diff --git a/app/api/analysis/route.ts b/app/api/analysis/route.ts
index ff9a803..86c54c8 100644
--- a/app/api/analysis/route.ts
+++ b/app/api/analysis/route.ts
@@ -13,6 +13,7 @@ import {
   requireAuthUser,
   unauthorizedResponse,
 } from "@/lib/auth-helpers";
+import { mapCreateAnalysisError } from "@/lib/create-analysis-errors";
 import { getMembership } from "@/lib/org/access";
 import { createLogger } from "@/lib/logger";
 import type { ApiResponse } from "@/types";
@@ -138,14 +139,18 @@ export async function POST(
       },
     });
   } catch (error) {
-    log.error("Failed to create analysis session", { error: String(error) });
+    const mapped = mapCreateAnalysisError(error);
+    log.error("Failed to create analysis session", {
+      error: String(error),
+      code: mapped.code,
+    });
     return NextResponse.json(
       {
         success: false as const,
-        error: "Failed to create analysis session.",
-        code: "INTERNAL_ERROR",
+        error: mapped.message,
+        code: mapped.code,
       },
-      { status: 500 }
+      { status: mapped.status }
     );
   }
 }
diff --git a/lib/auth-helpers.ts b/lib/auth-helpers.ts
index 58d462e..4223474 100644
--- a/lib/auth-helpers.ts
+++ b/lib/auth-helpers.ts
@@ -1,11 +1,19 @@
 import { auth } from "@/auth";
 import { NextResponse } from "next/server";
+import { prisma } from "@/lib/prisma";
 import type { ApiResponse } from "@/types";
 
 export async function requireAuthUser() {
   const session = await auth();
   const userId = session?.user?.id;
   if (!userId) return null;
+
+  const user = await prisma.user.findUnique({
+    where: { id: userId },
+    select: { id: true },
+  });
+  if (!user) return null;
+
   return { session, userId };
 }
 
diff --git a/lib/create-analysis-errors.test.ts b/lib/create-analysis-errors.test.ts
new file mode 100644
index 0000000..665aae9
--- /dev/null
+++ b/lib/create-analysis-errors.test.ts
@@ -0,0 +1,30 @@
+import { describe, it, expect } from "vitest";
+import { Prisma } from "@prisma/client";
+import { mapCreateAnalysisError } from "./create-analysis-errors";
+
+describe("mapCreateAnalysisError", () => {
+  it("maps database connection failures to DB_UNAVAILABLE", () => {
+    const error = new Prisma.PrismaClientInitializationError(
+      "tenant/user postgres.eccziupihegciupibxis not found",
+      "5.0.0"
+    );
+
+    const mapped = mapCreateAnalysisError(error);
+
+    expect(mapped.code).toBe("DB_UNAVAILABLE");
+    expect(mapped.status).toBe(503);
+    expect(mapped.message).toMatch(/Database unavailable|Service temporarily unavailable/);
+  });
+
+  it("maps foreign key violations to UNAUTHORIZED", () => {
+    const error = new Prisma.PrismaClientKnownRequestError(
+      "Foreign key constraint failed",
+      { code: "P2003", clientVersion: "5.0.0" }
+    );
+
+    const mapped = mapCreateAnalysisError(error);
+
+    expect(mapped.code).toBe("UNAUTHORIZED");
+    expect(mapped.status).toBe(401);
+  });
+});
diff --git a/lib/create-analysis-errors.ts b/lib/create-analysis-errors.ts
new file mode 100644
index 0000000..34bf6bc
--- /dev/null
+++ b/lib/create-analysis-errors.ts
@@ -0,0 +1,52 @@
+import { Prisma } from "@prisma/client";
+
+function isDatabaseUnavailable(error: unknown): boolean {
+  if (error instanceof Prisma.PrismaClientInitializationError) return true;
+  const message = String(error);
+  return (
+    message.includes("ENOTFOUND") ||
+    message.includes("Can't reach database server") ||
+    message.includes("tenant/user") ||
+    message.includes("P1001")
+  );
+}
+
+export function mapCreateAnalysisError(error: unknown): {
+  message: string;
+  status: number;
+  code: string;
+} {
+  if (error instanceof Prisma.PrismaClientKnownRequestError) {
+    if (error.code === "P2003") {
+      return {
+        message: "Session expired. Please sign in again.",
+        status: 401,
+        code: "UNAUTHORIZED",
+      };
+    }
+    if (error.code === "P2002") {
+      return {
+        message: "Could not allocate a unique share link. Please retry.",
+        status: 409,
+        code: "CONFLICT",
+      };
+    }
+  }
+
+  if (isDatabaseUnavailable(error)) {
+    return {
+      message:
+        process.env.NODE_ENV === "development"
+          ? "Database unavailable. Check DATABASE_URL / DIRECT_URL in .env.local and that your Supabase project is active."
+          : "Service temporarily unavailable. Try again shortly.",
+      status: 503,
+      code: "DB_UNAVAILABLE",
+    };
+  }
+
+  return {
+    message: "Failed to create analysis session.",
+    status: 500,
+    code: "INTERNAL_ERROR",
+  };
+}