Fix ATVM watcher install-only test flow extraction

Teach generated-spec TEST FLOW parsing to honor test-install-only runtime gates, including single-quoted Cypress.env checks, and suppress plugin branches when install-only mode disables them.

Document the 2026-04-16 install-only flow mismatch so future watcher updates keep Mattermost TEST FLOW aligned with the actual generated spec path.

atvm/watcher-service/atvm_run_watcher.py

@@ -1276,6 +1276,9 @@ def extract_test_flow_from_generated_spec(
                     runtime_settings[key] = match.group(1) == "true"
 
     def selected_plugin_gates() -> Optional[set[str]]:
+        install_only = runtime_settings.get("test-install-only")
+        if install_only is True:
+            return set()
         pure_plugin_type = runtime_settings.get("pure_plugin_type")
         if isinstance(pure_plugin_type, str):
             lowered = pure_plugin_type.lower()
@@ -1310,6 +1313,16 @@ def extract_test_flow_from_generated_spec(
         if normalized.startswith('if(Cypress.env("test-unaligned-fio")==true)'):
             value = runtime_settings.get("test-unaligned-fio")
             return True, value if isinstance(value, bool) else None
+        install_only_match = re.match(
+            r"""if\(Cypress\.env\((["'])test-install-only\1\)==(true|false)\)""",
+            normalized,
+        )
+        if install_only_match:
+            value = runtime_settings.get("test-install-only")
+            expected = install_only_match.group(2) == "true"
+            if isinstance(value, bool):
+                return True, value is expected
+            return True, None
         if normalized.startswith('if(Cypress.env("isRegularCutover")==false)'):
             value = runtime_settings.get("isRegularCutover")
             return True, (value is False) if isinstance(value, bool) else None