tui: preserve ansi styling when truncating output

docs/CHANGELOG.md

@@ -22,6 +22,8 @@
   clients can discover common actions and troubleshooting paths in-product.
 - The GitHub workflow formerly named deploy now runs CI only; production
   deployment remains a manual operator action.
+- Command output rendering now truncates ANSI-styled UTF-8 text without
+  counting escape sequences as visible width or cutting color codes.
 
 ## 2026-05-18 - Interactive input polish
 

include/utf8.h

@@ -15,9 +15,16 @@ uint32_t utf8_decode(const char *str, int *bytes_read);
 /* Calculate display width of a UTF-8 string (considering CJK double-width) */
 int utf8_string_width(const char *str);
 
+/* Calculate display width while treating ANSI escape sequences as zero-width */
+int utf8_ansi_string_width(const char *str);
+
 /* Truncate string to fit within max_width display characters */
 void utf8_truncate(char *str, int max_width);
 
+/* Truncate ANSI-styled UTF-8 text without cutting escape sequences */
+void utf8_ansi_truncate(const char *src, char *dst, size_t dst_size,
+                        int max_width);
+
 /* Count the number of UTF-8 characters in a string */
 int utf8_strlen(const char *str);
 

src/tui.c

@@ -621,11 +621,14 @@ void tui_render_command_output(client_t *client) {
 
     /* Title */
     const char *title = " COMMAND OUTPUT ";
-    int title_width = strlen(title);
+    char title_display[64];
+    utf8_ansi_truncate(title, title_display, sizeof(title_display), rw);
+    int title_width = utf8_ansi_string_width(title_display);
     int padding = rw - title_width;
     if (padding < 0) padding = 0;
 
-    buffer_appendf(buffer, sizeof(buffer), &pos, ANSI_REVERSE "%s", title);
+    buffer_appendf(buffer, sizeof(buffer), &pos, ANSI_REVERSE "%s",
+                   title_display);
     for (int i = 0; i < padding; i++) {
         buffer_append_bytes(buffer, sizeof(buffer), &pos, " ", 1);
     }
@@ -642,12 +645,7 @@ void tui_render_command_output(client_t *client) {
 
     while (line && line_count < max_lines) {
         char truncated[1024];
-        strncpy(truncated, line, sizeof(truncated) - 1);
-        truncated[sizeof(truncated) - 1] = '\0';
-
-        if (utf8_string_width(truncated) > rw) {
-            utf8_truncate(truncated, rw);
-        }
+        utf8_ansi_truncate(line, truncated, sizeof(truncated), rw);
 
         buffer_appendf(buffer, sizeof(buffer), &pos, "%s\r\n", truncated);
         line = strtok(NULL, "\n");

src/utf8.c

@@ -96,6 +96,49 @@ int utf8_string_width(const char *str) {
     return width;
 }
 
+static const char *skip_ansi_sequence(const char *p) {
+    if (!p || *p != '\033') {
+        return p;
+    }
+
+    if (p[1] == '[') {
+        const char *q = p + 2;
+        while (*q) {
+            unsigned char c = (unsigned char)*q;
+            if (c >= 0x40 && c <= 0x7E) {
+                return q + 1;
+            }
+            q++;
+        }
+        return p + 1;
+    }
+
+    return p[1] ? p + 2 : p + 1;
+}
+
+int utf8_ansi_string_width(const char *str) {
+    int width = 0;
+    int bytes_read;
+    const char *p = str;
+
+    if (!str) {
+        return 0;
+    }
+
+    while (*p != '\0') {
+        if (*p == '\033') {
+            p = skip_ansi_sequence(p);
+            continue;
+        }
+
+        uint32_t codepoint = utf8_decode(p, &bytes_read);
+        width += utf8_char_width(codepoint);
+        p += bytes_read;
+    }
+
+    return width;
+}
+
 /* Count the number of UTF-8 characters in a string */
 int utf8_strlen(const char *str) {
     int count = 0;
@@ -134,6 +177,72 @@ void utf8_truncate(char *str, int max_width) {
     *last_valid = '\0';
 }
 
+void utf8_ansi_truncate(const char *src, char *dst, size_t dst_size,
+                        int max_width) {
+    int width = 0;
+    int bytes_read;
+    size_t pos = 0;
+    bool copied_ansi = false;
+    bool last_ansi_was_reset = false;
+    bool truncated = false;
+    const char *p = src;
+
+    if (!dst || dst_size == 0) {
+        return;
+    }
+
+    dst[0] = '\0';
+    if (!src || max_width <= 0) {
+        return;
+    }
+
+    while (*p != '\0') {
+        if (*p == '\033') {
+            const char *end = skip_ansi_sequence(p);
+            size_t len = (size_t)(end - p);
+
+            if (pos + len >= dst_size) {
+                truncated = true;
+                break;
+            }
+            memcpy(dst + pos, p, len);
+            pos += len;
+            copied_ansi = true;
+            last_ansi_was_reset =
+                len == strlen(ANSI_RESET) && memcmp(p, ANSI_RESET, len) == 0;
+            p = end;
+            continue;
+        }
+
+        uint32_t codepoint = utf8_decode(p, &bytes_read);
+        int char_width = utf8_char_width(codepoint);
+
+        if (width + char_width > max_width) {
+            truncated = true;
+            break;
+        }
+        if (pos + (size_t)bytes_read >= dst_size) {
+            truncated = true;
+            break;
+        }
+
+        memcpy(dst + pos, p, (size_t)bytes_read);
+        pos += (size_t)bytes_read;
+        width += char_width;
+        p += bytes_read;
+    }
+
+    if (truncated && copied_ansi && !last_ansi_was_reset) {
+        size_t reset_len = strlen(ANSI_RESET);
+        if (pos + reset_len < dst_size) {
+            memcpy(dst + pos, ANSI_RESET, reset_len);
+            pos += reset_len;
+        }
+    }
+
+    dst[pos] = '\0';
+}
+
 /* Remove last UTF-8 character from string */
 void utf8_remove_last_char(char *str) {
     int len = strlen(str);

tests/unit/test_utf8.c

@@ -114,6 +114,22 @@ TEST(utf8_string_width_cjk_only) {
     assert(utf8_string_width("中文字符") == 8);
 }
 
+TEST(utf8_ansi_string_width_ignores_escape_sequences) {
+    assert(utf8_ansi_string_width("\033[1;36mHello\033[0m") == 5);
+    assert(utf8_ansi_string_width("\033[31m支持\033[0m") == 4);
+    assert(utf8_ansi_string_width("A\033[7;33m中\033[0mB") == 4);
+}
+
+TEST(utf8_ansi_truncate_preserves_escape_sequences) {
+    char out[64];
+
+    utf8_ansi_truncate("\033[31mHello世界\033[0m", out, sizeof(out), 7);
+    assert(strcmp(out, "\033[31mHello世\033[0m") == 0);
+
+    utf8_ansi_truncate("A\033[7;33m中文\033[0mB", out, sizeof(out), 5);
+    assert(strcmp(out, "A\033[7;33m中文\033[0m") == 0);
+}
+
 /* Test backspace handling */
 TEST(utf8_remove_last_char) {
     char buffer[256];
@@ -228,6 +244,8 @@ int main(void) {
     RUN_TEST(utf8_string_width_ascii);
     RUN_TEST(utf8_string_width_mixed);
     RUN_TEST(utf8_string_width_cjk_only);
+    RUN_TEST(utf8_ansi_string_width_ignores_escape_sequences);
+    RUN_TEST(utf8_ansi_truncate_preserves_escape_sequences);
     RUN_TEST(utf8_remove_last_char);
     RUN_TEST(utf8_remove_last_char_multibyte);
     RUN_TEST(utf8_remove_last_word);