harden: keep the test recovery phrase out of release bundles, match committed keys by content (closes #351)

The 12-word BIP-39 test phrase survived in every release bundle as dead
text: module.exports keeps DEBUG_MNEMONIC live even though wallet.js's only
use of it folds away in a release build, so it could not be tree-shaken.
Putting the value itself behind the __BUILD_DEBUG__ define makes esbuild fold
it to null, so no distributed bundle carries it. script/verify-build now
fails a release build if the phrase appears in any emitted file, so the fold
cannot silently regress; test-verify-build covers both the release failure
and the debug allowance.

tests/extensionId.test.js now scans the content of every tracked file for a
PEM private-key header instead of matching filename extensions alone, so a
key committed under an unexpected name is caught.

Model: opus-4-8

script/test-verify-build

@@ -37,6 +37,10 @@ DISCARD_DIST="$ROOT/script/discard-dist-on-failure"
 MARKER_ON="autistmask-build-debug=on"
 MARKER_OFF="autistmask-build-debug=off"
 
+# The same test recovery phrase verify-build searches release bundles for. Held
+# here too, the way the markers above are, so a case can plant it in a bundle.
+TEST_MNEMONIC="cube evolve unfold result inch risk jealous skill hotel bulb night wreck"
+
 RECEIPT_HEADER="autistmask-build-receipt v1"
 
 NEWLINE='
@@ -516,6 +520,24 @@ c_debug_build() {
     write_receipt
 }
 
+# A release bundle that still carries the test recovery phrase — the regression
+# verify-build guards against, and the reason DEBUG_MNEMONIC is behind the
+# __BUILD_DEBUG__ define in src/shared/constants.js. The receipt is regenerated
+# so the phrase is caught as bundle content, not incidentally as a stale digest.
+c_release_bundle_with_mnemonic() {
+    printf '/* %s */\n' "$TEST_MNEMONIC" >>dist/chrome/src/popup/index.js
+    write_receipt
+}
+
+# The same phrase in a debug build is expected: make build-debug ships it on
+# purpose, so the phrase check must stay quiet under --expect debug.
+c_debug_bundle_with_mnemonic() {
+    write_bundle dist/chrome/src/popup/index.js "$MARKER_ON"
+    write_bundle dist/firefox/src/popup/index.js "$MARKER_ON"
+    printf '/* %s */\n' "$TEST_MNEMONIC" >>dist/chrome/src/popup/index.js
+    write_receipt
+}
+
 c_no_dist() { rm -rf dist; }
 
 # --- dist discard -----------------------------------------------------------
@@ -753,6 +775,13 @@ run_cases() {
     check_case "debug bundles under --expect debug pass" \
         no debug 0 "2 bundle(s) $MARKER_ON" c_debug_build
 
+    check_case "release bundle carrying the test recovery phrase fails" \
+        no release 1 \
+        "carries the BIP-39 test recovery phrase" c_release_bundle_with_mnemonic
+
+    check_case "debug bundle carrying the test recovery phrase passes" \
+        no debug 0 "2 bundle(s) $MARKER_ON" c_debug_bundle_with_mnemonic
+
     check_case "no --expect argument" \
         no no-expect 1 "no --expect argument." c_control
 

script/verify-build

@@ -13,6 +13,12 @@
 # fallback branch; the property only exists in the emitted output, so it has to
 # be asserted against the emitted output.
 #
+# The DEBUG half also checks the phrase directly: a release build must not carry
+# the test recovery phrase in any emitted file. The phrase is behind the
+# __BUILD_DEBUG__ define in src/shared/constants.js and folds away in a release
+# build, but the marker only proves DEBUG compiled off, not that the fold
+# removed the string; the phrase grep is the assertion that it did.
+#
 # Which mode to expect is an ARGUMENT (--expect release|debug) and is never
 # taken from this script's environment. It used to be read from
 # AUTISTMASK_DEBUG here, which meant an operator with AUTISTMASK_DEBUG=1
@@ -67,6 +73,15 @@ TAB='	'
 MARKER_ON="autistmask-build-debug=on"
 MARKER_OFF="autistmask-build-debug=off"
 
+# The 12-word BIP-39 test recovery phrase from src/shared/constants.js. It is
+# behind the __BUILD_DEBUG__ define there, so a release build folds it out of
+# every bundle; this is the assertion that it stayed out. The phrase is a
+# publicly committed test value rather than a secret, but a BIP-39 phrase in a
+# distributed wallet artifact is exactly the string a scanner or auditor has to
+# stop and reason about, so a release build must not ship it. A debug build
+# ships it on purpose, so this is checked only when release is expected.
+TEST_MNEMONIC="cube evolve unfold result inch risk jealous skill hotel bulb night wreck"
+
 RECEIPT_HEADER="autistmask-build-receipt v1"
 
 # Set by the arguments.
@@ -283,6 +298,18 @@ check_entry() {
     receipt records $ENTRY_HASH and the file on disk is $SHA. Something wrote
     to dist/ after the build, so this artifact is not the one that was built."
 
+    # No emitted file of a release build may carry the test recovery phrase.
+    # Checked on every file, not only the audited bundles, so a copy that
+    # reached some other emitted file fails here too. A debug build ships the
+    # phrase deliberately, so this runs only when release was expected.
+    if [ "$EXPECT" = "$MARKER_OFF" ] && has_marker "$TEST_MNEMONIC" "$ENTRY_PATH"; then
+        fail "$ENTRY_PATH carries the BIP-39 test recovery phrase, which a
+    release build must fold out. The __BUILD_DEBUG__ define in build.js is what
+    drops it from src/shared/constants.js; check that DEBUG_MNEMONIC is still
+    behind that flag. A recovery phrase in a distributed bundle is exactly the
+    string an auditor or scanner has to stop on, so this is a hard failure."
+    fi
+
     if [ "$ENTRY_FLAG" = A ]; then
         read_marker "$ENTRY_PATH"
         [ "$MARKER" = "$EXPECT" ] ||