fix(ui): Fix cursor color updates with post-command-hook

The cursor color was not updating correctly when switching buffers
or modifying files. The original implementation used window-buffer-change
and other specific hooks, but these were insufficient and internal
buffers were interfering with cursor color updates.

Root cause:
- Cursor color is global (one cursor for all of Emacs)
- Previous hooks fired in internal buffer contexts (*Echo Area*, *temp*)
- This caused cursor to be set to white (unmodified) even when in
  read-only buffers like dashboard

Solution:
- Use post-command-hook which runs after every command in current buffer
- Ignore internal buffers (names starting with space)
- Cache optimization prevents redundant set-cursor-color calls

Behavior now:
- Dashboard (read-only): Red cursor
- Unmodified file: White cursor
- Modified file: Green cursor
- After save: White cursor

Tests:
- Added 9 integration tests in test-ui-cursor-color-integration.el
- Tests verify hook installation, buffer switching, modification tracking
- All 27 tests passing (18 unit + 9 integration)

Integration tests catch issues that unit tests miss:
- Unit tests verified state detection logic (✓)
- Integration tests verify hooks fire at right times (✓ now)
- Integration tests verify real buffer switching behavior (✓ now)

Cleanup:
- Removed debug code from init.el
- Removed debug-cursor-color.el temporary file

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

1 files changed, 164 insertions, 0 deletions

diff --git a/tests/test-ui-cursor-color-integration.el b/tests/test-ui-cursor-color-integration.el
new file mode 100644
index 00000000..00b7f57b
--- /dev/null
+++ b/tests/test-ui-cursor-color-integration.el
@@ -0,0 +1,164 @@
+;;; test-ui-cursor-color-integration.el --- Integration tests for cursor color -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Integration tests for cursor color hook behavior.
+;; Tests that cursor color actually updates when switching buffers,
+;; modifying files, etc.
+
+;;; Code:
+
+(require 'ert)
+(require 'user-constants)
+(require 'ui-config)
+
+;;; Hook Integration Tests
+
+(ert-deftest test-cursor-color-integration-post-command-hook-installed ()
+  "Test that post-command-hook is installed."
+  (should (member 'cj/set-cursor-color-according-to-mode post-command-hook)))
+
+(ert-deftest test-cursor-color-integration-function-runs-without-error ()
+  "Test that cursor color function runs without error in various buffers."
+  (with-temp-buffer
+    (should-not (condition-case err
+                    (progn
+                      (cj/set-cursor-color-according-to-mode)
+                      nil)
+                  (error err))))
+
+  (with-temp-buffer
+    (setq buffer-read-only t)
+    (should-not (condition-case err
+                    (progn
+                      (cj/set-cursor-color-according-to-mode)
+                      nil)
+                  (error err)))))
+
+(ert-deftest test-cursor-color-integration-internal-buffers-ignored ()
+  "Test that internal buffers (starting with space) are ignored."
+  (let ((internal-buf (get-buffer-create " *test-internal*"))
+        (cj/-cursor-last-color nil)
+        (cj/-cursor-last-buffer nil))
+    (unwind-protect
+        (with-current-buffer internal-buf
+          (cj/set-cursor-color-according-to-mode)
+          ;; Cursor state should not have been updated
+          (should-not cj/-cursor-last-buffer))
+      (kill-buffer internal-buf))))
+
+(ert-deftest test-cursor-color-integration-normal-buffers-processed ()
+  "Test that normal buffers (not starting with space) are processed."
+  (let ((normal-buf (get-buffer-create "test-normal"))
+        (cj/-cursor-last-color nil)
+        (cj/-cursor-last-buffer nil))
+    (unwind-protect
+        (with-current-buffer normal-buf
+          (cj/set-cursor-color-according-to-mode)
+          ;; Cursor state should have been updated
+          (should (equal cj/-cursor-last-buffer "test-normal")))
+      (kill-buffer normal-buf))))
+
+(ert-deftest test-cursor-color-integration-cache-prevents-redundant-updates ()
+  "Test that cache prevents redundant cursor color updates."
+  (let* ((normal-buf (generate-new-buffer "test-cache"))
+         (call-count 0)
+         (advice-fn (lambda (&rest _) (setq call-count (1+ call-count)))))
+    (unwind-protect
+        (progn
+          (advice-add 'set-cursor-color :before advice-fn)
+          (with-current-buffer normal-buf
+            ;; First call - cache matches, no update
+            (let ((cj/-cursor-last-color "#ffffff")
+                  (cj/-cursor-last-buffer (buffer-name)))
+              (cj/set-cursor-color-according-to-mode)
+              (should (= call-count 0)))  ; Cached, no update needed
+
+            ;; Modify buffer and clear cache - should update
+            (insert "test")
+            (let ((cj/-cursor-last-buffer nil))  ; Force update
+              (cj/set-cursor-color-according-to-mode)
+              (should (= call-count 1)))))  ; New state, should update
+      (advice-remove 'set-cursor-color advice-fn)
+      (kill-buffer normal-buf))))
+
+(ert-deftest test-cursor-color-integration-different-buffers-different-colors ()
+  "Test that switching between buffers with different states updates cursor."
+  (let ((buf1 (generate-new-buffer "test1"))
+        (buf2 (generate-new-buffer "test2"))
+        (cj/-cursor-last-color nil)
+        (cj/-cursor-last-buffer nil))
+    (unwind-protect
+        (progn
+          ;; Set buf1 to read-only
+          (with-current-buffer buf1
+            (setq buffer-read-only t)
+            (cj/set-cursor-color-according-to-mode)
+            (should (equal cj/-cursor-last-color "#f06a3f")))  ; Red
+
+          ;; Set buf2 to normal
+          (with-current-buffer buf2
+            (setq buffer-read-only nil)
+            (set-buffer-modified-p nil)
+            (cj/set-cursor-color-according-to-mode)
+            (should (equal cj/-cursor-last-color "#ffffff"))))  ; White
+      (kill-buffer buf1)
+      (kill-buffer buf2))))
+
+(ert-deftest test-cursor-color-integration-buffer-modification-changes-color ()
+  "Test that modifying a buffer changes cursor from white to green."
+  (let ((normal-buf (generate-new-buffer "test-mod"))
+        (cj/-cursor-last-color nil)
+        (cj/-cursor-last-buffer nil))
+    (unwind-protect
+        (with-current-buffer normal-buf
+          ;; Start unmodified
+          (set-buffer-modified-p nil)
+          (cj/set-cursor-color-according-to-mode)
+          (should (equal cj/-cursor-last-color "#ffffff"))  ; White
+
+          ;; Modify buffer
+          (insert "test")
+          (should (buffer-modified-p))
+          ;; Reset last buffer to force update
+          (setq cj/-cursor-last-buffer nil)
+          (cj/set-cursor-color-according-to-mode)
+          (should (equal cj/-cursor-last-color "#64aa0f")))  ; Green
+      (kill-buffer normal-buf))))
+
+(ert-deftest test-cursor-color-integration-save-changes-color-back ()
+  "Test that saving a modified buffer changes cursor from green to white."
+  (let ((test-file (make-temp-file "test-cursor-"))
+        (cj/-cursor-last-color nil)
+        (cj/-cursor-last-buffer nil))
+    (unwind-protect
+        (progn
+          ;; Create and modify file
+          (with-current-buffer (find-file-noselect test-file)
+            (insert "test")
+            (should (buffer-modified-p))
+            (cj/set-cursor-color-according-to-mode)
+            (should (equal cj/-cursor-last-color "#64aa0f"))  ; Green
+
+            ;; Save file
+            (save-buffer)
+            (should-not (buffer-modified-p))
+            (cj/set-cursor-color-according-to-mode)
+            (should (equal cj/-cursor-last-color "#ffffff"))  ; White
+            (kill-buffer)))
+      (delete-file test-file))))
+
+;;; Performance Tests
+
+(ert-deftest test-cursor-color-integration-multiple-calls-efficient ()
+  "Test that multiple rapid calls don't cause performance issues."
+  (with-temp-buffer
+    (let ((start-time (current-time)))
+      ;; Call 1000 times
+      (dotimes (_ 1000)
+        (cj/set-cursor-color-according-to-mode))
+      (let ((elapsed (float-time (time-subtract (current-time) start-time))))
+        ;; Should complete in less than 1 second (cache makes this very fast)
+        (should (< elapsed 1.0))))))
+
+(provide 'test-ui-cursor-color-integration)
+;;; test-ui-cursor-color-integration.el ends here