diff --git a/Cargo.lock b/Cargo.lock
index 1e99605..52eef1f 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2723,6 +2723,7 @@ dependencies = [
  "serde",
  "swactor-std",
  "tracing",
+ "web-time",
 ]
 
 [[package]]
@@ -3735,6 +3736,16 @@ dependencies = [
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "web-time"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aa30049b1c872b72c89866d458eae9f20380ab280ffd1b1e18df2d3e2d98cfe0"
+dependencies = [
+ "js-sys",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "winapi"
 version = "0.3.9"
diff --git a/Cargo.toml b/Cargo.toml
index 19c2995..2634ddc 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -22,11 +22,13 @@ serde = ["dep:serde"]
 tracing = ["dep:tracing"]
 no_random = [] # compile without access to a source of randomness
 transport = []  # transport-agnostic messaging (no mandatory deps; codec is user-provided)
+wasm = ["no_random", "dep:web-time"] # browser/wasm32 target support
 
 [dependencies]
 getrandom = { version = "0.2", optional = true }
 serde = { version = "1", features = ["derive"], optional = true }
 tracing = { version = "0.1", optional = true }
+web-time = { version = "0.2", optional = true }
 crossbeam-queue = "0.3.12"
 crossbeam-utils = "0.8.21"
 
diff --git a/big-feature-phase/notes/history.md b/big-feature-phase/notes/history.md
index 67e6a3f..abc909b 100644
--- a/big-feature-phase/notes/history.md
+++ b/big-feature-phase/notes/history.md
@@ -2,3 +2,6 @@
 
 ## Cycle 0 — Research (complete)
 Investigated Lunatic, wasmCloud, Actix-wasm attempts. Analyzed core swactor platform deps: 4 blockers (thread spawn, park/unpark, yield, Instant). User confirmed: performance-first, SharedArrayBuffer+wasm-threads, Rust-only actors, all feasible features, future STUN/TURN. Produced constraints.md, research_synthesis.md, 6 feature-stage docs. Next: Stage 1 platform abstraction.
+
+## Stage 1 — Platform Abstraction (complete)
+Added `wasm` feature + `web-time` dep. Replaced `std::time::Instant` → `crate::Instant` (cfg-gated re-export). Gated `Runtime::run()` and `RuntimeHandle` for non-wasm. Key finding: only `thread::spawn` needed gating — park/unpark/yield/Mutex/RwLock/atomics/crossbeam all work on wasm32 with atomics. Cleaned unused Mutex import in worker.rs. Updated crates/wasm/ to use `wasm` feature. All native tests pass, wasm32 compilation succeeds. Files changed: Cargo.toml, src/lib.rs, src/runtime.rs, src/worker.rs, crates/wasm/Cargo.toml.
diff --git a/big-feature-phase/notes/state.md b/big-feature-phase/notes/state.md
index e0f952a..df07bba 100644
--- a/big-feature-phase/notes/state.md
+++ b/big-feature-phase/notes/state.md
@@ -1,46 +1,47 @@
 ## Current Task
-Cycle 0 — Research
+Stage 1 — Platform Abstraction Layer
 Step: Complete
 Attempt: 1 of 3
 
 ## Key Files (read these first on resume)
 - `big-feature-phase/TASK.md` — workflow rules
-- `big-feature-phase/notes/constraints.md` — guardrails for in-browser runtime
-- `big-feature-phase/notes/research_synthesis.md` — P0-P4 priority ranking
-- `big-feature-phase/notes/feature-stages/01-platform-abstraction.md` — Stage 1 spec
-- `src/runtime.rs` — thread spawn (line 351), park handles (line 110), Instant (line 205)
-- `src/worker.rs` — backoff loop (lines 495-523), Instant timing (9 calls)
-- `src/delivery.rs` — TickContext.worker_threads (line 246)
-- `src/channel.rs` — crossbeam HybridChannel (validate wasm compilation)
-- `crates/wasm/src/lib.rs` — existing PoC browser runtime
+- `big-feature-phase/notes/constraints.md` — guardrails
+- `big-feature-phase/notes/feature-stages/02-single-worker-browser.md` — Stage 2 spec
+- `Cargo.toml` — `wasm` feature flag, `web-time` dep (lines 23, 30)
+- `src/lib.rs` — platform-aware `Instant` re-export (lines 20-24)
+- `src/runtime.rs` — cfg-gated `run()` (line 340) and `RuntimeHandle` (line 73)
+- `crates/wasm/Cargo.toml` — now uses `features = ["wasm"]`
+- `docs/development_history/in-browser/PLATFORM_ABSTRACTION.md` — what was done
 
 ## Last Action & Result
-Completed Cycle 0 research phase:
-- Investigated similar projects (Lunatic, wasmCloud, Actix wasm attempts)
-- Analyzed all platform-specific code in core swactor (4 blockers found)
-- User confirmed: Rust-only actors, performance-first, Web Workers, all features, full peer
-- Key decision: SharedArrayBuffer + wasm-threads (not postMessage isolation)
-- Wrote constraints.md, research_synthesis.md, 6 feature-stage docs
+Completed Stage 1 (Platform Abstraction Layer):
+- Added `web-time` dep + `wasm` feature (`no_random` + `web-time`)
+- Replaced `std::time::Instant` → `crate::Instant` in runtime.rs, worker.rs
+- cfg-gated `Runtime::run()` and `RuntimeHandle` for `not(target_arch = "wasm32")`
+- Removed unused `Mutex` import from worker.rs
+- Updated `crates/wasm/` to use `wasm` feature
+- Key finding: most std::sync/thread primitives work on wasm32 with atomics; only `thread::spawn` needed gating
+- All native tests pass, wasm32 compilation succeeds
 
 ## Next Action
-Begin Stage 1 (Platform Abstraction Layer) — `notes/feature-stages/01-platform-abstraction.md`:
-1. Add `web-time` dependency to core Cargo.toml
-2. Replace `std::time::Instant` with `web_time::Instant` in runtime.rs and worker.rs
-3. Implement `ParkHandle` abstraction with cfg gates
-4. Gate `Runtime::run()` thread spawning for non-wasm
-5. Validate crossbeam-queue compiles for wasm32 with atomics
-6. Add `wasm` feature flag
+Begin Stage 2 (Single-Worker Browser Runtime) — `notes/feature-stages/02-single-worker-browser.md`:
+1. Create `crates/wasm-browser/` crate structure
+2. Implement `BrowserRuntime` wasm-bindgen API (spawn, send, tick, try_recv, stats)
+3. Actor registration macro/pattern for JS-accessible spawning
+4. Auto-scheduling via setTimeout(0) loop
+5. Message serialization across JS↔Wasm boundary
+6. Tests (wasm-pack test or Node.js)
 
 ## Completed This Session
-- [x] Read TASK.md, state.md, history.md (context restart checklist)
-- [x] Investigated similar codebases (Lunatic, wasmCloud, Actix-wasm)
-- [x] Analyzed platform dependencies in core swactor
-- [x] Asked and resolved design questions with user
-- [x] Wrote `notes/constraints.md`
-- [x] Wrote `notes/research_synthesis.md`
-- [x] Created `notes/feature-stages/` with 6 stage docs
+- [x] Cycle 0 research artifacts (constraints.md, research_synthesis.md, 6 stage docs)
+- [x] Stage 1: `web-time` dep + `wasm` feature flag in Cargo.toml
+- [x] Stage 1: Platform-aware `Instant` re-export in src/lib.rs
+- [x] Stage 1: cfg-gated `Runtime::run()` and `RuntimeHandle` in src/runtime.rs
+- [x] Stage 1: Updated crates/wasm/ to use `wasm` feature
+- [x] Stage 1: Validated wasm32 compilation and native tests
+- [x] Stage 1: Development history doc
 
 ## Open Questions / Blockers
-- Need to verify crossbeam-queue compiles for wasm32 with atomics (Stage 1 task)
-- Need to find/verify correct `core::arch::wasm32` APIs for memory_atomic_wait/notify
-- Nightly Rust toolchain + wasm32 target needs to be set up in CI
+- Stage 2: Need to decide on message serialization (serde-wasm-bindgen vs raw bytes)
+- Stage 2: Actor registration pattern — macro vs manual factory map
+- Stage 3: Web Worker thread state initialization needs investigation (does std::thread::current() work in a Web Worker context?)
diff --git a/crates/wasm/Cargo.toml b/crates/wasm/Cargo.toml
index f4fda2e..445b85c 100644
--- a/crates/wasm/Cargo.toml
+++ b/crates/wasm/Cargo.toml
@@ -7,5 +7,5 @@ edition = "2024"
 crate-type = ["cdylib"]
 
 [dependencies]
-swactor = { path = "../..", default-features = false, features = ["no_random"] }
+swactor = { path = "../..", default-features = false, features = ["wasm"] }
 wasm-bindgen = "0.2"
diff --git a/docs/development_history/in-browser/PLATFORM_ABSTRACTION.md b/docs/development_history/in-browser/PLATFORM_ABSTRACTION.md
new file mode 100644
index 0000000..30738ed
--- /dev/null
+++ b/docs/development_history/in-browser/PLATFORM_ABSTRACTION.md
@@ -0,0 +1,82 @@
+# Platform Abstraction Layer — Development History
+
+> Stage 1 of the in-browser swactor runtime. Makes core swactor compile for
+> `wasm32-unknown-unknown` without behavioral changes on native targets.
+
+---
+
+## Changes
+
+### 1. `web-time` dependency + `wasm` feature flag
+
+**File**: `Cargo.toml`
+
+Added `web-time` as an optional dependency and a `wasm` feature that bundles
+`no_random` + `web-time`:
+
+```toml
+wasm = ["no_random", "dep:web-time"]
+web-time = { version = "0.2", optional = true }
+```
+
+`web-time` is a drop-in replacement for `std::time::Instant`:
+- Native: re-exports `std::time::Instant` (zero-cost)
+- wasm32: uses `performance.now()` via `js-sys`
+
+### 2. Platform-aware `Instant` re-export
+
+**File**: `src/lib.rs`
+
+```rust
+#[cfg(feature = "wasm")]
+pub(crate) use web_time::Instant;
+#[cfg(not(feature = "wasm"))]
+pub(crate) use std::time::Instant;
+```
+
+All modules (`runtime.rs`, `worker.rs`) now use `crate::Instant` instead of
+`std::time::Instant`. Single point of truth — no cfg noise in consumer code.
+
+### 3. cfg-gated `Runtime::run()` and `RuntimeHandle`
+
+**File**: `src/runtime.rs`
+
+`Runtime::run()` calls `std::thread::spawn()` which is not available on wasm32.
+Both `run()` and `RuntimeHandle` (which holds `JoinHandle<()>`) are gated:
+
+```rust
+#[cfg(not(target_arch = "wasm32"))]
+pub fn run(self) -> Result<RuntimeHandle, Error> { ... }
+```
+
+On wasm32, the browser crate will provide its own `run()` via Web Workers.
+`tick()` remains available on all platforms for single-threaded driving.
+
+### 4. Updated `crates/wasm/` to use `wasm` feature
+
+**File**: `crates/wasm/Cargo.toml`
+
+Changed from `features = ["no_random"]` to `features = ["wasm"]` to pick up
+the `web-time` Instant on wasm32.
+
+## What Did NOT Need Abstraction
+
+Key discovery: on wasm32 with the `+atomics` target feature, most of
+`std::sync` and `std::thread` works:
+
+- `OnceLock<Thread>` — compiles and works (futex-based)
+- `Thread::unpark()` — works (futex → `memory.atomic.notify`)
+- `thread::park_timeout()` — works (futex → `memory.atomic.wait32`)
+- `thread::yield_now()` — works (no-op on wasm)
+- `Mutex`, `RwLock` — work (futex-based)
+- `crossbeam-queue` — works (uses `core::sync::atomic`)
+- `AtomicBool/Usize/U64` — work (wasm atomic instructions)
+
+Only `std::thread::spawn()` and `JoinHandle` are not functional on wasm32.
+
+## Verification
+
+- `cargo test` — all native tests pass (no regressions)
+- `cargo test --features wasm` — all native tests pass with wasm feature
+- `cargo build --target wasm32-unknown-unknown --features wasm --no-default-features` — compiles
+- `cargo build --target wasm32-unknown-unknown -p wasm` — existing PoC crate compiles
diff --git a/src/lib.rs b/src/lib.rs
index 146ff90..00d9f72 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -18,6 +18,13 @@ pub mod runtime;
 #[cfg(feature = "transport")]
 pub mod transport;
 
+// Platform-aware Instant: web_time on wasm, std::time on native.
+// web_time is a no-op re-export of std::time::Instant on non-wasm targets.
+#[cfg(feature = "wasm")]
+pub(crate) use web_time::Instant;
+#[cfg(not(feature = "wasm"))]
+pub(crate) use std::time::Instant;
+
 #[cfg(feature = "getrandom")]
 pub(crate) fn get_random(buf: &mut [u8]) {
     getrandom::getrandom(buf).unwrap()
diff --git a/src/runtime.rs b/src/runtime.rs
index dd65928..a412f91 100644
--- a/src/runtime.rs
+++ b/src/runtime.rs
@@ -2,8 +2,10 @@ use std::any::Any;
 use std::cell::RefCell;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, Mutex, OnceLock};
-use std::thread::{self, JoinHandle, Thread};
-use std::time::Instant;
+#[cfg(not(target_arch = "wasm32"))]
+use std::thread::{self, JoinHandle};
+use std::thread::Thread;
+use crate::Instant;
 
 use crate::actor::{Actor, ActorAddress, ActorExited, ActorInterface, AnyActor, ExitReason, Message, StopSignal, TimerRequest};
 use crate::channel::{Receiver, Sender};
@@ -67,11 +69,13 @@ impl<R: Message> Ask<R> {
 }
 
 /// Handle for dealing with a runtime that has started via the `Runtime::run()` method.
+#[cfg(not(target_arch = "wasm32"))]
 pub struct RuntimeHandle {
     pub runtime: Arc<Runtime>,
     threads: Vec<JoinHandle<()>>,
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 impl RuntimeHandle {
     pub fn join(self) {
         for handle in self.threads {
@@ -333,6 +337,9 @@ impl Runtime {
     ///
     /// Works in both single-threaded and multi-threaded configurations.
     /// In single-threaded mode, one background thread is spawned.
+    ///
+    /// Not available on wasm32 — use the browser crate's Web Worker-based run instead.
+    #[cfg(not(target_arch = "wasm32"))]
     pub fn run(self) -> Result<RuntimeHandle, Error> {
         self.is_running.store(true, Ordering::Release);
 
diff --git a/src/worker.rs b/src/worker.rs
index 901fc99..446dc66 100644
--- a/src/worker.rs
+++ b/src/worker.rs
@@ -2,9 +2,9 @@ use std::any::Any;
 use std::cell::RefCell;
 use std::collections::{HashMap, HashSet, VecDeque};
 use std::sync::atomic::{AtomicBool, Ordering};
-use std::sync::{Arc, Mutex};
+use std::sync::Arc;
 use std::thread;
-use std::time::Instant;
+use crate::Instant;
 
 use crate::actor::{ActorAddress, ActorExited, AnyActor, CloneMsg, ContextInner, Ctx, ExitReason, StopReason, StopSignal, TimerRequest};
 use crate::channel::Receiver;