diff --git a/claude-plugins/plugins/base/skills/headless-screenshot/SKILL.md b/claude-plugins/plugins/base/skills/headless-screenshot/SKILL.md
index 1f22650e..cfe15be1 100644
--- a/claude-plugins/plugins/base/skills/headless-screenshot/SKILL.md
+++ b/claude-plugins/plugins/base/skills/headless-screenshot/SKILL.md
@@ -69,3 +69,36 @@ question is genuinely about *behavior*, not appearance. A missing
 emoji/glyph rendering as a box in the screenshot is usually a font
 availability artifact of the headless environment, not a real bug -
 don't mistake one for the other when reporting results.
+
+## Two false-positive traps (and their fixes)
+
+Both of these look exactly like a real product bug in a naive
+screenshot and aren't - check for them before filing anything, and
+use the fix below if you actually need an accurate render (e.g. to
+judge icon/glyph layout, not just to note "there'd be an icon here").
+
+- **Tofu boxes instead of emoji.** Plain `nixpkgs#chromium` has no
+  color-emoji font, so any 🖥/📡/🔨-style glyph renders as an empty
+  box. Add `nixpkgs#noto-fonts-color-emoji` to the `nix shell` - but a
+  `FONTCONFIG_FILE` that lists *only* the emoji dir throws away the
+  base fonts and blanks all normal text instead, which is its own
+  false alarm. Merge, don't override:
+  ```
+  cat > fonts.conf <<EOF
+  <?xml version="1.0"?>
+  <!DOCTYPE fontconfig SYSTEM "fonts.dtd">
+  <fontconfig>
+    <include ignore_missing="yes">/etc/fonts/fonts.conf</include>
+    <dir>$(nix eval --raw nixpkgs#noto-fonts-color-emoji)/share/fonts</dir>
+  </fontconfig>
+  EOF
+  FONTCONFIG_FILE=$PWD/fonts.conf nix shell nixpkgs#chromium nixpkgs#noto-fonts-color-emoji \
+    --command chromium --headless=new --disable-gpu --no-sandbox \
+    --screenshot=out.png --window-size=1440,900 "https://example/"
+  ```
+- **A bare "loading..." placeholder instead of real content.** A page
+  whose content arrives after the initial paint (SSE, a `fetch` on
+  mount) can get captured before that data lands - the default
+  `--screenshot` doesn't wait for it. Add
+  `--virtual-time-budget=8000` (milliseconds; tune to the page) to let
+  it actually settle first.