Isolate Agency MCP discovery from wrapper processes

.github/extensions/signals-dashboard/README.md

@@ -70,7 +70,8 @@ The canvas also exposes actions Copilot can invoke directly:
 `repo` is the default. At launch, Cairn asks Copilot for the enabled
 plugin-scoped MCP inventory and disables those ambient servers for the topic
 desk. User-, workspace-, organization-, and built-in resources are left alone.
-If discovery fails, Cairn fails open to the connected tool surface.
+If discovery fails, Copilot plugin MCP suppression fails open; Agency repo mode
+still omits Agency's own default MCPs.
 
 When Agency is installed, Cairn keeps the existing `agency copilot` launch and
 adds Agency's `--no-default-mcps` in repo mode. Outside Agency, the same profile

.github/extensions/signals-dashboard/extension.mjs

@@ -198,20 +198,17 @@ function terminateProcessTree(child) {
     }
 }
 
-// Capture the machine-readable plugin MCP inventory through a trusted absolute
-// executable resolved from PATH. Prefer Copilot directly; if Agency is the only
-// installed entry point, use its existing Copilot resolver.
+// Capture the underlying Copilot plugin inventory directly. Agency repo mode
+// separately suppresses its own default/config plugins, so discovery does not
+// need a wrapper process that can leave inherited pipes or descendants behind.
 function capturePluginMcpJson(workshopDir, agent) {
     return new Promise((resolve) => {
-        const command = agent.useAgency ? agent.agencyCommand : agent.copilotCommand;
+        const command = agent.copilotCommand;
         if (!command) {
             resolve(null);
             return;
         }
-        const args = agent.useAgency
-            ? ["copilot", "--no-default-mcps",
-                "plugins", "list", "--kind", "mcp", "--scope", "plugin", "--json"]
-            : ["plugins", "list", "--kind", "mcp", "--scope", "plugin", "--json"];
+        const args = ["plugins", "list", "--kind", "mcp", "--scope", "plugin", "--json"];
         const shim = process.platform === "win32" && /\.(cmd|bat)$/i.test(command);
         if (shim && !isSafeWindowsCmdShim(command)) {
             resolve(null);
@@ -271,8 +268,7 @@ function capturePluginMcpJson(workshopDir, agent) {
 }
 
 async function discoverPluginMcpNames(workshopDir, agent) {
-    const cacheKey = `${workshopDir}\0${agent.useAgency ? "agency" : "copilot"}\0` +
-        `${agent.useAgency ? agent.agencyCommand : agent.copilotCommand}`;
+    const cacheKey = `${workshopDir}\0${agent.copilotCommand || "missing"}`;
     const cached = mcpDiscoveryCache.get(cacheKey);
     if (cached && cached.expiresAt > Date.now()) return cached.value;
 
@@ -290,7 +286,8 @@ async function discoverPluginMcpNames(workshopDir, agent) {
 
 // Preserve the existing Agency-aware launch and layer the repo profile on top.
 // Repo mode suppresses ambient plugin MCPs; connected mode keeps today's tool
-// surface. Discovery fails open to connected behavior.
+// surface. Plugin discovery fails open, while Agency repo mode still suppresses
+// Agency's own default MCPs.
 async function deskAgentArgv(deskName, workshopDir, profile) {
     const resolved = resolveDeskAgent(workshopDir);
     if (!resolved) return null;

.github/extensions/signals-dashboard/launch-profile.mjs

@@ -73,8 +73,11 @@ export function buildDeskAgentArgv({
         ? [agencyCommand, "copilot"]
         : [copilotCommand, "--name", deskName];
 
-    if (profile === "repo" && discoverySucceeded) {
+    if (profile === "repo") {
         if (useAgency) argv.push("--no-default-mcps");
+    }
+
+    if (profile === "repo" && discoverySucceeded) {
         for (const name of pluginMcpNames) {
             if (SAFE_MCP_NAME.test(name)) argv.push("--disable-mcp-server", name);
         }

.github/extensions/signals-dashboard/launch-profile.test.mjs

@@ -118,7 +118,7 @@ test("builds a plain Copilot repo profile without Agency-only flags", () => {
     ]);
 });
 
-test("connected and discovery-failure launches preserve the existing tool surface", () => {
+test("connected preserves tools while Agency discovery failure still removes defaults", () => {
     assert.deepEqual(buildDeskAgentArgv({
         deskName: "cost-desk",
         workshopDir: "/workshop",
@@ -137,6 +137,6 @@ test("connected and discovery-failure launches preserve the existing tool surfac
         pluginMcpNames: [],
         discoverySucceeded: false,
     }), [
-        "agency", "copilot", "--add-dir", "/workshop",
+        "agency", "copilot", "--no-default-mcps", "--add-dir", "/workshop",
     ]);
 });