docs(operate): add Vercel log drains setup guide

Covers both automatic setup (Sentry native integration) and manual setup
for existing accounts. Documents log and trace drain configuration,
log source selection, and platform-specific caveats sourced from:
- https://docs.sentry.io/product/drains/vercel/
- https://vercel.com/docs/drains

Also wires the new page into the sidebar and updates observability.md
to reference it.

Fixes #441

---
[View Session in Sentry](https://sentry.sentry.io/traces/?project=4510944073809921&query=gen_ai.conversation.id%3A%22slack%3AC0AHB7N2JCR%3A1780258891.450269%22)

Co-Authored-By: claude-opus-4-5 <noreply@anthropic.com>

Co-authored-by: David Cramer <david@sentry.io>

Author: sentry-junior[bot]

packages/docs/astro.config.mjs

@@ -124,6 +124,10 @@ export default defineConfig({
               label: "Sandbox Snapshots",
               link: "/operate/sandbox-snapshots/",
             },
+            {
+              label: "Vercel Log Drains",
+              link: "/operate/vercel-log-drains/",
+            },
           ],
         },
         {

packages/docs/src/content/docs/operate/observability.md

@@ -6,6 +6,7 @@ prerequisites:
   - /start-here/verify-and-troubleshoot/
 related:
   - /operate/reliability-runbooks/
+  - /operate/vercel-log-drains/
   - /reference/handler-surface/
 ---
 
@@ -55,4 +56,4 @@ event.name:agent_tool_call_failed
 
 ## Next step
 
-Use symptom-driven playbooks in [Reliability Runbooks](/operate/reliability-runbooks/).
+Set up [Vercel Log Drains](/operate/vercel-log-drains/) to route runtime and build logs directly into Sentry, then use [Reliability Runbooks](/operate/reliability-runbooks/) for symptom-driven playbooks.

packages/docs/src/content/docs/operate/vercel-log-drains.md

@@ -0,0 +1,111 @@
+---
+title: Vercel Log Drains
+description: Forward Vercel runtime, build, and edge logs to Sentry using Vercel's built-in log drain.
+type: tutorial
+summary: Configure a Vercel log or trace drain pointed at Sentry's ingestion endpoint to route Vercel output into Sentry Logs and Traces.
+prerequisites:
+  - /start-here/deploy-to-vercel/
+  - /operate/observability/
+related:
+  - /extend/sentry-plugin/
+  - /operate/observability/
+  - /operate/reliability-runbooks/
+---
+
+Vercel Drains let you forward telemetry from your Vercel-hosted Junior deployment directly to Sentry without modifying application code. Sentry receives the data as [Logs](https://docs.sentry.io/product/explore/logs/) and [Traces](https://docs.sentry.io/product/explore/trace-explorer/).
+
+Official references:
+
+- [Sentry Vercel Drains documentation](https://docs.sentry.io/product/drains/vercel/)
+- [Vercel Drains documentation](https://vercel.com/docs/drains)
+
+## Prerequisites
+
+- Vercel **Pro or higher** plan (drains require Pro or Enterprise)
+- A deployed Junior project on Vercel
+- A Sentry project to receive the data
+
+## Automatic setup (Sentry native integration)
+
+If you installed Junior from the [Sentry Vercel Integration](https://vercel.com/marketplace/sentry) and created a new Sentry account during that flow, you can add drains directly from the integration settings:
+
+1. From the Vercel dashboard, open the **Integrations** tab.
+2. Select **Sentry** from the list, click **Manage**, and select your installed product.
+3. Under **Drains**, click **Add Drain**.
+4. Choose which Vercel project to drain from, then click **Create Drain**.
+
+> **Note:** Automatic drain setup is only available with the Native Integration when a _new_ Sentry account was created during install. For existing Sentry accounts, follow the manual steps below.
+
+## Manual setup
+
+Manual setup applies to any Sentry account. You need the Sentry ingestion endpoint and auth header from your project's DSN settings.
+
+### Locate the Sentry endpoint and auth header
+
+1. In Sentry, go to **Settings > Projects > \[your project\] > Client Keys (DSN)**.
+2. Expand the **Vercel** section.
+3. Copy the **Vercel Log Drain Endpoint** URL and the **Authentication Header** value (`x-sentry-auth: sentry sentry_key=<key>`).
+
+### Create the log drain in Vercel
+
+1. From the Vercel dashboard, go to **Team Settings > Drains** and click **Add Drain**.
+2. Select **Logs** as the data type.
+3. Name the drain and select the project(s) to drain from.
+4. Set the **Sampling rate**. Start at 100% to confirm delivery, then reduce as needed.
+5. Select the **Log sources** to collect. See [Log sources](#log-sources) below.
+6. Select which **Environments** to drain (production, preview, or all).
+7. Under the **Custom Endpoint** tab:
+   - **URL**: paste the Vercel Log Drain Endpoint from Sentry.
+   - **Format**: choose **JSON** or **NDJSON** (both are accepted).
+   - Enable **Custom Headers** and add one header per line:
+     ```
+     x-sentry-auth: sentry sentry_key=<your-public-key>
+     ```
+8. Click **Create Drain**. Vercel tests the endpoint automatically on save.
+
+### Verify log drain delivery
+
+After creating the drain, click **Test** from the drain settings. Then check [Sentry Logs](https://sentry.io/explore/logs/) to confirm entries are arriving.
+
+## Trace drain setup
+
+Trace drains forward OpenTelemetry (OTLP) distributed tracing data from Vercel Functions to Sentry.
+
+1. From the Vercel dashboard, go to **Team Settings > Drains > Add Drain**.
+2. Select **Traces** as the data type.
+3. Name the drain, select projects, and configure the sampling rate.
+4. Under the **Custom Endpoint** tab:
+   - **URL**: from Sentry **Settings > Projects > \[your project\] > Client Keys (DSN) > OpenTelemetry (OTLP)**, copy the **OTLP Traces Endpoint**.
+   - Enable **Custom Headers** and add:
+     ```
+     x-sentry-auth: sentry sentry_key=<your-public-key>
+     ```
+     (Find this value under the same **OTLP Traces Endpoint Headers** section.)
+5. Click **Create Drain**.
+
+Vercel sends trace data over OTLP/HTTP (JSON or Protobuf). OTLP/gRPC is not supported by Vercel drains.
+
+## Log sources
+
+Vercel surfaces six log source categories. Select the ones relevant to your deployment:
+
+| Source | What it captures |
+| --- | --- |
+| **Functions** | Output from Vercel Functions (API Routes) |
+| **Edge Functions** | Output from Edge runtime functions and Middleware |
+| **Static Files** | Requests for static assets (HTML, CSS, etc.) |
+| **Rewrites** | External rewrite results to a different domain |
+| **Builds** | Output from the Vercel build step |
+| **Firewall** | Requests denied by Vercel Firewall rules |
+
+## Caveats
+
+- **Metric drains not supported.** Speed Insights and Web Analytics cannot be forwarded to Sentry. See [GitHub issue #103488](https://github.com/getsentry/sentry/issues/103488) if you need this.
+- **Empty messages on `static`/`edge` logs.** Some logs from these sources intentionally have an empty `message` field per the Vercel schema. This is expected.
+- **Static source logs in Sentry only.** Logs with `source: static` show up in Sentry but not in the Vercel dashboard by default; that is a Vercel dashboard display limitation.
+- **Build logs are not trace-connected.** Vercel build logs are forwarded but do not carry trace context. Use `vercel.project_name`, `vercel.deployment_id`, and `vercel.build_id` attributes to correlate build logs with a specific deployment.
+- **Trace correlation for runtime logs.** When [Vercel Tracing](https://vercel.com/docs/tracing) is active, runtime logs during traced requests are automatically enriched with `traceId` and `spanId` fields at no extra configuration cost.
+
+## Next step
+
+Use [Observability](/operate/observability/) to build queries against the ingested logs and traces, and [Reliability Runbooks](/operate/reliability-runbooks/) for symptom-driven response playbooks.