diff --git a/.github/workflows/publish-jetbrains-bundled.yml b/.github/workflows/publish-jetbrains-bundled.yml
index 53de4637bdb..8f0134b15c7 100644
--- a/.github/workflows/publish-jetbrains-bundled.yml
+++ b/.github/workflows/publish-jetbrains-bundled.yml
@@ -142,6 +142,22 @@ jobs:
           JETBRAINS_PRIVATE_KEY: ${{ secrets.JETBRAINS_PRIVATE_KEY }}
           JETBRAINS_PRIVATE_KEY_PASSWORD: ${{ secrets.JETBRAINS_PRIVATE_KEY_PASSWORD }}
 
+      - name: Write signing secrets to temp files
+        run: |
+          dir="$RUNNER_TEMP/jetbrains-signing"
+          mkdir -m 700 -p "$dir"
+          chain="$dir/certificate-chain.pem"
+          key="$dir/private-key.pem"
+          umask 077
+          printf '%s' "$JETBRAINS_CERTIFICATE_CHAIN" > "$chain"
+          printf '%s' "$JETBRAINS_PRIVATE_KEY" > "$key"
+          chmod 600 "$chain" "$key"
+          echo "JETBRAINS_CERTIFICATE_CHAIN_FILE=$chain" >> "$GITHUB_ENV"
+          echo "JETBRAINS_PRIVATE_KEY_FILE=$key" >> "$GITHUB_ENV"
+        env:
+          JETBRAINS_CERTIFICATE_CHAIN: ${{ secrets.JETBRAINS_CERTIFICATE_CHAIN }}
+          JETBRAINS_PRIVATE_KEY: ${{ secrets.JETBRAINS_PRIVATE_KEY }}
+
       - name: Build signed bundled plugin
         working-directory: packages/kilo-jetbrains
         run: |
@@ -152,6 +168,9 @@ jobs:
             -Pkilo.cli.bundled=true
           )
 
+          # signPlugin and verifyPluginSignature run as separate Gradle invocations (see #12567)
+          # so the JETBRAINS_CERTIFICATE_CHAIN_FILE / JETBRAINS_PRIVATE_KEY_FILE env vars set in
+          # the previous step (rather than raw multiline secret content) must be present for both.
           ./gradlew clean buildPlugin "${args[@]}"
           ./gradlew signPlugin "${args[@]}"
           ./gradlew verifyPluginSignature "${args[@]}"
@@ -161,10 +180,12 @@ jobs:
           GITHUB_TOKEN: ${{ github.token }}
           VERSION: ${{ needs.validate.outputs.version }}
           CHANNEL: ${{ needs.validate.outputs.channel }}
-          JETBRAINS_CERTIFICATE_CHAIN: ${{ secrets.JETBRAINS_CERTIFICATE_CHAIN }}
-          JETBRAINS_PRIVATE_KEY: ${{ secrets.JETBRAINS_PRIVATE_KEY }}
           JETBRAINS_PRIVATE_KEY_PASSWORD: ${{ secrets.JETBRAINS_PRIVATE_KEY_PASSWORD }}
 
+      - name: Remove signing secret temp files
+        if: always()
+        run: rm -rf "$RUNNER_TEMP/jetbrains-signing"
+
       - name: Resolve bundled archive
         id: archive
         run: |
diff --git a/packages/kilo-jetbrains/build.gradle.kts b/packages/kilo-jetbrains/build.gradle.kts
index c13a70c2b64..3ad08aff36b 100644
--- a/packages/kilo-jetbrains/build.gradle.kts
+++ b/packages/kilo-jetbrains/build.gradle.kts
@@ -207,8 +207,15 @@ intellijPlatform {
     }
 
     signing {
-        certificateChain = providers.environmentVariable("JETBRAINS_CERTIFICATE_CHAIN")
-        privateKey = providers.environmentVariable("JETBRAINS_PRIVATE_KEY")
+        // File-based inputs are preferred over raw content: certificateChain/privateKey take
+        // precedence over certificateChainFile/privateKeyFile in the IntelliJ Platform Gradle
+        // plugin, and passing multiline PEM content straight through as a certificateChain/
+        // privateKey value can get mishandled as extra CLI arguments by the zip-signer CLI when
+        // signPlugin/verifyPluginSignature run as separate Gradle invocations. Both CI
+        // (.github/workflows/publish-jetbrains-bundled.yml) and local releases
+        // (script/build-version.sh) write the secrets to files and export the *_FILE variables.
+        certificateChainFile.fileProvider(providers.environmentVariable("JETBRAINS_CERTIFICATE_CHAIN_FILE").map { file(it) })
+        privateKeyFile.fileProvider(providers.environmentVariable("JETBRAINS_PRIVATE_KEY_FILE").map { file(it) })
         password = providers.environmentVariable("JETBRAINS_PRIVATE_KEY_PASSWORD")
     }