diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 00000000..529790ce
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,43 @@
+name: CI
+
+on:
+  push:
+  pull_request:
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  test:
+    name: Test and lint (host)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          components: clippy, rustfmt
+      - uses: Swatinem/rust-cache@v2
+      - run: cargo fmt --all -- --check
+      - run: cargo clippy --workspace --all-targets -- -D warnings
+      - run: cargo test --workspace
+
+  wasm:
+    name: wasm32 check (browser bundle crates)
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          targets: wasm32-unknown-unknown
+      - uses: Swatinem/rust-cache@v2
+      # Only the crates that go into the browser bundle. The root `improvise`
+      # crate is the terminal binary and depends on crossterm, which does not
+      # build for wasm — that is correct, not a gap (improvise-ywd).
+      - name: improvise-core
+        run: cargo check -p improvise-core --target wasm32-unknown-unknown
+      - name: improvise-formula
+        run: cargo check -p improvise-formula --target wasm32-unknown-unknown
+      - name: improvise-io
+        run: cargo check -p improvise-io --target wasm32-unknown-unknown
+      - name: improvise-command
+        run: cargo check -p improvise-command --target wasm32-unknown-unknown
diff --git a/Cargo.lock b/Cargo.lock
index 67077212..3ca15bfc 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -798,6 +798,7 @@ dependencies = [
  "serde_json",
  "tempfile",
  "unicode-width",
+ "web-time",
 ]
 
 [[package]]
@@ -2115,6 +2116,16 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "web-time"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5a6580f308b1fad9207618087a65c04e7a10bc77e02c8e84e9b00dd4b12fa0bb"
+dependencies = [
+ "js-sys",
+ "wasm-bindgen",
+]
+
 [[package]]
 name = "wezterm-bidi"
 version = "0.2.3"
diff --git a/context/repo-map.md b/context/repo-map.md
index 33e69806..474187d5 100644
--- a/context/repo-map.md
+++ b/context/repo-map.md
@@ -249,6 +249,20 @@ docs/design-notes.md                Product vision & non-goals
 
 ---
 
+## Wasm
+
+The browser bundle is `improvise-core`, `improvise-formula`, `improvise-io`
+and `improvise-command`. All four `cargo check --target
+wasm32-unknown-unknown` clean with no feature flags (improvise-ywd), gated by
+the `wasm` job in `.github/workflows/ci.yml`. The root `improvise` crate is
+the terminal binary and does **not** build for wasm — it depends on
+crossterm; that is correct, not a gap.
+
+`cargo check` passing is not the same as running. Two known runtime hazards
+it cannot see: `Instant::now()` panics on wasm (hence `web-time` in
+`improvise-command`), and any `std::fs` call compiles but fails in a browser
+— see improvise-fuj for the two effects that still bypass `Storage`.
+
 ## CLI
 
 ```
diff --git a/crates/improvise-command/Cargo.toml b/crates/improvise-command/Cargo.toml
index 179c3ae2..e5bd95c6 100644
--- a/crates/improvise-command/Cargo.toml
+++ b/crates/improvise-command/Cargo.toml
@@ -13,6 +13,9 @@ improvise-io = { path = "../improvise-io" }
 anyhow = "1"
 serde_json = "1"
 unicode-width = "^0.2"
+# Instant::now() panics on wasm32-unknown-unknown; web_time re-exports
+# std::time off-wasm and uses performance.now() on it (improvise-ywd).
+web-time = "1"
 
 [dev-dependencies]
 tempfile = "3"
diff --git a/crates/improvise-command/src/ui/app.rs b/crates/improvise-command/src/ui/app.rs
index 3e42894b..f558d117 100644
--- a/crates/improvise-command/src/ui/app.rs
+++ b/crates/improvise-command/src/ui/app.rs
@@ -3,7 +3,10 @@ use anyhow::Result;
 use std::collections::HashMap;
 use std::path::PathBuf;
 use std::sync::Arc;
-use std::time::{Duration, Instant};
+use std::time::Duration;
+// Not std::time::Instant: that panics on wasm32-unknown-unknown, and this
+// crate is part of the browser bundle (improvise-ywd).
+use web_time::Instant;
 
 use std::rc::Rc;
 
diff --git a/flake.nix b/flake.nix
index 217e77fa..e34b292e 100644
--- a/flake.nix
+++ b/flake.nix
@@ -25,6 +25,10 @@
 
       rustToolchain = pkgs.rust-bin.stable.latest.default.override {
         extensions = ["rust-src" "clippy" "rustfmt" "llvm-tools-preview"];
+        # The browser deployment targets wasm; without this, the wasm audit
+        # (improvise-ywd) and the OPFS backend (improvise-i34) cannot even be
+        # checked, let alone fixed.
+        targets = ["wasm32-unknown-unknown"];
       };
 
       cargoNix = import ./Cargo.nix {
diff --git a/prolog-sessions/kb.pl b/prolog-sessions/kb.pl
index f27afb7a..1a08f837 100644
--- a/prolog-sessions/kb.pl
+++ b/prolog-sessions/kb.pl
@@ -188,3 +188,21 @@ invariant(prefix_is_an_address,'ViewState::transient_prefix stores the (KeyCode,
 decision('improvise-jc8',flip_the_arc,'Arc<Keymap> moved out of ViewState and back into KeymapSet, which already owns every keymap. Motivated by a hard dependency cycle -- Keymap is in improvise-command, which will depend on improvise-protocol once reduce_full lives there -- not by serde.').
 work_done('improvise-jc8',refactor,'ViewState no longer holds Arc<Keymap>; four characterization tests written before the change pinned gg/ZZ/prefix-consumption/records-inheritance, plus two new guards for flatness and parent resolution.').
 location(prefix_resolution,'crates/improvise-command/src/command/keymap.rs','KeymapSet::prefix_keymap, SetTransientPrefix').
+
+% ── Wasm compatibility (improvise-ywd, audited 2026-08-30) ──────────────────
+wasm_bundle_crate('improvise-core').
+wasm_bundle_crate('improvise-formula').
+wasm_bundle_crate('improvise-io').
+wasm_bundle_crate('improvise-command').
+not_in_wasm_bundle('improvise', 'terminal binary; depends on crossterm').
+wasm_checks_clean(all_bundle_crates, no_feature_flags_needed).
+% Hazards a compile check cannot see.
+wasm_runtime_hazard(instant_now, 'panics on wasm32-unknown-unknown', fixed_with(web_time)).
+wasm_runtime_hazard(std_fs, 'compiles on wasm but fails in a browser', tracked_as('improvise-fuj')).
+wasm_non_hazard(dirs, 'declared in root Cargo.toml but used nowhere').
+wasm_non_hazard(chrono_local_now, 'never called').
+wasm_non_hazard(std_env, 'only in a test').
+wasm_non_hazard(flate2, 'compiles for wasm as-is').
+invariant(compile_check_is_not_runtime_proof,'the wasm CI gate is cargo check, so it catches nothing that merely panics at runtime: Instant and std::fs both COMPILE for wasm32-unknown-unknown').
+work_done('improvise-ywd',audit,'added wasm32-unknown-unknown to the flake toolchain, which was the real blocker; all four bundle crates then checked clean with zero source changes. Swapped Instant for web_time and added the CI wasm job.').
+location(wasm_ci,'.github/workflows/ci.yml','wasm job').