DTRC-32091 expose IDE MCP tools to ACP agents when no tool filter is configured

McpToolFilter.MaskBased.fromMaskList treated a null mask list the same as an empty/blank one and returned ProhibitAll. ACP agents without an explicit idea_mcp_allowed_tools / mcp.tool.filter resolve their session tool filter to null, so every IDE MCP tool (including the dotTrace analyze tools) was denied and the execute_tool router exposed nothing but itself.

This was latent until MCP tool-state filtering was unified to also apply the session filter in VIA_ROUTER mode; previously router mode hardcoded AllowAll, so the null->ProhibitAll mapping had no visible effect.

Treat a null mask (no filter configured) as AllowAll, matching the documented "null exposes all tools" contract, while keeping an explicitly empty/blank string as ProhibitAll. The fix lives in the shared community filter, so it covers both the AIA and AIR ACP paths.


(cherry picked from commit 1e55c1950ea1630b38061037df5321f01804f2e8)

NET-MR-18836


(cherry picked from commit 5249db4a775d13cd4bfcb386ced1474ec22800b3)

IJ-CR-216670

GitOrigin-RevId: 235b9d76ff51ababb12935aaa4cc35cef92b1471

plugins/mcp-server/src/com/intellij/mcpserver/McpToolFilter.kt

@@ -77,14 +77,19 @@ sealed interface McpToolFilter {
 
     companion object {
       /**
-       * Creates a MaskBased filter from a mask list string.
+       * Creates a tool filter from a mask list string.
        *
        * @param maskList comma-separated list of mask patterns with +/- prefixes
-       * @return a new MaskBased filter that denies all if maskList is empty, or AllowAll if null/blank
+       * @return [AllowAll] when [maskList] is `null` (no filter configured — expose all tools),
+       *         [ProhibitAll] when it is an explicitly empty/blank string (deny all),
+       *         otherwise a [MaskBased] filter built from the patterns.
        */
       fun fromMaskList(maskList: String?): McpToolFilter {
-        if (maskList.isNullOrBlank()) {
-          return ProhibitAll // Empty mask = deny all
+        if (maskList == null) {
+          return AllowAll // No filter configured = expose all tools
+        }
+        if (maskList.isBlank()) {
+          return ProhibitAll // Explicitly empty mask = deny all
         }
         return MaskBased(maskList)
       }

plugins/mcp-server/tests/testSrc/com/intellij/mcpserver/McpToolFilterTest.kt

@@ -127,6 +127,13 @@ class McpToolFilterTest {
     assertThat(filter.shouldInclude("read_file")).isFalse()
   }
 
+  @Test
+  fun `MaskBased fromMaskList returns allow-all filter for null`() {
+    val filter = McpToolFilter.MaskBased.fromMaskList(null)
+
+    assertThat(filter).isInstanceOf(McpToolFilter.AllowAll::class.java)
+  }
+
   @Test
   fun `MaskBased fromMaskList returns prohibit-all filter for empty string`() {
     val filter = McpToolFilter.MaskBased.fromMaskList("")