diff --git a/Firmware/Compiled/DC29.uf2 b/Firmware/Compiled/DC29.uf2
new file mode 100644
index 0000000..ff2780f
Binary files /dev/null and b/Firmware/Compiled/DC29.uf2 differ
diff --git a/Firmware/Source/DC29/src/serialconsole.c b/Firmware/Source/DC29/src/serialconsole.c
index 429a785..7f5188a 100644
--- a/Firmware/Source/DC29/src/serialconsole.c
+++ b/Firmware/Source/DC29/src/serialconsole.c
@@ -465,236 +465,267 @@ void updateSerialConsole(void){
 					udi_cdc_putc(data);//echo input
 					if(data == 13){ //enter
 						int newKeymapCounter = 0;
+						uint8_t pending_modifier = 0;
 						for(int x=0; x<newKeystrokeCounter; x++){
 							if(newKeystroke[x] == '['){
 								x++;
-								if(newKeystroke[x] == 'c' && newKeystroke[x+1] == 't' && newKeystroke[x+2] == 'r' && newKeystroke[x+3] == 'l' && newKeystroke[x+4] == ']' && newKeystroke[x+5] != '['){
-									newKeymap[newKeymapCounter] = HID_MODIFIER_LEFT_CTRL;
-									newKeymapCounter ++;
+								if(newKeystroke[x] == 'c' && newKeystroke[x+1] == 't' && newKeystroke[x+2] == 'r' && newKeystroke[x+3] == 'l' && newKeystroke[x+4] == ']'){
+									pending_modifier |= HID_MODIFIER_LEFT_CTRL;
 									x += 4;
-								} else if(newKeystroke[x] == 'a' && newKeystroke[x+1] == 'l' && newKeystroke[x+2] == 't' && newKeystroke[x+3] == ']' && newKeystroke[x+4] != '['){
-									newKeymap[newKeymapCounter] = HID_MODIFIER_LEFT_ALT;
-									newKeymapCounter ++;
+								} else if(newKeystroke[x] == 'a' && newKeystroke[x+1] == 'l' && newKeystroke[x+2] == 't' && newKeystroke[x+3] == ']'){
+									pending_modifier |= HID_MODIFIER_LEFT_ALT;
 									x += 3;
-								} else if(newKeystroke[x] == 's' && newKeystroke[x+1] == 'h' && newKeystroke[x+2] == 'i' && newKeystroke[x+3] == 'f' && newKeystroke[x+4] == 't' && newKeystroke[x+5] == ']' && newKeystroke[x+6] != '['){
-									newKeymap[newKeymapCounter] = HID_MODIFIER_LEFT_SHIFT;
-									newKeymapCounter ++;
+								} else if(newKeystroke[x] == 's' && newKeystroke[x+1] == 'h' && newKeystroke[x+2] == 'i' && newKeystroke[x+3] == 'f' && newKeystroke[x+4] == 't' && newKeystroke[x+5] == ']'){
+									pending_modifier |= HID_MODIFIER_LEFT_SHIFT;
 									x += 5;
-								} else if(newKeystroke[x] == 'g' && newKeystroke[x+1] == 'u' && newKeystroke[x+2] == 'i' && newKeystroke[x+3] == ']' && newKeystroke[x+4] != '['){
-									newKeymap[newKeymapCounter] = HID_MODIFIER_LEFT_UI;
-									newKeymapCounter ++;
+								} else if(newKeystroke[x] == 'g' && newKeystroke[x+1] == 'u' && newKeystroke[x+2] == 'i' && newKeystroke[x+3] == ']'){
+									pending_modifier |= HID_MODIFIER_LEFT_UI;
 									x += 3;
-								} else if(newKeystroke[x] == 'p' && newKeystroke[x+1] == 'l' && newKeystroke[x+2] == 'a' && newKeystroke[x+3] == 'y' && newKeystroke[x+4] == ']' && newKeystroke[x+5] != '['){
+								} else if(newKeystroke[x] == 'p' && newKeystroke[x+1] == 'l' && newKeystroke[x+2] == 'a' && newKeystroke[x+3] == 'y' && newKeystroke[x+4] == ']'){
 									newKeymap[newKeymapCounter] = 240;//media key identifier
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = HID_MEDIA_PLAY;
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 4;
-								} else if(newKeystroke[x] == 'n' && newKeystroke[x+1] == 'e' && newKeystroke[x+2] == 'x' && newKeystroke[x+3] == 't' && newKeystroke[x+4] == ']' && newKeystroke[x+5] != '['){
+								} else if(newKeystroke[x] == 'n' && newKeystroke[x+1] == 'e' && newKeystroke[x+2] == 'x' && newKeystroke[x+3] == 't' && newKeystroke[x+4] == ']'){
 									newKeymap[newKeymapCounter] = 240;//media key identifier
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = HID_MEDIA_NEXT;
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 4;
-								} else if(newKeystroke[x] == 'b' && newKeystroke[x+1] == 'a' && newKeystroke[x+2] == 'c' && newKeystroke[x+3] == 'k' && newKeystroke[x+4] == ']' && newKeystroke[x+5] != '['){
+								} else if(newKeystroke[x] == 'b' && newKeystroke[x+1] == 'a' && newKeystroke[x+2] == 'c' && newKeystroke[x+3] == 'k' && newKeystroke[x+4] == ']'){
 									newKeymap[newKeymapCounter] = 240;//media key identifier
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = HID_MEDIA_BACK;
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 4;
-								} else if(newKeystroke[x] == 's' && newKeystroke[x+1] == 't' && newKeystroke[x+2] == 'o' && newKeystroke[x+3] == 'p' && newKeystroke[x+4] == ']' && newKeystroke[x+5] != '['){
+								} else if(newKeystroke[x] == 's' && newKeystroke[x+1] == 't' && newKeystroke[x+2] == 'o' && newKeystroke[x+3] == 'p' && newKeystroke[x+4] == ']'){
 									newKeymap[newKeymapCounter] = 240;//media key identifier
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = HID_MEDIA_STOP;
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 4;
-								} else if(newKeystroke[x] == 'e' && newKeystroke[x+1] == 'j' && newKeystroke[x+2] == 'e' && newKeystroke[x+3] == 'c' && newKeystroke[x+4] == 't' && newKeystroke[x+5] != ']' && newKeystroke[x+6] != '['){
+								} else if(newKeystroke[x] == 'e' && newKeystroke[x+1] == 'j' && newKeystroke[x+2] == 'e' && newKeystroke[x+3] == 'c' && newKeystroke[x+4] == 't' && newKeystroke[x+5] == ']'){
 									newKeymap[newKeymapCounter] = 240;//media key identifier
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = HID_MEDIA_EJECT;
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 5;
-								} else if(newKeystroke[x] == 'm' && newKeystroke[x+1] == 'u' && newKeystroke[x+2] == 't' && newKeystroke[x+3] == 'e' && newKeystroke[x+4] == ']' && newKeystroke[x+5] != '['){
+								} else if(newKeystroke[x] == 'm' && newKeystroke[x+1] == 'u' && newKeystroke[x+2] == 't' && newKeystroke[x+3] == 'e' && newKeystroke[x+4] == ']'){
 									newKeymap[newKeymapCounter] = 240;//media key identifier
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = HID_MEDIA_MUTE;
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 4;
-								} else if(newKeystroke[x] == 'v' && newKeystroke[x+1] == 'o' && newKeystroke[x+2] == 'l' && newKeystroke[x+3] == '+' && newKeystroke[x+4] == ']' && newKeystroke[x+5] != '['){
+								} else if(newKeystroke[x] == 'v' && newKeystroke[x+1] == 'o' && newKeystroke[x+2] == 'l' && newKeystroke[x+3] == '+' && newKeystroke[x+4] == ']'){
 									newKeymap[newKeymapCounter] = 240;//media key identifier
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = HID_MEDIA_VOL_PLUS;
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 4;
-								} else if(newKeystroke[x] == 'v' && newKeystroke[x+1] == 'o' && newKeystroke[x+2] == 'l' && newKeystroke[x+3] == '-' && newKeystroke[x+4] == ']' && newKeystroke[x+5] != '['){
+								} else if(newKeystroke[x] == 'v' && newKeystroke[x+1] == 'o' && newKeystroke[x+2] == 'l' && newKeystroke[x+3] == '-' && newKeystroke[x+4] == ']'){
 									newKeymap[newKeymapCounter] = 240;//media key identifier
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = HID_MEDIA_VOL_MINUS;
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 4;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '1' && newKeystroke[x+2] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 58;//F1
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 2;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '2' && newKeystroke[x+2] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 59;//F2
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 2;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '3' && newKeystroke[x+2] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 60;//F3
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 2;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '4' && newKeystroke[x+2] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 61;//F4
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 2;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '5' && newKeystroke[x+2] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 62;//F5
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 2;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '6' && newKeystroke[x+2] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 63;//F6
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 2;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '7' && newKeystroke[x+2] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 64;//F7
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 2;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '8' && newKeystroke[x+2] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 65;//F8
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 2;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '9' && newKeystroke[x+2] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 66;//F9
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 2;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '1' && newKeystroke[x+2] == '0' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 67;//F10
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '1' && newKeystroke[x+2] == '1' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 68;//F11
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '1' && newKeystroke[x+2] == '2' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 69;//F12
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '1' && newKeystroke[x+2] == '3' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 104;//F13
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '1' && newKeystroke[x+2] == '4' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 105;//F14
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '1' && newKeystroke[x+2] == '5' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 106;//F15
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '1' && newKeystroke[x+2] == '6' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 107;//F16
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '1' && newKeystroke[x+2] == '7' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 108;//F17
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '1' && newKeystroke[x+2] == '8' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 109;//F18
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '1' && newKeystroke[x+2] == '9' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 110;//F19
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '2' && newKeystroke[x+2] == '0' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 111;//F20
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '2' && newKeystroke[x+2] == '1' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 112;//F21
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '2' && newKeystroke[x+2] == '2' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 113;//F22
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '2' && newKeystroke[x+2] == '3' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 114;//F23
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'F' && newKeystroke[x+1] == '2' && newKeystroke[x+2] == '4' && newKeystroke[x+3] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 115;//F24
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 3;
 								} else if(newKeystroke[x] == 'n' && newKeystroke[x+1] == 'o' && newKeystroke[x+2] == 'n' && newKeystroke[x+3] == 'e' && newKeystroke[x+4] == ']'){
-									newKeymap[newKeymapCounter] = 0; //No modifiers
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter ++;
 									newKeymap[newKeymapCounter] = 0; //No key
 									newKeymapCounter ++;
+									pending_modifier = 0;
 									x += 4;
 								}
 							} else {
 								if(ascii_to_hid[newKeystroke[x]] > 127){
-									newKeymap[newKeymapCounter] = HID_MODIFIER_LEFT_SHIFT;
+									newKeymap[newKeymapCounter] = HID_MODIFIER_LEFT_SHIFT | pending_modifier;
 									newKeymapCounter++;
 									newKeymap[newKeymapCounter] = ascii_to_hid[newKeystroke[x]]-128;
 									newKeymapCounter++;
 								} else {
-									newKeymap[newKeymapCounter] = 0;
+									newKeymap[newKeymapCounter] = pending_modifier;
 									newKeymapCounter++;
 									newKeymap[newKeymapCounter] = ascii_to_hid[newKeystroke[x]];
 									newKeymapCounter++;
 								}
+								pending_modifier = 0;
 							}
 						}
 							if(newKeymapCounter + keymaplength < 231){
diff --git a/VALIDATION_NOTES.md b/VALIDATION_NOTES.md
new file mode 100644
index 0000000..b60ac85
--- /dev/null
+++ b/VALIDATION_NOTES.md
@@ -0,0 +1,69 @@
+# Validation Notes — Issue #5 Modifier Key Fix
+
+End-to-end verification of the modifier key parser fix on real DEF CON 29 badge
+hardware (SAMD21G16B). This document captures what was tested, the build
+configuration that produced working firmware, and gotchas encountered during
+the test cycle.
+
+## What Was Verified
+
+Built the fix on Windows with Microchip Studio 7.0, flashed via UF2, and
+exercised the keymap parser through the badge's serial console:
+
+| Macro Set Via Serial | Parser Result | What It Sends | Hardware Behavior |
+|---|---|---|---|
+| `[ctrl]p` (single modifier) | Accepted, returned to main menu | Ctrl+P | (set successfully; per-button physical test pending) |
+| `[ctrl][shift]p` (multi-modifier — the bug case) | Accepted, returned to main menu | Ctrl+Shift+P | (set successfully) |
+| `[gui][shift]s` (multi-modifier with system-visible effect) | Accepted | Win+Shift+S | Snipping Tool overlay appears on host |
+
+The acceptance of multi-modifier macros without falling through to "Invalid
+Input" is the parser-level confirmation. Pre-fix, multi-modifier strings
+silently produced wrong modifier bytes (e.g., `[ctrl]p` → LEFT_CTRL +
+LEFT_SHIFT + RIGHT_CTRL).
+
+## Build Configuration That Produced Working Firmware
+
+The previous `Firmware/Compiled/DC29.uf2` committed in this branch was built
+with the wrong linker script (ORIGIN=0x0) and was rejected by the badge's UF2
+bootloader, which expects the application at 0x2000. The replacement `.uf2`
+in this commit was built with:
+
+- **Device defines**: `__SAMD21G16B__` only (do **not** add `__SAMD21J18A__` —
+  with both defined, `samd21.h`'s `#elif` chain selects `samd21j18a.h`, which
+  doesn't define `NVMCTRL_RWW_EEPROM_SIZE` and breaks `nvm.c`).
+- **Linker script**: `src/samd21g16b_flash.ld` (this is the in-tree custom
+  script with `ORIGIN = 0x00000000+0x2000`, not the ASF default at
+  `src/ASF/sam0/utils/linker_scripts/samd21/gcc/samd21j18a_flash.ld` which
+  has ORIGIN=0x0).
+- **Configuration**: Release (Debug doesn't fit in 56KB).
+- **Toolchain**: arm-none-eabi-gcc 6.3.1 from Microchip Studio.
+
+The Microchip Studio `.cproj` was edited so that **both** the Release
+preprocessor symbols and Release linker flags reflect the above. Note that the
+cproj contains two `<armgcc.linker.miscellaneous.LinkerFlags>` entries inside
+the Release `<PropertyGroup>`; both must point at `samd21g16b_flash.ld`. UF2
+conversion was done from `DC29.hex` using a custom PowerShell port of
+`uf2conv.py` (Python isn't required on the build machine).
+
+## Validation Gotcha — Button-During-Reboot Trap
+
+When flashing, holding the bottom-right button across the bootloader's reboot
+keeps the badge in DFU mode after the new firmware is written. From the host
+this looks identical to a firmware crash: drive stays mounted, top-left LED
+keeps pulsing, no COM port enumerates. We spent significant time chasing
+imaginary firmware crashes (comparing vector tables, checking memory layout,
+inspecting startup code) before unplug-and-replug **without holding any
+button** booted the firmware cleanly.
+
+**Recommended flash workflow:**
+1. Hold bottom-right button.
+2. Plug in USB.
+3. **Release the button as soon as the bootloader drive (D:, E:, etc.) appears.**
+4. Drag/copy the `.uf2` onto the drive.
+5. When the drive disappears, badge has rebooted into the new firmware. Verify
+   a CDC serial port appears (e.g., `COM3` on Windows, `/dev/ttyACM*` on
+   Linux/Mac).
+
+If the firmware appears not to boot after a flash, **before** debugging the
+build, unplug and replug without touching any button. The firmware is almost
+certainly fine.