diff --git a/.github/workflows/build-observer-firmwares-beta.yml b/.github/workflows/build-observer-firmwares-beta.yml
index ddb89647..3b27d4a0 100644
--- a/.github/workflows/build-observer-firmwares-beta.yml
+++ b/.github/workflows/build-observer-firmwares-beta.yml
@@ -38,6 +38,9 @@ on:
       - 'LICENSE'
       - '.vscode/**'
       - '.claude/**'
+      # Throwaway build worktrees never affect the binaries.
+      - '.build-wt-*'
+      - '.build-wt-*/**'
 
 # Own group: serialize beta builds against each other only. Concurrency groups are
 # repo-wide, not per-branch, so sharing one with the production workflows let an
diff --git a/.github/workflows/build-observer-firmwares.yml b/.github/workflows/build-observer-firmwares.yml
index 35514591..804139b7 100644
--- a/.github/workflows/build-observer-firmwares.yml
+++ b/.github/workflows/build-observer-firmwares.yml
@@ -25,6 +25,9 @@ on:
       - 'LICENSE'
       - '.vscode/**'
       - '.claude/**'
+      # Throwaway build worktrees never affect the binaries.
+      - '.build-wt-*'
+      - '.build-wt-*/**'
 
 # Own group: serialize builds against each other only. Do NOT share this group
 # with sync-flasher-content.yml — a mixed code+docs commit triggers both, and a
diff --git a/.gitignore b/.gitignore
index ae3815fb..d3d96b7e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -24,4 +24,7 @@ ssl_certs/cacert.pem
 platformio.local.ini
 .cursor/*
 .claude/*
-.cursorrules
\ No newline at end of file
+.cursorrules
+# Throwaway build worktrees; committing one adds a stray gitlink that makes every
+# CI checkout warn "No url found for submodule path ... in .gitmodules".
+.build-wt-*/