feat: Claude Code pre-bash hooks for PowerShell and path enforcement

Block inline pwsh -Command/-c (force .ps1 file approach) and
Windows backslash paths in Bash commands (enforce forward slashes).

Eliminates the 2-3 retry loop on PowerShell operations and prevents
the /tmp path mismatch that caused the stale-payload Syncro incident.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/hooks/pre-bash-backslash.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+# Pre-tool hook: block Windows backslash paths in Bash commands.
+#
+# Blocks patterns like C:\Users\foo passed inside Bash command strings.
+# Enforces forward slashes: C:/Users/foo
+#
+# Why: Git Bash mangles backslash paths — C:\tmp writes to a different
+# directory than the Write tool's C:\tmp, causing stale payload bugs.
+
+input=$(cat)
+cmd=$(echo "$input" | jq -r '.tool_input.command // ""' 2>/dev/null)
+
+# Match a drive letter followed by a literal backslash in the command.
+# In the extracted command string (not JSON-escaped), backslash is just \.
+if echo "$cmd" | grep -qE '[A-Za-z]:\\[A-Za-z/\\]'; then
+    echo "BLOCKED: Use forward slashes for Windows paths in Bash commands."
+    echo ""
+    echo "  Wrong:   C:\\Users\\guru\\file.txt"
+    echo "  Correct: C:/Users/guru/file.txt"
+    echo ""
+    echo "Git Bash converts backslash paths unpredictably. PowerShell and Windows"
+    echo "APIs both accept forward slashes without issue."
+    exit 2
+fi
+
+exit 0