diff --git a/docs/linuxcnc-source-policy.md b/docs/linuxcnc-source-policy.md
index 4c44ead..0c7784d 100644
--- a/docs/linuxcnc-source-policy.md
+++ b/docs/linuxcnc-source-policy.md
@@ -16,6 +16,10 @@ Hard rules:
   LinuxCNC source before implementation.
 - Browser-side wasm filesystem behavior must use OPFS-backed storage. Do not
   add browser filesystem paths that bypass OPFS.
+- Browser app and wasm bridge code must not persist CNC programs, LinuxCNC
+  parameter files, or mirrored workspace files through non-OPFS browser storage
+  APIs such as Local Storage, IndexedDB, File Picker writes, WebKit filesystem
+  APIs, or FileReader-backed import paths.
 
 Allowed project code:
 
@@ -61,6 +65,8 @@ Efficiency rules:
   permission to expand the pass into another workstream.
 - Do not add a smoke-only behavior path when the LinuxCNC-backed route already
   exists; add coverage to the source-backed route instead.
+- Keep browser filesystem guardrails negative as well as positive: require the
+  OPFS bridge and reject browser app/wasm storage APIs that could bypass it.
 - Smoke tests are verification guardrails. They must not be expanded with new
   functional CNC behavior unless that behavior is directly routed to, copied
   from, or checked against the relevant LinuxCNC source in the same narrow
diff --git a/test-all-native.sh b/test-all-native.sh
index ff895ee..5e255f7 100755
--- a/test-all-native.sh
+++ b/test-all-native.sh
@@ -504,6 +504,9 @@ grep -F 'cached `nm --defined-only` symbol export signatures' docs/linuxcnc-sour
 grep -F 'Cache wasm blocker analyzer output' docs/linuxcnc-source-policy.md >/dev/null
 grep -F 'signature must include the blocker wrapper script, analyzer script' docs/linuxcnc-source-policy.md >/dev/null
 grep -F 'sha256sum test-linuxcnc-wasm-blockers.sh' test-linuxcnc-wasm-blockers.sh >/dev/null
+grep -F 'browser app/wasm code must not add filesystem persistence outside OPFS' test-native.sh >/dev/null
+grep -F 'browser app/wasm code must not add filesystem persistence outside OPFS' test-linuxcnc-wasm-cmake-safe-probe.sh >/dev/null
+grep -F 'reject browser app/wasm storage APIs that could bypass it' docs/linuxcnc-source-policy.md >/dev/null
 grep -F 'Persistent native, source-link, source-syntax, and wasm-safe CMake probe' docs/linuxcnc-source-policy.md >/dev/null
 grep -F 'copies and byte-compares `cnc_sim.js` and `cnc_sim.wasm` under' docs/linuxcnc-source-policy.md >/dev/null
 grep -F '`CNC_SIM_BUILD_JOBS` must be a positive integer and defaults to `8`.' docs/linuxcnc-source-policy.md >/dev/null
diff --git a/test-linuxcnc-wasm-cmake-safe-probe.sh b/test-linuxcnc-wasm-cmake-safe-probe.sh
index 4242203..3383358 100755
--- a/test-linuxcnc-wasm-cmake-safe-probe.sh
+++ b/test-linuxcnc-wasm-cmake-safe-probe.sh
@@ -753,6 +753,10 @@ grep -F -- './test-web-wasm-node-smoke.sh' build-wasm.sh >/dev/null
 grep -F -- './test-web-wasm-browser-smoke.sh' build-wasm.sh >/dev/null
 grep -F 'const opfsOptions = options.opfs ?? (isOpfsAvailable() ? {} : false)' web/src/wasm-core.js >/dev/null
 grep -F 'OPFS cannot be disabled in browser contexts with OPFS support' web/src/wasm-core.js >/dev/null
+if grep -R -n -E 'localStorage|sessionStorage|indexedDB|showOpenFilePicker|showSaveFilePicker|webkitRequestFileSystem|FileReader' web/src; then
+    echo "browser app/wasm code must not add filesystem persistence outside OPFS" >&2
+    exit 1
+fi
 grep -F 'async function opfsEntryExists(workspacePath, relativePath)' web/src/wasm-core.js >/dev/null
 grep -F 'async function statOpfsEntry(workspacePath, relativePath)' web/src/wasm-core.js >/dev/null
 grep -F 'async function readOpfsDirectoryTree(workspacePath, relativePath, relativeRoot = "")' web/src/wasm-core.js >/dev/null
diff --git a/test-native.sh b/test-native.sh
index d4fc6f0..f642e6e 100755
--- a/test-native.sh
+++ b/test-native.sh
@@ -227,6 +227,10 @@ grep -F '"parameters/rs274ngc.var"' web/test-browser-wasm-smoke-opfs-parameter-s
 grep -F '"parameters/rs274ngc.var.bak"' web/test-browser-wasm-smoke-opfs-parameter-sections.js >/dev/null
 grep -F 'const opfsOptions = options.opfs ?? (isOpfsAvailable() ? {} : false)' web/src/wasm-core.js >/dev/null
 grep -F 'OPFS cannot be disabled in browser contexts with OPFS support' web/src/wasm-core.js >/dev/null
+if grep -R -n -E 'localStorage|sessionStorage|indexedDB|showOpenFilePicker|showSaveFilePicker|webkitRequestFileSystem|FileReader' web/src; then
+    echo "browser app/wasm code must not add filesystem persistence outside OPFS" >&2
+    exit 1
+fi
 grep -F 'LinuxCNC source basis: rs274ngc_pre.cc restore_parameters() reads the' web/src/wasm-core.js >/dev/null
 grep -F 'before replacing the main file and managing filename + ".bak".' web/src/wasm-core.js >/dev/null
 grep -F 'await removeOpfsEntry(workspacePath, `${path}.new`, false);' web/src/wasm-core.js >/dev/null