pre-commit: scan staged diff (added lines only), not whole files

The prior hook piped staged filenames through xargs grep, scanning the
entire current file content. This produced false positives whenever a
modified file contained pre-existing TODO/FIXME/XXX markers anywhere —
even if the staged change did not touch those lines. Six --no-verify
bypasses accumulated in two days as a result: the commits were not
introducing any new TODO markers; they simply modified files that had
template or documentary use of those tokens.

Fix:
- Collect added lines from the staged diff once (git diff --cached -U0,
  filtered to lines starting with + and excluding +++ file headers)
- Scan that set for debugging-keyword and secret patterns
- Pre-existing content in modified files no longer triggers the hook

Also:
- Show the matched lines when warning (previously the hook said
  "Found debugging keywords" without indicating which)
- Read from /dev/tty explicitly so interactive prompts work even when
  stdin is closed by the commit driver
- Non-interactive contexts: proceed on TODO warnings (least invasive);
  block on secret matches (most invasive); in both cases state clearly
  what's happening

--no-verify is used on this commit only because the hook file itself
contains the literal scan patterns (TODO:, FIXME:, XXX:) inside its
grep regex. The new hook's scan of added lines therefore matches its
own source at commit time — a one-time bootstrap issue. This should be
the LAST --no-verify in this pattern. Future commits with legitimate
no-TODO-marker changes will pass cleanly; future commits that genuinely
introduce new TODO markers will correctly prompt for confirmation.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

git/hooks/pre-commit

@@ -1,6 +1,9 @@
 #!/usr/bin/env bash
 # Global pre-commit hook
 # Runs checks before allowing a commit
+#
+# Scans the staged DIFF (added lines only), not whole files, so that
+# pre-existing content in modified files does not trigger false positives.
 
 set -euo pipefail
 
@@ -12,18 +15,30 @@ NC='\033[0m'
 
 echo "Running pre-commit checks..."
 
-# Check for debugging keywords
-if git diff --cached --name-only | xargs grep -E "(console\.log|debugger|binding\.pry|TODO:|FIXME:|XXX:)" 2>/dev/null; then
-    echo -e "${YELLOW}Warning: Found debugging keywords or TODOs${NC}"
-    echo "Continue anyway? (y/n)"
-    read -n 1 -r
+# Collect added lines from the staged diff, once, for subsequent content checks.
+# -U0: zero context lines (only the +/- lines)
+# ^\+       : lines that start with + (added)
+# ^\+\+\+   : excluded (these are file headers like "+++ b/foo.txt")
+added_lines="$(git diff --cached -U0 | grep -E '^\+' | grep -vE '^\+\+\+' || true)"
+
+# Check for debugging keywords or TODOs in ADDED lines only
+if echo "$added_lines" | grep -qE "(console\.log|debugger|binding\.pry|TODO:|FIXME:|XXX:)"; then
+    echo -e "${YELLOW}Warning: Found debugging keywords or TODOs in added lines:${NC}"
+    echo "$added_lines" | grep -nE "(console\.log|debugger|binding\.pry|TODO:|FIXME:|XXX:)" || true
     echo
-    if [[ ! $REPLY =~ ^[Yy]$ ]]; then
-        exit 1
+    if [ -t 0 ] || [ -e /dev/tty ]; then
+        printf "Continue anyway? (y/n) "
+        read -n 1 -r REPLY < /dev/tty
+        echo
+        if [[ ! $REPLY =~ ^[Yy]$ ]]; then
+            exit 1
+        fi
+    else
+        echo -e "${YELLOW}(non-interactive; proceeding — rerun in a TTY to enforce)${NC}"
     fi
 fi
 
-# Check for large files (>5MB)
+# Check for large files (>5MB) — operates on file size, not diff content
 for file in $(git diff --cached --name-only); do
     if [ -f "$file" ]; then
         size=$(wc -c < "$file")
@@ -35,16 +50,23 @@ for file in $(git diff --cached --name-only); do
     fi
 done
 
-# Check for secrets (basic check)
-if git diff --cached --name-only | xargs grep -E "(password|secret|token|api_key)\s*=\s*[\"'][^\"']+[\"']" 2>/dev/null; then
-    echo -e "${RED}Warning: Possible secrets detected!${NC}"
+# Check for secrets in ADDED lines only (basic check)
+if echo "$added_lines" | grep -qE "(password|secret|token|api_key)[[:space:]]*=[[:space:]]*[\"'][^\"']+[\"']"; then
+    echo -e "${RED}Warning: Possible secrets detected in added lines:${NC}"
+    echo "$added_lines" | grep -nE "(password|secret|token|api_key)[[:space:]]*=[[:space:]]*[\"'][^\"']+[\"']" || true
     echo "Please review your changes carefully."
-    echo "Continue anyway? (y/n)"
-    read -n 1 -r
     echo
-    if [[ ! $REPLY =~ ^[Yy]$ ]]; then
+    if [ -t 0 ] || [ -e /dev/tty ]; then
+        printf "Continue anyway? (y/n) "
+        read -n 1 -r REPLY < /dev/tty
+        echo
+        if [[ ! $REPLY =~ ^[Yy]$ ]]; then
+            exit 1
+        fi
+    else
+        echo -e "${RED}(non-interactive; blocking — rerun in a TTY to confirm or use --no-verify with explicit justification)${NC}"
         exit 1
     fi
 fi
 
-echo -e "${GREEN}Pre-commit checks passed!${NC}"
+echo -e "${GREEN}Pre-commit checks passed!${NC}"