diff --git a/PROVESFlightControllerReference/Components/StartupManager/StartupManager.cpp b/PROVESFlightControllerReference/Components/StartupManager/StartupManager.cpp
index 22609ff2..128f92bd 100644
--- a/PROVESFlightControllerReference/Components/StartupManager/StartupManager.cpp
+++ b/PROVESFlightControllerReference/Components/StartupManager/StartupManager.cpp
@@ -7,6 +7,7 @@
 #include "PROVESFlightControllerReference/Components/StartupManager/StartupManager.hpp"
 
 #include "Os/File.hpp"
+#include "Os/FileSystem.hpp"
 #include "PROVESFlightControllerReference/Components/StartupManager/HardCodedStartup.h"
 #include <zephyr/drivers/rtc.h>
 
@@ -94,7 +95,10 @@ StartupManager::Status write(const Fw::StringBase& file_path, const T& value) {
     if (status == Os::File::OP_OK) {
         FwSizeType size = sizeof(data_buffer);
         status = file.write(data_buffer, size);
-        if (status == Os::File::OP_OK && size == sizeof(data_buffer)) {
+        // Flush before close so the data has reached storage before callers (e.g. the atomic
+        // rename in persist_boot_count) treat the write as durable. close() returns void and
+        // cannot report a flush failure.
+        if (status == Os::File::OP_OK && size == sizeof(data_buffer) && file.flush() == Os::File::OP_OK) {
             return_status = StartupManager::SUCCESS;
         }
     }
@@ -102,6 +106,11 @@ StartupManager::Status write(const Fw::StringBase& file_path, const T& value) {
     return return_status;
 }
 
+// Boot counts beyond this are treated as file corruption rather than real history: a hard reset
+// (e.g. the watchdog power cycle used for command-loss recovery) can tear the flash write and leave
+// a well-formed file full of junk, which would otherwise be incremented and persisted forever.
+static constexpr FwSizeType MAX_PLAUSIBLE_BOOT_COUNT = 1000000;
+
 FwSizeType StartupManager ::get_boot_count(bool increment) {
     // Read the boot count file path from parameter and assert that it is either valid or the default value
     FwSizeType boot_count = 0;
@@ -109,20 +118,45 @@ FwSizeType StartupManager ::get_boot_count(bool increment) {
     auto boot_count_file = this->paramGet_BOOT_COUNT_FILE(is_valid);
     FW_ASSERT(is_valid == Fw::ParamValid::VALID || is_valid == Fw::ParamValid::DEFAULT);
 
-    // Open the boot count file and add one to the current boot count ensuring a minimum of 1 in the case
-    // of read failure. Since read will retain the `0` initial value on read failure, we can ignore the error
-    // status returned by the read.
+    // Read the current count ensuring a minimum of 1 after increment in the case of read failure.
+    // Since read will retain the `0` initial value on read failure, we can ignore the error status.
     (void)read<FwSizeType, sizeof(FwSizeType)>(boot_count_file, boot_count);
+    if (boot_count > MAX_PLAUSIBLE_BOOT_COUNT) {
+        this->log_WARNING_HI_BootCountCorrupted(static_cast<I64>(boot_count));
+        boot_count = 0;
+    }
     boot_count = FW_MAX(1, increment ? boot_count + 1 : boot_count);
-    // Rewrite the updated boot count back to the file, and on failure emit a warning about the inability to
-    // persist the boot count.
-    StartupManager::Status status = write<FwSizeType, sizeof(FwSizeType)>(boot_count_file, boot_count);
-    if (status != StartupManager::SUCCESS) {
-        this->log_WARNING_LO_BootCountUpdateFailure();
+
+    // Only the once-per-boot increment writes the file; plain reads (GET_BOOT_COUNT) must not.
+    // Every write is a window for a reset to tear the file, and the count is queried far more
+    // often than it changes. On failure, run_handler retries on subsequent ticks.
+    if (increment) {
+        StartupManager::Status status = this->persist_boot_count(boot_count_file, boot_count);
+        this->m_boot_count_persisted = (status == StartupManager::SUCCESS);
+        if (!this->m_boot_count_persisted && !this->m_boot_count_write_logged) {
+            this->log_WARNING_LO_BootCountUpdateFailure();
+            this->m_boot_count_write_logged = true;
+        }
     }
     return boot_count;
 }
 
+StartupManager::Status StartupManager ::persist_boot_count(const Fw::StringBase& file_path, FwSizeType value) {
+    // Write to a temp file, then rename over the target. The flight FS is FAT (ELM FatFs), whose
+    // rename is not guaranteed power-cut atomic - but the new data is fully written and flushed
+    // before it replaces the old file, so a reset can no longer tear the value mid-write (the
+    // observed failure). Worst case during the rename window is a missing file, which reads as a
+    // failed read and re-initializes the count - detectable, unlike silent garbage.
+    Fw::String temp_path(file_path);
+    temp_path += ".tmp";
+    StartupManager::Status status = write<FwSizeType, sizeof(FwSizeType)>(temp_path, value);
+    if (status == StartupManager::SUCCESS &&
+        Os::FileSystem::rename(temp_path.toChar(), file_path.toChar()) != Os::FileSystem::OP_OK) {
+        status = StartupManager::FAILURE;
+    }
+    return status;
+}
+
 Fw::Time StartupManager ::update_quiescence_start() {
     Fw::ParamValid is_valid;
     auto time_file = this->paramGet_QUIESCENCE_START_FILE(is_valid);
@@ -260,6 +294,16 @@ void StartupManager ::run_handler(FwIndexType portNum, U32 context) {
         this->runSequence_out(0, first_sequence);
         this->m_transmit_enable_ticks = this->paramGet_TRANSMIT_ENABLE_TICKS(is_valid);
         FW_ASSERT(is_valid == Fw::ParamValid::VALID || is_valid == Fw::ParamValid::DEFAULT);
+    } else if (!this->m_boot_count_persisted) {
+        // The first-tick write can fail transiently (e.g. filesystem not ready yet). Re-attempt each
+        // tick until the count is durably stored, so the increment is delayed rather than lost.
+        auto boot_count_file = this->paramGet_BOOT_COUNT_FILE(is_valid);
+        FW_ASSERT(is_valid == Fw::ParamValid::VALID || is_valid == Fw::ParamValid::DEFAULT);
+        this->m_boot_count_persisted =
+            (this->persist_boot_count(boot_count_file, this->m_boot_count) == StartupManager::SUCCESS);
+        if (this->m_boot_count_persisted) {
+            this->m_boot_count_write_logged = false;
+        }
     }
 
 #if DEFAULT_STARTUP_VALUE == 1
diff --git a/PROVESFlightControllerReference/Components/StartupManager/StartupManager.fpp b/PROVESFlightControllerReference/Components/StartupManager/StartupManager.fpp
index ccb96a99..2d746732 100644
--- a/PROVESFlightControllerReference/Components/StartupManager/StartupManager.fpp
+++ b/PROVESFlightControllerReference/Components/StartupManager/StartupManager.fpp
@@ -54,6 +54,10 @@ module Components {
         event BootCountUpdateFailure() severity warning low \
             format "Failed to update boot count file"
 
+        @ Event emitted when the boot count file holds an implausible value (torn or corrupt write)
+        event BootCountCorrupted(raw: I64) severity warning high \
+            format "Boot count file corrupt (raw value {}) - treating as unreadable"
+
         @ Event emitted when the quiescence file was not updated
         event QuiescenceFileInitFailure() severity warning low \
             format "Failed to initialize quiescence start time file"
diff --git a/PROVESFlightControllerReference/Components/StartupManager/StartupManager.hpp b/PROVESFlightControllerReference/Components/StartupManager/StartupManager.hpp
index 25b56e6b..e0185cbc 100644
--- a/PROVESFlightControllerReference/Components/StartupManager/StartupManager.hpp
+++ b/PROVESFlightControllerReference/Components/StartupManager/StartupManager.hpp
@@ -30,16 +30,27 @@ class StartupManager final : public StartupManagerComponentBase {
     //! Destroy StartupManager object
     ~StartupManager();
 
-    //! \brief read and increment the boot count
+    //! \brief read and optionally increment the boot count
     //!
-    //! Reads the boot count from the boot count file, increments it, and writes it back to the file. If the read
-    //! fails, the boot count will be initialized to 1. If the write fails, a warning will be emitted.
+    //! Reads the boot count from the boot count file. If the read fails or the stored value is implausible
+    //! (torn/corrupt write), the count is treated as unread and initializes to 1 on increment. Only the
+    //! increment path writes the file; plain reads leave it untouched. If the write fails, a warning is
+    //! emitted and the write is retried on subsequent run ticks.
     //!
-    //! \warning this function will modify the boot count file on disk.
+    //! \warning this function will modify the boot count file on disk when increment is true.
     //!
     //! \return The updated boot count
     FwSizeType get_boot_count(bool increment);
 
+    //! \brief durably persist the boot count via write-to-temp + rename
+    //!
+    //! The new value is fully written and flushed before it replaces the old file, so a reset
+    //! cannot tear the value mid-write. FAT's rename is not power-cut atomic; the residual worst
+    //! case is a missing file, which reads as a failed read rather than silent garbage.
+    //!
+    //! \return Status of the persist operation
+    Status persist_boot_count(const Fw::StringBase& file_path, FwSizeType value);
+
     //! \brief get and possibly initialize the quiescence start time
     //!
     //! Reads the quiescence start time from the quiescence start time file. If the read fails, the current time is
@@ -141,7 +152,9 @@ class StartupManager final : public StartupManagerComponentBase {
   private:
     Fw::Time m_quiescence_start;              //!< Time of the start of the quiescence wait
     FwOpcodeType m_stored_opcode;             //!< Stored opcode for delayed response
-    FwSizeType m_boot_count;                  //!< Current boot count
+    FwSizeType m_boot_count = 0;              //!< Current boot count (0 = first run tick not yet processed)
+    bool m_boot_count_persisted = false;      //!< Whether the incremented boot count has reached the file
+    bool m_boot_count_write_logged = false;   //!< Warning already emitted for the current persist-failure streak
     U32 m_stored_sequence;                    //!< Stored sequence number for delayed response
     std::atomic<bool> m_waiting;              //!< Indicates if waiting for quiescence
     Fw::String m_sequence_file;               //!< The filepath for the sequence last initiated
diff --git a/PROVESFlightControllerReference/Components/StartupManager/docs/sdd.md b/PROVESFlightControllerReference/Components/StartupManager/docs/sdd.md
index 3ef0dce3..fa87289a 100644
--- a/PROVESFlightControllerReference/Components/StartupManager/docs/sdd.md
+++ b/PROVESFlightControllerReference/Components/StartupManager/docs/sdd.md
@@ -8,7 +8,7 @@ The StartupManager component manages boot counting, quiescence waiting periods,
 
 The StartupManager serves four primary functions:
 
-1. Boot Counting: Tracks the number of system boots persistently across power cycles
+1. Boot Counting: Tracks the number of system boots persistently across power cycles, hardened against file corruption from hard resets (see [Boot count persistence](#boot-count-persistence))
 2. Quiescence Wait: Implements a configurable waiting period (default 45 minutes) before allowing full system startup, useful for missions requiring initial stabilization
 3. Startup Sequence: Automatically dispatches and monitors the execution of startup command sequences
 4. Hard-coded Radio Enable: When enabled at compile time (`DEFAULT_STARTUP_VALUE == 1` in `HardCodedStartup.h`), after `TRANSMIT_ENABLE_TICKS` 1 Hz run ticks, asserts `enableTransmit` to enable LoRa transmission independently of the startup sequence file. When disabled (`DEFAULT_STARTUP_VALUE == 0`), the countdown does not run and transmit is not asserted automatically — preferred for ground testing so the radio does not turn on accidentally.
@@ -48,6 +48,15 @@ On each 1 Hz `run`, when `DEFAULT_STARTUP_VALUE == 1` and `m_transmit_enable_tic
 
 `HardCodedStartup.h` defines `DEFAULT_STARTUP_VALUE`:
 
+### Boot count persistence
+
+The boot count lives in `BOOT_COUNT_FILE` on the flight filesystem (FAT — ELM FatFs, see `prj.conf`) and is incremented lazily on the first 1 Hz `run` tick of each boot. Hard resets (e.g. the watchdog power cycle used for command-loss recovery) can land while a write is in flight, so the persistence path is hardened in four ways:
+
+1. **Corruption guard**: a read that returns a value above 1,000,000 is treated as a failed read (the file contained torn/junk data) and reported via `BootCountCorrupted` with the raw value. The count then re-initializes on the next increment instead of propagating garbage. Observed on HWIL: a torn write left the file reading `0x02FE191005000001`, and the next boot persisted exactly garbage+1.
+2. **Read-only queries**: `GET_BOOT_COUNT` never writes the file. Only the once-per-boot increment does, minimizing the window in which a reset can tear a write.
+3. **Increment retry**: if the first-tick persist fails (e.g. filesystem not ready), `run` re-attempts it each tick until it succeeds — the increment is delayed, not lost. `BootCountUpdateFailure` is emitted once per failure streak.
+4. **Write-then-rename persist**: the value is written to `<BOOT_COUNT_FILE>.tmp`, flushed, and renamed over the target. FAT's rename is not guaranteed power-cut atomic, but the new data is fully on storage before it replaces the old file, closing the torn-in-place-write window that produced the observed garbage. The residual worst case during the rename window is a missing file, which reads as a failed read (count re-initializes, visibly) rather than silent corruption.
+
 
 ## Port Descriptions
 
@@ -65,6 +74,8 @@ On each 1 Hz `run`, when `DEFAULT_STARTUP_VALUE == 1` and `m_transmit_enable_tic
 | State Variable | Type | Description |
 |----------------|------|-------------|
 | `m_boot_count` | `FwSizeType` | Current boot count. Zero indicates uninitialized state |
+| `m_boot_count_persisted` | `bool` | Whether the incremented boot count has durably reached the file; drives the per-tick retry |
+| `m_boot_count_write_logged` | `bool` | `BootCountUpdateFailure` already emitted for the current persist-failure streak |
 | `m_quiescence_start` | `Fw::Time` | Time when quiescence period started (mission epoch) |
 | `m_waiting` | `std::atomic<bool>` | True when waiting for quiescence period to elapse |
 | `m_stored_opcode` | `FwOpcodeType` | Opcode of pending `WAIT_FOR_QUIESCENCE` command |
@@ -95,7 +106,8 @@ On each 1 Hz `run`, when `DEFAULT_STARTUP_VALUE == 1` and `m_transmit_enable_tic
 | Name | Severity | Arguments | Description |
 |------|----------|-----------|-------------|
 | `CurrentBootCount` | ACTIVITY_LO | `i: I64` | Emitted by `GET_BOOT_COUNT` with the current boot count |
-| `BootCountUpdateFailure` | WARNING_LO | None | Emitted when the boot count file cannot be updated. Boot count was incremented in memory but not persisted |
+| `BootCountUpdateFailure` | WARNING_LO | None | Emitted once per failure streak when the boot count file cannot be updated. The increment is retried on each subsequent `run` tick until it persists |
+| `BootCountCorrupted` | WARNING_HI | `raw: I64` | Emitted when the boot count file holds an implausible value (> 1,000,000), indicating a torn or corrupt write. The value is treated as unreadable |
 | `QuiescenceFileInitFailure` | WARNING_LO | None | Emitted when the quiescence start time file cannot be initialized. System will use current time but cannot persist it |
 | `StartupSequenceFinished` | ACTIVITY_LO | None | Emitted when the startup sequence completes successfully |
 | `StartupSequenceFailed` | WARNING_LO | `response: Fw.CmdResponse` | Emitted when the startup sequence fails, includes the failure response code |
@@ -121,3 +133,5 @@ On each 1 Hz `run`, when `DEFAULT_STARTUP_VALUE == 1` and `m_transmit_enable_tic
 | REQ-SM-007 | StartupManager shall handle file I/O errors gracefully | Verification: Remove file permissions and verify warning events are emitted |
 | REQ-SM-008 | When `DEFAULT_STARTUP_VALUE == 1`, StartupManager shall enable LoRa transmit after `TRANSMIT_ENABLE_TICKS` 1 Hz ticks | Verification: Confirm `HardcodedRadioEnable` and RF transmit after the configured delay |
 | REQ-SM-009 | When `DEFAULT_STARTUP_VALUE == 0`, StartupManager shall not assert `enableTransmit` from the hard-coded countdown | Verification: Build with gate disabled and confirm no `HardcodedRadioEnable` / automatic TX after boot |
+| REQ-SM-010 | StartupManager shall not propagate an implausible boot count read from a corrupt file | Verification: Write junk to `BOOT_COUNT_FILE`, reboot, confirm `BootCountCorrupted` and a re-initialized count |
+| REQ-SM-011 | StartupManager shall persist the boot count atomically and retry a failed increment until it is durably stored | Verification: HWIL `test_safe_09` asserts boot count == initial+1 across a watchdog hard reset |
diff --git a/docs-site/components/StartupManager.md b/docs-site/components/StartupManager.md
index 3ef0dce3..fa87289a 100644
--- a/docs-site/components/StartupManager.md
+++ b/docs-site/components/StartupManager.md
@@ -8,7 +8,7 @@ The StartupManager component manages boot counting, quiescence waiting periods,
 
 The StartupManager serves four primary functions:
 
-1. Boot Counting: Tracks the number of system boots persistently across power cycles
+1. Boot Counting: Tracks the number of system boots persistently across power cycles, hardened against file corruption from hard resets (see [Boot count persistence](#boot-count-persistence))
 2. Quiescence Wait: Implements a configurable waiting period (default 45 minutes) before allowing full system startup, useful for missions requiring initial stabilization
 3. Startup Sequence: Automatically dispatches and monitors the execution of startup command sequences
 4. Hard-coded Radio Enable: When enabled at compile time (`DEFAULT_STARTUP_VALUE == 1` in `HardCodedStartup.h`), after `TRANSMIT_ENABLE_TICKS` 1 Hz run ticks, asserts `enableTransmit` to enable LoRa transmission independently of the startup sequence file. When disabled (`DEFAULT_STARTUP_VALUE == 0`), the countdown does not run and transmit is not asserted automatically — preferred for ground testing so the radio does not turn on accidentally.
@@ -48,6 +48,15 @@ On each 1 Hz `run`, when `DEFAULT_STARTUP_VALUE == 1` and `m_transmit_enable_tic
 
 `HardCodedStartup.h` defines `DEFAULT_STARTUP_VALUE`:
 
+### Boot count persistence
+
+The boot count lives in `BOOT_COUNT_FILE` on the flight filesystem (FAT — ELM FatFs, see `prj.conf`) and is incremented lazily on the first 1 Hz `run` tick of each boot. Hard resets (e.g. the watchdog power cycle used for command-loss recovery) can land while a write is in flight, so the persistence path is hardened in four ways:
+
+1. **Corruption guard**: a read that returns a value above 1,000,000 is treated as a failed read (the file contained torn/junk data) and reported via `BootCountCorrupted` with the raw value. The count then re-initializes on the next increment instead of propagating garbage. Observed on HWIL: a torn write left the file reading `0x02FE191005000001`, and the next boot persisted exactly garbage+1.
+2. **Read-only queries**: `GET_BOOT_COUNT` never writes the file. Only the once-per-boot increment does, minimizing the window in which a reset can tear a write.
+3. **Increment retry**: if the first-tick persist fails (e.g. filesystem not ready), `run` re-attempts it each tick until it succeeds — the increment is delayed, not lost. `BootCountUpdateFailure` is emitted once per failure streak.
+4. **Write-then-rename persist**: the value is written to `<BOOT_COUNT_FILE>.tmp`, flushed, and renamed over the target. FAT's rename is not guaranteed power-cut atomic, but the new data is fully on storage before it replaces the old file, closing the torn-in-place-write window that produced the observed garbage. The residual worst case during the rename window is a missing file, which reads as a failed read (count re-initializes, visibly) rather than silent corruption.
+
 
 ## Port Descriptions
 
@@ -65,6 +74,8 @@ On each 1 Hz `run`, when `DEFAULT_STARTUP_VALUE == 1` and `m_transmit_enable_tic
 | State Variable | Type | Description |
 |----------------|------|-------------|
 | `m_boot_count` | `FwSizeType` | Current boot count. Zero indicates uninitialized state |
+| `m_boot_count_persisted` | `bool` | Whether the incremented boot count has durably reached the file; drives the per-tick retry |
+| `m_boot_count_write_logged` | `bool` | `BootCountUpdateFailure` already emitted for the current persist-failure streak |
 | `m_quiescence_start` | `Fw::Time` | Time when quiescence period started (mission epoch) |
 | `m_waiting` | `std::atomic<bool>` | True when waiting for quiescence period to elapse |
 | `m_stored_opcode` | `FwOpcodeType` | Opcode of pending `WAIT_FOR_QUIESCENCE` command |
@@ -95,7 +106,8 @@ On each 1 Hz `run`, when `DEFAULT_STARTUP_VALUE == 1` and `m_transmit_enable_tic
 | Name | Severity | Arguments | Description |
 |------|----------|-----------|-------------|
 | `CurrentBootCount` | ACTIVITY_LO | `i: I64` | Emitted by `GET_BOOT_COUNT` with the current boot count |
-| `BootCountUpdateFailure` | WARNING_LO | None | Emitted when the boot count file cannot be updated. Boot count was incremented in memory but not persisted |
+| `BootCountUpdateFailure` | WARNING_LO | None | Emitted once per failure streak when the boot count file cannot be updated. The increment is retried on each subsequent `run` tick until it persists |
+| `BootCountCorrupted` | WARNING_HI | `raw: I64` | Emitted when the boot count file holds an implausible value (> 1,000,000), indicating a torn or corrupt write. The value is treated as unreadable |
 | `QuiescenceFileInitFailure` | WARNING_LO | None | Emitted when the quiescence start time file cannot be initialized. System will use current time but cannot persist it |
 | `StartupSequenceFinished` | ACTIVITY_LO | None | Emitted when the startup sequence completes successfully |
 | `StartupSequenceFailed` | WARNING_LO | `response: Fw.CmdResponse` | Emitted when the startup sequence fails, includes the failure response code |
@@ -121,3 +133,5 @@ On each 1 Hz `run`, when `DEFAULT_STARTUP_VALUE == 1` and `m_transmit_enable_tic
 | REQ-SM-007 | StartupManager shall handle file I/O errors gracefully | Verification: Remove file permissions and verify warning events are emitted |
 | REQ-SM-008 | When `DEFAULT_STARTUP_VALUE == 1`, StartupManager shall enable LoRa transmit after `TRANSMIT_ENABLE_TICKS` 1 Hz ticks | Verification: Confirm `HardcodedRadioEnable` and RF transmit after the configured delay |
 | REQ-SM-009 | When `DEFAULT_STARTUP_VALUE == 0`, StartupManager shall not assert `enableTransmit` from the hard-coded countdown | Verification: Build with gate disabled and confirm no `HardcodedRadioEnable` / automatic TX after boot |
+| REQ-SM-010 | StartupManager shall not propagate an implausible boot count read from a corrupt file | Verification: Write junk to `BOOT_COUNT_FILE`, reboot, confirm `BootCountCorrupted` and a re-initialized count |
+| REQ-SM-011 | StartupManager shall persist the boot count atomically and retry a failed increment until it is durably stored | Verification: HWIL `test_safe_09` asserts boot count == initial+1 across a watchdog hard reset |