diff --git a/.github/workflows/zsh-n.yml b/.github/workflows/zsh-n.yml
index 34b59e7..934a28b 100644
--- a/.github/workflows/zsh-n.yml
+++ b/.github/workflows/zsh-n.yml
@@ -25,6 +25,7 @@ on:
       - "tests/fixtures/plugin-standard-callbacks/**"
       - "tests/self-update-reload.zsh"
       - "tests/snippet-directory-mirror.zsh"
+      - "tests/source-hygiene.zsh"
       - "tests/subst-nesting.zsh"
       - "tests/version-reporting.zsh"
   pull_request:
@@ -47,6 +48,7 @@ on:
       - "tests/fixtures/plugin-standard-callbacks/**"
       - "tests/self-update-reload.zsh"
       - "tests/snippet-directory-mirror.zsh"
+      - "tests/source-hygiene.zsh"
       - "tests/subst-nesting.zsh"
       - "tests/version-reporting.zsh"
   workflow_dispatch: {}
@@ -259,6 +261,17 @@ jobs:
       - name: Test message formatting
         run: zsh -f tests/message-formatting.zsh
 
+  source-hygiene:
+    name: Source Hygiene
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out code
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - name: Install Zsh
+        run: sudo apt update && sudo apt-get install -yq zsh
+      - name: Test source hygiene
+        run: zsh -f tests/source-hygiene.zsh
+
   subst-nesting:
     name: Subst Nesting
     runs-on: ubuntu-latest
diff --git a/lib/zsh/autoload.zsh b/lib/zsh/autoload.zsh
index d136afd..b7f4d58 100755
--- a/lib/zsh/autoload.zsh
+++ b/lib/zsh/autoload.zsh
@@ -299,14 +299,6 @@ ZI[EXTENDED_GLOB]=""
   fi
   return 0
 } # ]]]
-# FUNCTION: .zi-at-eval [[[
-.zi-at-eval() {
-  local atclone="$2" atpull="$1"
-  integer retval
-  @zi-substitute atclone atpull
-  [[ $atpull = "%atclone" ]] && { eval "$atclone"; retval=$?; } || { eval "$atpull"; retval=$?; }
-  return $retval
-} # ]]]
 
 #
 # Format functions
@@ -1917,7 +1909,7 @@ ZI[EXTENDED_GLOB]=""
   +zi-message "{mmdsh}{happy} Zi{rst} » {info3}update took {num}$SECONDS{info3} seconds{rst}{…}"
   return "$retval"
 } # ]]]
-# FUNCTION: .zi-update-in-parallel [[[
+# FUNCTION: .zi-update-all-parallel [[[
 .zi-update-all-parallel() {
   builtin emulate -LR zsh ${=${options[xtrace]:#off}:+-o xtrace}
   builtin setopt extended_glob warn_create_global typeset_silent no_short_loops no_monitor no_notify
diff --git a/tests/source-hygiene.zsh b/tests/source-hygiene.zsh
new file mode 100644
index 0000000..7324399
--- /dev/null
+++ b/tests/source-hygiene.zsh
@@ -0,0 +1,80 @@
+#!/usr/bin/env zsh
+# -*- mode: zsh; sh-indentation: 2; indent-tabs-mode: nil; sh-basic-offset: 2; -*-
+# vim: ft=zsh sw=2 ts=2 et
+#
+# Structural checks over the shipped sources. Neither can be caught by a
+# behavioural test: a duplicate definition whose copies agree behaves correctly
+# until they drift, and a wrong header misleads only the next reader. Both are
+# cheap to assert and expensive to rediscover.
+
+builtin emulate -R zsh
+setopt extended_glob pipe_fail
+
+fail() {
+  builtin print -u2 -r -- "not ok - $1"
+  exit 1
+}
+
+typeset project_root="${ZI_TEST_CHECKOUT:-${0:A:h:h}}"
+builtin cd -q "$project_root" || fail "enter the project root"
+
+typeset -a sources
+sources=( zi.zsh lib/zsh/*.zsh(N) )
+(( ${#sources} )) || fail "locate the shipped sources"
+
+# A top-level definition: a name in column one followed by `()'. Indented
+# definitions are anonymous or nested helpers and are deliberately not counted.
+typeset -r name_class='[A-Za-z_@.:+][A-Za-z0-9_@.:+-]#'
+
+typeset -A seen_in
+typeset -a duplicates mismatches
+typeset src name header defined
+typeset -a lines
+typeset -i i j
+
+for src in "${sources[@]}"; do
+  lines=( "${(@f)$(<$src)}" )
+
+  for (( i = 1; i <= ${#lines}; i++ )); do
+    # Every function is defined exactly once across the shipped sources. Both
+    # libraries are sourced conditionally and in different orders depending on
+    # the command, so a second definition does not reliably override the first:
+    # which one wins varies by code path. `.zi-at-eval' was defined in both
+    # lib/zsh/autoload.zsh and lib/zsh/install.zsh with matching behaviour and
+    # different wording, exactly the shape that becomes a heisenbug once the
+    # two drift.
+    if [[ ${lines[i]} == (#b)(${~name_class})[[:space:]]#'()'* ]]; then
+      name="${match[1]}"
+      if [[ -n ${seen_in[$name]} ]]; then
+        duplicates+=( "${name}: ${seen_in[$name]} and ${src}:${i}" )
+      else
+        seen_in[$name]="${src}:${i}"
+      fi
+      continue
+    fi
+
+    # Every `# FUNCTION: <name>' header names the function it precedes.
+    if [[ ${lines[i]} == (#b)'#'[[:space:]]#'FUNCTION:'[[:space:]]#(${~name_class})* ]]; then
+      header="${match[1]%.}"
+      for (( j = i + 1; j <= i + 6 && j <= ${#lines}; j++ )); do
+        [[ ${lines[j]} == (#b)(${~name_class})[[:space:]]#'()'* ]] || continue
+        defined="${match[1]}"
+        [[ $header == $defined ]] ||
+          mismatches+=( "${src}:${i} header '${header}' precedes '${defined}'" )
+        break
+      done
+    fi
+  done
+done
+
+if (( ${#duplicates} )); then
+  builtin print -u2 -rl -- "functions defined more than once:" "${duplicates[@]}"
+  fail "a function is defined in more than one shipped source"
+fi
+
+if (( ${#mismatches} )); then
+  builtin print -u2 -rl -- "FUNCTION headers naming a different function:" "${mismatches[@]}"
+  fail "a FUNCTION header does not match the function it precedes"
+fi
+
+builtin print -r -- "ok - every function is defined once and every FUNCTION header matches (${#seen_in} functions)"
diff --git a/zi.zsh b/zi.zsh
index ea35881..f81e5b5 100644
--- a/zi.zsh
+++ b/zi.zsh
@@ -2379,7 +2379,7 @@ builtin setopt no_aliases
     "the list of the {cmd}subcommands$bcol.{rst}"
   }
 } # ]]]
-# FUNCTION: +zi-parse-opts. [[[
+# FUNCTION: .zi-parse-opts. [[[
 .zi-parse-opts() {
   builtin emulate -LR zsh ${=${options[xtrace]:#off}:+-o xtrace}
   builtin setopt extended_glob typeset_silent no_short_loops rc_quotes no_auto_pushd