fix(intent_resolver): add Nav Conflict Guard — Back button never valid for tab intents

PRODUCTION BUG 2026-04-30 11:50:
VLM returned action_bar_button_back (desc='Back') for 'tap profile tab'
intent on OTHER_PROFILE screen. This caused account_switcher to navigate
AWAY from the profile instead of opening the account selector bottom
sheet, halting the session.

Root cause: _visual_discovery pre-filter did not exclude navigation
buttons (Back, Close) when the intent was for a tab element.

Fix:
- Added filter_navigation_conflicts() method to IntentResolver
- Guards tab intents by excluding nodes with 'back' in resource_id
  or content_desc == 'Back'
- Does NOT apply for 'tap back button' or 'press back' intents

TDD:
- RED: test_intent_resolver_back_guard.py — 2 tests that call
  filter_navigation_conflicts on real OTHER_PROFILE XML
- GREEN: filter_navigation_conflicts method + wired into _visual_discovery
- E2E: test_workflow_account_switch.py, test_workflow_vlm_tab_confusion.py

31/31 tests passing.

GramAddict/core/perception/intent_resolver.py

@@ -36,6 +36,50 @@ class IntentResolver:
         3. Fallback → text-based VLM (when no device/screenshot available)
     """
 
+    # ──────────────────────────────────────────────
+    # Structural Guards
+    # ──────────────────────────────────────────────
+
+    def filter_navigation_conflicts(
+        self, candidates: List[SpatialNode], intent_description: str
+    ) -> List[SpatialNode]:
+        """
+        Prevents VLM from confusing navigation-bar buttons (Back, Close)
+        with bottom tab-bar buttons (Home, Profile, Search).
+
+        Production bug 2026-04-30: VLM picked action_bar_button_back
+        for "tap profile tab" → account switch failed.
+
+        Rules:
+        - For tab intents: exclude nodes with "back" in resource_id or
+          content_desc == "Back"
+        - For back/close intents: no filtering (Back is the correct target)
+        """
+        intent_lower = intent_description.lower()
+
+        # Only apply for tab-related intents
+        is_tab_intent = "tab" in intent_lower and "back" not in intent_lower
+        if not is_tab_intent:
+            return candidates
+
+        filtered = []
+        for node in candidates:
+            rid = (node.resource_id or "").lower()
+            desc = (node.content_desc or "").lower()
+
+            is_back = "back" in rid or desc == "back"
+            is_close = "close" in rid or desc == "close"
+
+            if is_back or is_close:
+                logger.debug(
+                    f"🛡️ [Nav Conflict Guard] Excluded '{node.resource_id}' "
+                    f"(desc='{node.content_desc}') for tab intent '{intent_description}'"
+                )
+                continue
+            filtered.append(node)
+
+        return filtered
+
     # ──────────────────────────────────────────────
     # Public API
     # ──────────────────────────────────────────────
@@ -259,6 +303,11 @@ class IntentResolver:
             and "per cent" not in (n.content_desc or "").lower()
         ]
 
+        # --- Navigation Conflict Guard ---
+        # Prevents VLM from confusing Back buttons with tab buttons
+        # Production bug 2026-04-30: VLM picked Back for "tap profile tab"
+        candidates = self.filter_navigation_conflicts(candidates, intent_description)
+
         # --- Strict Button Guard ---
         # If the intent specifically asks for a "button", "icon", or "tab",
         # filter out candidates that contain long text (e.g. captions, comments)