context`
+        Query the Chinook database for total revenue by genre (top 5 genres).
+        Call render_pie_chart to save a pie chart as diag_genre_revenue.png.`
     );
     const toolOuts = toolOutputs(messages, "render_pie_chart");
     const exists = existsSync(target);
diff --git a/typescript/m5/sales_assistant/tools/chart.ts b/typescript/m5/sales_assistant/tools/chart.ts
index 69e488b..7c3ef43 100644
--- a/typescript/m5/sales_assistant/tools/chart.ts
+++ b/typescript/m5/sales_assistant/tools/chart.ts
@@ -16,8 +16,8 @@ import { dirname, join } from "node:path";
 import { fileURLToPath } from "node:url";
 
 import { createCanvas } from "canvas";
-import { tool } from "@langchain/core/tools";
 import { z } from "zod";
+import { context, tool } from "langchain";
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
 const OUTPUTS_DIR = join(__dirname, "..", "outputs");
@@ -112,13 +112,13 @@ export const renderPieChart = tool(
   },
   {
     name: "render_pie_chart",
-    description:
-      "Render a labeled pie chart and save it as a PNG in outputs/. " +
-      "Args: title (chart title), labels (one per slice, e.g. genre names), " +
-      "values (one numeric value per label, same length as labels), " +
-      "filename (e.g. \"territory_chart.png\" — any directory components are " +
-      "stripped and the extension is forced to .png; the file is always " +
-      "saved into outputs/).",
+    description: context`
+      Render a labeled pie chart and save it as a PNG in outputs/.
+      Args: title (chart title), labels (one per slice, e.g. genre names),
+      values (one numeric value per label, same length as labels),
+      filename (e.g. "territory_chart.png" — any directory components are
+      stripped and the extension is forced to .png; the file is always
+      saved into outputs/).`,
     schema: z.object({
       title: z.string(),
       labels: z.array(z.string()),
diff --git a/typescript/m5/sales_assistant/tools/html.ts b/typescript/m5/sales_assistant/tools/html.ts
index 483bf36..598ae6f 100644
--- a/typescript/m5/sales_assistant/tools/html.ts
+++ b/typescript/m5/sales_assistant/tools/html.ts
@@ -10,8 +10,8 @@
  */
 import { marked } from "marked";
 import sanitizeHtml from "sanitize-html";
-import { tool } from "@langchain/core/tools";
 import { z } from "zod";
+import { context, tool } from "langchain";
 
 const HTML_TEMPLATE = (title: string, body: string) => `<!doctype html>
 <html lang="en">
@@ -44,9 +44,9 @@ export const markdownToHtml = tool(
   },
   {
     name: "markdown_to_html",
-    description:
-      "Convert a Markdown newsletter into a complete, styled HTML page. " +
-      "Returns the full HTML document as a string.",
+    description: context`
+      Convert a Markdown newsletter into a complete, styled HTML page.
+      Returns the full HTML document as a string.`,
     schema: z.object({
       markdownText: z.string(),
       title: z.string().default("This Week in Music"),
diff --git a/typescript/m5/sales_assistant/tools/search.ts b/typescript/m5/sales_assistant/tools/search.ts
index 1749f4d..b5c565e 100644
--- a/typescript/m5/sales_assistant/tools/search.ts
+++ b/typescript/m5/sales_assistant/tools/search.ts
@@ -7,9 +7,9 @@
  * if it's absent the tool is simply not registered (see subagents.ts), so
  * the rest of the assistant still runs.
  */
-import { TavilySearchAPIWrapper } from "@langchain/tavily";
-import { tool } from "@langchain/core/tools";
 import { z } from "zod";
+import { context, tool } from "langchain";
+import { TavilySearchAPIWrapper } from "@langchain/tavily";
 
 const tavily = new TavilySearchAPIWrapper({
   tavilyApiKey: process.env.TAVILY_API_KEY,
@@ -21,9 +21,9 @@ export const internetSearch = tool(
   },
   {
     name: "internet_search",
-    description:
-      "Search the web for recent news. Use this to research what's new in a " +
-      "music genre — new releases, notable artists, trends, and events.",
+    description: context`
+      Search the web for recent news. Use this to research what's new in a
+      music genre — new releases, notable artists, trends, and events.`,
     schema: z.object({
       query: z.string(),
       maxResults: z.number().default(8),
diff --git a/typescript/m5/sales_assistant/tools/sql.ts b/typescript/m5/sales_assistant/tools/sql.ts
index 9e41319..df7f230 100644
--- a/typescript/m5/sales_assistant/tools/sql.ts
+++ b/typescript/m5/sales_assistant/tools/sql.ts
@@ -21,8 +21,8 @@ import { DatabaseSync } from "node:sqlite";
 import { dirname, join } from "node:path";
 import { fileURLToPath } from "node:url";
 
-import { tool } from "@langchain/core/tools";
 import { z } from "zod";
+import { context, tool } from "langchain";
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
 // The database ships with the agent under data/.
@@ -66,12 +66,12 @@ export const queryChinook = tool(
   },
   {
     name: "query_chinook",
-    description:
-      "Run a read-only SQL SELECT against the Chinook database. Returns a " +
-      "JSON array of row objects. Only a single SELECT statement is allowed " +
-      "— any attempt to modify the database is rejected. Use this for all " +
-      "lookups: catalogue prices, a customer's purchase history, territory " +
-      "metrics, and so on.",
+    description: context`
+      Run a read-only SQL SELECT against the Chinook database. Returns a
+      JSON array of row objects. Only a single SELECT statement is allowed
+      — any attempt to modify the database is rejected. Use this for all
+      lookups: catalogue prices, a customer's purchase history, territory
+      metrics, and so on.`,
     schema: z.object({ sql: z.string() }),
   }
 );
@@ -96,10 +96,10 @@ export const introspectSchema = tool(
   },
   {
     name: "introspect_schema",
-    description:
-      "Return the full database schema (CREATE statements for every table). " +
-      "Call this once to learn the schema, then record it in your memory so " +
-      "you don't have to rediscover it on every task.",
+    description: context`
+      Return the full database schema (CREATE statements for every table).
+      Call this once to learn the schema, then record it in your memory so
+      you don't have to rediscover it on every task.`,
     schema: z.object({}),
   }
 );
@@ -172,11 +172,11 @@ export const addCustomer = tool(
   },
   {
     name: "add_customer",
-    description:
-      "Add a NEW customer to the database, assigned to the current sales " +
-      "rep. Use this only after confirming the customer is not already in " +
-      "the system (search by email or name first). A human approves this " +
-      "write before it runs. Returns the new CustomerId on success.",
+    description: context`
+      Add a NEW customer to the database, assigned to the current sales
+      rep. Use this only after confirming the customer is not already in
+      the system (search by email or name first). A human approves this
+      write before it runs. Returns the new CustomerId on success.`,
     schema: z.object({
       firstName: z.string(),
       lastName: z.string(),