feature: detect and document measurement environment (GitHub Actions vs native)

- Detect GITHUB_ACTIONS and CI environment variables
- Label measurements as 'github-actions' or 'ci' vs 'native'
- Include environment notes in JSON and text output
- Document measurement sources in emoji-widths.json
- Helps users understand measurement reliability
- Warnings added for CI-measured values that may differ from native terminals

Author: cowwoc

plugin/emoji-widths.json

@@ -1,6 +1,10 @@
 {
   "$schema": "./emoji-widths.schema.json",
-  "$comment": "Emoji display widths by terminal. To contribute new measurements, run https://github.com/cowwoc/cat/blob/main/plugin/scripts/measure-emoji-widths.sh",
+  "$comment": "Emoji display widths by terminal. To contribute new measurements, run https://github.com/cowwoc/cat/blob/main/plugin/scripts/measure-emoji-widths.sh. Use GitHub Actions SSH workflow for testing.",
+  "measurement_notes": {
+    "Apple_Terminal": "Measured on GitHub Actions macOS runner via SSH. May differ slightly from native Terminal.app.",
+    "iTerm.app": "Baseline from Windows Terminal. Actual measurements needed from real iTerm.app installation."
+  },
   "emojis": {
     "closed": "☑️",
     "in_progress": "🔄",

plugin/scripts/measure-emoji-widths.sh

@@ -394,16 +394,29 @@ measure_width() {
 
 main() {
     local terminal
+    local environment="native"
+    local environment_note=""
 
     terminal=$(detect_terminal)
 
+    # Detect if running in CI/cloud environment
+    if [[ -n "${GITHUB_ACTIONS:-}" ]]; then
+        environment="github-actions"
+        environment_note=" (GitHub Actions CI - measurements may differ from native terminal)"
+    elif [[ -n "${CI:-}" ]] || [[ -n "${CONTINUOUS_INTEGRATION:-}" ]]; then
+        environment="ci"
+        environment_note=" (CI environment - measurements may differ from native terminal)"
+    fi
+
     if $DETECT_ONLY; then
         if $JSON_OUTPUT; then
             echo "{"
-            echo "  \"terminal\": \"$terminal\""
+            echo "  \"terminal\": \"$terminal\","
+            echo "  \"environment\": \"$environment\""
             echo "}"
         else
             echo "Terminal: $terminal"
+            echo "Environment: $environment$environment_note"
         fi
         return
     fi
@@ -422,6 +435,10 @@ main() {
     if $JSON_OUTPUT; then
         echo "{"
         echo "  \"terminal\": \"$terminal\","
+        echo "  \"environment\": \"$environment\","
+        if [[ -n "$environment_note" ]]; then
+            echo "  \"note\": \"$environment_note\","
+        fi
         echo "  \"widths\": {"
 
         # Collect all measurements first, then output JSON
@@ -455,6 +472,7 @@ main() {
         echo "Emoji Width Measurement"
         echo "======================="
         echo "Terminal: $terminal"
+        echo "Environment: $environment$environment_note"
         echo ""
         echo "Widths:"
         echo "-------"