fix(mcp): warn when MCP env expansion is blocked

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/features/claude-code-mcp-loader/env-expander.test.ts

@@ -42,6 +42,41 @@ describe("expandEnvVars", () => {
     })
   })
 
+  describe("#given a benign environment variable in the builtin allowlist", () => {
+    it("#when expanding the value #then it returns the env value", () => {
+      // given
+      process.env.TMPDIR = "/tmp/omo"
+      process.env.LANG = "en_US.UTF-8"
+      process.env.XDG_CONFIG_HOME = "/Users/tester/.config"
+
+      // when
+      const expanded = expandEnvVars(
+        "${TMPDIR}|${LANG}|${XDG_CONFIG_HOME}"
+      )
+
+      // then
+      expect(expanded).toBe("/tmp/omo|en_US.UTF-8|/Users/tester/.config")
+    })
+  })
+
+  describe("#given a blocked non-sensitive environment variable reference", () => {
+    it("#when expanding the value #then it returns an empty string and logs a warning", () => {
+      // given
+      process.env.PROJECT_ROOT = "/Users/tester/project"
+      const logSpy = spyOn(shared, "log").mockImplementation(() => {})
+
+      // when
+      const expanded = expandEnvVars("${PROJECT_ROOT}")
+
+      // then
+      expect(expanded).toBe("")
+      expect(logSpy).toHaveBeenCalledWith(
+        expect.stringContaining("Blocked MCP env var expansion"),
+        expect.objectContaining({ varName: "PROJECT_ROOT" })
+      )
+    })
+  })
+
   describe("#given a blocked variable with a default value", () => {
     it("#when expanding the value #then it uses the default instead of the sensitive env var", () => {
       // given

src/features/claude-code-mcp-loader/env-expander.ts

@@ -9,11 +9,13 @@ export function expandEnvVars(value: string): string {
     /\$\{([^}:]+)(?::-([^}]*))?\}/g,
     (_, varName: string, defaultValue?: string) => {
       if (!isAllowedMcpEnvVar(varName)) {
-        if (isSensitiveMcpEnvVar(varName)) {
-          log(`Blocked MCP env var expansion for sensitive variable "${varName}"`, {
-            varName,
-          })
-        }
+        const isSensitive = isSensitiveMcpEnvVar(varName)
+        const reason = isSensitive ? "sensitive variable" : "not in allowlist"
+
+        log(`Blocked MCP env var expansion for ${reason} "${varName}"`, {
+          varName,
+          sensitive: isSensitive,
+        })
 
         if (defaultValue !== undefined) return defaultValue
         return ""