feat(face-diagnostic): make report face names describe-face buttons

Render each real face name in the Face Diagnosis report as a button that runs describe-face on it, carrying the face as button data; anonymous specs and non-faces stay plain text. Also add face-diagnostic to the module-header allowlist now that it is required in init.el and carries the header contract.

Claude-Session: https://claude.ai/code/session_01BqrdWUo9GcznYX2pZr76gZ

2 files changed, 26 insertions, 0 deletions

diff --git a/tests/test-face-diagnostic.el b/tests/test-face-diagnostic.el
index 241425fc5..32595b464 100644
--- a/tests/test-face-diagnostic.el
+++ b/tests/test-face-diagnostic.el
@@ -286,6 +286,31 @@
       (should (string-match-p "Real font" report))
       (should (string-match-p "Provenance" report)))))
 
+(ert-deftest test-face-diag-face-button-real-face-is-button ()
+  "Normal: a real face renders as a `describe-face' button carrying the face.
+Visible label is unchanged; the button data is the face so RET/mouse opens it."
+  (let ((s (cj/--face-diag-face-button 'bold)))
+    (should (equal (substring-no-properties s) "bold"))
+    (should (get-text-property 0 'button s))
+    (should (eq (get-text-property 0 'button-data s) 'bold))))
+
+(ert-deftest test-face-diag-face-button-non-face-is-plain ()
+  "Boundary: a symbol that is not a face stays plain text, no button."
+  (let ((s (cj/--face-diag-face-button 'cj-not-a-real-face-xyz)))
+    (should (equal s "cj-not-a-real-face-xyz"))
+    (should-not (get-text-property 0 'button s))))
+
+(ert-deftest test-face-diag-face-button-anonymous-spec-is-plain ()
+  "Error: an anonymous (:attr val ...) spec is not a face, so no button."
+  (let ((s (cj/--face-diag-face-button '(:foreground "red"))))
+    (should-not (get-text-property 0 'button s))))
+
+(ert-deftest test-face-diag-render-faces-buttonizes-real-face ()
+  "Normal: a real face in the stack render carries a button property."
+  (let ((s (cj/--face-diag-render-faces '(bold))))
+    (should (string-match-p "bold" s))
+    (should (get-text-property 0 'button s))))
+
 (ert-deftest test-face-diag-render-banner-out-of-scope ()
   "Boundary: a terminal classification renders a banner naming the ANSI source."
   (should (string-match-p "terminal" (cj/--face-diag-render-banner 'terminal-ansi)))
diff --git a/tests/test-init-module-headers.el b/tests/test-init-module-headers.el
index 4b6ac05c4..478819b89 100644
--- a/tests/test-init-module-headers.el
+++ b/tests/test-init-module-headers.el
@@ -105,6 +105,7 @@
     "erc-config"
     "eshell-config"
     "eww-config"
+    "face-diagnostic"
     "flyspell-and-abbrev"
     "games-config"
     "gloss-config"