chore(dev): Enforce frontend filename casing in pre-commit

.pre-commit-config.yaml

@@ -89,6 +89,15 @@ repos:
         always_run: true
         pass_filenames: false
         language: system
+      # Case-only renames break macOS (case-insensitive) checkouts when casing
+      # drifts between branches. Existing check-case-conflict only catches two
+      # distinct paths that collide when lowercased, not a single-file rename.
+      - id: prevent-case-only-rename
+        name: prevent case-only renames
+        entry: bash tools/prevent_case_only_rename.sh
+        always_run: true
+        pass_filenames: false
+        language: system
 
       # Javascript linting, formatting.
       # We're using the local node_modules to simplify things, otherwise would

tools/prevent_case_only_rename.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+# Reject staged case-only renames (Foo.tsx -> foo.tsx).
+# These break macOS case-insensitive checkouts when casing drifts across branches.
+# check-case-conflict only catches two distinct paths that collide when lowercased.
+set -euo pipefail
+
+git diff --cached -M --name-status | awk -F '\t' '
+  $1 ~ /^R/ && tolower($2) == tolower($3) && $2 != $3 {
+    print "case-only rename forbidden:", $2, "->", $3
+    err = 1
+  }
+  END { exit err + 0 }
+'