[201_90] fix inner product symbol display in tab cycle popup

TeXmacs/progs/math/math-edit.scm

@@ -833,7 +833,7 @@ list | boolean
                           (let ((lb (cadr body))
                                 (rb (caddr body)))
                             `(symbol-completion
-                              ,(string-append lb rb)))))
+                              ,lb))))
                     ;; 预留位置：可以在此添加其他函数的处理逻辑
 
                     (else #f)))))))))))

devel/201_90.md

@@ -0,0 +1,32 @@
+# [201_90] Fix Inner Product symbol display in Tab cycling popup
+
+### What
+The `math-bracket-open` case in `lambda-to-symbol` was concatenating the left and right bracket symbols (e.g., `"<langle><rangle>"`). This produced a compound string that the `widget-box` rendering engine (using the `roman` font) could not render correctly, showing as a red broken symbol or `--`. Changed the logic to return only the left bracket symbol (`lb`), which renders correctly as a single TeXmacs symbol (e.g., `⟨`).
+
+### Why
+When cycling through math variants for the `<` key (which includes the inner product `⟨⟩` as the 7th variant), the popup window showed a broken/red symbol instead of the angle brackets. This made it difficult for users to identify the inner product variant in the Tab cycling menu.
+
+### How
+In `TeXmacs/progs/math/math-edit.scm`:
+
+Modified `lambda-to-symbol` to return only the left bracket symbol for `math-bracket-open`:
+
+```diff
+ ((math-bracket-open)
+  (and (>= (length (cdr body)) 2)
+       (string? (cadr body))
+       (string? (caddr body))
+       (let ((lb (cadr body))
+             (rb (caddr body)))
+         `(symbol-completion
+-          ,(string-append lb rb)))))
++          ,lb))))
+```
+
+### How to test
+1. Open Mogan Editor
+2. Enter math mode by pressing `$`
+3. Type `<`
+4. Press `Tab` repeatedly (7 times) to reach the inner product `⟨⟩` variant
+5. Verify that the popup window shows the left angle bracket `⟨` clearly (instead of a broken red symbol or `--`)
+6. Press `Tab` once more to return to `<` and verify the cycle continues correctly