[AIT-273] Message per response guide for Vercel AI SDK

[matt423]

Description

Follow existing message per response guides, add guide for Vercel AI SDK.

Review App

Checklist

• Commits have been rebased.
• Linting has been run against the changed file(s).
• The PR adheres to the writing style guide and contribution guide.

Summary by CodeRabbit

• Documentation
  • Added a new guide for streaming Vercel AI SDK responses using the message-per-response pattern over Ably, including prerequisites, setup instructions, and example implementations for publishers and subscribers.

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[coderabbitai]

Walkthrough

This PR adds a new guide document for implementing token streaming with Vercel AI SDK using a message-per-response pattern, including a corresponding navigation entry. The guide covers setup, prerequisites, and code examples demonstrating publisher and subscriber implementations for streaming responses via Ably.

Changes

Cohort / File(s)	Summary
Navigation Configuration src/data/nav/aitransport.ts	Added new navigation entry for "Vercel AI SDK token streaming - message per response" guide under Guides → Token streaming section
Documentation src/pages/docs/guides/ai-transport/vercel-message-per-response.mdx	New guide document covering token streaming implementation using message-per-response pattern, including prerequisites, setup steps, code examples for publisher/subscriber implementations, event type handling, message serial management, and performance considerations

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~15 minutes

Possibly related PRs

• [AIT-205] Add Vercel AI SDK message per token guide #3128: Adds a sibling guide page for message-per-token token streaming pattern and corresponding navigation entry under the same Guides → Token streaming section in the NavProduct configuration.

Suggested reviewers

• GregHolmes
• mschristensen

Poem

🐰 A message flows, response by response,
Through Vercel's streams, no need to force,
With Ably's aid, we guide the way,
Token by token, sent to stay,
Documentation bright and clear! 📚✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main change: adding a message per response guide for Vercel AI SDK, which matches the primary objective of creating a new guide article.
Linked Issues check	✅ Passed	The PR fulfills AIT-273's requirement by adding a comprehensive guide documenting token streaming with the Vercel AI SDK, including setup, implementation examples, and historical retrieval patterns.
Out of Scope Changes check	✅ Passed	All changes are directly related to adding the requested guide: navigation entry in aitransport.ts and the new documentation file vercel-message-per-response.mdx are both in scope for AIT-273.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing touches

• 📝 Generate docstrings

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[matt423]

@coderabbitai review

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✅ Actions performed

Review triggered.

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@src/pages/docs/guides/ai-transport/vercel-message-per-response.mdx`:
- Around line 40-46: Update the installation command and version note to
reference AI SDK 6.x: replace the install line "npm install ai@^5 ably@^2" with
"npm install ai@^6 ably@^2" (or "ai@6" per style) and change the Aside text that
currently says "This guide uses version 5.x of the AI SDK" to "This guide uses
version 6.x of the AI SDK" (or similar wording), ensuring any other mentions of
"5.x" in this file are updated unless the guide is intentionally for legacy v5
users.

🧹 Nitpick comments (1)

src/pages/docs/guides/ai-transport/vercel-message-per-response.mdx (1)

196-231: Consider adding basic error handling for production readiness.

The publish/append pattern is correct, but the example lacks error handling. While this is a guide focused on the happy path, a brief mention of error handling strategies (e.g., try-catch around the initial publish, handling append failures) would help users build more robust implementations.

💡 Optional: Add minimal error handling

     case 'text-start':
       // Publish initial empty message when response starts
-      const result = await channel.publish({
-        name: 'response',
-        data: ''
-      });
-
-      // Capture the message serial for appending tokens
-      msgSerial = result.serials[0];
+      try {
+        const result = await channel.publish({
+          name: 'response',
+          data: ''
+        });
+        // Capture the message serial for appending tokens
+        msgSerial = result.serials[0];
+      } catch (err) {
+        console.error('Failed to publish initial message:', err);
+      }
       break;