diff --git a/src/mcpd/src/services/mcp-proxy-service.ts b/src/mcpd/src/services/mcp-proxy-service.ts
index 8e92079..df85367 100644
--- a/src/mcpd/src/services/mcp-proxy-service.ts
+++ b/src/mcpd/src/services/mcp-proxy-service.ts
@@ -62,6 +62,59 @@ function parseStreamableResponse(body: string): McpProxyResponse {
   return JSON.parse(body) as McpProxyResponse;
 }
 
+/**
+ * Decide how mcpd opens a STDIO session against a running container.
+ *
+ *   attach → connect to PID 1's stdin/stdout
+ *   exec   → spawn a NEW process inside the container
+ *
+ * Pure and exported so the choice is testable: it is subtle, and getting it
+ * wrong fails silently rather than loudly (see the injector case below).
+ */
+export function chooseStdioMode(server: {
+  name: string;
+  id: string;
+  secretDelivery?: string | null;
+  command?: string[] | null;
+  packageName?: string | null;
+  dockerImage?: string | null;
+  runtime?: string | null;
+}): StdioMode {
+  // Injected delivery MUST attach, whatever the server type.
+  //
+  // The secrets exist only in PID 1's environment: the container command is a
+  // shell that sources /vault/secrets/<name> and execs the real server, so the
+  // values live in that process and nowhere else — not in the pod spec, which
+  // is the entire point of the feature.
+  //
+  // `exec` spawns a NEW process, which never sourced the file and so starts
+  // with empty credentials. The server comes up, answers tools/list, and fails
+  // every authenticated call — the exact silent-empty-token failure this
+  // feature exists to prevent. Observed as
+  // `Readiness check (list_datasources) failed: process exited 1` on a pod
+  // whose PID 1 demonstrably held the token.
+  //
+  // Safe because wrapCommandForInjector execs rather than forks, so PID 1 IS
+  // the server process.
+  if (server.secretDelivery === 'injector') return { kind: 'attach' };
+
+  if (server.command !== null && server.command !== undefined && server.command.length > 0) {
+    return { kind: 'exec', command: server.command };
+  }
+  if (server.packageName !== null && server.packageName !== undefined && server.packageName !== '') {
+    return { kind: 'exec', command: buildRuntimeSpawnCmd(server.runtime ?? 'node', server.packageName) };
+  }
+  // Image entrypoint IS the MCP server.
+  if (server.dockerImage !== null && server.dockerImage !== undefined && server.dockerImage !== '') {
+    return { kind: 'attach' };
+  }
+
+  throw new InvalidStateError(
+    `Server '${server.name}' (${server.id}) uses STDIO transport but has no ` +
+    `packageName, command, or dockerImage. Configure one of these.`,
+  );
+}
+
 export class McpProxyService {
   /** Session IDs per server for streamable-http protocol */
   private sessions = new Map<string, string>();
@@ -159,20 +212,15 @@ export class McpProxyService {
       //   - command set      → exec the given command in the container.
       //   - dockerImage only → attach to PID 1 (image entrypoint IS the MCP server).
       //   - nothing          → unreachable, reject.
-      const runtime = (server.runtime as string | null) ?? 'node';
-      let mode: StdioMode;
-      if (command && command.length > 0) {
-        mode = { kind: 'exec', command };
-      } else if (packageName) {
-        mode = { kind: 'exec', command: buildRuntimeSpawnCmd(runtime, packageName) };
-      } else if (dockerImage) {
-        mode = { kind: 'attach' };
-      } else {
-        throw new InvalidStateError(
-          `Server '${server.name}' (${server.id}) uses STDIO transport but has no ` +
-          `packageName, command, or dockerImage. Configure one of these.`,
-        );
-      }
+      const mode = chooseStdioMode({
+        name: server.name as string,
+        id: server.id as string,
+        secretDelivery: server.secretDelivery as string | null,
+        command,
+        packageName,
+        dockerImage,
+        runtime: server.runtime as string | null,
+      });
 
       // Try persistent connection first
       try {
@@ -181,7 +229,7 @@ export class McpProxyService {
         this.removeClient(instance.containerId);
         // Fall back to one-shot exec when we have a command to run.
         if (mode.kind === 'exec') {
-          return sendViaStdio(this.orchestrator, instance.containerId, packageName, method, params, 120_000, command, runtime);
+          return sendViaStdio(this.orchestrator, instance.containerId, packageName, method, params, 120_000, command, (server.runtime as string | null) ?? 'node');
         }
         // Attach mode has no one-shot equivalent, but the failure is usually
         // a stale pipe from an in-place container restart — retry once
diff --git a/src/mcpd/tests/stdio-mode.test.ts b/src/mcpd/tests/stdio-mode.test.ts
new file mode 100644
index 0000000..a5342d9
--- /dev/null
+++ b/src/mcpd/tests/stdio-mode.test.ts
@@ -0,0 +1,44 @@
+/**
+ * How mcpd opens a STDIO session: attach to PID 1, or exec a new process.
+ *
+ * Subtle and silent when wrong. With injected secret delivery the credentials
+ * exist ONLY in PID 1's environment (a shell sourced /vault/secrets/<name> and
+ * exec'd the server), so an `exec` starts a process with empty credentials —
+ * the server comes up, answers tools/list, and fails every authenticated call.
+ */
+import { describe, it, expect } from 'vitest';
+import { chooseStdioMode } from '../src/services/mcp-proxy-service.js';
+
+const base = { name: 's', id: 'id1' };
+
+describe('chooseStdioMode', () => {
+  it('attaches for an injector server even though it has a packageName', () => {
+    // The regression: packageName would otherwise select exec, and exec loses
+    // the secrets entirely.
+    expect(chooseStdioMode({ ...base, secretDelivery: 'injector', packageName: '@leval/mcp-grafana' }))
+      .toEqual({ kind: 'attach' });
+  });
+
+  it('attaches for an injector server even though it has an explicit command', () => {
+    expect(chooseStdioMode({ ...base, secretDelivery: 'injector', command: ['node', 'x.js'] }))
+      .toEqual({ kind: 'attach' });
+  });
+
+  it('still execs a package server on the default env delivery', () => {
+    const m = chooseStdioMode({ ...base, secretDelivery: 'env', packageName: '@leval/mcp-grafana', runtime: 'node' });
+    expect(m.kind).toBe('exec');
+  });
+
+  it('still prefers an explicit command over packageName on env delivery', () => {
+    expect(chooseStdioMode({ ...base, secretDelivery: 'env', command: ['node', 'x.js'], packageName: 'p' }))
+      .toEqual({ kind: 'exec', command: ['node', 'x.js'] });
+  });
+
+  it('attaches for an image-entrypoint server, as before', () => {
+    expect(chooseStdioMode({ ...base, dockerImage: 'gitea/mcp:latest' })).toEqual({ kind: 'attach' });
+  });
+
+  it('rejects a server with no way to start', () => {
+    expect(() => chooseStdioMode({ ...base })).toThrow(/packageName, command, or dockerImage/);
+  });
+});