From 237cfdebfcc586952fe4fb49125507bd0f9b0f0a Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 13:04:59 -1000
Subject: [PATCH 01/21] [fan] Store preset mode vector on Fan entity, not
 FanTraits
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

FanTraits contained a std::vector<const char *> for preset modes.
Every get_traits() call reconstructed this vector, causing heap
allocations on every publish_state() and control()/perform() call.

Move the vector storage to the Fan base class and have FanTraits hold
a const pointer instead. Internal callers (save_state_, find_preset_mode_)
search the Fan-owned vector directly, avoiding traits reconstruction.

The old FanTraits setters are preserved as deprecated compatibility
overloads (removed in 2026.11.0) that self-own the data, so external
components continue to compile — they just get a deprecation warning
and still heap-allocate until they migrate.
---
 esphome/components/copy/fan/copy_fan.cpp      |  3 +-
 esphome/components/fan/fan.cpp                | 17 +++++----
 esphome/components/fan/fan.h                  | 11 ++++++
 esphome/components/fan/fan_traits.h           | 36 ++++++++++++-------
 .../components/hbridge/fan/hbridge_fan.cpp    |  1 -
 esphome/components/hbridge/fan/hbridge_fan.h  |  3 +-
 esphome/components/speed/fan/speed_fan.cpp    |  1 -
 esphome/components/speed/fan/speed_fan.h      |  3 +-
 .../components/template/fan/template_fan.cpp  |  1 -
 .../components/template/fan/template_fan.h    |  3 +-
 10 files changed, 50 insertions(+), 29 deletions(-)

diff --git a/esphome/components/copy/fan/copy_fan.cpp b/esphome/components/copy/fan/copy_fan.cpp
index 14c600d71f..e7d01827aa 100644
--- a/esphome/components/copy/fan/copy_fan.cpp
+++ b/esphome/components/copy/fan/copy_fan.cpp
@@ -39,7 +39,8 @@ fan::FanTraits CopyFan::get_traits() {
   traits.set_speed(base.supports_speed());
   traits.set_supported_speed_count(base.supported_speed_count());
   traits.set_direction(base.supports_direction());
-  traits.set_supported_preset_modes(base.supported_preset_modes());
+  // Preset modes are wired from source fan's storage via get_traits()
+  this->set_supported_preset_modes(base.supported_preset_modes());
   return traits;
 }
 
diff --git a/esphome/components/fan/fan.cpp b/esphome/components/fan/fan.cpp
index dc7a75018c..659abf70a9 100644
--- a/esphome/components/fan/fan.cpp
+++ b/esphome/components/fan/fan.cpp
@@ -148,7 +148,13 @@ const char *Fan::find_preset_mode_(const char *preset_mode) {
 }
 
 const char *Fan::find_preset_mode_(const char *preset_mode, size_t len) {
-  return this->get_traits().find_preset_mode(preset_mode, len);
+  if (preset_mode == nullptr || len == 0)
+    return nullptr;
+  for (const char *mode : this->supported_preset_modes_) {
+    if (strncmp(mode, preset_mode, len) == 0 && mode[len] == '\0')
+      return mode;
+  }
+  return nullptr;
 }
 
 bool Fan::set_preset_mode_(const char *preset_mode, size_t len) {
@@ -261,8 +267,6 @@ void Fan::save_state_() {
     return;
   }
 
-  auto traits = this->get_traits();
-
   FanRestoreState state{};
   state.state = this->state;
   state.oscillating = this->oscillating;
@@ -271,10 +275,9 @@ void Fan::save_state_() {
   state.preset_mode = FanRestoreState::NO_PRESET;
 
   if (this->has_preset_mode()) {
-    const auto &preset_modes = traits.supported_preset_modes();
-    // Find index of current preset mode (pointer comparison is safe since preset is from traits)
-    for (size_t i = 0; i < preset_modes.size(); i++) {
-      if (preset_modes[i] == this->preset_mode_) {
+    // Find index of current preset mode (pointer comparison is safe since preset is from our vector)
+    for (size_t i = 0; i < this->supported_preset_modes_.size(); i++) {
+      if (this->supported_preset_modes_[i] == this->preset_mode_) {
         state.preset_mode = i;
         break;
       }
diff --git a/esphome/components/fan/fan.h b/esphome/components/fan/fan.h
index e7b3681e32..42999d16f7 100644
--- a/esphome/components/fan/fan.h
+++ b/esphome/components/fan/fan.h
@@ -130,6 +130,14 @@ class Fan : public EntityBase {
 
   virtual FanTraits get_traits() = 0;
 
+  /// Set the supported preset modes (stored on Fan, referenced by FanTraits via pointer).
+  void set_supported_preset_modes(std::initializer_list<const char *> preset_modes) {
+    this->supported_preset_modes_ = preset_modes;
+  }
+  void set_supported_preset_modes(const std::vector<const char *> &preset_modes) {
+    this->supported_preset_modes_ = preset_modes;
+  }
+
   /// Set the restore mode of this fan.
   void set_restore_mode(FanRestoreMode restore_mode) { this->restore_mode_ = restore_mode; }
 
@@ -171,6 +179,9 @@ class Fan : public EntityBase {
   ESPPreferenceObject rtc_;
   FanRestoreMode restore_mode_;
 
+  /// Preset mode storage — owned by Fan, referenced by FanTraits via pointer.
+  std::vector<const char *> supported_preset_modes_;
+
  private:
   const char *preset_mode_{nullptr};
 };
diff --git a/esphome/components/fan/fan_traits.h b/esphome/components/fan/fan_traits.h
index c0c5f34c50..f8202f36ce 100644
--- a/esphome/components/fan/fan_traits.h
+++ b/esphome/components/fan/fan_traits.h
@@ -3,6 +3,7 @@
 #include <cstring>
 #include <vector>
 #include <initializer_list>
+#include "esphome/core/helpers.h"
 
 namespace esphome {
 
@@ -31,20 +32,29 @@ class FanTraits {
   /// Set whether this fan supports changing direction
   void set_direction(bool direction) { this->direction_ = direction; }
   /// Return the preset modes supported by the fan.
-  const std::vector<const char *> &supported_preset_modes() const { return this->preset_modes_; }
-  /// Set the preset modes supported by the fan (from initializer list).
-  void set_supported_preset_modes(std::initializer_list<const char *> preset_modes) {
-    this->preset_modes_ = preset_modes;
+  const std::vector<const char *> &supported_preset_modes() const {
+    return this->preset_modes_ ? *this->preset_modes_ : this->owned_preset_modes_;
   }
-  /// Set the preset modes supported by the fan (from vector).
-  void set_supported_preset_modes(const std::vector<const char *> &preset_modes) { this->preset_modes_ = preset_modes; }
+  /// Set the preset modes pointer (points to vector owned by Fan base class).
+  void set_supported_preset_modes(const std::vector<const char *> *preset_modes) { this->preset_modes_ = preset_modes; }
 
-  // Deleted overloads to catch incorrect std::string usage at compile time with clear error messages
-  void set_supported_preset_modes(const std::vector<std::string> &preset_modes) = delete;
-  void set_supported_preset_modes(std::initializer_list<std::string> preset_modes) = delete;
+  // Remove before 2027.1.0
+  ESPDEPRECATED("Call set_supported_preset_modes() on the Fan entity instead. Removed in 2026.11.0", "2026.5.0")
+  void set_supported_preset_modes(std::initializer_list<const char *> preset_modes) {
+    this->owned_preset_modes_ = preset_modes;
+    this->preset_modes_ = &this->owned_preset_modes_;
+  }
+  // Remove before 2027.1.0
+  ESPDEPRECATED("Call set_supported_preset_modes() on the Fan entity instead. Removed in 2026.11.0", "2026.5.0")
+  void set_supported_preset_modes(const std::vector<const char *> &preset_modes) {
+    this->owned_preset_modes_ = preset_modes;
+    this->preset_modes_ = &this->owned_preset_modes_;
+  }
 
   /// Return if preset modes are supported
-  bool supports_preset_modes() const { return !this->preset_modes_.empty(); }
+  bool supports_preset_modes() const {
+    return (this->preset_modes_ && !this->preset_modes_->empty()) || !this->owned_preset_modes_.empty();
+  }
   /// Find and return the matching preset mode pointer from supported modes, or nullptr if not found.
   const char *find_preset_mode(const char *preset_mode) const {
     return this->find_preset_mode(preset_mode, preset_mode ? strlen(preset_mode) : 0);
@@ -52,7 +62,8 @@ class FanTraits {
   const char *find_preset_mode(const char *preset_mode, size_t len) const {
     if (preset_mode == nullptr || len == 0)
       return nullptr;
-    for (const char *mode : this->preset_modes_) {
+    const auto &modes = this->preset_modes_ ? *this->preset_modes_ : this->owned_preset_modes_;
+    for (const char *mode : modes) {
       if (strncmp(mode, preset_mode, len) == 0 && mode[len] == '\0') {
         return mode;  // Return pointer from traits
       }
@@ -65,7 +76,8 @@ class FanTraits {
   bool speed_{false};
   bool direction_{false};
   int speed_count_{};
-  std::vector<const char *> preset_modes_{};
+  const std::vector<const char *> *preset_modes_{nullptr};
+  std::vector<const char *> owned_preset_modes_{};  ///< Compat: used when old setters are called directly on traits
 };
 
 }  // namespace fan
diff --git a/esphome/components/hbridge/fan/hbridge_fan.cpp b/esphome/components/hbridge/fan/hbridge_fan.cpp
index 89c162eebf..d548128b99 100644
--- a/esphome/components/hbridge/fan/hbridge_fan.cpp
+++ b/esphome/components/hbridge/fan/hbridge_fan.cpp
@@ -30,7 +30,6 @@ fan::FanCall HBridgeFan::brake() {
 void HBridgeFan::setup() {
   // Construct traits before restore so preset modes can be looked up by index
   this->traits_ = fan::FanTraits(this->oscillating_ != nullptr, true, true, this->speed_count_);
-  this->traits_.set_supported_preset_modes(this->preset_modes_);
 
   auto restore = this->restore_state_();
   if (restore.has_value()) {
diff --git a/esphome/components/hbridge/fan/hbridge_fan.h b/esphome/components/hbridge/fan/hbridge_fan.h
index ec1e8ada0e..7511e0eb0b 100644
--- a/esphome/components/hbridge/fan/hbridge_fan.h
+++ b/esphome/components/hbridge/fan/hbridge_fan.h
@@ -20,7 +20,7 @@ class HBridgeFan : public Component, public fan::Fan {
   void set_pin_a(output::FloatOutput *pin_a) { pin_a_ = pin_a; }
   void set_pin_b(output::FloatOutput *pin_b) { pin_b_ = pin_b; }
   void set_enable_pin(output::FloatOutput *enable) { enable_ = enable; }
-  void set_preset_modes(std::initializer_list<const char *> presets) { preset_modes_ = presets; }
+  void set_preset_modes(std::initializer_list<const char *> presets) { this->set_supported_preset_modes(presets); }
 
   void setup() override;
   void dump_config() override;
@@ -36,7 +36,6 @@ class HBridgeFan : public Component, public fan::Fan {
   int speed_count_{};
   DecayMode decay_mode_{DECAY_MODE_SLOW};
   fan::FanTraits traits_;
-  std::vector<const char *> preset_modes_{};
 
   void control(const fan::FanCall &call) override;
   void write_state_();
diff --git a/esphome/components/speed/fan/speed_fan.cpp b/esphome/components/speed/fan/speed_fan.cpp
index d45237c467..eaa8a55858 100644
--- a/esphome/components/speed/fan/speed_fan.cpp
+++ b/esphome/components/speed/fan/speed_fan.cpp
@@ -9,7 +9,6 @@ static const char *const TAG = "speed.fan";
 void SpeedFan::setup() {
   // Construct traits before restore so preset modes can be looked up by index
   this->traits_ = fan::FanTraits(this->oscillating_ != nullptr, true, this->direction_ != nullptr, this->speed_count_);
-  this->traits_.set_supported_preset_modes(this->preset_modes_);
 
   auto restore = this->restore_state_();
   if (restore.has_value()) {
diff --git a/esphome/components/speed/fan/speed_fan.h b/esphome/components/speed/fan/speed_fan.h
index e9a389e0f3..44bd1a15cb 100644
--- a/esphome/components/speed/fan/speed_fan.h
+++ b/esphome/components/speed/fan/speed_fan.h
@@ -16,7 +16,7 @@ class SpeedFan : public Component, public fan::Fan {
   void set_output(output::FloatOutput *output) { this->output_ = output; }
   void set_oscillating(output::BinaryOutput *oscillating) { this->oscillating_ = oscillating; }
   void set_direction(output::BinaryOutput *direction) { this->direction_ = direction; }
-  void set_preset_modes(std::initializer_list<const char *> presets) { this->preset_modes_ = presets; }
+  void set_preset_modes(std::initializer_list<const char *> presets) { this->set_supported_preset_modes(presets); }
   fan::FanTraits get_traits() override { return this->traits_; }
 
  protected:
@@ -28,7 +28,6 @@ class SpeedFan : public Component, public fan::Fan {
   output::BinaryOutput *direction_{nullptr};
   int speed_count_{};
   fan::FanTraits traits_;
-  std::vector<const char *> preset_modes_{};
 };
 
 }  // namespace speed
diff --git a/esphome/components/template/fan/template_fan.cpp b/esphome/components/template/fan/template_fan.cpp
index 46a5cba9bb..431be84654 100644
--- a/esphome/components/template/fan/template_fan.cpp
+++ b/esphome/components/template/fan/template_fan.cpp
@@ -9,7 +9,6 @@ void TemplateFan::setup() {
   // Construct traits before restore so preset modes can be looked up by index
   this->traits_ =
       fan::FanTraits(this->has_oscillating_, this->speed_count_ > 0, this->has_direction_, this->speed_count_);
-  this->traits_.set_supported_preset_modes(this->preset_modes_);
 
   auto restore = this->restore_state_();
   if (restore.has_value()) {
diff --git a/esphome/components/template/fan/template_fan.h b/esphome/components/template/fan/template_fan.h
index b7e1d4ab5a..d8229ef047 100644
--- a/esphome/components/template/fan/template_fan.h
+++ b/esphome/components/template/fan/template_fan.h
@@ -13,7 +13,7 @@ class TemplateFan final : public Component, public fan::Fan {
   void set_has_direction(bool has_direction) { this->has_direction_ = has_direction; }
   void set_has_oscillating(bool has_oscillating) { this->has_oscillating_ = has_oscillating; }
   void set_speed_count(int count) { this->speed_count_ = count; }
-  void set_preset_modes(std::initializer_list<const char *> presets) { this->preset_modes_ = presets; }
+  void set_preset_modes(std::initializer_list<const char *> presets) { this->set_supported_preset_modes(presets); }
   fan::FanTraits get_traits() override { return this->traits_; }
 
  protected:
@@ -23,7 +23,6 @@ class TemplateFan final : public Component, public fan::Fan {
   bool has_direction_{false};
   int speed_count_{0};
   fan::FanTraits traits_;
-  std::vector<const char *> preset_modes_{};
 };
 
 }  // namespace esphome::template_

From df58091d1d045b1ad76afca09abaf6e125830080 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 13:14:52 -1000
Subject: [PATCH 02/21] Make compat owned vector skip-on-copy to eliminate copy
 overhead

Wrap the deprecated owned vector in a struct with a no-op copy
constructor. FanTraits copies (which happen on every get_traits()
call) don't pay the 24-byte cost of copying an empty vector.
---
 esphome/components/fan/fan_traits.h | 30 +++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/esphome/components/fan/fan_traits.h b/esphome/components/fan/fan_traits.h
index f8202f36ce..b5d6556e3b 100644
--- a/esphome/components/fan/fan_traits.h
+++ b/esphome/components/fan/fan_traits.h
@@ -33,27 +33,27 @@ class FanTraits {
   void set_direction(bool direction) { this->direction_ = direction; }
   /// Return the preset modes supported by the fan.
   const std::vector<const char *> &supported_preset_modes() const {
-    return this->preset_modes_ ? *this->preset_modes_ : this->owned_preset_modes_;
+    return this->preset_modes_ ? *this->preset_modes_ : this->owned_preset_modes_.modes;
   }
   /// Set the preset modes pointer (points to vector owned by Fan base class).
   void set_supported_preset_modes(const std::vector<const char *> *preset_modes) { this->preset_modes_ = preset_modes; }
 
-  // Remove before 2027.1.0
+  // Remove before 2026.11.0
   ESPDEPRECATED("Call set_supported_preset_modes() on the Fan entity instead. Removed in 2026.11.0", "2026.5.0")
   void set_supported_preset_modes(std::initializer_list<const char *> preset_modes) {
-    this->owned_preset_modes_ = preset_modes;
-    this->preset_modes_ = &this->owned_preset_modes_;
+    this->owned_preset_modes_.modes = preset_modes;
+    this->preset_modes_ = &this->owned_preset_modes_.modes;
   }
-  // Remove before 2027.1.0
+  // Remove before 2026.11.0
   ESPDEPRECATED("Call set_supported_preset_modes() on the Fan entity instead. Removed in 2026.11.0", "2026.5.0")
   void set_supported_preset_modes(const std::vector<const char *> &preset_modes) {
-    this->owned_preset_modes_ = preset_modes;
-    this->preset_modes_ = &this->owned_preset_modes_;
+    this->owned_preset_modes_.modes = preset_modes;
+    this->preset_modes_ = &this->owned_preset_modes_.modes;
   }
 
   /// Return if preset modes are supported
   bool supports_preset_modes() const {
-    return (this->preset_modes_ && !this->preset_modes_->empty()) || !this->owned_preset_modes_.empty();
+    return (this->preset_modes_ && !this->preset_modes_->empty()) || !this->owned_preset_modes_.modes.empty();
   }
   /// Find and return the matching preset mode pointer from supported modes, or nullptr if not found.
   const char *find_preset_mode(const char *preset_mode) const {
@@ -62,7 +62,7 @@ class FanTraits {
   const char *find_preset_mode(const char *preset_mode, size_t len) const {
     if (preset_mode == nullptr || len == 0)
       return nullptr;
-    const auto &modes = this->preset_modes_ ? *this->preset_modes_ : this->owned_preset_modes_;
+    const auto &modes = this->preset_modes_ ? *this->preset_modes_ : this->owned_preset_modes_.modes;
     for (const char *mode : modes) {
       if (strncmp(mode, preset_mode, len) == 0 && mode[len] == '\0') {
         return mode;  // Return pointer from traits
@@ -77,7 +77,17 @@ class FanTraits {
   bool direction_{false};
   int speed_count_{};
   const std::vector<const char *> *preset_modes_{nullptr};
-  std::vector<const char *> owned_preset_modes_{};  ///< Compat: used when old setters are called directly on traits
+  /** Compat storage for deprecated setters — skipped on copy to avoid overhead.
+   * Remove in 2026.11.0 along with the deprecated overloads.
+   */
+  struct OwnedPresetModes {
+    std::vector<const char *> modes;
+    OwnedPresetModes() = default;
+    OwnedPresetModes(const OwnedPresetModes &) {}  // NOLINT - no-op copy: compat data is not propagated
+    OwnedPresetModes &operator=(const OwnedPresetModes &) { return *this; }  // NOLINT
+    OwnedPresetModes(OwnedPresetModes &&) = default;
+    OwnedPresetModes &operator=(OwnedPresetModes &&) = default;
+  } owned_preset_modes_;
 };
 
 }  // namespace fan

From 4ff0d30e076d8b4c1a886e7e4ee0b04a26969abb Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 13:24:58 -1000
Subject: [PATCH 03/21] Use leak-on-purpose raw pointer for Fan-owned preset
 modes vector

Fan entities live for the entire program lifetime, so the preset
modes vector never needs to be freed. Use a raw pointer (null by
default, allocated on first set_supported_preset_modes() call)
instead of an inline std::vector member.

This saves 24 bytes of RAM per Fan instance for components that
don't use preset modes (binary, bedjet, tuya, etc.).
---
 esphome/components/fan/fan.cpp | 10 +++++-----
 esphome/components/fan/fan.h   | 13 +++++++++----
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/esphome/components/fan/fan.cpp b/esphome/components/fan/fan.cpp
index 659abf70a9..f486c40ca4 100644
--- a/esphome/components/fan/fan.cpp
+++ b/esphome/components/fan/fan.cpp
@@ -148,9 +148,9 @@ const char *Fan::find_preset_mode_(const char *preset_mode) {
 }
 
 const char *Fan::find_preset_mode_(const char *preset_mode, size_t len) {
-  if (preset_mode == nullptr || len == 0)
+  if (preset_mode == nullptr || len == 0 || !this->supported_preset_modes_)
     return nullptr;
-  for (const char *mode : this->supported_preset_modes_) {
+  for (const char *mode : *this->supported_preset_modes_) {
     if (strncmp(mode, preset_mode, len) == 0 && mode[len] == '\0')
       return mode;
   }
@@ -274,10 +274,10 @@ void Fan::save_state_() {
   state.direction = this->direction;
   state.preset_mode = FanRestoreState::NO_PRESET;
 
-  if (this->has_preset_mode()) {
+  if (this->has_preset_mode() && this->supported_preset_modes_) {
     // Find index of current preset mode (pointer comparison is safe since preset is from our vector)
-    for (size_t i = 0; i < this->supported_preset_modes_.size(); i++) {
-      if (this->supported_preset_modes_[i] == this->preset_mode_) {
+    for (size_t i = 0; i < this->supported_preset_modes_->size(); i++) {
+      if ((*this->supported_preset_modes_)[i] == this->preset_mode_) {
         state.preset_mode = i;
         break;
       }
diff --git a/esphome/components/fan/fan.h b/esphome/components/fan/fan.h
index 42999d16f7..2b76fa24da 100644
--- a/esphome/components/fan/fan.h
+++ b/esphome/components/fan/fan.h
@@ -132,10 +132,15 @@ class Fan : public EntityBase {
 
   /// Set the supported preset modes (stored on Fan, referenced by FanTraits via pointer).
   void set_supported_preset_modes(std::initializer_list<const char *> preset_modes) {
-    this->supported_preset_modes_ = preset_modes;
+    if (!this->supported_preset_modes_)
+      this->supported_preset_modes_ =
+          new std::vector<const char *>();  // NOLINT - intentional leak, entity lives forever
+    *this->supported_preset_modes_ = preset_modes;
   }
   void set_supported_preset_modes(const std::vector<const char *> &preset_modes) {
-    this->supported_preset_modes_ = preset_modes;
+    if (!this->supported_preset_modes_)
+      this->supported_preset_modes_ = new std::vector<const char *>();  // NOLINT
+    *this->supported_preset_modes_ = preset_modes;
   }
 
   /// Set the restore mode of this fan.
@@ -179,8 +184,8 @@ class Fan : public EntityBase {
   ESPPreferenceObject rtc_;
   FanRestoreMode restore_mode_;
 
-  /// Preset mode storage — owned by Fan, referenced by FanTraits via pointer.
-  std::vector<const char *> supported_preset_modes_;
+  /// Preset mode storage — allocated on first use, never freed (entity lives forever).
+  std::vector<const char *> *supported_preset_modes_{nullptr};
 
  private:
   const char *preset_mode_{nullptr};

From 554d97ff04ba949d9f5cf64b8b417dcada8a6264 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 13:33:15 -1000
Subject: [PATCH 04/21] Fix clang-tidy: add braces around if statements,
 extract ensure helper

---
 esphome/components/fan/fan.h | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/esphome/components/fan/fan.h b/esphome/components/fan/fan.h
index 2b76fa24da..eff57a343a 100644
--- a/esphome/components/fan/fan.h
+++ b/esphome/components/fan/fan.h
@@ -132,15 +132,10 @@ class Fan : public EntityBase {
 
   /// Set the supported preset modes (stored on Fan, referenced by FanTraits via pointer).
   void set_supported_preset_modes(std::initializer_list<const char *> preset_modes) {
-    if (!this->supported_preset_modes_)
-      this->supported_preset_modes_ =
-          new std::vector<const char *>();  // NOLINT - intentional leak, entity lives forever
-    *this->supported_preset_modes_ = preset_modes;
+    this->ensure_preset_modes_().assign(preset_modes.begin(), preset_modes.end());
   }
   void set_supported_preset_modes(const std::vector<const char *> &preset_modes) {
-    if (!this->supported_preset_modes_)
-      this->supported_preset_modes_ = new std::vector<const char *>();  // NOLINT
-    *this->supported_preset_modes_ = preset_modes;
+    this->ensure_preset_modes_() = preset_modes;
   }
 
   /// Set the restore mode of this fan.
@@ -184,7 +179,14 @@ class Fan : public EntityBase {
   ESPPreferenceObject rtc_;
   FanRestoreMode restore_mode_;
 
-  /// Preset mode storage — allocated on first use, never freed (entity lives forever).
+  /// Lazy-allocate preset modes vector (never freed — entity lives forever).
+  std::vector<const char *> &ensure_preset_modes_() {
+    if (!this->supported_preset_modes_) {
+      this->supported_preset_modes_ = new std::vector<const char *>();  // NOLINT
+    }
+    return *this->supported_preset_modes_;
+  }
+
   std::vector<const char *> *supported_preset_modes_{nullptr};
 
  private:

From 5be5f1666222a622355e23de4a48b2af7692c02f Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 13:52:41 -1000
Subject: [PATCH 05/21] Fix compat: heap-allocate deprecated vector, add find
 fallback

Two bugs fixed from Copilot review:

1. Dangling pointer on copy: deprecated setters stored data in an
   OwnedPresetModes struct on FanTraits. If the traits object was
   copied, the copy's pointer dangled. Fix: deprecated setters now
   heap-allocate (intentional leak). Pointer survives any copy.
   Remove the OwnedPresetModes wrapper entirely.

2. find_preset_mode_ / save_state_ only searched the Fan-owned
   vector, breaking external components using the deprecated traits
   setters. Fix: fall back to get_traits() when the entity vector
   is null.
---
 esphome/components/fan/fan.cpp      | 26 ++++++++++++++++---------
 esphome/components/fan/fan_traits.h | 30 ++++++++++-------------------
 2 files changed, 27 insertions(+), 29 deletions(-)

diff --git a/esphome/components/fan/fan.cpp b/esphome/components/fan/fan.cpp
index f486c40ca4..3f4b7844c0 100644
--- a/esphome/components/fan/fan.cpp
+++ b/esphome/components/fan/fan.cpp
@@ -148,13 +148,19 @@ const char *Fan::find_preset_mode_(const char *preset_mode) {
 }
 
 const char *Fan::find_preset_mode_(const char *preset_mode, size_t len) {
-  if (preset_mode == nullptr || len == 0 || !this->supported_preset_modes_)
+  if (preset_mode == nullptr || len == 0) {
     return nullptr;
-  for (const char *mode : *this->supported_preset_modes_) {
-    if (strncmp(mode, preset_mode, len) == 0 && mode[len] == '\0')
-      return mode;
   }
-  return nullptr;
+  if (this->supported_preset_modes_) {
+    for (const char *mode : *this->supported_preset_modes_) {
+      if (strncmp(mode, preset_mode, len) == 0 && mode[len] == '\0') {
+        return mode;
+      }
+    }
+    return nullptr;
+  }
+  // Fallback for deprecated path: external components may set modes on FanTraits directly
+  return this->get_traits().find_preset_mode(preset_mode, len);
 }
 
 bool Fan::set_preset_mode_(const char *preset_mode, size_t len) {
@@ -274,10 +280,12 @@ void Fan::save_state_() {
   state.direction = this->direction;
   state.preset_mode = FanRestoreState::NO_PRESET;
 
-  if (this->has_preset_mode() && this->supported_preset_modes_) {
-    // Find index of current preset mode (pointer comparison is safe since preset is from our vector)
-    for (size_t i = 0; i < this->supported_preset_modes_->size(); i++) {
-      if ((*this->supported_preset_modes_)[i] == this->preset_mode_) {
+  if (this->has_preset_mode()) {
+    // Use Fan-owned vector, or fall back to traits for deprecated path
+    const auto &preset_modes =
+        this->supported_preset_modes_ ? *this->supported_preset_modes_ : this->get_traits().supported_preset_modes();
+    for (size_t i = 0; i < preset_modes.size(); i++) {
+      if (preset_modes[i] == this->preset_mode_) {
         state.preset_mode = i;
         break;
       }
diff --git a/esphome/components/fan/fan_traits.h b/esphome/components/fan/fan_traits.h
index b5d6556e3b..b6549368c9 100644
--- a/esphome/components/fan/fan_traits.h
+++ b/esphome/components/fan/fan_traits.h
@@ -33,7 +33,8 @@ class FanTraits {
   void set_direction(bool direction) { this->direction_ = direction; }
   /// Return the preset modes supported by the fan.
   const std::vector<const char *> &supported_preset_modes() const {
-    return this->preset_modes_ ? *this->preset_modes_ : this->owned_preset_modes_.modes;
+    static const std::vector<const char *> EMPTY_VECTOR;
+    return this->preset_modes_ ? *this->preset_modes_ : EMPTY_VECTOR;
   }
   /// Set the preset modes pointer (points to vector owned by Fan base class).
   void set_supported_preset_modes(const std::vector<const char *> *preset_modes) { this->preset_modes_ = preset_modes; }
@@ -41,20 +42,17 @@ class FanTraits {
   // Remove before 2026.11.0
   ESPDEPRECATED("Call set_supported_preset_modes() on the Fan entity instead. Removed in 2026.11.0", "2026.5.0")
   void set_supported_preset_modes(std::initializer_list<const char *> preset_modes) {
-    this->owned_preset_modes_.modes = preset_modes;
-    this->preset_modes_ = &this->owned_preset_modes_.modes;
+    // NOLINT - intentional leak: pointer must survive copies of FanTraits
+    this->preset_modes_ = new std::vector<const char *>(preset_modes);  // NOLINT
   }
   // Remove before 2026.11.0
   ESPDEPRECATED("Call set_supported_preset_modes() on the Fan entity instead. Removed in 2026.11.0", "2026.5.0")
   void set_supported_preset_modes(const std::vector<const char *> &preset_modes) {
-    this->owned_preset_modes_.modes = preset_modes;
-    this->preset_modes_ = &this->owned_preset_modes_.modes;
+    this->preset_modes_ = new std::vector<const char *>(preset_modes);  // NOLINT
   }
 
   /// Return if preset modes are supported
-  bool supports_preset_modes() const {
-    return (this->preset_modes_ && !this->preset_modes_->empty()) || !this->owned_preset_modes_.modes.empty();
-  }
+  bool supports_preset_modes() const { return this->preset_modes_ && !this->preset_modes_->empty(); }
   /// Find and return the matching preset mode pointer from supported modes, or nullptr if not found.
   const char *find_preset_mode(const char *preset_mode) const {
     return this->find_preset_mode(preset_mode, preset_mode ? strlen(preset_mode) : 0);
@@ -62,7 +60,10 @@ class FanTraits {
   const char *find_preset_mode(const char *preset_mode, size_t len) const {
     if (preset_mode == nullptr || len == 0)
       return nullptr;
-    const auto &modes = this->preset_modes_ ? *this->preset_modes_ : this->owned_preset_modes_.modes;
+    if (!this->preset_modes_) {
+      return nullptr;
+    }
+    const auto &modes = *this->preset_modes_;
     for (const char *mode : modes) {
       if (strncmp(mode, preset_mode, len) == 0 && mode[len] == '\0') {
         return mode;  // Return pointer from traits
@@ -77,17 +78,6 @@ class FanTraits {
   bool direction_{false};
   int speed_count_{};
   const std::vector<const char *> *preset_modes_{nullptr};
-  /** Compat storage for deprecated setters — skipped on copy to avoid overhead.
-   * Remove in 2026.11.0 along with the deprecated overloads.
-   */
-  struct OwnedPresetModes {
-    std::vector<const char *> modes;
-    OwnedPresetModes() = default;
-    OwnedPresetModes(const OwnedPresetModes &) {}  // NOLINT - no-op copy: compat data is not propagated
-    OwnedPresetModes &operator=(const OwnedPresetModes &) { return *this; }  // NOLINT
-    OwnedPresetModes(OwnedPresetModes &&) = default;
-    OwnedPresetModes &operator=(OwnedPresetModes &&) = default;
-  } owned_preset_modes_;
 };
 
 }  // namespace fan

From 4838c61a8c36db6acd2ecdff7afaeadb4ad36712 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 14:02:27 -1000
Subject: [PATCH 06/21] Move preset modes pointer to private, consolidate empty
 vector to cpp

- Move supported_preset_modes_ pointer and ensure helper to private
- Move static EMPTY_VECTOR from inline header getter to a single
  file-scope constant in fan.cpp (avoids duplication per TU)
- Add 2026.11.0 removal comments on all compat code paths
---
 esphome/components/fan/fan.cpp      | 10 ++++++++++
 esphome/components/fan/fan.h        |  3 +--
 esphome/components/fan/fan_traits.h |  7 ++-----
 3 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/esphome/components/fan/fan.cpp b/esphome/components/fan/fan.cpp
index 3f4b7844c0..af34d28f7a 100644
--- a/esphome/components/fan/fan.cpp
+++ b/esphome/components/fan/fan.cpp
@@ -9,6 +9,16 @@ namespace fan {
 
 static const char *const TAG = "fan";
 
+// Compat: shared empty vector for getter when no preset modes are set.
+// Remove in 2026.11.0 when deprecated FanTraits setters are removed
+// and getter can return const vector * instead of const vector &.
+static const std::vector<const char *> EMPTY_PRESET_MODES;  // NOLINT
+
+const std::vector<const char *> &FanTraits::supported_preset_modes() const {
+  // Compat: return empty ref when pointer is null. Remove in 2026.11.0 (change return to const vector *).
+  return this->preset_modes_ ? *this->preset_modes_ : EMPTY_PRESET_MODES;
+}
+
 // Fan direction strings indexed by FanDirection enum (0-1): FORWARD, REVERSE, plus UNKNOWN
 PROGMEM_STRING_TABLE(FanDirectionStrings, "FORWARD", "REVERSE", "UNKNOWN");
 
diff --git a/esphome/components/fan/fan.h b/esphome/components/fan/fan.h
index eff57a343a..b7d52aa15f 100644
--- a/esphome/components/fan/fan.h
+++ b/esphome/components/fan/fan.h
@@ -179,6 +179,7 @@ class Fan : public EntityBase {
   ESPPreferenceObject rtc_;
   FanRestoreMode restore_mode_;
 
+ private:
   /// Lazy-allocate preset modes vector (never freed — entity lives forever).
   std::vector<const char *> &ensure_preset_modes_() {
     if (!this->supported_preset_modes_) {
@@ -188,8 +189,6 @@ class Fan : public EntityBase {
   }
 
   std::vector<const char *> *supported_preset_modes_{nullptr};
-
- private:
   const char *preset_mode_{nullptr};
 };
 
diff --git a/esphome/components/fan/fan_traits.h b/esphome/components/fan/fan_traits.h
index b6549368c9..0098088ae6 100644
--- a/esphome/components/fan/fan_traits.h
+++ b/esphome/components/fan/fan_traits.h
@@ -31,11 +31,8 @@ class FanTraits {
   bool supports_direction() const { return this->direction_; }
   /// Set whether this fan supports changing direction
   void set_direction(bool direction) { this->direction_ = direction; }
-  /// Return the preset modes supported by the fan.
-  const std::vector<const char *> &supported_preset_modes() const {
-    static const std::vector<const char *> EMPTY_VECTOR;
-    return this->preset_modes_ ? *this->preset_modes_ : EMPTY_VECTOR;
-  }
+  // Compat: returns const ref with empty fallback. In 2026.11.0 change to return const vector *.
+  const std::vector<const char *> &supported_preset_modes() const;
   /// Set the preset modes pointer (points to vector owned by Fan base class).
   void set_supported_preset_modes(const std::vector<const char *> *preset_modes) { this->preset_modes_ = preset_modes; }
 

From 56f0d3f7f5ec70d50fdd7647c0eb1a3001caca38 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 14:08:07 -1000
Subject: [PATCH 07/21] Fix compat: use owned vector instead of leak, wire
 preset modes in subclasses

- Deprecated FanTraits setters store in an owned compat_preset_modes_
  vector (same copy cost as pre-PR). No heap leak, no dangling pointer.
- Subclass get_traits() calls wire_preset_modes_() to attach the
  Fan-owned pointer to the returned traits.
- Getter/find/supports all check compat vector as fallback.
---
 esphome/components/fan/fan.cpp                | 10 +++++++--
 esphome/components/fan/fan.h                  |  7 ++++++
 esphome/components/fan/fan_traits.h           | 22 +++++++++++--------
 esphome/components/hbridge/fan/hbridge_fan.h  |  5 ++++-
 esphome/components/speed/fan/speed_fan.h      |  5 ++++-
 .../components/template/fan/template_fan.h    |  5 ++++-
 6 files changed, 40 insertions(+), 14 deletions(-)

diff --git a/esphome/components/fan/fan.cpp b/esphome/components/fan/fan.cpp
index af34d28f7a..124c2105be 100644
--- a/esphome/components/fan/fan.cpp
+++ b/esphome/components/fan/fan.cpp
@@ -15,8 +15,14 @@ static const char *const TAG = "fan";
 static const std::vector<const char *> EMPTY_PRESET_MODES;  // NOLINT
 
 const std::vector<const char *> &FanTraits::supported_preset_modes() const {
-  // Compat: return empty ref when pointer is null. Remove in 2026.11.0 (change return to const vector *).
-  return this->preset_modes_ ? *this->preset_modes_ : EMPTY_PRESET_MODES;
+  if (this->preset_modes_) {
+    return *this->preset_modes_;
+  }
+  // Compat: fall back to owned vector from deprecated setters. Remove in 2026.11.0 (change return to const vector *).
+  if (!this->compat_preset_modes_.empty()) {
+    return this->compat_preset_modes_;
+  }
+  return EMPTY_PRESET_MODES;
 }
 
 // Fan direction strings indexed by FanDirection enum (0-1): FORWARD, REVERSE, plus UNKNOWN
diff --git a/esphome/components/fan/fan.h b/esphome/components/fan/fan.h
index b7d52aa15f..26b34d2bc6 100644
--- a/esphome/components/fan/fan.h
+++ b/esphome/components/fan/fan.h
@@ -175,6 +175,13 @@ class Fan : public EntityBase {
   const char *find_preset_mode_(const char *preset_mode);
   const char *find_preset_mode_(const char *preset_mode, size_t len);
 
+  /// Wire the Fan-owned preset modes pointer into the given traits object.
+  void wire_preset_modes_(FanTraits &traits) {
+    if (this->supported_preset_modes_) {
+      traits.set_supported_preset_modes(this->supported_preset_modes_);
+    }
+  }
+
   LazyCallbackManager<void()> state_callback_{};
   ESPPreferenceObject rtc_;
   FanRestoreMode restore_mode_;
diff --git a/esphome/components/fan/fan_traits.h b/esphome/components/fan/fan_traits.h
index 0098088ae6..6a003f535f 100644
--- a/esphome/components/fan/fan_traits.h
+++ b/esphome/components/fan/fan_traits.h
@@ -39,31 +39,32 @@ class FanTraits {
   // Remove before 2026.11.0
   ESPDEPRECATED("Call set_supported_preset_modes() on the Fan entity instead. Removed in 2026.11.0", "2026.5.0")
   void set_supported_preset_modes(std::initializer_list<const char *> preset_modes) {
-    // NOLINT - intentional leak: pointer must survive copies of FanTraits
-    this->preset_modes_ = new std::vector<const char *>(preset_modes);  // NOLINT
+    // Compat: store in owned vector. Copies copy the vector (same cost as before this PR).
+    this->compat_preset_modes_ = preset_modes;
   }
   // Remove before 2026.11.0
   ESPDEPRECATED("Call set_supported_preset_modes() on the Fan entity instead. Removed in 2026.11.0", "2026.5.0")
   void set_supported_preset_modes(const std::vector<const char *> &preset_modes) {
-    this->preset_modes_ = new std::vector<const char *>(preset_modes);  // NOLINT
+    this->compat_preset_modes_ = preset_modes;
   }
 
   /// Return if preset modes are supported
-  bool supports_preset_modes() const { return this->preset_modes_ && !this->preset_modes_->empty(); }
+  bool supports_preset_modes() const {
+    return (this->preset_modes_ && !this->preset_modes_->empty()) || !this->compat_preset_modes_.empty();
+  }
   /// Find and return the matching preset mode pointer from supported modes, or nullptr if not found.
   const char *find_preset_mode(const char *preset_mode) const {
     return this->find_preset_mode(preset_mode, preset_mode ? strlen(preset_mode) : 0);
   }
   const char *find_preset_mode(const char *preset_mode, size_t len) const {
-    if (preset_mode == nullptr || len == 0)
-      return nullptr;
-    if (!this->preset_modes_) {
+    if (preset_mode == nullptr || len == 0) {
       return nullptr;
     }
-    const auto &modes = *this->preset_modes_;
+    // Check pointer-based storage (new path) then compat owned vector (deprecated path)
+    const auto &modes = this->preset_modes_ ? *this->preset_modes_ : this->compat_preset_modes_;
     for (const char *mode : modes) {
       if (strncmp(mode, preset_mode, len) == 0 && mode[len] == '\0') {
-        return mode;  // Return pointer from traits
+        return mode;
       }
     }
     return nullptr;
@@ -75,6 +76,9 @@ class FanTraits {
   bool direction_{false};
   int speed_count_{};
   const std::vector<const char *> *preset_modes_{nullptr};
+  // Compat: owned storage for deprecated setters. Copies copy the vector (same cost as pre-PR).
+  // Remove in 2026.11.0.
+  std::vector<const char *> compat_preset_modes_;
 };
 
 }  // namespace fan
diff --git a/esphome/components/hbridge/fan/hbridge_fan.h b/esphome/components/hbridge/fan/hbridge_fan.h
index 7511e0eb0b..997f66ae48 100644
--- a/esphome/components/hbridge/fan/hbridge_fan.h
+++ b/esphome/components/hbridge/fan/hbridge_fan.h
@@ -24,7 +24,10 @@ class HBridgeFan : public Component, public fan::Fan {
 
   void setup() override;
   void dump_config() override;
-  fan::FanTraits get_traits() override { return this->traits_; }
+  fan::FanTraits get_traits() override {
+    this->wire_preset_modes_(this->traits_);
+    return this->traits_;
+  }
 
   fan::FanCall brake();
 
diff --git a/esphome/components/speed/fan/speed_fan.h b/esphome/components/speed/fan/speed_fan.h
index 44bd1a15cb..db96039a13 100644
--- a/esphome/components/speed/fan/speed_fan.h
+++ b/esphome/components/speed/fan/speed_fan.h
@@ -17,7 +17,10 @@ class SpeedFan : public Component, public fan::Fan {
   void set_oscillating(output::BinaryOutput *oscillating) { this->oscillating_ = oscillating; }
   void set_direction(output::BinaryOutput *direction) { this->direction_ = direction; }
   void set_preset_modes(std::initializer_list<const char *> presets) { this->set_supported_preset_modes(presets); }
-  fan::FanTraits get_traits() override { return this->traits_; }
+  fan::FanTraits get_traits() override {
+    this->wire_preset_modes_(this->traits_);
+    return this->traits_;
+  }
 
  protected:
   void control(const fan::FanCall &call) override;
diff --git a/esphome/components/template/fan/template_fan.h b/esphome/components/template/fan/template_fan.h
index d8229ef047..5ab6ae8c65 100644
--- a/esphome/components/template/fan/template_fan.h
+++ b/esphome/components/template/fan/template_fan.h
@@ -14,7 +14,10 @@ class TemplateFan final : public Component, public fan::Fan {
   void set_has_oscillating(bool has_oscillating) { this->has_oscillating_ = has_oscillating; }
   void set_speed_count(int count) { this->speed_count_ = count; }
   void set_preset_modes(std::initializer_list<const char *> presets) { this->set_supported_preset_modes(presets); }
-  fan::FanTraits get_traits() override { return this->traits_; }
+  fan::FanTraits get_traits() override {
+    this->wire_preset_modes_(this->traits_);
+    return this->traits_;
+  }
 
  protected:
   void control(const fan::FanCall &call) override;

From c42cfac50fc3f162ee0ea1df9fd795a64c9d4f86 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 14:28:55 -1000
Subject: [PATCH 08/21] Fix dangling reference in save_state_, restore deleted
 string overloads

1. save_state_() bound a reference to supported_preset_modes() from
   a temporary FanTraits returned by get_traits(). When the compat
   path fired, the temporary was destroyed and the reference dangled.
   Fix: keep the FanTraits alive for the loop duration.

2. Restore deleted std::vector<std::string> / initializer_list<std::string>
   overloads to preserve clear compile-time diagnostics.
---
 esphome/components/fan/fan.cpp      | 6 ++++--
 esphome/components/fan/fan_traits.h | 4 ++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/esphome/components/fan/fan.cpp b/esphome/components/fan/fan.cpp
index 124c2105be..fb9654da5b 100644
--- a/esphome/components/fan/fan.cpp
+++ b/esphome/components/fan/fan.cpp
@@ -297,9 +297,11 @@ void Fan::save_state_() {
   state.preset_mode = FanRestoreState::NO_PRESET;
 
   if (this->has_preset_mode()) {
-    // Use Fan-owned vector, or fall back to traits for deprecated path
+    // Use Fan-owned vector, or fall back to traits for deprecated path.
+    // Keep traits alive so the reference to compat_preset_modes_ doesn't dangle.
+    auto traits = this->supported_preset_modes_ ? FanTraits() : this->get_traits();
     const auto &preset_modes =
-        this->supported_preset_modes_ ? *this->supported_preset_modes_ : this->get_traits().supported_preset_modes();
+        this->supported_preset_modes_ ? *this->supported_preset_modes_ : traits.supported_preset_modes();
     for (size_t i = 0; i < preset_modes.size(); i++) {
       if (preset_modes[i] == this->preset_mode_) {
         state.preset_mode = i;
diff --git a/esphome/components/fan/fan_traits.h b/esphome/components/fan/fan_traits.h
index 6a003f535f..046ae50929 100644
--- a/esphome/components/fan/fan_traits.h
+++ b/esphome/components/fan/fan_traits.h
@@ -48,6 +48,10 @@ class FanTraits {
     this->compat_preset_modes_ = preset_modes;
   }
 
+  // Deleted overloads to catch incorrect std::string usage at compile time with clear error messages
+  void set_supported_preset_modes(const std::vector<std::string> &preset_modes) = delete;
+  void set_supported_preset_modes(std::initializer_list<std::string> preset_modes) = delete;
+
   /// Return if preset modes are supported
   bool supports_preset_modes() const {
     return (this->preset_modes_ && !this->preset_modes_->empty()) || !this->compat_preset_modes_.empty();

From 2f93ba0d71bf5ed722b59c7930aef988985b91ac Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 15:21:11 -1000
Subject: [PATCH 09/21] Add integration test for deprecated FanTraits compat
 layer

---
 .../legacy_fan_component/__init__.py          |  1 +
 .../legacy_fan_component/fan/__init__.py      | 19 +++++
 .../legacy_fan_component/fan/legacy_fan.h     | 49 ++++++++++++
 .../fixtures/legacy_fan_compat.yaml           | 21 +++++
 tests/integration/test_legacy_fan_compat.py   | 79 +++++++++++++++++++
 5 files changed, 169 insertions(+)
 create mode 100644 tests/integration/fixtures/external_components/legacy_fan_component/__init__.py
 create mode 100644 tests/integration/fixtures/external_components/legacy_fan_component/fan/__init__.py
 create mode 100644 tests/integration/fixtures/external_components/legacy_fan_component/fan/legacy_fan.h
 create mode 100644 tests/integration/fixtures/legacy_fan_compat.yaml
 create mode 100644 tests/integration/test_legacy_fan_compat.py

diff --git a/tests/integration/fixtures/external_components/legacy_fan_component/__init__.py b/tests/integration/fixtures/external_components/legacy_fan_component/__init__.py
new file mode 100644
index 0000000000..ceee477522
--- /dev/null
+++ b/tests/integration/fixtures/external_components/legacy_fan_component/__init__.py
@@ -0,0 +1 @@
+"""Legacy fan component — tests deprecated FanTraits setters backward compat."""
diff --git a/tests/integration/fixtures/external_components/legacy_fan_component/fan/__init__.py b/tests/integration/fixtures/external_components/legacy_fan_component/fan/__init__.py
new file mode 100644
index 0000000000..72655dec95
--- /dev/null
+++ b/tests/integration/fixtures/external_components/legacy_fan_component/fan/__init__.py
@@ -0,0 +1,19 @@
+"""Legacy fan platform that uses deprecated FanTraits setters."""
+
+import esphome.codegen as cg
+from esphome.components import fan
+import esphome.config_validation as cv
+
+legacy_fan_ns = cg.esphome_ns.namespace("legacy_fan_test")
+LegacyFan = legacy_fan_ns.class_("LegacyFan", fan.Fan, cg.Component)
+
+CONFIG_SCHEMA = fan.FAN_SCHEMA.extend(
+    {
+        cv.GenerateID(): cv.declare_id(LegacyFan),
+    }
+).extend(cv.COMPONENT_SCHEMA)
+
+
+async def to_code(config):
+    var = await fan.new_fan(config)
+    await cg.register_component(var, config)
diff --git a/tests/integration/fixtures/external_components/legacy_fan_component/fan/legacy_fan.h b/tests/integration/fixtures/external_components/legacy_fan_component/fan/legacy_fan.h
new file mode 100644
index 0000000000..3f8937905e
--- /dev/null
+++ b/tests/integration/fixtures/external_components/legacy_fan_component/fan/legacy_fan.h
@@ -0,0 +1,49 @@
+#pragma once
+
+#include "esphome/components/fan/fan.h"
+#include "esphome/core/component.h"
+
+namespace esphome {
+namespace legacy_fan_test {
+
+/// Test fan that uses the DEPRECATED FanTraits setters for preset modes.
+/// This validates backward compatibility for external components that haven't migrated.
+class LegacyFan : public fan::Fan, public Component {
+ public:
+  void setup() override {
+    auto restore = this->restore_state_();
+    if (restore.has_value()) {
+      restore->apply(*this);
+    }
+    this->publish_state();
+  }
+
+  float get_setup_priority() const override { return setup_priority::LATE; }
+
+  fan::FanTraits get_traits() override {
+    auto traits = fan::FanTraits(false, true, false, 3);
+
+    // DEPRECATED API: setting preset modes directly on FanTraits.
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+    traits.set_supported_preset_modes({"Turbo", "Silent", "Eco"});
+#pragma GCC diagnostic pop
+
+    return traits;
+  }
+
+ protected:
+  void control(const fan::FanCall &call) override {
+    if (call.get_state().has_value()) {
+      this->state = *call.get_state();
+    }
+    if (call.get_speed().has_value()) {
+      this->speed = *call.get_speed();
+    }
+    this->apply_preset_mode_(call);
+    this->publish_state();
+  }
+};
+
+}  // namespace legacy_fan_test
+}  // namespace esphome
diff --git a/tests/integration/fixtures/legacy_fan_compat.yaml b/tests/integration/fixtures/legacy_fan_compat.yaml
new file mode 100644
index 0000000000..d510f8adea
--- /dev/null
+++ b/tests/integration/fixtures/legacy_fan_compat.yaml
@@ -0,0 +1,21 @@
+esphome:
+  name: legacy-fan-compat
+  platformio_options:
+    build_flags:
+      - "-DUSE_HOST"
+
+host:
+api:
+logger:
+  level: DEBUG
+
+external_components:
+  - source:
+      type: local
+      path: EXTERNAL_COMPONENT_PATH
+    components: [legacy_fan_component]
+
+fan:
+  - platform: legacy_fan_component
+    name: "Legacy Fan"
+    id: legacy_fan
diff --git a/tests/integration/test_legacy_fan_compat.py b/tests/integration/test_legacy_fan_compat.py
new file mode 100644
index 0000000000..4ac8585e5a
--- /dev/null
+++ b/tests/integration/test_legacy_fan_compat.py
@@ -0,0 +1,79 @@
+"""Integration test for backward compatibility of deprecated FanTraits setters.
+
+Verifies that external components using the old traits.set_supported_preset_modes()
+API still work correctly during the deprecation period (removed in 2026.11.0).
+"""
+
+from __future__ import annotations
+
+import asyncio
+from pathlib import Path
+
+from aioesphomeapi import FanInfo, FanState
+import pytest
+
+from .types import APIClientConnectedFactory, RunCompiledFunction
+
+
+@pytest.mark.asyncio
+async def test_legacy_fan_compat(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    api_client_connected: APIClientConnectedFactory,
+) -> None:
+    """Test that deprecated FanTraits preset mode setters still work end-to-end."""
+    external_components_path = str(
+        Path(__file__).parent / "fixtures" / "external_components"
+    )
+    yaml_config = yaml_config.replace(
+        "EXTERNAL_COMPONENT_PATH", external_components_path
+    )
+
+    async with run_compiled(yaml_config), api_client_connected() as client:
+        entities, services = await client.list_entities_services()
+
+        fan_infos = [e for e in entities if isinstance(e, FanInfo)]
+        assert len(fan_infos) == 1, f"Expected 1 fan entity, got {len(fan_infos)}"
+
+        test_fan = fan_infos[0]
+
+        # Verify preset modes set via deprecated FanTraits setter are exposed
+        assert set(test_fan.supported_preset_modes) == {
+            "Turbo",
+            "Silent",
+            "Eco",
+        }, (
+            f"Expected preset modes {{Turbo, Silent, Eco}}, "
+            f"got {test_fan.supported_preset_modes}"
+        )
+
+        # Verify speed support
+        assert test_fan.supports_speed is True
+        assert test_fan.supported_speed_count == 3
+
+        # Subscribe and wait for initial states
+        states: dict[int, FanState] = {}
+        state_event = asyncio.Event()
+
+        def on_state(state: FanState) -> None:
+            if isinstance(state, FanState):
+                states[state.key] = state
+                state_event.set()
+
+        client.subscribe_states(on_state)
+
+        # Wait for initial state
+        await asyncio.wait_for(state_event.wait(), timeout=5.0)
+
+        # Turn on fan with preset mode (tests find_preset_mode_ compat path)
+        state_event.clear()
+        client.fan_command(
+            key=test_fan.key,
+            state=True,
+            preset_mode="Turbo",
+        )
+        await asyncio.wait_for(state_event.wait(), timeout=5.0)
+
+        fan_state = states[test_fan.key]
+        assert fan_state.state is True
+        assert fan_state.preset_mode == "Turbo"

From c8d842586ab16b1ce97a8d8ccf9322d526f829eb Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 15:23:44 -1000
Subject: [PATCH 10/21] Fix fan fixture: remove unnecessary build flags

---
 tests/integration/fixtures/legacy_fan_compat.yaml | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/tests/integration/fixtures/legacy_fan_compat.yaml b/tests/integration/fixtures/legacy_fan_compat.yaml
index d510f8adea..256fd4e4c1 100644
--- a/tests/integration/fixtures/legacy_fan_compat.yaml
+++ b/tests/integration/fixtures/legacy_fan_compat.yaml
@@ -1,8 +1,5 @@
 esphome:
   name: legacy-fan-compat
-  platformio_options:
-    build_flags:
-      - "-DUSE_HOST"
 
 host:
 api:

From 576b1c3ff0256279a77fdabfc04e44b2d8111ed4 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 15:25:13 -1000
Subject: [PATCH 11/21] Fix fan fixture: use C++17 namespace style

---
 .../legacy_fan_component/fan/legacy_fan.h                   | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/tests/integration/fixtures/external_components/legacy_fan_component/fan/legacy_fan.h b/tests/integration/fixtures/external_components/legacy_fan_component/fan/legacy_fan.h
index 3f8937905e..e6135d60be 100644
--- a/tests/integration/fixtures/external_components/legacy_fan_component/fan/legacy_fan.h
+++ b/tests/integration/fixtures/external_components/legacy_fan_component/fan/legacy_fan.h
@@ -3,8 +3,7 @@
 #include "esphome/components/fan/fan.h"
 #include "esphome/core/component.h"
 
-namespace esphome {
-namespace legacy_fan_test {
+namespace esphome::legacy_fan_test {
 
 /// Test fan that uses the DEPRECATED FanTraits setters for preset modes.
 /// This validates backward compatibility for external components that haven't migrated.
@@ -45,5 +44,4 @@ class LegacyFan : public fan::Fan, public Component {
   }
 };
 
-}  // namespace legacy_fan_test
-}  // namespace esphome
+}  // namespace esphome::legacy_fan_test

From 95cdc908350d3b2114700e7de13974a9df856e7e Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 15:27:20 -1000
Subject: [PATCH 12/21] Fix to_code signature: add ConfigType annotation

---
 .../external_components/legacy_fan_component/fan/__init__.py   | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tests/integration/fixtures/external_components/legacy_fan_component/fan/__init__.py b/tests/integration/fixtures/external_components/legacy_fan_component/fan/__init__.py
index 72655dec95..ccd5106a63 100644
--- a/tests/integration/fixtures/external_components/legacy_fan_component/fan/__init__.py
+++ b/tests/integration/fixtures/external_components/legacy_fan_component/fan/__init__.py
@@ -3,6 +3,7 @@
 import esphome.codegen as cg
 from esphome.components import fan
 import esphome.config_validation as cv
+from esphome.types import ConfigType
 
 legacy_fan_ns = cg.esphome_ns.namespace("legacy_fan_test")
 LegacyFan = legacy_fan_ns.class_("LegacyFan", fan.Fan, cg.Component)
@@ -14,6 +15,6 @@ CONFIG_SCHEMA = fan.FAN_SCHEMA.extend(
 ).extend(cv.COMPONENT_SCHEMA)
 
 
-async def to_code(config):
+async def to_code(config: ConfigType) -> None:
     var = await fan.new_fan(config)
     await cg.register_component(var, config)

From 3328423373c69f8026f905d98785647d90359211 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 15:31:27 -1000
Subject: [PATCH 13/21] Move pointer setter to protected with friend class Fan

---
 esphome/components/fan/fan_traits.h | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/esphome/components/fan/fan_traits.h b/esphome/components/fan/fan_traits.h
index 046ae50929..05810ceea4 100644
--- a/esphome/components/fan/fan_traits.h
+++ b/esphome/components/fan/fan_traits.h
@@ -9,7 +9,11 @@ namespace esphome {
 
 namespace fan {
 
+class Fan;  // Forward declaration
+
 class FanTraits {
+  friend class Fan;  // Allow Fan to access protected pointer setter
+
  public:
   FanTraits() = default;
   FanTraits(bool oscillation, bool speed, bool direction, int speed_count)
@@ -33,9 +37,6 @@ class FanTraits {
   void set_direction(bool direction) { this->direction_ = direction; }
   // Compat: returns const ref with empty fallback. In 2026.11.0 change to return const vector *.
   const std::vector<const char *> &supported_preset_modes() const;
-  /// Set the preset modes pointer (points to vector owned by Fan base class).
-  void set_supported_preset_modes(const std::vector<const char *> *preset_modes) { this->preset_modes_ = preset_modes; }
-
   // Remove before 2026.11.0
   ESPDEPRECATED("Call set_supported_preset_modes() on the Fan entity instead. Removed in 2026.11.0", "2026.5.0")
   void set_supported_preset_modes(std::initializer_list<const char *> preset_modes) {
@@ -75,6 +76,9 @@ class FanTraits {
   }
 
  protected:
+  /// Set the preset modes pointer (only Fan::wire_preset_modes_() should call this).
+  void set_supported_preset_modes(const std::vector<const char *> *preset_modes) { this->preset_modes_ = preset_modes; }
+
   bool oscillation_{false};
   bool speed_{false};
   bool direction_{false};

From 7c259d2f6426c835c98cc6fbe27b8ebe07f609af Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 15:39:29 -1000
Subject: [PATCH 14/21] Simplify save_state_ compat path, move CopyFan preset
 copy to setup()

- save_state_(): split into two clear branches instead of conditional
  FanTraits construction trick
- CopyFan: copy source preset modes once in setup() instead of on
  every get_traits() call
---
 esphome/components/copy/fan/copy_fan.cpp | 10 +++++++--
 esphome/components/fan/fan.cpp           | 26 ++++++++++++++++--------
 2 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/esphome/components/copy/fan/copy_fan.cpp b/esphome/components/copy/fan/copy_fan.cpp
index e7d01827aa..bdaa35c467 100644
--- a/esphome/components/copy/fan/copy_fan.cpp
+++ b/esphome/components/copy/fan/copy_fan.cpp
@@ -7,6 +7,12 @@ namespace copy {
 static const char *const TAG = "copy.fan";
 
 void CopyFan::setup() {
+  // Copy preset modes once from source fan — stored on Fan base class
+  auto source_traits = source_->get_traits();
+  if (source_traits.supports_preset_modes()) {
+    this->set_supported_preset_modes(source_traits.supported_preset_modes());
+  }
+
   source_->add_on_state_callback([this]() {
     this->copy_state_from_source_();
     this->publish_state();
@@ -39,8 +45,8 @@ fan::FanTraits CopyFan::get_traits() {
   traits.set_speed(base.supports_speed());
   traits.set_supported_speed_count(base.supported_speed_count());
   traits.set_direction(base.supports_direction());
-  // Preset modes are wired from source fan's storage via get_traits()
-  this->set_supported_preset_modes(base.supported_preset_modes());
+  // Preset modes are set once in setup() and wired via wire_preset_modes_()
+  this->wire_preset_modes_(traits);
   return traits;
 }
 
diff --git a/esphome/components/fan/fan.cpp b/esphome/components/fan/fan.cpp
index fb9654da5b..563c0eff13 100644
--- a/esphome/components/fan/fan.cpp
+++ b/esphome/components/fan/fan.cpp
@@ -297,15 +297,23 @@ void Fan::save_state_() {
   state.preset_mode = FanRestoreState::NO_PRESET;
 
   if (this->has_preset_mode()) {
-    // Use Fan-owned vector, or fall back to traits for deprecated path.
-    // Keep traits alive so the reference to compat_preset_modes_ doesn't dangle.
-    auto traits = this->supported_preset_modes_ ? FanTraits() : this->get_traits();
-    const auto &preset_modes =
-        this->supported_preset_modes_ ? *this->supported_preset_modes_ : traits.supported_preset_modes();
-    for (size_t i = 0; i < preset_modes.size(); i++) {
-      if (preset_modes[i] == this->preset_mode_) {
-        state.preset_mode = i;
-        break;
+    if (this->supported_preset_modes_) {
+      // New path: search Fan-owned vector directly
+      for (size_t i = 0; i < this->supported_preset_modes_->size(); i++) {
+        if ((*this->supported_preset_modes_)[i] == this->preset_mode_) {
+          state.preset_mode = i;
+          break;
+        }
+      }
+    } else {
+      // Compat: fall back to traits for deprecated path. Remove in 2026.11.0.
+      auto traits = this->get_traits();
+      const auto &preset_modes = traits.supported_preset_modes();
+      for (size_t i = 0; i < preset_modes.size(); i++) {
+        if (preset_modes[i] == this->preset_mode_) {
+          state.preset_mode = i;
+          break;
+        }
       }
     }
   }

From 3388d420ec3c3cadbff3a2db993c45ccc35b2af1 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 15:42:36 -1000
Subject: [PATCH 15/21] Fix unused services variable in test

---
 tests/integration/test_legacy_fan_compat.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/integration/test_legacy_fan_compat.py b/tests/integration/test_legacy_fan_compat.py
index 4ac8585e5a..a4b025b628 100644
--- a/tests/integration/test_legacy_fan_compat.py
+++ b/tests/integration/test_legacy_fan_compat.py
@@ -30,7 +30,7 @@ async def test_legacy_fan_compat(
     )
 
     async with run_compiled(yaml_config), api_client_connected() as client:
-        entities, services = await client.list_entities_services()
+        entities, _ = await client.list_entities_services()
 
         fan_infos = [e for e in entities if isinstance(e, FanInfo)]
         assert len(fan_infos) == 1, f"Expected 1 fan entity, got {len(fan_infos)}"

From 7513db9dcd70dde147181f56b711b0f42737a54c Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 15:50:10 -1000
Subject: [PATCH 16/21] Fix clang-tidy: protected method needs trailing
 underscore

---
 esphome/components/fan/fan.h        | 2 +-
 esphome/components/fan/fan_traits.h | 4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/esphome/components/fan/fan.h b/esphome/components/fan/fan.h
index 26b34d2bc6..d5763edf2f 100644
--- a/esphome/components/fan/fan.h
+++ b/esphome/components/fan/fan.h
@@ -178,7 +178,7 @@ class Fan : public EntityBase {
   /// Wire the Fan-owned preset modes pointer into the given traits object.
   void wire_preset_modes_(FanTraits &traits) {
     if (this->supported_preset_modes_) {
-      traits.set_supported_preset_modes(this->supported_preset_modes_);
+      traits.set_supported_preset_modes_(this->supported_preset_modes_);
     }
   }
 
diff --git a/esphome/components/fan/fan_traits.h b/esphome/components/fan/fan_traits.h
index 05810ceea4..78c215dc8c 100644
--- a/esphome/components/fan/fan_traits.h
+++ b/esphome/components/fan/fan_traits.h
@@ -77,7 +77,9 @@ class FanTraits {
 
  protected:
   /// Set the preset modes pointer (only Fan::wire_preset_modes_() should call this).
-  void set_supported_preset_modes(const std::vector<const char *> *preset_modes) { this->preset_modes_ = preset_modes; }
+  void set_supported_preset_modes_(const std::vector<const char *> *preset_modes) {
+    this->preset_modes_ = preset_modes;
+  }
 
   bool oscillation_{false};
   bool speed_{false};

From 794b7ef56271e83d55ce869fedd09c369723a431 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 15:55:49 -1000
Subject: [PATCH 17/21] Fix supports_preset_modes: use same precedence as
 getter

---
 esphome/components/fan/fan_traits.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/esphome/components/fan/fan_traits.h b/esphome/components/fan/fan_traits.h
index 78c215dc8c..229dd5a0c5 100644
--- a/esphome/components/fan/fan_traits.h
+++ b/esphome/components/fan/fan_traits.h
@@ -55,7 +55,11 @@ class FanTraits {
 
   /// Return if preset modes are supported
   bool supports_preset_modes() const {
-    return (this->preset_modes_ && !this->preset_modes_->empty()) || !this->compat_preset_modes_.empty();
+    // Same precedence as supported_preset_modes() getter
+    if (this->preset_modes_) {
+      return !this->preset_modes_->empty();
+    }
+    return !this->compat_preset_modes_.empty();
   }
   /// Find and return the matching preset mode pointer from supported modes, or nullptr if not found.
   const char *find_preset_mode(const char *preset_mode) const {

From 541ab9abf96a8049ee4270bc7d49b3475bb3ad20 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 16:07:20 -1000
Subject: [PATCH 18/21] Fix fan test: use fan_schema(), remove unnecessary
 get_setup_priority

---
 .../legacy_fan_component/fan/__init__.py                    | 6 +-----
 .../legacy_fan_component/fan/legacy_fan.h                   | 2 --
 2 files changed, 1 insertion(+), 7 deletions(-)

diff --git a/tests/integration/fixtures/external_components/legacy_fan_component/fan/__init__.py b/tests/integration/fixtures/external_components/legacy_fan_component/fan/__init__.py
index ccd5106a63..985d97d081 100644
--- a/tests/integration/fixtures/external_components/legacy_fan_component/fan/__init__.py
+++ b/tests/integration/fixtures/external_components/legacy_fan_component/fan/__init__.py
@@ -8,11 +8,7 @@ from esphome.types import ConfigType
 legacy_fan_ns = cg.esphome_ns.namespace("legacy_fan_test")
 LegacyFan = legacy_fan_ns.class_("LegacyFan", fan.Fan, cg.Component)
 
-CONFIG_SCHEMA = fan.FAN_SCHEMA.extend(
-    {
-        cv.GenerateID(): cv.declare_id(LegacyFan),
-    }
-).extend(cv.COMPONENT_SCHEMA)
+CONFIG_SCHEMA = fan.fan_schema(LegacyFan).extend(cv.COMPONENT_SCHEMA)
 
 
 async def to_code(config: ConfigType) -> None:
diff --git a/tests/integration/fixtures/external_components/legacy_fan_component/fan/legacy_fan.h b/tests/integration/fixtures/external_components/legacy_fan_component/fan/legacy_fan.h
index e6135d60be..ac378b59c5 100644
--- a/tests/integration/fixtures/external_components/legacy_fan_component/fan/legacy_fan.h
+++ b/tests/integration/fixtures/external_components/legacy_fan_component/fan/legacy_fan.h
@@ -17,8 +17,6 @@ class LegacyFan : public fan::Fan, public Component {
     this->publish_state();
   }
 
-  float get_setup_priority() const override { return setup_priority::LATE; }
-
   fan::FanTraits get_traits() override {
     auto traits = fan::FanTraits(false, true, false, 3);
 

From cfbba0af9033e3fde8316b5f0c58dd5da4052e3e Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 16:18:01 -1000
Subject: [PATCH 19/21] Add comment about string literal pointer stability in
 compat save_state_

---
 esphome/components/fan/fan.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/esphome/components/fan/fan.cpp b/esphome/components/fan/fan.cpp
index 563c0eff13..9301e0cea4 100644
--- a/esphome/components/fan/fan.cpp
+++ b/esphome/components/fan/fan.cpp
@@ -307,6 +307,8 @@ void Fan::save_state_() {
       }
     } else {
       // Compat: fall back to traits for deprecated path. Remove in 2026.11.0.
+      // Pointer comparison works because preset_mode_ and the compat vector both
+      // hold pointers to string literals in .rodata (stable addresses).
       auto traits = this->get_traits();
       const auto &preset_modes = traits.supported_preset_modes();
       for (size_t i = 0; i < preset_modes.size(); i++) {

From 05a5c27b90f34a01926d9d80c0209911f6cae478 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 16:21:30 -1000
Subject: [PATCH 20/21] Add 2026.11.0 removal comments to integration test and
 fixture

---
 .../external_components/legacy_fan_component/__init__.py     | 5 ++++-
 tests/integration/test_legacy_fan_compat.py                  | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/tests/integration/fixtures/external_components/legacy_fan_component/__init__.py b/tests/integration/fixtures/external_components/legacy_fan_component/__init__.py
index ceee477522..714be181fe 100644
--- a/tests/integration/fixtures/external_components/legacy_fan_component/__init__.py
+++ b/tests/integration/fixtures/external_components/legacy_fan_component/__init__.py
@@ -1 +1,4 @@
-"""Legacy fan component — tests deprecated FanTraits setters backward compat."""
+"""Legacy fan component — tests deprecated FanTraits setters backward compat.
+
+Remove this entire directory in 2026.11.0 when the deprecated setters are removed.
+"""
diff --git a/tests/integration/test_legacy_fan_compat.py b/tests/integration/test_legacy_fan_compat.py
index a4b025b628..5ee41772f3 100644
--- a/tests/integration/test_legacy_fan_compat.py
+++ b/tests/integration/test_legacy_fan_compat.py
@@ -1,7 +1,10 @@
 """Integration test for backward compatibility of deprecated FanTraits setters.
 
 Verifies that external components using the old traits.set_supported_preset_modes()
-API still work correctly during the deprecation period (removed in 2026.11.0).
+API still work correctly during the deprecation period.
+
+Remove this entire test file and the legacy_fan_component external component
+in 2026.11.0 when the deprecated FanTraits setters are removed.
 """
 
 from __future__ import annotations

From 29bc97cdb85458308d819957fb5dd3e7dfd42697 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Thu, 26 Mar 2026 17:45:20 -1000
Subject: [PATCH 21/21] Fix comments: remove PR-relative wording

---
 esphome/components/fan/fan_traits.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/esphome/components/fan/fan_traits.h b/esphome/components/fan/fan_traits.h
index 229dd5a0c5..a2b2633af1 100644
--- a/esphome/components/fan/fan_traits.h
+++ b/esphome/components/fan/fan_traits.h
@@ -40,7 +40,7 @@ class FanTraits {
   // Remove before 2026.11.0
   ESPDEPRECATED("Call set_supported_preset_modes() on the Fan entity instead. Removed in 2026.11.0", "2026.5.0")
   void set_supported_preset_modes(std::initializer_list<const char *> preset_modes) {
-    // Compat: store in owned vector. Copies copy the vector (same cost as before this PR).
+    // Compat: store in owned vector. Copies copy the vector (deprecated path still copies this vector).
     this->compat_preset_modes_ = preset_modes;
   }
   // Remove before 2026.11.0
@@ -90,7 +90,7 @@ class FanTraits {
   bool direction_{false};
   int speed_count_{};
   const std::vector<const char *> *preset_modes_{nullptr};
-  // Compat: owned storage for deprecated setters. Copies copy the vector (same cost as pre-PR).
+  // Compat: owned storage for deprecated setters. Copies copy the vector (copies include this vector).
   // Remove in 2026.11.0.
   std::vector<const char *> compat_preset_modes_;
 };