fix(mcp): make BTrace MCP deployment work and test it end to end

.github/workflows/mcp-e2e.yml

@@ -0,0 +1,90 @@
+name: MCP e2e
+
+# Runs the BTrace MCP server end-to-end tests against a BTrace distribution built from source, so the
+# job never depends on a published or locally installed io.btrace:btrace artifact. No LLM is involved.
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'plugins/btrace-observability/mcp/**'
+      - '.github/workflows/mcp-e2e.yml'
+  pull_request:
+    paths:
+      - 'plugins/btrace-observability/mcp/**'
+      - '.github/workflows/mcp-e2e.yml'
+  workflow_dispatch:
+    inputs:
+      btrace-ref:
+        description: 'BTrace branch, tag or SHA to build (default: the repository default branch)'
+        required: false
+        default: ''
+
+permissions:
+  contents: read
+
+concurrency:
+  group: mcp-e2e-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  e2e:
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    steps:
+      # setup-java registers every JDK in ~/.m2/toolchains.xml, where Gradle discovers toolchains.
+      # BTrace builds with toolchains 8 to 26; the MCP module uses 11. The last entry is JAVA_HOME.
+      - name: Set up JDKs
+        uses: actions/setup-java@03ad4de0992f5dab5e18fcb136590ce7c4a0ac95 # v5
+        with:
+          distribution: temurin
+          java-version: |
+            8
+            11
+            17
+            24
+            26
+            21
+
+      - name: Check out agent plugins
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7
+
+      - name: Check out BTrace
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7
+        with:
+          repository: btraceio/btrace
+          ref: ${{ inputs.btrace-ref }}
+          path: btrace
+
+      - name: Set up Gradle
+        uses: gradle/actions/setup-gradle@3f131e8634966bd73d06cc69884922b02e6faf92 # v6
+
+      - name: Build the BTrace distribution JAR
+        working-directory: btrace
+        run: ./gradlew --no-daemon :btrace-dist:btraceJar
+
+      - name: Locate the BTrace JAR
+        run: |
+          shopt -s nullglob
+          jars=("$GITHUB_WORKSPACE"/btrace/btrace-dist/build/resources/main/v*/libs/btrace.jar)
+          if [ "${#jars[@]}" -ne 1 ]; then
+            echo "::error::expected exactly one btrace.jar, found ${#jars[@]}: ${jars[*]}"
+            exit 1
+          fi
+          echo "BTRACE_JAR=${jars[0]}" >> "$GITHUB_ENV"
+          echo "Using ${jars[0]} from BTrace $(git -C btrace rev-parse --short HEAD)"
+
+      - name: Run MCP end-to-end tests
+        working-directory: plugins/btrace-observability/mcp
+        run: ./gradlew --no-daemon e2eTest
+
+      - name: Upload e2e logs and reports
+        if: failure()
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7
+        with:
+          name: mcp-e2e-logs
+          retention-days: 7
+          path: |
+            plugins/btrace-observability/mcp/build/e2e
+            plugins/btrace-observability/mcp/build/reports/tests/e2eTest
+            plugins/btrace-observability/mcp/build/test-results/e2eTest

plugins/btrace-observability/.codex-plugin/mcp.json

@@ -0,0 +1,9 @@
+{
+  "mcpServers": {
+    "btrace": {
+      "command": "jbang",
+      "args": ["mcp/src/main/java/io/btrace/mcp/BTraceMcpServer.java"],
+      "cwd": "."
+    }
+  }
+}

plugins/btrace-observability/.codex-plugin/plugin.json

@@ -15,6 +15,7 @@
     "diagnostics"
   ],
   "skills": "./skills/",
+  "mcpServers": "./.codex-plugin/mcp.json",
   "interface": {
     "displayName": "BTrace Observability",
     "shortDescription": "Diagnose Java behavior with focused probes.",

plugins/btrace-observability/mcp/README.md

@@ -20,3 +20,21 @@ Run its unit tests with:
 ```
 
 `./gradlew check` enforces at least 80% line coverage for the MCP Java code.
+
+Run the end-to-end tests with:
+
+```sh
+./gradlew e2eTest
+```
+
+They exercise every tool and prompt against a sample JVM, observing probe effects through `@Export`
+counters read with `jcmd`. No LLM is involved. By default they launch the server through JBang, as
+the plugin manifests do, which needs `jbang` on `PATH` and a resolvable `io.btrace:btrace` artifact,
+so they are not part of `check`. To test against a BTrace build instead, such as in CI, point them
+at its masked JAR:
+
+```sh
+BTRACE_JAR=/path/to/btrace/btrace-dist/build/resources/main/v<version>/libs/btrace.jar ./gradlew e2eTest
+```
+
+The `list_probes` case is disabled because the BTrace client exits the JVM after listing probes.

plugins/btrace-observability/mcp/build.gradle

@@ -34,6 +34,43 @@ tasks.withType(Test).configureEach {
     jvmArgs '--add-modules', 'jdk.attach'
 }
 
+// End-to-end tests run the real server against a live sample JVM, so they are not part of `check`.
+// By default the server is launched through JBang, as the plugin manifests do, which needs jbang on
+// PATH and a resolvable io.btrace:btrace artifact. Set BTRACE_JAR (or -PbtraceJar) to a masked
+// btrace.jar, e.g. from a CI build of BTrace, to run the compiled server against that JAR instead.
+def btraceJar = providers.gradleProperty('btraceJar')
+    .orElse(providers.environmentVariable('BTRACE_JAR'))
+    .map { it.trim() ? it.trim() : null }
+
+sourceSets {
+    e2eTest
+}
+
+configurations {
+    e2eTestImplementation.extendsFrom testImplementation
+    e2eTestRuntimeOnly.extendsFrom testRuntimeOnly
+}
+
+dependencies {
+    e2eTestImplementation sourceSets.main.output
+}
+
+tasks.register('e2eTest', Test) {
+    description = 'Runs the MCP server end-to-end against a sample JVM.'
+    group = 'verification'
+    testClassesDirs = sourceSets.e2eTest.output.classesDirs
+    classpath = sourceSets.e2eTest.runtimeClasspath
+    shouldRunAfter tasks.named('test')
+    outputs.upToDateWhen { false }
+    systemProperty 'e2e.serverScript', file('src/main/java/io/btrace/mcp/BTraceMcpServer.java').absolutePath
+    systemProperty 'e2e.sampleClasspath', sourceSets.e2eTest.output.classesDirs.asPath
+    systemProperty 'e2e.logDir', layout.buildDirectory.dir('e2e').get().asFile.absolutePath
+    if (btraceJar.isPresent()) {
+        systemProperty 'e2e.btraceJar', file(btraceJar.get()).absolutePath
+        systemProperty 'e2e.serverClasspath', sourceSets.main.runtimeClasspath.asPath
+    }
+}
+
 jacoco {
     toolVersion = '0.8.13'
 }