Add short URL redirects for content codes

Support /[code] redirects to full URLs (e.g., /b232e -> /blog/b232e/slug/).
The middleware now detects 5-character codes at the root level and
redirects to the canonical URL using a 301 permanent redirect.

- Add KIND_TO_COLLECTION mapping to code.ts
- Add getCollection() method to Code class
- Update middleware to handle root-level short code URLs
- Fix test for error message to include T kind

Author: claude

src/middleware.ts

@@ -1,10 +1,34 @@
 import { defineMiddleware } from "astro:middleware";
 import { getCollection } from "astro:content";
-import { Code } from "@/utils/code";
+import { Code, KIND_TO_COLLECTION, type Kind } from "@/utils/code";
 
 export const onRequest = defineMiddleware(async (context, next) => {
   const url = new URL(context.request.url);
 
+  // Handle short code URLs like /b232e -> /blog/b232e/slug/
+  const shortCodeMatch = url.pathname.match(/^\/([brpt][0-9a-f]{4})\/?$/i);
+  if (shortCodeMatch) {
+    const shortCode = shortCodeMatch[1].toLowerCase();
+    const kindChar = shortCode[0].toUpperCase() as Kind;
+    const collection = KIND_TO_COLLECTION[kindChar];
+
+    const entry = (
+      await getCollection(collection, ({ id }) => {
+        return shortCode === id.slice(0, 5).toLowerCase();
+      })
+    ).at(0);
+
+    if (entry) {
+      const { code, slug } = Code.parseId(entry.id);
+      const newUrl = new URL(url);
+      newUrl.pathname = `/${collection}/${code}/${slug}/`;
+      return context.redirect(newUrl.toString(), 301);
+    }
+
+    // No match, continue to 404
+    return next();
+  }
+
   // Handle /blog/*, /projects/*, /research/*, and /talks/* paths
   const match = url.pathname.match(/^\/(blog|projects|research|talks)\//);
   const matchedType = match?.[1] as "blog" | "projects" | "research" | "talks" | undefined;

src/utils/code.ts

@@ -2,7 +2,15 @@ const EPOCH = Date.UTC(2000, 0, 1); // January 1, 2000 UTC
 const BASE16_CHARS = "0123456789ABCDEF" as const;
 
 export const VALID_KINDS = ["B", "R", "P", "T"] as const;
-export type Kind = typeof VALID_KINDS[number];
+export type Kind = (typeof VALID_KINDS)[number];
+
+export const KIND_TO_COLLECTION = {
+  B: "blog",
+  R: "research",
+  P: "projects",
+  T: "talks",
+} as const;
+export type Collection = (typeof KIND_TO_COLLECTION)[Kind];
 
 function isValidKind(char: string): char is Kind {
   return VALID_KINDS.includes(char as Kind);
@@ -155,6 +163,13 @@ export class Code {
     return this.toString();
   }
 
+  /**
+   * Get the collection name for this code's kind
+   */
+  getCollection(): Collection {
+    return KIND_TO_COLLECTION[this.kind];
+  }
+
   /**
    * Helper to generate getStaticPaths for Astro routes
    * @param collection - The collection to get entries from
@@ -275,7 +290,7 @@ if (import.meta.vitest) {
     });
 
     it("should reject codes with invalid kind", () => {
-      expect(() => Code.fromCode("X2391")).toThrow("Invalid kind 'X'. Must be one of: B, R, P");
+      expect(() => Code.fromCode("X2391")).toThrow("Invalid kind 'X'. Must be one of: B, R, P, T");
     });
 
     it("should reject codes with non-hex characters in date portion", () => {
@@ -400,4 +415,22 @@ if (import.meta.vitest) {
       expect(url).toBe("/research/r24e5/parsing-techniques/");
     });
   });
+
+  describe("Code.getCollection()", () => {
+    it("should return 'blog' for kind B", () => {
+      expect(Code.fromCode("B2392").getCollection()).toBe("blog");
+    });
+
+    it("should return 'research' for kind R", () => {
+      expect(Code.fromCode("R2392").getCollection()).toBe("research");
+    });
+
+    it("should return 'projects' for kind P", () => {
+      expect(Code.fromCode("P2392").getCollection()).toBe("projects");
+    });
+
+    it("should return 'talks' for kind T", () => {
+      expect(Code.fromCode("T2392").getCollection()).toBe("talks");
+    });
+  });
 }