diff --git a/packages/vinext/src/server/pregenerated-concrete-paths.ts b/packages/vinext/src/server/pregenerated-concrete-paths.ts
new file mode 100644
index 000000000..a8898becc
--- /dev/null
+++ b/packages/vinext/src/server/pregenerated-concrete-paths.ts
@@ -0,0 +1,107 @@
+import { normalizePathnameForRouteMatch } from "../routing/utils.js";
+import { normalizePath } from "./normalize-path.js";
+
+declare global {
+  var __VINEXT_PREGENERATED_CONCRETE_PATHS: unknown;
+}
+
+// Uses the non-strict `normalizePathnameForRouteMatch` on purpose, rather than
+// the strict variant the live request pipeline uses to compute `cleanPathname`
+// (see `app-rsc-request-normalization.ts`). Registry seeding runs over
+// build-time data and must not throw, whereas the strict variant rejects
+// malformed percent-encoding so the runtime can return a 400. The two only
+// diverge on malformed encoding (e.g. `%GG`), which the runtime rejects before
+// any lookup happens, so valid pathnames normalize identically and lookups
+// still match. Do not "fix" this to the strict variant — it would reintroduce a
+// build-time throw on malformed seed data.
+export function normalizePregeneratedPathname(pathname: string): string {
+  return normalizePath(normalizePathnameForRouteMatch(pathname));
+}
+
+/**
+ * Stores concrete URL paths pre-rendered at build time per route pattern.
+ * Used by the PPR fallback-shell guard to avoid serving fallback shells for
+ * known routes whose exact cache entry is temporarily absent.
+ *
+ * Populated by `seed-cache.ts` (Node) or from `globalThis.__VINEXT_PREGENERATED_CONCRETE_PATHS`
+ * injected by `deploy.ts` after prerender (Workers).
+ */
+const concreteUrlPathsByRoute = new Map<string, Set<string>>();
+
+export function clearPregeneratedConcretePaths(): void {
+  concreteUrlPathsByRoute.clear();
+}
+
+/**
+ * Records a concrete URL path for a route pattern. The pathname is normalized
+ * here so this is the single source of truth: every caller — the Worker global
+ * table and the Node `seed-cache.ts` path — stores the canonical form that
+ * matches the runtime `cleanPathname` lookup without having to pre-normalize.
+ */
+export function addPregeneratedConcretePath(routePattern: string, pathname: string): void {
+  const normalized = normalizePregeneratedPathname(pathname);
+  let paths = concreteUrlPathsByRoute.get(routePattern);
+  if (!paths) {
+    paths = new Set();
+    concreteUrlPathsByRoute.set(routePattern, paths);
+  }
+  paths.add(normalized);
+}
+
+/**
+ * Returns the live backing `Set` for a route pattern (not a copy) to keep
+ * lookups allocation-free on the serving hot path. The `ReadonlySet` type
+ * forbids mutation at compile time. Callers must treat the result as
+ * point-in-time and must NOT retain it across a re-seed: each
+ * `initPregeneratedPathsFromGlobals` call runs `clearPregeneratedConcretePaths`,
+ * which empties the map, leaving any previously-returned reference stale. Read
+ * it, use it, drop it — never cache the reference.
+ */
+export function getRenderedConcreteUrlPathsForRoute(
+  routePattern: string,
+): ReadonlySet<string> | undefined {
+  return concreteUrlPathsByRoute.get(routePattern);
+}
+
+/**
+ * Populate the registry from `globalThis.__VINEXT_PREGENERATED_CONCRETE_PATHS`.
+ * No-op when the global is not set (Node path — seed-cache handles it later).
+ * `addPregeneratedConcretePath` normalizes each pathname so it matches the
+ * runtime `cleanPathname`.
+ */
+export function initPregeneratedPathsFromGlobals(): void {
+  const raw = globalThis.__VINEXT_PREGENERATED_CONCRETE_PATHS;
+  const data = parsePregeneratedConcretePaths(raw);
+  if (!data) return;
+  clearPregeneratedConcretePaths();
+  for (const [routePattern, pathnames] of data) {
+    for (const pathname of pathnames) {
+      addPregeneratedConcretePath(routePattern, pathname);
+    }
+  }
+}
+
+// Validates the global table shape strictly: a single malformed entry rejects
+// the whole payload. Repeated `routePattern` entries are NOT deduped here by
+// design — if `deploy.ts` ever emits the same pattern twice, the paths merge
+// additively into one `Set` via `addPregeneratedConcretePath`, which dedups by
+// value, so the merged result is identical to a single combined entry. No
+// one-entry-per-pattern invariant is enforced because none is needed.
+function parsePregeneratedConcretePaths(value: unknown): Array<[string, string[]]> | undefined {
+  if (!Array.isArray(value)) return undefined;
+  const result: Array<[string, string[]]> = [];
+  for (const entry of value) {
+    if (!Array.isArray(entry)) return undefined;
+    if (entry.length !== 2) return undefined;
+    const [pattern, paths] = entry;
+    if (typeof pattern !== "string") return undefined;
+    if (!Array.isArray(paths)) return undefined;
+    const strings: string[] = [];
+    for (const p of paths) {
+      if (typeof p !== "string") return undefined;
+      strings.push(p);
+    }
+    result.push([pattern, strings]);
+  }
+  return result;
+}
diff --git a/packages/vinext/src/server/prerender-route-params.ts b/packages/vinext/src/server/prerender-route-params.ts
index d2bdbfb94..282716edf 100644
--- a/packages/vinext/src/server/prerender-route-params.ts
+++ b/packages/vinext/src/server/prerender-route-params.ts
@@ -9,7 +9,8 @@ export type PrerenderRouteParamsPayload = {
   routePattern: string;
 };
 
-type PrerenderRouteParamsRouteMatch =
+/** @public exported for #1716 serving consumers; not yet referenced in-repo */
+export type PrerenderRouteParamsRouteMatch =
   | {
       kind: "exact";
       params: PrerenderRouteParams;
@@ -145,7 +146,7 @@ export function prerenderRouteParamsPayloadMatchesRoute(
   return match?.kind === "exact";
 }
 
-function matchPrerenderRouteParamsPayload(
+export function matchPrerenderRouteParamsPayload(
   payload: PrerenderRouteParamsPayload | null,
   routePattern: string,
   params: PrerenderRouteParams,
diff --git a/tests/pregenerated-concrete-paths.test.ts b/tests/pregenerated-concrete-paths.test.ts
new file mode 100644
index 000000000..b07b67101
--- /dev/null
+++ b/tests/pregenerated-concrete-paths.test.ts
@@ -0,0 +1,89 @@
+import { describe, it, expect, afterEach } from "vite-plus/test";
+import {
+  clearPregeneratedConcretePaths,
+  addPregeneratedConcretePath,
+  getRenderedConcreteUrlPathsForRoute,
+  initPregeneratedPathsFromGlobals,
+  normalizePregeneratedPathname,
+} from "../packages/vinext/src/server/pregenerated-concrete-paths.js";
+
+describe("pregenerated concrete paths", () => {
+  afterEach(() => {
+    clearPregeneratedConcretePaths();
+  });
+
+  it("returns undefined for an unknown route pattern", () => {
+    expect(getRenderedConcreteUrlPathsForRoute("/en/blog/[slug]")).toBeUndefined();
+  });
+
+  it("stores and retrieves pathnames for a route pattern", () => {
+    addPregeneratedConcretePath("/:locale/blog/:slug", "/en/blog/hello");
+    addPregeneratedConcretePath("/:locale/blog/:slug", "/fr/blog/bonjour");
+
+    const paths = getRenderedConcreteUrlPathsForRoute("/:locale/blog/:slug");
+    expect(paths).toBeDefined();
+    expect([...paths!]).toEqual(["/en/blog/hello", "/fr/blog/bonjour"]);
+  });
+
+  it("supports independent route patterns", () => {
+    addPregeneratedConcretePath("/:locale/blog/:slug", "/en/blog/hello");
+    addPregeneratedConcretePath("/products/:id", "/products/42");
+
+    expect([...getRenderedConcreteUrlPathsForRoute("/:locale/blog/:slug")!]).toEqual([
+      "/en/blog/hello",
+    ]);
+    expect([...getRenderedConcreteUrlPathsForRoute("/products/:id")!]).toEqual(["/products/42"]);
+  });
+
+  it("returns an empty state after clear", () => {
+    addPregeneratedConcretePath("/en/blog/[slug]", "/en/blog/persistent");
+    expect(getRenderedConcreteUrlPathsForRoute("/en/blog/[slug]")).toBeDefined();
+
+    clearPregeneratedConcretePaths();
+
+    expect(getRenderedConcreteUrlPathsForRoute("/en/blog/[slug]")).toBeUndefined();
+  });
+
+  it("clears stale paths from a previous build on re-population (issue 3)", () => {
+    // Build A
+    addPregeneratedConcretePath("/en/blog/[slug]", "/en/blog/old");
+    addPregeneratedConcretePath("/en/blog/[slug]", "/en/blog/also-old");
+    expect(getRenderedConcreteUrlPathsForRoute("/en/blog/[slug]")!.size).toBe(2);
+
+    // Build B — clear and re-seed without the old paths
+    clearPregeneratedConcretePaths();
+    addPregeneratedConcretePath("/en/blog/[slug]", "/en/blog/new");
+
+    const paths = getRenderedConcreteUrlPathsForRoute("/en/blog/[slug]")!;
+    expect(paths.has("/en/blog/old")).toBe(false);
+    expect(paths.has("/en/blog/also-old")).toBe(false);
+    expect(paths.has("/en/blog/new")).toBe(true);
+    expect(paths.size).toBe(1);
+  });
+
+  it("normalizes percent-encoded pathnames", () => {
+    expect(normalizePregeneratedPathname("/en/blog/hello%20world")).toBe("/en/blog/hello world");
+  });
+
+  it("normalizes un-normalized pathnames recorded directly", () => {
+    addPregeneratedConcretePath("/:locale/blog/:slug", "/en/blog/hello%20world");
+    addPregeneratedConcretePath("/:locale/blog/:slug", "//en/./blog/world");
+
+    expect([...getRenderedConcreteUrlPathsForRoute("/:locale/blog/:slug")!]).toEqual([
+      "/en/blog/hello world",
+      "/en/blog/world",
+    ]);
+  });
+
+  it("initializes from the Worker global concrete-path table", () => {
+    globalThis.__VINEXT_PREGENERATED_CONCRETE_PATHS = [
+      ["/:locale/blog/:slug", ["/en/blog/hello%20world"]],
+    ];
+    initPregeneratedPathsFromGlobals();
+    delete globalThis.__VINEXT_PREGENERATED_CONCRETE_PATHS;
+
+    expect([...getRenderedConcreteUrlPathsForRoute("/:locale/blog/:slug")!]).toEqual([
+      "/en/blog/hello world",
+    ]);
+  });
+});
diff --git a/tests/prerender-route-params.test.ts b/tests/prerender-route-params.test.ts
index 23c95bb31..37833bada 100644
--- a/tests/prerender-route-params.test.ts
+++ b/tests/prerender-route-params.test.ts
@@ -1,6 +1,7 @@
 import { describe, expect, it } from "vite-plus/test";
 import {
   encodePrerenderRouteParams,
+  matchPrerenderRouteParamsPayload,
   prerenderRouteParamsPayloadMatchesRoute,
   type PrerenderRouteParamsPayload,
 } from "../packages/vinext/src/server/prerender-route-params.js";
@@ -95,14 +96,96 @@ describe("prerenderRouteParamsPayloadMatchesRoute", () => {
   });
 });
 
+describe("matchPrerenderRouteParamsPayload", () => {
+  it("returns kind exact when payload has no fallbackParamNames", () => {
+    const payload: PrerenderRouteParamsPayload = {
+      routePattern: "/:locale/blog/:slug",
+      params: { locale: "en", slug: "hello%20world" },
+    };
+
+    expect(
+      matchPrerenderRouteParamsPayload(payload, "/:locale/blog/:slug", {
+        locale: "en",
+        slug: "hello world",
+      }),
+    ).toEqual({ kind: "exact", params: { locale: "en", slug: "hello%20world" } });
+  });
+
+  it("returns kind fallback-shell when payload has fallbackParamNames", () => {
+    const payload: PrerenderRouteParamsPayload = {
+      routePattern: "/:locale/blog/:slug",
+      params: { locale: "en", slug: "%5Bslug%5D" },
+      fallbackParamNames: ["slug"],
+    };
+
+    expect(
+      matchPrerenderRouteParamsPayload(payload, "/:locale/blog/:slug", {
+        locale: "en",
+        slug: "[slug]",
+      }),
+    ).toEqual({
+      fallbackParamNames: ["slug"],
+      kind: "fallback-shell",
+      params: { locale: "en", slug: "%5Bslug%5D" },
+    });
+  });
+
+  it("rejects fallback-shell payloads that name params outside the route pattern", () => {
+    const payload: PrerenderRouteParamsPayload = {
+      routePattern: "/:locale/blog/:slug",
+      params: { locale: "en", slug: "%5Bslug%5D" },
+      fallbackParamNames: ["missing"],
+    };
+
+    expect(
+      matchPrerenderRouteParamsPayload(payload, "/:locale/blog/:slug", {
+        locale: "en",
+        slug: "[slug]",
+      }),
+    ).toBeNull();
+  });
+
+  it("matches fallback-shell catch-all placeholders as route param arrays", () => {
+    const payload: PrerenderRouteParamsPayload = {
+      routePattern: "/:locale/docs/:slug+",
+      params: { locale: "fr", slug: ["%5B...slug%5D"] },
+      fallbackParamNames: ["slug"],
+    };
+
+    expect(
+      matchPrerenderRouteParamsPayload(payload, "/:locale/docs/:slug+", {
+        locale: "fr",
+        slug: ["[...slug]"],
+      }),
+    ).toEqual({
+      fallbackParamNames: ["slug"],
+      kind: "fallback-shell",
+      params: { locale: "fr", slug: ["%5B...slug%5D"] },
+    });
+  });
+});
+
 describe("encodePrerenderRouteParams", () => {
-  it("round-trips fallbackParamNames when provided", () => {
-    const payload = encodePrerenderRouteParams("/product/:id", { id: "abc" }, ["id"]);
+  it("encodes exact params without fallbackParamNames", () => {
+    const result = encodePrerenderRouteParams("/product/:id", { id: "abc" });
 
-    expect(payload).toEqual({
+    expect(result).toEqual({
       routePattern: "/product/:id",
       params: { id: "abc" },
-      fallbackParamNames: ["id"],
+    });
+  });
+
+  it("encodes fallback-shell params with fallbackParamNames", () => {
+    const result = encodePrerenderRouteParams(
+      "/:locale/blog/:slug",
+      { locale: "en", slug: "[slug]" },
+      ["slug"],
+    );
+
+    expect(result).toEqual({
+      fallbackParamNames: ["slug"],
+      routePattern: "/:locale/blog/:slug",
+      params: { locale: "en", slug: "%5Bslug%5D" },
     });
   });
 
@@ -122,4 +205,16 @@ describe("encodePrerenderRouteParams", () => {
   it("returns null when there are no dynamic params even with fallbackParamNames", () => {
     expect(encodePrerenderRouteParams("/about", {}, ["id"])).toBe(null);
   });
+
+  it("percent-encodes param values", () => {
+    const result = encodePrerenderRouteParams("/:locale/blog/:slug", {
+      locale: "en",
+      slug: "hello world & more",
+    });
+
+    expect(result).toEqual({
+      routePattern: "/:locale/blog/:slug",
+      params: { locale: "en", slug: "hello%20world%20%26%20more" },
+    });
+  });
 });