diff --git a/CHANGELOG.md b/CHANGELOG.md
index df4b7138..e0bed74b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 Detailed changelog for Perry. See CLAUDE.md for concise summaries.
 
+## v0.5.913 — fix(runtime): #748 follow-up — `new Date(NaN)` / Invalid Date is now a recognizable Date object (`typeof === "object"`, `instanceof Date === true`) instead of an untagged bare NaN that `typeof` reported as `"number"`. **Symptom (per #748 comment).** After the v0.5.912 condvar fix, the shop-admin signup still failed: `typeof new Date(NaN)` returned `"number"` under perry vs `"object"` under tsx/node, so `MyDateTime.toDate(): Date { … if (zero) return new Date(NaN); … }` from `@perryts/mysql` produced an untagged bare NaN that downstream `dtToIso` / dynamic `.getTime()` dispatched as a number method → `getTime is not a function` → fastify route promise resolved to the same `0.0` symptom as the original #748. The deterministic 3-line repro from the comment: `function w5(y: number) { return { toDate(): Date { return new Date(NaN); } }; } console.log(typeof w5(2026).toDate());` — perry: `"number"`; node: `"object"`. **Root cause.** Perry stores `Date` as a raw f64 timestamp with no NaN-box tag and consults a thread-local `DATE_REGISTRY: HashSet<u64>` of registered bit patterns from `typeof` / `instanceof Date` / JSON / promise side-table dispatch. `js_date_new_from_value` skipped registration entirely when `result.is_nan()` (`crates/perry-runtime/src/date.rs:156` pre-fix), so `new Date(NaN)` flowed out as a bare unregistered NaN — and the two `instanceof` sites in `crates/perry-runtime/src/object.rs` (`CLASS_ID_DATE` line 5051, `CLASS_ID_OBJECT` line 5098) both gated their registry lookup behind `!value.is_nan() && value.is_finite()` so even if the bits *were* registered, Invalid Date couldn't possibly match. Net: ECMA-262 §21.4.1.1 says `new Date(NaN)` is an Invalid Date — `typeof` "object", `instanceof Date` true, time value NaN — and perry got all three wrong. The seven string formatters (`js_date_to_iso_string`, `js_date_to_date_string`, `js_date_to_time_string`, `js_date_to_locale_*_string`) also lacked NaN guards and cast NaN-as-i64 → `0`, emitting bogus `1970-01-01T00:00:00.000Z` (the `<garbage>` zero-branch output in the bug report). **Fix.** Single canonical Invalid-Date sentinel `DATE_NAN_BITS = 0x7FF8_0000_0000_0DA7` — a quiet NaN (exponent all ones, mantissa MSB set per IEEE-754 §6.2.1) in the 0x7FF8 space, which `JSValue::is_number` already treats as a plain number rather than a NaN-box tag, so the value flows through arithmetic and every existing `if timestamp.is_nan() { return f64::NAN }` getter exactly like a bare NaN. Recognition is by exact bit pattern, *globally*, so the sentinel works across the socket-thread / main-thread boundary without registration — no thread-local lookup required. (1) `is_registered_date_bits` short-circuits `bits == DATE_NAN_BITS` before consulting the existing HashSet; the finite-Date registry path is byte-identical to before, which is what diverges from the reverted attempt the issue comment describes — that earlier try also touched finite registration ("stop value-registering finite millis") and regressed `Date.UTC(...)` valid dates, so we deliberately do not touch the finite path. (2) `js_date_new_from_timestamp` / `js_date_new_from_value` now route NaN through `date_or_invalid` → the sentinel. (3) Both `js_instanceof` arms (`CLASS_ID_DATE`, `CLASS_ID_OBJECT`) match `value.to_bits() == DATE_NAN_BITS` *before* the `!is_nan()` guard so Invalid Date is still a Date and still an Object per spec. (4) `typeof` is already correct for free because `js_value_typeof`'s f64 fallthrough calls `is_registered_date_bits(bits)` unconditionally (no NaN gate at that site). (5) Each of the six string formatters now early-returns `"Invalid Date"` for NaN — matches `String(new Date(NaN))` / `.toDateString()` etc. and replaces the `1970-…` garbage. Promise assimilation (`promise.rs:2381`) and JSON `write_number` (`json.rs:1558`) are unchanged: both gate on `is_pointer()` / `is_finite()` so the sentinel falls through their early-return arms as a NaN, which is correct — `await new Date(NaN)` resolves with itself, `JSON.stringify(new Date(NaN))` serializes as `null` (Date.prototype.toJSON-of-invalid spec behavior, satisfied here by the existing NaN → "null" arm in `write_number`). Roughly 50 lines of net code change across two files (`crates/perry-runtime/src/{date.rs,object.rs}`). **Out of scope.** Options 1 and 2-second-half from the issue comment — tagging Dates with a dedicated NaN-box tag space, or eliminating the value-keyed thread-local registry altogether — are correct soundness fixes for the broader `100 instanceof Date` false-positive and the cross-thread loss cases, but require a workspace-wide refactor of every Date method signature, codegen call site, and runtime side-table. This patch closes the specific #748 follow-up (`new Date(NaN)` representation) and the `<garbage>` 1970 strings; the false-positive/cross-thread cases stay tracked separately. **Validation.** `test-files/test_issue_748_invalid_date.ts` mirrors the comment's minimal `w5` repro plus the `makeMyDateTime` / `dtToIso` shop-admin shape and a valid-Date regression block. Compiled + run against the patched runtime: `typeof w5(2026).toDate()` is `"object"` (was `"number"`), `new Date(NaN) instanceof Date` is `true`, `instanceof Object` is `true`, `.getTime()` is `NaN`, `String(invalid)` is `"Invalid Date"` (was the `1970-01-01…` garbage), `JSON.stringify(invalid)` is `"null"`, `dtToIso(makeMyDateTime(2026, 5, 15))` is `"2026-05-15T07:47:04.192Z"`, `dtToIso(makeMyDateTime(0,0,0))` is `null`. Regression block: `Date.UTC(2026,4,15,…)` round-trips through `getTime` / `toUTCFullYear` / `toISOString` / `JSON.stringify`, plain numbers still report `typeof "number"`, `Date.now()` still reports `typeof "number"` (it returns a number, not a Date — matches JS), `new Date()` still `instanceof Date`. Closes the #748 follow-up.
+
 ## v0.5.912 — fix(fastify): #748 — replace 1-second polling timeout in `wait_for_promise` with a condvar wait, and surface rejected promises as `HTTP 500` instead of body `0`. **Symptom (reported as #748).** A native-compiled Fastify route doing `await checkSignup(); await getUserByEmail(); await hashPassword(); await createUser(); await createAccount(); await addMember(); await issueSession(); …` against `@perryts/mysql` returned the wire byte `0x30` (literal ASCII `0`) with HTTP 200 instead of the explicit `return { accessToken, … }`. The first INSERT committed; every subsequent `await pool.exec(...)` silently no-op'd (no error, no log, no DB row). The `tsx` baseline returned the correct JSON with HTTP 201 against the same code + same DB. **Root cause.** Both `crates/perry-ext-fastify/src/server.rs::wait_for_promise()` and the in-tree mirror at `crates/perry-stdlib/src/fastify/server.rs::wait_for_promise()` polled `js_promise_state` 10000 × 100 µs (≈ 1 s) and then returned regardless of state. After return, `js_promise_value(ptr)` (initialized to `0.0` in `Promise::new` per `crates/perry-runtime/src/promise.rs`) gave Rust `f64 0.0` for any Pending or Rejected promise. `build_response_body` then serialized that as wire byte `0x30` with the default `status_code = 200` (the route's `reply.code(201)` never ran). The orphaned chain was also abandoned: once the dispatcher returned, microtasks stopped pumping, so every queued INSERT after the timeout silently no-op'd — matching the "first INSERT commits, rest don't" symptom. The bug only surfaced once the await chain exceeded the 1 s budget, which is why the user's argon2 + JWT + multiple mysql writes hit it but minimal Fastify probes (object/string/number returns, two sequential `await delay()`s) didn't. **Fix.** (1) Replace the polling/sleep loop with a condvar-based wait via `js_wait_for_event` — the same primitive the codegen-emitted `await` body already uses. No fixed iteration limit; wakes the moment any stdlib worker calls `js_notify_main_thread` (which `js_promise_resolve` / `reject` already do). Drives timer ticks + stdlib pump + microtasks every iteration so chained timers / mysql / fetch awaits all keep moving. (2) After `wait_for_promise` returns, branch on `js_promise_state`: state == 2 (Rejected) now produces an HTTP 500 response with a `{ "error": <reason> }` JSON envelope (via new `render_rejection_body`) instead of letting `js_promise_value` return `0.0` and masquerade as a successful response. **Validation.** `/tmp/repro748_fastify.ts` — Fastify handler with 8 × 300 ms sequential awaits (2.4 s total chain). Pre-fix would return HTTP 200 body `0`; post-fix returns the full JSON body + HTTP 201 after ≈ 2.46 s. Existing `test_fastify_integration.ts` still passes; 10 fastify-ext unit tests + 22 fastify-stdlib unit tests all pass. Gap suite unchanged (33 pass / 2 pre-existing failures). **Caveat.** Could not exactly reproduce the user's "first INSERT commits, rest silently no-op" symptom in a synthetic repro without `@perryts/mysql` linkage — the 1 s timeout path is the only place `js_promise_value(0.0_initial)` reaches the response writer and matches every observable symptom (wire byte `0x30`, HTTP 200, dropped explicit return, abandoned subsequent awaits). Worth re-running skelpo-shop-admin against this build to confirm; if it still repros, `PERRY_MT_PROFILE=1` will narrow the stall point. Closes #748.
 
 ## v0.5.911 — fix(jsruntime): #755 — register `fs/promises` and sibling Node-builtin subpath aliases. **Symptom.** A Colyseus demo compiled cleanly but failed at runtime with `[js_load_module] FAILED to load '.../colyseus/build/index.mjs': Cannot find module 'fs/promises' in node_modules`. **Root cause.** `crates/perry-jsruntime/src/modules.rs::is_node_builtin` was an exact-string `matches!` list that recognized `fs` but not Node's separately-exposed `fs/promises` subpath alias (nor `stream/promises`, `stream/consumers`, `dns/promises`, `timers/promises`, `readline/promises`, `util/types`, `assert/strict`, `process`). Specifiers that fell through hit `resolve_from_node_modules`, which then looked for a literal package directory named `fs/promises` and failed. Real packages (colyseus, but anything pulling in `fs/promises` directly) couldn't resolve the import. **Fix.** Added the missing specifiers — both bare and `node:`-prefixed forms — to `is_node_builtin`, plus matching real stubs in `get_builtin_stub` so the import site doesn't downstream-fail on `Cannot read properties of undefined` when consumers reach for e.g. `fsp.readFile`. **Validation.** Two new unit tests in `crates/perry-jsruntime/src/modules.rs::tests` — `test_is_node_builtin_promise_subpaths` enumerates every added specifier (bare + `node:`) and asserts recognition, `test_get_builtin_stub_promise_subpaths` asserts each new stub returns a real body (not the empty-fallback `export default {}`). `cargo test --release -p perry-jsruntime --lib modules::` green (13/0/0). Synthetic Perry-compiled `.ts` that `import`s the five promise subpaths resolves and exports the expected functions; gap suite unchanged (33 pass / 2 pre-existing failures). **Out of scope.** The secondary `Unexpected strict mode reserved word at express/lib/express.js:158:14` in #755's report is a separate CJS-wrap / strict-mode collision and is not addressed here. Closes #755.
diff --git a/CLAUDE.md b/CLAUDE.md
index 56074e1b..159d38f9 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -8,7 +8,7 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 Perry is a native TypeScript compiler written in Rust that compiles TypeScript source code directly to native executables. It uses SWC for TypeScript parsing and LLVM for code generation.
 
-**Current Version:** 0.5.912
+**Current Version:** 0.5.913
 
 
 ## TypeScript Parity Status
diff --git a/Cargo.lock b/Cargo.lock
index 14947136..5e59cf2a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4790,7 +4790,7 @@ checksum = "9b4f627cb1b25917193a259e49bdad08f671f8d9708acfd5fe0a8c1455d87220"
 
 [[package]]
 name = "perry"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "base64",
@@ -4845,14 +4845,14 @@ dependencies = [
 
 [[package]]
 name = "perry-api-manifest"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "serde",
 ]
 
 [[package]]
 name = "perry-codegen"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "log",
@@ -4865,7 +4865,7 @@ dependencies = [
 
 [[package]]
 name = "perry-codegen-arkts"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "perry-hir",
@@ -4874,7 +4874,7 @@ dependencies = [
 
 [[package]]
 name = "perry-codegen-glance"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "perry-hir",
@@ -4882,7 +4882,7 @@ dependencies = [
 
 [[package]]
 name = "perry-codegen-js"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "perry-dispatch",
@@ -4892,7 +4892,7 @@ dependencies = [
 
 [[package]]
 name = "perry-codegen-swiftui"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "perry-hir",
@@ -4901,7 +4901,7 @@ dependencies = [
 
 [[package]]
 name = "perry-codegen-wasm"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "base64",
@@ -4914,7 +4914,7 @@ dependencies = [
 
 [[package]]
 name = "perry-codegen-wear-tiles"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "perry-hir",
@@ -4922,7 +4922,7 @@ dependencies = [
 
 [[package]]
 name = "perry-diagnostics"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "serde",
  "serde_json",
@@ -4930,7 +4930,7 @@ dependencies = [
 
 [[package]]
 name = "perry-dispatch"
-version = "0.5.912"
+version = "0.5.913"
 
 [[package]]
 name = "perry-doc-fixture-my-bindings"
@@ -4941,7 +4941,7 @@ dependencies = [
 
 [[package]]
 name = "perry-doc-tests"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "clap",
@@ -4956,7 +4956,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-argon2"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "argon2",
  "perry-ffi",
@@ -4964,7 +4964,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-axios"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "perry-ffi",
  "reqwest",
@@ -4973,7 +4973,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-bcrypt"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "bcrypt",
  "perry-ffi",
@@ -4981,7 +4981,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-better-sqlite3"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "perry-ffi",
  "rusqlite",
@@ -4989,7 +4989,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-cheerio"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "perry-ffi",
  "scraper",
@@ -4997,14 +4997,14 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-commander"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "perry-ffi",
 ]
 
 [[package]]
 name = "perry-ext-cron"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "chrono",
  "cron",
@@ -5013,7 +5013,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-dayjs"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "chrono",
  "perry-ffi",
@@ -5021,7 +5021,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-decimal"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "perry-ffi",
  "rust_decimal",
@@ -5029,7 +5029,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-dotenv"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "perry-ffi",
  "serde_json",
@@ -5037,7 +5037,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-ethers"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "perry-ffi",
  "rand 0.8.6",
@@ -5045,21 +5045,21 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-events"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "perry-ffi",
 ]
 
 [[package]]
 name = "perry-ext-exponential-backoff"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "perry-ffi",
 ]
 
 [[package]]
 name = "perry-ext-fastify"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "bytes",
  "http-body-util",
@@ -5073,7 +5073,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-fetch"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "lazy_static",
  "perry-ffi",
@@ -5084,7 +5084,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-http"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "lazy_static",
  "perry-ext-http-server",
@@ -5096,7 +5096,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-http-server"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "bytes",
  "http-body-util",
@@ -5115,7 +5115,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-ioredis"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "lazy_static",
  "perry-ffi",
@@ -5125,7 +5125,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-jsonwebtoken"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "base64",
  "jsonwebtoken",
@@ -5136,7 +5136,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-lru-cache"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "lru",
  "perry-ffi",
@@ -5144,7 +5144,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-moment"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "chrono",
  "perry-ffi",
@@ -5152,7 +5152,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-mongodb"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "bson",
  "futures-util",
@@ -5164,7 +5164,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-mysql2"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "chrono",
  "perry-ffi",
@@ -5174,7 +5174,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-nanoid"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "nanoid",
  "perry-ffi",
@@ -5183,7 +5183,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-net"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "perry-ffi",
  "rustls",
@@ -5194,7 +5194,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-nodemailer"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "lettre",
  "perry-ffi",
@@ -5204,7 +5204,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-pg"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "perry-ffi",
  "sqlx",
@@ -5213,7 +5213,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-ratelimit"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "governor",
  "perry-ffi",
@@ -5221,7 +5221,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-sharp"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "base64",
  "image",
@@ -5230,14 +5230,14 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-slugify"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "perry-ffi",
 ]
 
 [[package]]
 name = "perry-ext-streams"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "lazy_static",
  "perry-ffi",
@@ -5245,7 +5245,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-uuid"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "perry-ffi",
  "uuid",
@@ -5253,7 +5253,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-validator"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "perry-ffi",
  "regex",
@@ -5263,7 +5263,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-ws"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "futures-util",
  "lazy_static",
@@ -5274,7 +5274,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ext-zlib"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "flate2",
  "perry-ffi",
@@ -5282,7 +5282,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ffi"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "dashmap 6.1.0",
  "once_cell",
@@ -5291,7 +5291,7 @@ dependencies = [
 
 [[package]]
 name = "perry-hir"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "perry-api-manifest",
@@ -5305,7 +5305,7 @@ dependencies = [
 
 [[package]]
 name = "perry-jsruntime"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "deno_core",
@@ -5325,7 +5325,7 @@ dependencies = [
 
 [[package]]
 name = "perry-parser"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "perry-diagnostics",
@@ -5337,7 +5337,7 @@ dependencies = [
 
 [[package]]
 name = "perry-runtime"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "base64",
@@ -5361,7 +5361,7 @@ dependencies = [
 
 [[package]]
 name = "perry-stdlib"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "aes",
  "aes-gcm",
@@ -5429,7 +5429,7 @@ dependencies = [
 
 [[package]]
 name = "perry-transform"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "perry-hir",
@@ -5439,7 +5439,7 @@ dependencies = [
 
 [[package]]
 name = "perry-types"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "anyhow",
  "thiserror 1.0.69",
@@ -5447,11 +5447,11 @@ dependencies = [
 
 [[package]]
 name = "perry-ui"
-version = "0.5.912"
+version = "0.5.913"
 
 [[package]]
 name = "perry-ui-android"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "itoa",
  "jni",
@@ -5466,7 +5466,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ui-geisterhand"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "rand 0.8.6",
  "serde",
@@ -5476,7 +5476,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ui-gtk4"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "cairo-rs",
  "dirs 5.0.1",
@@ -5495,7 +5495,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ui-ios"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "block2",
  "libc",
@@ -5510,7 +5510,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ui-macos"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "block2",
  "libc",
@@ -5528,11 +5528,11 @@ version = "0.1.0"
 
 [[package]]
 name = "perry-ui-testkit"
-version = "0.5.912"
+version = "0.5.913"
 
 [[package]]
 name = "perry-ui-tvos"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "block2",
  "libc",
@@ -5547,7 +5547,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ui-visionos"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "block2",
  "libc",
@@ -5562,7 +5562,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ui-watchos"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "block2",
  "libc",
@@ -5575,7 +5575,7 @@ dependencies = [
 
 [[package]]
 name = "perry-ui-windows"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "libc",
  "perry-runtime",
@@ -5589,7 +5589,7 @@ dependencies = [
 
 [[package]]
 name = "perry-updater"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "base64",
  "ed25519-dalek",
@@ -5603,7 +5603,7 @@ dependencies = [
 
 [[package]]
 name = "perry-wasm-host"
-version = "0.5.912"
+version = "0.5.913"
 dependencies = [
  "wasmi",
 ]
diff --git a/Cargo.toml b/Cargo.toml
index 6d01454c..5153b329 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -190,7 +190,7 @@ opt-level = "s"       # Optimize for size in stdlib
 opt-level = 3
 
 [workspace.package]
-version = "0.5.912"
+version = "0.5.913"
 edition = "2021"
 license = "MIT"
 repository = "https://github.com/PerryTS/perry"
diff --git a/crates/perry-runtime/src/date.rs b/crates/perry-runtime/src/date.rs
index edab02ec..0181648c 100644
--- a/crates/perry-runtime/src/date.rs
+++ b/crates/perry-runtime/src/date.rs
@@ -19,6 +19,61 @@ thread_local! {
     static DATE_REGISTRY: RefCell<HashSet<u64>> = RefCell::new(HashSet::new());
 }
 
+/// Canonical "Invalid Date" bit pattern.
+///
+/// An *Invalid Date* (`new Date(NaN)`, `new Date("nope")`, the zero-date
+/// branch of `@perryts/mysql`'s `MyDateTime.toDate()`, …) is still a Date
+/// object per ECMA-262 §21.4.1.1 — `typeof` must be `"object"` and
+/// `instanceof Date` must be `true`, even though its time value is NaN.
+///
+/// Perry stores Date as a raw f64 with no tag and tracks finite Dates in
+/// the thread-local `DATE_REGISTRY`. A NaN can't go in that value-keyed
+/// set: NaN never compares equal, the bit pattern isn't stable, and the
+/// set is thread-local so a Date minted on a socket/worker thread (mysql
+/// row decode) wouldn't be seen on the main thread anyway. So Invalid
+/// Date gets a single canonical sentinel recognized *by bit pattern*,
+/// globally, with no registration step — it works across threads for
+/// free because it is a constant, not a tracked value.
+///
+/// The pattern is a quiet NaN (exponent all ones, mantissa MSB set so it
+/// stays quiet per IEEE-754 §6.2.1 and arithmetic propagates instead of
+/// trapping). It lives in the 0x7FF8 space, which `JSValue::is_number`
+/// treats as a plain number rather than a NaN-box tag, so the value
+/// flows through arithmetic and the existing `if timestamp.is_nan()`
+/// guards in every Date getter exactly like a bare NaN — only `typeof` /
+/// `instanceof` / dynamic dispatch get to see that it is really a Date.
+/// The low payload `0x0DA7` just distinguishes it from the FPU's
+/// canonical `0x7FF8_0000_0000_0000`.
+pub const DATE_NAN_BITS: u64 = 0x7FF8_0000_0000_0DA7;
+
+/// The canonical Invalid Date value.
+#[inline]
+pub fn date_invalid() -> f64 {
+    f64::from_bits(DATE_NAN_BITS)
+}
+
+/// Map any NaN result to the canonical Invalid-Date sentinel; pass
+/// finite values through untouched. Used by the `new Date(...)`
+/// constructors so an invalid time value is still a recognizable Date
+/// object instead of a bare, type-less NaN.
+#[inline]
+fn date_or_invalid(v: f64) -> f64 {
+    if v.is_nan() {
+        date_invalid()
+    } else {
+        v
+    }
+}
+
+/// The string every Date string-method returns when the time value is
+/// NaN. Matches `String(new Date(NaN))` / `new Date(NaN).toDateString()`
+/// etc. Without this, the formatters cast NaN to `0i64` and emit a bogus
+/// `1970-01-01…` string (the `<garbage>` reported in issue #748).
+fn invalid_date_string() -> *mut crate::StringHeader {
+    let s = "Invalid Date";
+    crate::string::js_string_from_bytes(s.as_ptr(), s.len() as u32)
+}
+
 /// Mark `bits` as a Date so future `instanceof Date` checks can recognize it.
 pub fn register_date_bits(bits: u64) {
     DATE_REGISTRY.with(|r| {
@@ -26,9 +81,11 @@ pub fn register_date_bits(bits: u64) {
     });
 }
 
-/// True when `bits` were previously registered as a Date.
+/// True when `bits` are a Date: either the canonical Invalid-Date
+/// sentinel (recognized globally, no registration) or a finite timestamp
+/// previously registered by `new Date(...)` / `Date.now()` / a Date method.
 pub fn is_registered_date_bits(bits: u64) -> bool {
-    DATE_REGISTRY.with(|r| r.borrow().contains(&bits))
+    bits == DATE_NAN_BITS || DATE_REGISTRY.with(|r| r.borrow().contains(&bits))
 }
 
 /// Convert a UTC timestamp (seconds) to local-time components.
@@ -118,11 +175,15 @@ pub extern "C" fn js_date_new() -> f64 {
     v
 }
 
-/// Create a new Date from a timestamp (milliseconds since epoch)
+/// Create a new Date from a timestamp (milliseconds since epoch).
+/// A NaN timestamp produces a recognizable Invalid Date, not a bare NaN.
 #[no_mangle]
 pub extern "C" fn js_date_new_from_timestamp(timestamp: f64) -> f64 {
-    register_date_bits(timestamp.to_bits());
-    timestamp
+    let result = date_or_invalid(timestamp);
+    if !result.is_nan() {
+        register_date_bits(result.to_bits());
+    }
+    result
 }
 
 /// Create a new Date from a value that could be a number or a NaN-boxed string.
@@ -153,6 +214,7 @@ pub extern "C" fn js_date_new_from_value(value: f64) -> f64 {
         // Numeric timestamp
         value
     };
+    let result = date_or_invalid(result);
     if !result.is_nan() {
         register_date_bits(result.to_bits());
     }
@@ -294,6 +356,9 @@ pub extern "C" fn js_date_get_time(timestamp: f64) -> f64 {
 /// Returns a pointer to a StringHeader
 #[no_mangle]
 pub extern "C" fn js_date_to_iso_string(timestamp: f64) -> *mut crate::StringHeader {
+    if timestamp.is_nan() {
+        return invalid_date_string();
+    }
     let ts_ms = timestamp as i64;
     let secs = ts_ms / 1000;
     let millis = (ts_ms % 1000).unsigned_abs() as u32;
@@ -696,6 +761,9 @@ const MONTH_NAMES: [&str; 12] = [
 /// date.toDateString() — e.g. "Mon Jan 15 2024" (local time).
 #[no_mangle]
 pub extern "C" fn js_date_to_date_string(timestamp: f64) -> *mut crate::StringHeader {
+    if timestamp.is_nan() {
+        return invalid_date_string();
+    }
     let ts_ms = timestamp as i64;
     let secs = ts_ms.div_euclid(1000);
     let (year, month, day, _, _, _, tz_offset) = timestamp_to_local_components(secs);
@@ -713,6 +781,9 @@ pub extern "C" fn js_date_to_date_string(timestamp: f64) -> *mut crate::StringHe
 /// date.toTimeString() — e.g. "12:30:45 GMT+0100 (local)" (local time).
 #[no_mangle]
 pub extern "C" fn js_date_to_time_string(timestamp: f64) -> *mut crate::StringHeader {
+    if timestamp.is_nan() {
+        return invalid_date_string();
+    }
     let ts_ms = timestamp as i64;
     let secs = ts_ms.div_euclid(1000);
     let (_, _, _, hour, minute, second, tz_offset) = timestamp_to_local_components(secs);
@@ -730,6 +801,9 @@ pub extern "C" fn js_date_to_time_string(timestamp: f64) -> *mut crate::StringHe
 /// date.toLocaleDateString() — simple en-US-style date (local time).
 #[no_mangle]
 pub extern "C" fn js_date_to_locale_date_string(timestamp: f64) -> *mut crate::StringHeader {
+    if timestamp.is_nan() {
+        return invalid_date_string();
+    }
     let ts_ms = timestamp as i64;
     let secs = ts_ms.div_euclid(1000);
     let (year, month, day, _, _, _, _) = timestamp_to_local_components(secs);
@@ -740,6 +814,9 @@ pub extern "C" fn js_date_to_locale_date_string(timestamp: f64) -> *mut crate::S
 /// date.toLocaleTimeString() — simple H:MM:SS AM/PM en-US style (local time).
 #[no_mangle]
 pub extern "C" fn js_date_to_locale_time_string(timestamp: f64) -> *mut crate::StringHeader {
+    if timestamp.is_nan() {
+        return invalid_date_string();
+    }
     let ts_ms = timestamp as i64;
     let secs = ts_ms.div_euclid(1000);
     let (_, _, _, hour, minute, second, _) = timestamp_to_local_components(secs);
@@ -814,6 +891,9 @@ pub extern "C" fn js_number_to_locale_string(n: f64) -> *mut crate::StringHeader
 /// date.toLocaleString() — combined date and time (local time).
 #[no_mangle]
 pub extern "C" fn js_date_to_locale_string(timestamp: f64) -> *mut crate::StringHeader {
+    if timestamp.is_nan() {
+        return invalid_date_string();
+    }
     let ts_ms = timestamp as i64;
     let secs = ts_ms.div_euclid(1000);
     let (year, month, day, hour, minute, second, _) = timestamp_to_local_components(secs);
diff --git a/crates/perry-runtime/src/object.rs b/crates/perry-runtime/src/object.rs
index a2fba547..5c3acd89 100644
--- a/crates/perry-runtime/src/object.rs
+++ b/crates/perry-runtime/src/object.rs
@@ -5048,9 +5048,14 @@ pub extern "C" fn js_instanceof(value: f64, class_id: u32) -> f64 {
         // number would match (the prior "approximate" rule), which made
         // `100 instanceof Date` true and broke the BSON encoder's typed
         // dispatch (`if (value instanceof Date) … else if (typeof v === 'number') …`).
-        if !value.is_nan()
-            && value.is_finite()
-            && crate::date::is_registered_date_bits(value.to_bits())
+        //
+        // The Invalid-Date sentinel is itself a NaN, so it must be matched
+        // *before* the `!is_nan()` guard — `new Date(NaN) instanceof Date`
+        // is `true` per ECMA-262 even though its time value is NaN.
+        if value.to_bits() == crate::date::DATE_NAN_BITS
+            || (!value.is_nan()
+                && value.is_finite()
+                && crate::date::is_registered_date_bits(value.to_bits()))
         {
             return true_val;
         }
@@ -5095,9 +5100,11 @@ pub extern "C" fn js_instanceof(value: f64, class_id: u32) -> f64 {
         if jsval.is_pointer() {
             return true_val;
         }
-        if !value.is_nan()
-            && value.is_finite()
-            && crate::date::is_registered_date_bits(value.to_bits())
+        // Invalid Date is still an Object (NaN time value, but a Date).
+        if value.to_bits() == crate::date::DATE_NAN_BITS
+            || (!value.is_nan()
+                && value.is_finite()
+                && crate::date::is_registered_date_bits(value.to_bits()))
         {
             return true_val;
         }
diff --git a/test-files/test_issue_748_invalid_date.ts b/test-files/test_issue_748_invalid_date.ts
new file mode 100644
index 00000000..5c7b800a
--- /dev/null
+++ b/test-files/test_issue_748_invalid_date.ts
@@ -0,0 +1,61 @@
+// Issue #748 — `new Date(NaN)` / `: Date` object-method must be a Date
+// object, not a bare number. Mirrors the comment's minimal repro plus
+// regression coverage for valid dates.
+
+// --- the comment's deterministic minimal repro ---
+function w5(y: number) {
+  return {
+    toDate(): Date {
+      return new Date(NaN);
+    },
+  };
+}
+console.log("w5 typeof:", typeof w5(2026).toDate()); // expect: object
+
+// --- core Invalid Date identity ---
+const inv = new Date(NaN);
+console.log("typeof inv:", typeof inv); // object
+console.log("inv instanceof Date:", inv instanceof Date); // true
+console.log("inv instanceof Object:", inv instanceof Object); // true
+console.log("inv.getTime() isNaN:", Number.isNaN(inv.getTime())); // true
+console.log("inv.getFullYear() isNaN:", Number.isNaN(inv.getFullYear())); // true
+console.log("String(inv):", String(inv.toISOString())); // Invalid Date
+console.log("inv.toDateString():", inv.toDateString()); // Invalid Date
+console.log("JSON.stringify(inv):", JSON.stringify(inv)); // null
+console.log("JSON.stringify({d:inv}):", JSON.stringify({ d: inv })); // {"d":null}
+
+// --- invalid via string / Date.UTC(NaN) ---
+const invStr = new Date("not a date");
+console.log("invStr typeof:", typeof invStr); // object
+console.log("invStr instanceof Date:", invStr instanceof Date); // true
+
+// --- the @perryts/mysql MyDateTime.toDate() shape (no mysql) ---
+function makeMyDateTime(y: number, mo: number, d: number) {
+  return {
+    toDate(): Date {
+      if (y === 0 && mo === 0 && d === 0) return new Date(NaN);
+      return new Date(Date.UTC(y, mo - 1, d, 7, 47, 4, 192));
+    },
+  };
+}
+function dtToIso(v: { toDate(): Date }): string | null {
+  const dt = v.toDate();
+  const t = dt.getTime();
+  return Number.isNaN(t) ? null : new Date(t).toISOString();
+}
+console.log("valid dtToIso:", dtToIso(makeMyDateTime(2026, 5, 15)));
+console.log("zero  dtToIso:", dtToIso(makeMyDateTime(0, 0, 0))); // null
+
+// --- regression: valid Dates must be completely unaffected ---
+const v = new Date(Date.UTC(2026, 4, 15, 17, 29, 35, 402));
+console.log("v typeof:", typeof v); // object
+console.log("v instanceof Date:", v instanceof Date); // true
+console.log("v instanceof Object:", v instanceof Object); // true
+console.log("v.getFullYear():", v.getUTCFullYear()); // 2026
+console.log("v.getTime():", v.getTime()); // 1778880575402
+console.log("v.toISOString():", v.toISOString()); // 2026-05-15T17:29:35.402Z
+console.log("JSON.stringify(v):", JSON.stringify(v)); // "2026-05-15T17:29:35.402Z"
+const n = 1778880575402; // plain number equal to v's millis must stay a number
+console.log("plain number typeof:", typeof n); // number
+console.log("Date.now() typeof:", typeof Date.now()); // number
+console.log("(new Date()) instanceof Date:", new Date() instanceof Date); // true