Harden track_presence generator option and fix test fixtures

Set the presence flag after the submessage decode, dump it in verbose
protobuf dumps, and raise at generation time when track_presence is set
on a field where it has no effect. Retire the absent-field expectation
in the integration test so the UTC phase sees the first matching state,
and align the Sydney TZ strings with the 03:00 fall-back the struct
helper uses.

esphome/components/api/api_pb2.cpp

@@ -1250,8 +1250,8 @@ bool ParsedTimezone::decode_length(uint32_t field_id, ProtoLengthDelimited value
 bool GetTimeResponse::decode_length(uint32_t field_id, ProtoLengthDelimited value) {
   switch (field_id) {
     case 3:
-      this->has_parsed_timezone = true;
       value.decode_to_message(this->parsed_timezone);
+      this->has_parsed_timezone = true;
       break;
     default:
       return false;

esphome/components/api/api_pb2_dump.cpp

@@ -1468,6 +1468,7 @@ const char *ParsedTimezone::dump_to(DumpBuffer &out) const {
 const char *GetTimeResponse::dump_to(DumpBuffer &out) const {
   MessageDumpHelper helper(out, ESPHOME_PSTR("GetTimeResponse"));
   dump_field(out, ESPHOME_PSTR("epoch_seconds"), this->epoch_seconds);
+  dump_field(out, ESPHOME_PSTR("has_parsed_timezone"), this->has_parsed_timezone);
   out.append(2, ' ').append_p(ESPHOME_PSTR("parsed_timezone")).append(": ");
   this->parsed_timezone.dump_to(out);
   out.append("\n");

script/api_protobuf/api_protobuf.py

@@ -498,6 +498,15 @@ def create_field_type_info(
     needs_encode: bool = True,
 ) -> TypeInfo:
     """Create the appropriate TypeInfo instance for a field, handling repeated fields and custom options."""
+    if get_field_opt(field, pb.track_presence, False) and (
+        field.label == FieldDescriptorProto.LABEL_REPEATED
+        or field.type != 11
+        or not needs_decode
+    ):
+        raise ValueError(
+            f"track_presence on field '{field.name}' has no effect; it requires "
+            "a non-repeated message field in a message that is decoded"
+        )
     if field.label == FieldDescriptorProto.LABEL_REPEATED:
         # Check if this is a packed_buffer field (zero-copy packed repeated)
         if get_field_opt(field, pb.packed_buffer, False):
@@ -541,6 +550,8 @@ def create_field_type_info(
         return PointerToStringBufferType(field, None)
 
     validate_field_type(field.type, field.name)
+    if field.type == 11:
+        return MessageType(field, needs_decode, needs_encode)
     return TYPE_INFO[field.type](field)
 
 
@@ -955,10 +966,13 @@ class MessageType(TypeInfo):
     def decode_length_content(self) -> str:
         # Custom decode that doesn't use templates
         if self._track_presence:
+            # decode_to_message() cannot report failure, so setting the flag
+            # afterwards only documents intent; a status-returning decode could
+            # gate it for real without touching callers.
             return (
                 f"case {self.number}:\n"
-                f"      this->has_{self.name} = true;\n"
                 f"      value.decode_to_message(this->{self.field_name});\n"
+                f"      this->has_{self.name} = true;\n"
                 f"      break;"
             )
         return f"case {self.number}: value.decode_to_message(this->{self.field_name}); break;"
@@ -968,7 +982,10 @@ class MessageType(TypeInfo):
 
     @property
     def dump_content(self) -> str:
-        o = f'out.append(2, \' \').append_p(ESPHOME_PSTR("{self.name}")).append(": ");\n'
+        o = ""
+        if self._track_presence:
+            o += f'dump_field(out, ESPHOME_PSTR("has_{self.name}"), this->has_{self.name});\n'
+        o += f'out.append(2, \' \').append_p(ESPHOME_PSTR("{self.name}")).append(": ");\n'
         o += f"this->{self.field_name}.dump_to(out);\n"
         o += 'out.append("\\n");'
         return o

tests/components/time/posix_tz.cpp

@@ -84,7 +84,7 @@ static ParsedTimezone make_new_zealand() {
   return tz;
 }
 
-// Helper to build Australia/Sydney timezone (AEST-10AEDT,M10.1.0,M4.1.0)
+// Helper to build Australia/Sydney timezone (AEST-10AEDT,M10.1.0,M4.1.0/3)
 static ParsedTimezone make_australia_sydney() {
   ParsedTimezone tz{};
   tz.std_offset_seconds = -10 * 3600;
@@ -674,9 +674,9 @@ TEST(RecalcTimestampLocal, FallBackRepeatedHour) {
 }
 
 TEST(RecalcTimestampLocal, SouthernHemisphereDST) {
-  // Set timezone to Australia/Sydney (AEST-10AEDT,M10.1.0,M4.1.0)
+  // Set timezone to Australia/Sydney (AEST-10AEDT,M10.1.0,M4.1.0/3)
   // DST starts first Sunday of October, ends first Sunday of April
-  const char *tz_str = "AEST-10AEDT,M10.1.0,M4.1.0";
+  const char *tz_str = "AEST-10AEDT,M10.1.0,M4.1.0/3";
   setenv("TZ", tz_str, 1);
   tzset();
   auto tz = make_australia_sydney();
@@ -817,7 +817,7 @@ TEST(RecalcTimestampLocal, MinimalFieldsNoDST) {
 TEST(RecalcTimestampLocal, YearBoundaryDST) {
   // Test southern hemisphere DST across year boundary
   // Australia/Sydney: DST active from October to April (spans Jan 1)
-  const char *tz_str = "AEST-10AEDT,M10.1.0,M4.1.0";
+  const char *tz_str = "AEST-10AEDT,M10.1.0,M4.1.0/3";
   setenv("TZ", tz_str, 1);
   tzset();
   auto tz = make_australia_sydney();

tests/integration/test_api_get_time_response_timezone.py

@@ -55,6 +55,9 @@ async def test_api_get_time_response_timezone(
         client._connection.send_messages((resp,))
         await tracker.await_must_not_change(future, "tz_offset", timeout=1.0)
         assert tracker.sensor_states["tz_offset"][-1] == target
+        # Retire the expectation so it cannot swallow the first matching state
+        # meant for the next phase
+        future.cancel()
 
         # Present but all zero (genuine UTC): applied
         future = tracker.expect("tz_offset", 0)