Track parsed_timezone presence and escape host TZ codegen

esphome/components/api/api.proto

@@ -1007,7 +1007,7 @@ message GetTimeResponse {
   // Assistant 2026.3.0 that send only the string leave the device on its
   // codegen-configured timezone (or UTC).
   string timezone = 2 [deprecated = true];
-  ParsedTimezone parsed_timezone = 3;
+  ParsedTimezone parsed_timezone = 3 [(track_presence) = true];
 }
 
 // ==================== USER-DEFINES SERVICES ====================

esphome/components/api/api_connection.cpp

@@ -1205,12 +1205,11 @@ void APIConnection::on_get_time_response(const GetTimeResponse &value) {
     homeassistant::global_homeassistant_time->set_epoch_time(value.epoch_seconds);
 #if defined(USE_HOMEASSISTANT_TIMEZONE) && defined(USE_TIME_TIMEZONE)
     // Apply only if the sender provided pre-parsed timezone data (Home Assistant 2026.3.0
-    // and newer). Older clients send only the deprecated timezone string, which is no
-    // longer decoded; for them the struct stays all-zero and the device keeps its
-    // codegen-configured timezone. Actual UTC (all zeros) is also skipped, which is
-    // harmless since UTC is the default.
-    const auto &pt = value.parsed_timezone;
-    if (pt.std_offset_seconds != 0 || pt.dst_start.type != enums::DST_RULE_TYPE_NONE) {
+    // and newer); field presence distinguishes a genuine all-zero UTC timezone from an
+    // absent field. Older clients send only the deprecated timezone string, which is no
+    // longer decoded; for them the device keeps its codegen-configured timezone.
+    if (value.has_parsed_timezone) {
+      const auto &pt = value.parsed_timezone;
       time::ParsedTimezone tz{};
       tz.std_offset_seconds = pt.std_offset_seconds;
       tz.dst_offset_seconds = pt.dst_offset_seconds;

esphome/components/api/api_options.proto

@@ -116,4 +116,10 @@ extend google.protobuf.FieldOptions {
     // the per-byte loop when the upper bits are non-zero (the common case
     // for real MAC addresses, since OUIs occupy the top 24 bits).
     optional bool mac_address = 50019 [default=false];
+
+    // track_presence: Track whether this message-typed field was present on the wire.
+    // Generates a `bool has_<field>{false};` member on the decoding side that is set
+    // to true when the field arrives, so an all-default submessage can be told apart
+    // from an absent one (e.g. a UTC ParsedTimezone, which is all zeros).
+    optional bool track_presence = 50020 [default=false];
 }

esphome/components/api/api_pb2.cpp

@@ -1250,6 +1250,7 @@ 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);
       break;
     default:

esphome/components/api/api_pb2.h

@@ -1289,6 +1289,7 @@ class GetTimeResponse final : public ProtoDecodableMessage {
 #endif
   uint32_t epoch_seconds{0};
   ParsedTimezone parsed_timezone{};
+  bool has_parsed_timezone{false};
 #ifdef HAS_PROTO_MESSAGE_DUMP
   const char *dump_to(DumpBuffer &out) const override;
 #endif

esphome/components/time/__init__.py

@@ -36,6 +36,7 @@ from esphome.const import (
     PLATFORM_RTL87XX,
 )
 from esphome.core import CORE, CoroPriority, EsphomeError, coroutine_with_priority
+from esphome.helpers import cpp_string_escape
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -412,7 +413,7 @@ async def setup_time_core_(time_var, config):
 
         if CORE.is_host:
             # Host platform also needs setenv("TZ")/tzset() for libc compatibility
-            cg.add(cg.RawExpression(f'setenv("TZ", "{timezone}", 1)'))
+            cg.add(cg.RawExpression(f'setenv("TZ", {cpp_string_escape(timezone)}, 1)'))
             cg.add(cg.RawExpression("tzset()"))
 
         # Pre-parse at codegen time, emit struct directly

script/api_protobuf/api_protobuf.py

@@ -937,9 +937,29 @@ class MessageType(TypeInfo):
         # runtime polymorphism through virtual function calls.
         return None
 
+    @property
+    def public_content(self) -> list[str]:
+        content = [self.class_member]
+        if self._track_presence:
+            content.append(f"bool has_{self.name}{{false}};")
+        return content
+
+    @property
+    def _track_presence(self) -> bool:
+        # Use getattr to handle older versions of api_options_pb2
+        opt = getattr(pb, "track_presence", None)
+        return opt is not None and get_field_opt(self._field, opt, False)
+
     @property
     def decode_length_content(self) -> str:
         # Custom decode that doesn't use templates
+        if self._track_presence:
+            return (
+                f"case {self.number}:\n"
+                f"      this->has_{self.name} = true;\n"
+                f"      value.decode_to_message(this->{self.field_name});\n"
+                f"      break;"
+            )
         return f"case {self.number}: value.decode_to_message(this->{self.field_name}); break;"
 
     def dump(self, name: str) -> str:

tests/components/time/test.host.yaml

@@ -0,0 +1,10 @@
+network:
+
+api:
+
+time:
+  - platform: homeassistant
+    # Angle-bracket name pins the explicit-timezone host codegen path
+    # (setenv/tzset plus pre-parsed struct emission) with characters that
+    # would break unescaped string interpolation.
+    timezone: "<+07>-7"