diff --git a/CMakeLists.txt b/CMakeLists.txt
index c192efd..2a83f8a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -80,7 +80,7 @@ set(CST_CORE_SOURCES
 set(CST_SOURCES ${CST_CORE_SOURCES} src/main.c)
 
 if(CST_BUILD_TUI)
-  list(APPEND CST_SOURCES src/tui.c)
+  list(APPEND CST_SOURCES src/textsel.c src/tui.c)
 else()
   list(APPEND CST_SOURCES src/tui_stub.c)
 endif()
@@ -151,9 +151,17 @@ endif()
 # --- tests ---
 enable_testing()
 set(_CST_SMALL_TESTS test_ctl_frontier test_ctl_heredoc test_json_baseline
-    test_replay_starvation test_replay_real test_mm_tool)
+    test_replay_starvation test_replay_real test_mm_tool test_textsel
+    test_markdown)
 foreach(t ${_CST_SMALL_TESTS})
-  if(t STREQUAL test_ctl_frontier OR t STREQUAL test_ctl_heredoc)
+  if(t STREQUAL test_textsel)
+    add_executable(${t} tests/${t}.c src/textsel.c)
+  elseif(t STREQUAL test_markdown)
+    add_executable(${t} tests/${t}.c)
+    target_include_directories(${t} PRIVATE "${SD_DIR}/include")
+    target_link_libraries(${t} PRIVATE "${SASHIDOWN_A}")
+    add_dependencies(${t} sashidown)
+  elseif(t STREQUAL test_ctl_frontier OR t STREQUAL test_ctl_heredoc)
     add_executable(${t} tests/${t}.c src/ctl_parse.c)
   elseif(t STREQUAL test_json_baseline)
     add_executable(${t} tests/${t}.c src/json_baseline.c vendor/cjson/cJSON.c)
diff --git a/Makefile b/Makefile
index b572109..c9a2cdb 100644
--- a/Makefile
+++ b/Makefile
@@ -80,7 +80,7 @@ CORE_SRC = \
 	src/models.c \
 	src/metrics.c
 
-SRC = $(CORE_SRC) src/tui.c src/main.c
+SRC = $(CORE_SRC) src/textsel.c src/tui.c src/main.c
 OBJ = $(SRC:.c=.o)
 HDRS = $(wildcard include/*.h) $(wildcard src/tools/*.h) $(CJSON_DIR)/cJSON.h
 
@@ -104,6 +104,8 @@ TESTS = \
 	tests/test_models \
 	tests/test_sandbox \
 	tests/test_keymap \
+	tests/test_textsel \
+	tests/test_markdown \
 	tests/test_shell_compact \
 	tests/test_skills \
 	tests/test_plugins \
@@ -161,6 +163,12 @@ tests/test_replay_real: tests/test_replay_real.c src/ctl_parse.c src/json_baseli
 tests/test_mm_tool: tests/test_mm_tool.c src/mm_tool.c include/mm_tool.h
 	$(CC) $(CFLAGS) $(CPPFLAGS) -o $@ tests/test_mm_tool.c src/mm_tool.c
 
+tests/test_textsel: tests/test_textsel.c src/textsel.c include/cst_textsel.h
+	$(CC) $(CFLAGS) $(CPPFLAGS) -o $@ tests/test_textsel.c src/textsel.c
+
+tests/test_markdown: tests/test_markdown.c $(SD_DIR)/libsashidown.a
+	$(CC) $(CFLAGS) $(CPPFLAGS) -o $@ tests/test_markdown.c $(LDFLAGS) -lsashidown -lm
+
 tests/test_%: tests/test_%.c $(CORE_SRC) $(HDRS)
 	$(CC) $(CFLAGS) $(CPPFLAGS) -o $@ $< $(CORE_SRC) $(TEST_LIBS)
 
diff --git a/README.md b/README.md
index 7d5a7f3..ea7c125 100644
--- a/README.md
+++ b/README.md
@@ -336,7 +336,8 @@ TUI 中 `/tools off NAME`、`/tools on NAME` 可临时开关单个工具。
 | Ctrl+X t / d / s | 全部 Thought 默认展开或折叠 / 全部 tool 输出 / 侧栏 |
 | Ctrl+X a / k / g | 子 agent 面板 / skills / 插件 |
 | Ctrl+X h、F1 / Ctrl+X q | 快捷键列表 / 退出 |
-| 鼠标点击 | 展开/折叠 tool 卡片和 Thought、在输入框里定位光标、点模式行切换 Build/Plan、在选择框里选中（`/mouse` 关闭后可用终端原生选择复制） |
+| 鼠标点击 | 展开/折叠 tool 卡片和 Thought、在输入框里定位光标、点模式行切换 Build/Plan、在选择框里选中 |
+| 鼠标拖动 / 双击 / 三击 | 在对话区选中文字（按字符 / 词 / 行），松开即通过 OSC 52 复制到剪贴板；拖到上下边缘会自动滚动。Shift+拖动或 `/mouse` 关闭后用终端原生选择 |
 | Esc | 取消当前 turn（不会退出） |
 | Ctrl+C 两次 / 空输入 Ctrl+D | 退出 |
 
diff --git a/docs/compat.md b/docs/compat.md
index 5b7a387..57baf24 100644
--- a/docs/compat.md
+++ b/docs/compat.md
@@ -81,9 +81,15 @@ take the agent down.
 - UTF-8 locale gives the full UI. Under a non-UTF-8 locale, or with
   `CST_ASCII=1`, box and icon glyphs fall back to ASCII.
 - `NO_COLOR=1` turns colours off.
-- `/copy` uses OSC 52. iTerm2 needs "Applications in terminal may access
-  clipboard"; tmux needs `set -g set-clipboard on`; Windows Terminal (WSL)
-  supports it out of the box.
+- `/copy` and mouse selection use OSC 52. iTerm2 needs "Applications in
+  terminal may access clipboard"; tmux needs `set -g set-clipboard on`;
+  Windows Terminal (WSL), kitty, WezTerm, foot and WHC Shell support it out of
+  the box.
+- Mouse selection: the TUI turns on button-motion reporting (`?1002h`) on top
+  of what ncurses enables, so dragging over the transcript selects text
+  (double-click a word, triple-click a line) and releasing copies it. Terminals
+  without 1002 still get clicks and the wheel. Shift+drag bypasses the TUI and
+  uses the terminal's own selection.
 - Bracketed paste needs ncurses (all platforms above).
 - macOS Terminal.app sends Option+Enter as Esc+Enter only with "Use Option as
   Meta key"; Ctrl+N always inserts a newline.
@@ -128,6 +134,9 @@ TUI:
 - [ ] `/diff`, `/export`, `/status`, `/tools off grep`, `/yolo` work
 - [ ] Mouse: click a tool card to expand it, click in the input to move the
       cursor, click a picker row; `/mouse` turns it off
+- [ ] Drag over a wrapped reply: it highlights, the status row says "Copied",
+      and pasting gives the paragraph without extra line breaks; double-click
+      copies a word
 - [ ] Tab toggles Build/Plan, Shift+Tab cycles ask/auto/yolo, Ctrl+P opens the palette
 - [ ] `/model` lists the provider's `/models` (marked `(api)`); a wrong key is re-asked
 - [ ] `auto` mode: `echo x > ~/outside` in run_shell asks "Rerun outside the
diff --git a/include/cst_textsel.h b/include/cst_textsel.h
new file mode 100644
index 0000000..393b5df
--- /dev/null
+++ b/include/cst_textsel.h
@@ -0,0 +1,41 @@
+#ifndef CST_TEXTSEL_H
+#define CST_TEXTSEL_H
+
+#include <stddef.h>
+#include <wchar.h>
+
+/* UTF-8 / ANSI helpers shared by the TUI renderer and mouse selection, so both
+ * agree on which character occupies each column. */
+int cst_utf8_decode(const char *s, size_t avail, wchar_t *wc, size_t *eaten);
+/* wcwidth(), with an East-Asian / ASCII heuristic on Windows. */
+int cst_wcwidth(wchar_t wc);
+/* Columns of wc; 1 for non-printing characters. */
+int cst_utf8_width(wchar_t wc);
+/* Length of the escape sequence at s (CSI or two-byte ESC), 0 if none. */
+size_t cst_ansi_skip(const char *s, size_t n);
+
+typedef struct {
+  char *s; /* NUL-terminated once anything was appended */
+  size_t n, cap;
+} cst_selbuf_t;
+
+void cst_selbuf_free(cst_selbuf_t *b);
+int cst_selbuf_putc(cst_selbuf_t *b, char c);
+
+/* Appends the text drawn in columns [c1, c2] of a row whose content `line`
+ * (ANSI escapes allowed) starts at column `indent`; c2 < 0 means the end of
+ * the row. A wide character is taken whole when either of its cells is in
+ * range. With `trim`, trailing spaces of the appended part are dropped.
+ * Returns 0, or -1 when out of memory. */
+int cst_textsel_append(cst_selbuf_t *b, const char *line, int indent, int c1,
+                       int c2, int trim);
+
+/* Column span [*c1, *c2] of the word under column `col`; just that cell (or
+ * both cells of a wide character) when it is not on a word character. */
+void cst_textsel_word(const char *line, int indent, int col, int *c1, int *c2);
+
+/* Widens [*c1, *c2] so that neither end splits a wide character; highlighting
+ * half of one desynchronizes curses from the terminal. *c2 < 0 is left as is. */
+void cst_textsel_snap(const char *line, int indent, int *c1, int *c2);
+
+#endif
diff --git a/include/cst_version.h b/include/cst_version.h
index 9c7e088..75d6277 100644
--- a/include/cst_version.h
+++ b/include/cst_version.h
@@ -1,6 +1,6 @@
 #ifndef CST_VERSION_H
 #define CST_VERSION_H
 
-#define CST_VERSION "0.4.0"
+#define CST_VERSION "0.5.0"
 
 #endif
diff --git a/src/textsel.c b/src/textsel.c
new file mode 100644
index 0000000..0be8583
--- /dev/null
+++ b/src/textsel.c
@@ -0,0 +1,194 @@
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE /* wcwidth */
+#endif
+
+#include "cst_textsel.h"
+
+#include <stdlib.h>
+#include <string.h>
+#include <wctype.h>
+
+int cst_utf8_decode(const char *s, size_t avail, wchar_t *wc, size_t *eaten) {
+  if (avail == 0)
+    return -1;
+  mbstate_t st;
+  memset(&st, 0, sizeof(st));
+  size_t n = mbrtowc(wc, s, avail, &st);
+  if (n == (size_t)-1 || n == (size_t)-2 || n == 0) {
+    *wc = (unsigned char)s[0];
+    *eaten = 1;
+    return 0;
+  }
+  *eaten = n;
+  return 0;
+}
+
+int cst_wcwidth(wchar_t wc) {
+#ifdef _WIN32
+  unsigned long c = (unsigned long)wc;
+  if (c == 0)
+    return 0;
+  if (c < 32 || (c >= 0x7f && c < 0xa0))
+    return -1;
+  if (c >= 0x1100 &&
+      (c <= 0x115f || c == 0x2329 || c == 0x232a ||
+       (c >= 0x2e80 && c <= 0xa4cf && c != 0x303f) ||
+       (c >= 0xac00 && c <= 0xd7a3) || (c >= 0xf900 && c <= 0xfaff) ||
+       (c >= 0xfe10 && c <= 0xfe19) || (c >= 0xfe30 && c <= 0xfe6f) ||
+       (c >= 0xff00 && c <= 0xff60) || (c >= 0xffe0 && c <= 0xffe6) ||
+       (c >= 0x20000 && c <= 0x2fffd) || (c >= 0x30000 && c <= 0x3fffd)))
+    return 2;
+  return 1;
+#else
+  return wcwidth(wc);
+#endif
+}
+
+int cst_utf8_width(wchar_t wc) {
+  int w = cst_wcwidth(wc);
+  if (w < 0)
+    return 1;
+  return w;
+}
+
+size_t cst_ansi_skip(const char *s, size_t n) {
+  if (n < 2 || (unsigned char)s[0] != 0x1b)
+    return 0;
+  if (s[1] == '[') {
+    size_t i = 2;
+    while (i < n) {
+      unsigned char c = (unsigned char)s[i++];
+      if (c >= 0x40 && c <= 0x7e)
+        return i;
+    }
+    return 0;
+  }
+  return 2;
+}
+
+void cst_selbuf_free(cst_selbuf_t *b) {
+  free(b->s);
+  b->s = NULL;
+  b->n = b->cap = 0;
+}
+
+static int selbuf_put(cst_selbuf_t *b, const char *p, size_t n) {
+  if (b->n + n + 1 > b->cap) {
+    size_t nc = b->cap ? b->cap * 2 : 256;
+    while (nc < b->n + n + 1)
+      nc *= 2;
+    char *ns = realloc(b->s, nc);
+    if (!ns)
+      return -1;
+    b->s = ns;
+    b->cap = nc;
+  }
+  memcpy(b->s + b->n, p, n);
+  b->n += n;
+  b->s[b->n] = 0;
+  return 0;
+}
+
+int cst_selbuf_putc(cst_selbuf_t *b, char c) { return selbuf_put(b, &c, 1); }
+
+/* One drawn character: its bytes in the line and the columns it covers. */
+typedef struct {
+  size_t off, len;
+  int col, width;
+  wchar_t wc;
+} cell_t;
+
+/* Advances to the next drawn character of line, skipping escapes. */
+static int next_cell(const char *line, size_t n, size_t *i, int *col,
+                     cell_t *c) {
+  while (*i < n) {
+    size_t skip = cst_ansi_skip(line + *i, n - *i);
+    if (skip) {
+      *i += skip;
+      continue;
+    }
+    size_t eaten;
+    cst_utf8_decode(line + *i, n - *i, &c->wc, &eaten);
+    c->off = *i;
+    c->len = eaten;
+    c->col = *col;
+    c->width = cst_utf8_width(c->wc);
+    *i += eaten;
+    *col += c->width;
+    return 1;
+  }
+  return 0;
+}
+
+int cst_textsel_append(cst_selbuf_t *b, const char *line, int indent, int c1,
+                       int c2, int trim) {
+  size_t n = line ? strlen(line) : 0, i = 0;
+  size_t start = b->n;
+  int col = indent;
+  cell_t c;
+  while (next_cell(line, n, &i, &col, &c)) {
+    if (c2 >= 0 && c.col > c2)
+      break;
+    if (c.width == 0 || c.col + c.width - 1 < c1)
+      continue;
+    if (selbuf_put(b, line + c.off, c.len) < 0)
+      return -1;
+  }
+  if (trim)
+    while (b->n > start && b->s[b->n - 1] == ' ')
+      b->s[--b->n] = 0;
+  return 0;
+}
+
+static int is_word(wchar_t wc) {
+  return iswalnum((wint_t)wc) || (wc < 128 && wc && strchr("_-./:@~%+=?&#$", (int)wc));
+}
+
+void cst_textsel_snap(const char *line, int indent, int *c1, int *c2) {
+  size_t n = line ? strlen(line) : 0, i = 0;
+  int x = indent;
+  cell_t c;
+  while (next_cell(line, n, &i, &x, &c)) {
+    if (c.width < 2)
+      continue;
+    int last = c.col + c.width - 1;
+    if (*c1 > c.col && *c1 <= last)
+      *c1 = c.col;
+    if (*c2 >= c.col && *c2 < last)
+      *c2 = last;
+  }
+}
+
+void cst_textsel_word(const char *line, int indent, int col, int *c1, int *c2) {
+  *c1 = *c2 = col;
+  size_t n = line ? strlen(line) : 0, i = 0;
+  int x = indent;
+  cell_t c;
+  int run_start = -1, in_run = 0;
+  while (next_cell(line, n, &i, &x, &c)) {
+    if (c.width == 0)
+      continue;
+    int word = is_word(c.wc);
+    if (word && !in_run)
+      run_start = c.col;
+    in_run = word;
+    if (col >= c.col && col < c.col + c.width) {
+      if (!word) {
+        *c1 = c.col;
+        *c2 = c.col + c.width - 1;
+        return;
+      }
+      *c1 = run_start;
+      *c2 = c.col + c.width - 1;
+      cell_t d;
+      while (next_cell(line, n, &i, &x, &d)) {
+        if (d.width == 0)
+          continue;
+        if (!is_word(d.wc))
+          break;
+        *c2 = d.col + d.width - 1;
+      }
+      return;
+    }
+  }
+}
diff --git a/src/tui.c b/src/tui.c
index e2c8ad9..2a1866a 100644
--- a/src/tui.c
+++ b/src/tui.c
@@ -10,6 +10,7 @@
 #include "cst_plugins.h"
 #include "cst_skills.h"
 #include "cst_subagent.h"
+#include "cst_textsel.h"
 #include "cst_perms.h"
 #include "cst_sandbox.h"
 #include "cst_tools.h"
@@ -61,23 +62,7 @@ static int g_utf8 = 1; /* locale can show non-ASCII text */
 #ifndef KEY_RESIZE
 #define KEY_RESIZE 0632
 #endif
-/* MinGW often lacks wcwidth; simple East-Asian / ASCII heuristic. */
-static int cst_wcwidth(wchar_t wc) {
-  if (wc == 0)
-    return 0;
-  if (wc < 32 || (wc >= 0x7f && wc < 0xa0))
-    return -1;
-  if (wc >= 0x1100 &&
-      (wc <= 0x115f || wc == 0x2329 || wc == 0x232a ||
-       (wc >= 0x2e80 && wc <= 0xa4cf && wc != 0x303f) ||
-       (wc >= 0xac00 && wc <= 0xd7a3) || (wc >= 0xf900 && wc <= 0xfaff) ||
-       (wc >= 0xfe10 && wc <= 0xfe19) || (wc >= 0xfe30 && wc <= 0xfe6f) ||
-       (wc >= 0xff00 && wc <= 0xff60) || (wc >= 0xffe0 && wc <= 0xffe6) ||
-       (wc >= 0x20000 && wc <= 0x2fffd) || (wc >= 0x30000 && wc <= 0x3fffd)))
-    return 2;
-  return 1;
-}
-#define wcwidth cst_wcwidth
+#define wcwidth cst_wcwidth /* MinGW often lacks wcwidth */
 #else
 #include <ncurses.h>
 #endif
@@ -139,6 +124,12 @@ static int cst_clock_gettime_mono(struct timespec *ts) {
 #define KEY_KITTY_REPLY (KEY_OWN_BASE + 3)
 #define KEY_KITTY_BASE (KEY_OWN_BASE + 16)
 #define KITTY_CP_END 128
+/* Transcript selection states. */
+#define SEL_NONE 0
+#define SEL_PRESS 1 /* button down, not moved off the pressed cell yet */
+#define SEL_DRAG 2
+#define SEL_SHOWN 3 /* released; highlighted until the next input */
+#define MULTI_CLICK_MS 400
 
 #ifdef NCURSES_VERSION
 static int g_kitty_on;
@@ -301,6 +292,15 @@ typedef struct {
   int row_blk_cap;
   int cmd_x0, cmd_x1;         /* "ctrl+p commands" in the status row */
   int mouse_on;
+  int log_start;              /* display line shown in logw row 0 */
+  /* Mouse selection in the transcript: display line + logw column. */
+  int sel_state;              /* SEL_* */
+  int sel_mode;               /* 1 characters, 2 words, 3 lines */
+  int sel_ay, sel_ax;         /* anchor */
+  int sel_y, sel_x;           /* current end */
+  int sel_press_y, sel_press_x; /* screen cell of the press */
+  int sel_clicks, sel_click_y, sel_click_x;
+  struct timespec sel_click_at;
   const char *tip;
   const char *sandbox_name;   /* "landlock" / "seatbelt" / "rules" */
   char where[300];            /* ~/path:branch */
@@ -404,26 +404,10 @@ static size_t utf8_prev_len(const char *s, size_t len) {
 }
 
 static int utf8_decode(const char *s, size_t avail, wchar_t *wc, size_t *eaten) {
-  if (avail == 0)
-    return -1;
-  mbstate_t st;
-  memset(&st, 0, sizeof(st));
-  size_t n = mbrtowc(wc, s, avail, &st);
-  if (n == (size_t)-1 || n == (size_t)-2 || n == 0) {
-    *wc = (unsigned char)s[0];
-    *eaten = 1;
-    return 0;
-  }
-  *eaten = n;
-  return 0;
+  return cst_utf8_decode(s, avail, wc, eaten);
 }
 
-static int utf8_width(wchar_t wc) {
-  int w = wcwidth(wc);
-  if (w < 0)
-    return 1;
-  return w;
-}
+static int utf8_width(wchar_t wc) { return cst_utf8_width(wc); }
 
 static int utf8_cols(const char *s, size_t n) {
   int cols = 0;
@@ -454,20 +438,7 @@ static size_t utf8_fit_cols(const char *s, size_t n, int max_cols) {
   return i;
 }
 
-static size_t ansi_skip(const char *s, size_t n) {
-  if (n < 2 || (unsigned char)s[0] != 0x1b)
-    return 0;
-  if (s[1] == '[') {
-    size_t i = 2;
-    while (i < n) {
-      unsigned char c = (unsigned char)s[i++];
-      if (c >= 0x40 && c <= 0x7e)
-        return i;
-    }
-    return 0;
-  }
-  return 2;
-}
+static size_t ansi_skip(const char *s, size_t n) { return cst_ansi_skip(s, n); }
 
 static char *xstrdup(const char *s) {
   if (!s)
@@ -1272,6 +1243,8 @@ typedef struct {
   int fill;   /* pair painted across the whole row (0 = none) */
   int bar;    /* pair for a "┃" in column 0 (0 = none) */
   int blk;    /* hist block index, -1 for live / none */
+  int cont;     /* soft-wrapped continuation of the previous row */
+  int cont_pad; /* leading columns of a continuation that only indent */
 } dline_t;
 
 static int g_dl_blk = -1; /* block being flattened, stamped into dline_t */
@@ -1311,6 +1284,8 @@ static int dlines_push(dlines_t *dl, const char *text, int pair, int bold,
   L->fill = 0;
   L->bar = 0;
   L->blk = g_dl_blk;
+  L->cont = 0;
+  L->cont_pad = 0;
   return 0;
 }
 
@@ -1341,10 +1316,10 @@ static void push_wrapped(dlines_t *dl, const char *prefix, const char *body,
   /* Walk body; for ANSI text, wrap on visible columns skipping SGR. */
   size_t n = strlen(body);
   size_t i = 0;
-  int first = 1;
+  int first = 1, soft = 0;
   while (i < n && dl->n < MAX_RENDER_LINES) {
     size_t start = i;
-    int col = 0;
+    int col = 0, pad = 0;
     while (i < n) {
       size_t sg = 0;
       if ((unsigned char)body[i] == 0x1b) {
@@ -1387,7 +1362,7 @@ static void push_wrapped(dlines_t *dl, const char *prefix, const char *body,
       first = 0;
     } else {
       /* continuation indent matching prefix visual width */
-      int pad = pref_cols;
+      pad = pref_cols;
       if (pad < 0)
         pad = 0;
       if (pad > 40)
@@ -1400,10 +1375,11 @@ static void push_wrapped(dlines_t *dl, const char *prefix, const char *body,
         line[pad] = 0;
       }
     }
-    dlines_push(dl, line, pair, bold, dim);
-    if (i < n && body[i - 1] != '\n' && col >= body_w) {
-      /* soft wrap — already advanced */
+    if (dlines_push(dl, line, pair, bold, dim) == 0 && soft) {
+      dl->lines[dl->n - 1].cont = 1;
+      dl->lines[dl->n - 1].cont_pad = pad;
     }
+    soft = body[i - 1] != '\n';
   }
 }
 
@@ -2338,7 +2314,7 @@ static const char *const TIPS[] = {
     "/undo reverts the file changes of the last turn",
     "/provider switches provider; keys are saved per provider",
     "Click a tool card or Thought to expand it",
-    "Shift+drag selects text while mouse support is on",
+    "Drag over the transcript to copy it; double-click copies a word",
 };
 
 static void draw_home(tui_t *t) {
@@ -2548,6 +2524,57 @@ static void draw_side(tui_t *t) {
   wrefresh(s);
 }
 
+/* Ordered selection [y1:x1, y2:x2] over display lines, snapped to words or
+ * whole lines by the click count; x2 < 0 means the end of the line. */
+static void sel_range(const tui_t *t, const dlines_t *dl, int *y1, int *x1,
+                      int *y2, int *x2) {
+  int ay = t->sel_ay, ax = t->sel_ax, by = t->sel_y, bx = t->sel_x;
+  if (by < ay || (by == ay && bx < ax)) {
+    int ty = ay, tx = ax;
+    ay = by, ax = bx, by = ty, bx = tx;
+  }
+  if (t->sel_mode == 2) {
+    int c1, c2;
+    if (ay >= 0 && ay < dl->n) {
+      cst_textsel_word(dl->lines[ay].text, dl->lines[ay].indent, ax, &c1, &c2);
+      ax = c1;
+    }
+    if (by >= 0 && by < dl->n) {
+      cst_textsel_word(dl->lines[by].text, dl->lines[by].indent, bx, &c1, &c2);
+      bx = c2;
+    }
+  } else if (t->sel_mode == 3) {
+    while (ay > 0 && ay < dl->n && dl->lines[ay].cont)
+      ay--;
+    while (by + 1 < dl->n && dl->lines[by + 1].cont)
+      by++;
+    ax = 0;
+    bx = -1;
+  }
+  *y1 = ay, *x1 = ax, *y2 = by, *x2 = bx;
+}
+
+static void draw_selection(tui_t *t, const dlines_t *dl, int h, int w) {
+  if (t->sel_state != SEL_DRAG && t->sel_state != SEL_SHOWN)
+    return;
+  int y1, x1, y2, x2;
+  sel_range(t, dl, &y1, &x1, &y2, &x2);
+  for (int row = 0; row < h; row++) {
+    int li = t->log_start + row;
+    if (li < y1 || li > y2)
+      continue;
+    int a = li == y1 ? x1 : 0;
+    int b = li == y2 && x2 >= 0 ? x2 : w - 1;
+    if (li < dl->n)
+      cst_textsel_snap(dl->lines[li].text, dl->lines[li].indent, &a, &b);
+    if (b >= w)
+      b = w - 1;
+    if (a <= b)
+      mvwchgat(t->logw, row, a, b - a + 1, A_REVERSE,
+               HAS_COLOR() ? CP_PANEL : 0, NULL);
+  }
+}
+
 static void draw_log(tui_t *t) {
   if (!t->logw)
     return;
@@ -2581,6 +2608,7 @@ static void draw_log(tui_t *t) {
   int start = total - h - t->log_scroll;
   if (start < 0)
     start = 0;
+  t->log_start = start;
 
   if (t->row_blk_cap < h) {
     int *nb = realloc(t->row_blk, (size_t)h * sizeof(int));
@@ -2604,6 +2632,7 @@ static void draw_log(tui_t *t) {
     if (L->bar)
       put_wc(t->logw, row, 0, L'┃', HAS_COLOR() ? (int)COLOR_PAIR(L->bar) : 0);
   }
+  draw_selection(t, &dl, h, w);
   if (t->log_scroll > 0 && h > 2) {
     char more[128];
     snprintf(more, sizeof(more),
@@ -2777,8 +2806,17 @@ static int input_visual_rows(const tui_t *t) {
 }
 
 static void apply_mouse(const tui_t *t) {
-  mousemask(t->mouse_on ? (mmask_t)ALL_MOUSE_EVENTS : 0, NULL);
+  mousemask(t->mouse_on ? (mmask_t)(ALL_MOUSE_EVENTS | REPORT_MOUSE_POSITION)
+                        : 0,
+            NULL);
   mouseinterval(0);
+#ifdef NCURSES_VERSION
+  /* ncurses only asks for presses and releases (1000). 1002 also reports
+   * motion while a button is held, for drag selection; terminals treat it as
+   * replacing 1000, so it goes after mousemask and is turned off explicitly. */
+  printf(t->mouse_on ? "\033[?1002h" : "\033[?1002l");
+  fflush(stdout);
+#endif
 }
 
 static void free_windows(tui_t *t) {
@@ -3919,7 +3957,7 @@ static void cmd_help(tui_t *t, char *arg, int *quit) {
   push_system_line(t, "  Enter send · Esc cancel turn · Ctrl+C twice or Ctrl+D "
                       "quit · Ctrl+P command palette");
   push_system_line(t, "  Mouse: click cards / Thought to expand, wheel scrolls, "
-                      "Shift+drag selects · /mouse");
+                      "drag copies (double-click word, triple line) · /mouse");
   push_system_line(t, "  Rebind in keybinds.json next to settings.json");
   push_system_line(t, "");
 }
@@ -4346,8 +4384,10 @@ static void cmd_mouse(tui_t *t, char *arg, int *quit) {
   (void)quit;
   t->mouse_on = !t->mouse_on;
   apply_mouse(t);
-  push_system_line(t, t->mouse_on ? "(mouse on · Shift+drag selects text)"
-                                  : "(mouse off · the terminal selects text)");
+  push_system_line(t, t->mouse_on
+                          ? "(mouse on · drag selects and copies (OSC 52) · "
+                            "Shift+drag uses the terminal's own selection)"
+                          : "(mouse off · the terminal selects text)");
 }
 
 static void cmd_max_steps(tui_t *t, char *arg, int *quit) {
@@ -4533,25 +4573,16 @@ static void cmd_export(tui_t *t, char *arg, int *quit) {
   push_system_line(t, "(exported to %s)", path);
 }
 
-static void cmd_copy(tui_t *t, char *arg, int *quit) {
-  (void)arg;
-  (void)quit;
-  const char *text = NULL;
-  for (int i = t->hist.n - 1; i >= 0 && !text; i--)
-    if (t->hist.items[i].kind == BLK_ASSISTANT && t->hist.items[i].body)
-      text = t->hist.items[i].body;
-  if (!text || !text[0]) {
-    push_system_line(t, "Nothing to copy yet");
-    return;
-  }
+/* Puts text on the terminal's clipboard; returns the bytes sent, 0 on
+ * failure. */
+static size_t osc52_copy(const char *text, size_t n) {
   static const char b64[] =
       "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
-  size_t n = strlen(text);
   if (n > 75000)
     n = 75000; /* many terminals cap OSC 52 near 100 KB */
   char *enc = malloc((n + 2) / 3 * 4 + 1);
   if (!enc)
-    return;
+    return 0;
   size_t o = 0;
   for (size_t i = 0; i < n; i += 3) {
     unsigned v = (unsigned char)text[i] << 16;
@@ -4571,8 +4602,24 @@ static void cmd_copy(tui_t *t, char *arg, int *quit) {
     printf("\033]52;c;%s\a", enc);
   fflush(stdout);
   free(enc);
-  push_system_line(t, "(copied %zu bytes of the last reply via OSC 52 — the "
-                      "terminal must allow clipboard access)", n);
+  return n;
+}
+
+static void cmd_copy(tui_t *t, char *arg, int *quit) {
+  (void)arg;
+  (void)quit;
+  const char *text = NULL;
+  for (int i = t->hist.n - 1; i >= 0 && !text; i--)
+    if (t->hist.items[i].kind == BLK_ASSISTANT && t->hist.items[i].body)
+      text = t->hist.items[i].body;
+  if (!text || !text[0]) {
+    push_system_line(t, "Nothing to copy yet");
+    return;
+  }
+  size_t n = osc52_copy(text, strlen(text));
+  if (n)
+    push_system_line(t, "(copied %zu bytes of the last reply via OSC 52 — the "
+                        "terminal must allow clipboard access)", n);
 }
 
 static void cmd_init(tui_t *t, char *arg, int *quit) {
@@ -4906,7 +4953,7 @@ static const slash_cmd_t SLASH[] = {
      1, cmd_approval},
     {"yolo", "", "", "toggle approving everything", 1, cmd_yolo},
     {"sidebar", "", "", "show or hide the session sidebar", 1, cmd_sidebar},
-    {"mouse", "", "", "toggle mouse support (Shift+drag selects)", 1,
+    {"mouse", "", "", "toggle mouse support (drag copies)", 1,
      cmd_mouse},
     {"max-steps", "", "[N]", "tool steps allowed per turn", 1, cmd_max_steps},
     {"status", "", "", "session, model, context and settings", 1, cmd_status},
@@ -5437,6 +5484,145 @@ static int handle_click(tui_t *t, int y, int x, int busy) {
   return 0;
 }
 
+/* Transcript cell under screen (y, x) as display line + column. Outside the
+ * transcript returns 0, unless `clamp` pulls the point to its nearest edge. */
+static int log_cell(const tui_t *t, int y, int x, int clamp, int *li,
+                    int *col) {
+  if (t->home || !t->logw)
+    return 0;
+  int lh, lw;
+  getmaxyx(t->logw, lh, lw);
+  int ry = y - t->log_y, rx = x - t->log_x;
+  if (!clamp && (ry < 0 || ry >= lh || rx < 0 || rx >= lw))
+    return 0;
+  *li = t->log_start + clampi(ry, 0, lh - 1);
+  *col = clampi(rx, 0, lw - 1);
+  return 1;
+}
+
+static void sel_clear(tui_t *t) {
+  int shown = t->sel_state == SEL_DRAG || t->sel_state == SEL_SHOWN;
+  t->sel_state = SEL_NONE;
+  if (shown)
+    draw_log(t);
+}
+
+static void sel_copy(tui_t *t) {
+  int h, w;
+  getmaxyx(t->logw, h, w);
+  (void)h;
+  dlines_t dl = {0};
+  build_display(t, &dl, w);
+  int y1, x1, y2, x2;
+  sel_range(t, &dl, &y1, &x1, &y2, &x2);
+  cst_selbuf_t b = {0};
+  for (int k = y1 < 0 ? 0 : y1; k <= y2 && k < dl.n; k++) {
+    const dline_t *L = &dl.lines[k];
+    int c1 = k == y1 ? x1 : 0, c2 = k == y2 ? x2 : -1;
+    if (k > y1) {
+      if (!L->cont)
+        cst_selbuf_putc(&b, '\n');
+      else if (c1 < L->indent + L->cont_pad)
+        c1 = L->indent + L->cont_pad;
+    }
+    int joined = k < y2 && k + 1 < dl.n && dl.lines[k + 1].cont;
+    cst_textsel_append(&b, L->text, L->indent, c1, c2, !joined);
+  }
+  dlines_free(&dl);
+  if (b.n && osc52_copy(b.s, b.n)) {
+    size_t chars = 0;
+    for (size_t i = 0; i < b.n; i++)
+      chars += ((unsigned char)b.s[i] & 0xC0) != 0x80;
+    char msg[96];
+    snprintf(msg, sizeof(msg), "Copied %zu characters (OSC 52)", chars);
+    set_status(t, msg);
+    draw_status(t);
+  }
+  cst_selbuf_free(&b);
+}
+
+/* Drag while the button is held: extend the selection, scrolling the
+ * transcript when the pointer is above or below it. */
+static void sel_motion(tui_t *t, int y, int x) {
+  int lh, lw;
+  getmaxyx(t->logw, lh, lw);
+  (void)lw;
+  int ry = y - t->log_y;
+  if (ry < 0 || ry >= lh) {
+    int before = t->log_scroll;
+    t->log_scroll += ry < 0 ? 1 : -1;
+    if (t->log_scroll < 0)
+      t->log_scroll = 0;
+    if (t->log_scroll != before)
+      draw_log(t); /* updates log_start */
+  }
+  int li, col;
+  if (!log_cell(t, y, x, 1, &li, &col))
+    return;
+  if (t->sel_state == SEL_PRESS && li == t->sel_ay && col == t->sel_ax)
+    return;
+  t->sel_state = SEL_DRAG;
+  t->sel_y = li;
+  t->sel_x = col;
+  draw_log(t);
+}
+
+/* Wheel, clicks and drag selection; -2 means quit. */
+static int on_mouse(tui_t *t, const MEVENT *ev, int busy) {
+  mmask_t b = ev->bstate;
+  if (b & BUTTON4_PRESSED) {
+    t->log_scroll += SCROLL_SPEED;
+    draw_log(t);
+    return 0;
+  }
+  if (b & BUTTON5_PRESSED) {
+    t->log_scroll -= SCROLL_SPEED;
+    if (t->log_scroll < 0)
+      t->log_scroll = 0;
+    draw_log(t);
+    return 0;
+  }
+  if (b & REPORT_MOUSE_POSITION) {
+    if (t->sel_state == SEL_PRESS || t->sel_state == SEL_DRAG)
+      sel_motion(t, ev->y, ev->x);
+    return 0;
+  }
+  if (b & (BUTTON1_PRESSED | BUTTON1_CLICKED)) {
+    sel_clear(t);
+    int li, col;
+    if (!(b & BUTTON1_PRESSED) || !log_cell(t, ev->y, ev->x, 0, &li, &col))
+      return handle_click(t, ev->y, ev->x, busy);
+    if (t->sel_clicks && since_ms(&t->sel_click_at) < MULTI_CLICK_MS &&
+        li == t->sel_click_y && abs(col - t->sel_click_x) <= 1)
+      t->sel_clicks = t->sel_clicks % 3 + 1;
+    else
+      t->sel_clicks = 1;
+    clock_gettime(CLOCK_MONOTONIC, &t->sel_click_at);
+    t->sel_click_y = li;
+    t->sel_click_x = col;
+    t->sel_mode = t->sel_clicks;
+    t->sel_ay = t->sel_y = li;
+    t->sel_ax = t->sel_x = col;
+    t->sel_press_y = ev->y;
+    t->sel_press_x = ev->x;
+    t->sel_state = t->sel_clicks > 1 ? SEL_DRAG : SEL_PRESS;
+    if (t->sel_state == SEL_DRAG)
+      draw_log(t);
+    return 0;
+  }
+  if (b & BUTTON1_RELEASED) {
+    if (t->sel_state == SEL_PRESS) {
+      t->sel_state = SEL_NONE;
+      return handle_click(t, t->sel_press_y, t->sel_press_x, busy);
+    }
+    if (t->sel_state == SEL_DRAG) {
+      sel_copy(t);
+      t->sel_state = SEL_SHOWN;
+    }
+  }
+  return 0;
+}
+
 /* Tab completes after "/" at the start or an "@word" under the cursor. */
 static int wants_completion(const tui_t *t) {
   if (t->in_len && t->inbuf[0] == '/')
@@ -6192,6 +6378,9 @@ int cst_tui_run(cst_agent_t *agent) {
     int rc = tui_wget_wch(t.input, &wch);
     if (rc == ERR)
       continue;
+    if (t.sel_state == SEL_SHOWN &&
+        !(rc == KEY_CODE_YES && (wch == KEY_MOUSE || wch == KEY_RESIZE)))
+      sel_clear(&t);
 
     if (!t.in_paste &&
         !(rc == KEY_CODE_YES &&
@@ -6263,6 +6452,7 @@ int cst_tui_run(cst_agent_t *agent) {
         continue;
       }
       if (wch == KEY_RESIZE) {
+        t.sel_state = SEL_NONE; /* display lines rewrap */
         layout(&t);
         wtimeout(t.input, 80);
         redraw_all(&t);
@@ -6271,18 +6461,8 @@ int cst_tui_run(cst_agent_t *agent) {
       if (wch == KEY_MOUSE) {
         MEVENT ev;
         if (getmouse(&ev) == OK) {
-          if (ev.bstate & BUTTON4_PRESSED) {
-            t.log_scroll += SCROLL_SPEED;
-            draw_log(&t);
-          } else if (ev.bstate & BUTTON5_PRESSED) {
-            t.log_scroll -= SCROLL_SPEED;
-            if (t.log_scroll < 0)
-              t.log_scroll = 0;
-            draw_log(&t);
-          } else if (ev.bstate & (BUTTON1_PRESSED | BUTTON1_CLICKED)) {
-            if (handle_click(&t, ev.y, ev.x, busy) == -2)
-              goto out;
-          }
+          if (on_mouse(&t, &ev, busy) == -2)
+            goto out;
           draw_input(&t); /* keep the terminal cursor in the box */
         }
         continue;
@@ -6495,7 +6675,7 @@ out:
   tui_free(&t);
 #ifdef NCURSES_VERSION
   kitty_restore();
-  printf("\033[?2004l");
+  printf("\033[?1002l\033[?2004l");
   fflush(stdout);
 #endif
   endwin();
diff --git a/tests/test_markdown.c b/tests/test_markdown.c
new file mode 100644
index 0000000..0fe8351
--- /dev/null
+++ b/tests/test_markdown.c
@@ -0,0 +1,109 @@
+#include "sashidown.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define CHECK(c)                                                               \
+  do {                                                                         \
+    if (!(c)) {                                                                \
+      fprintf(stderr, "%s:%d: CHECK(%s) failed\n", __FILE__, __LINE__, #c);   \
+      exit(1);                                                                 \
+    }                                                                          \
+  } while (0)
+
+/* SASHIDOWN_FMT_ANSI_PLAIN theme */
+#define ITALIC "\033[3m"
+#define ITALIC_OFF "\033[23m"
+#define BOLD "\033[1m"
+#define BOLD_OFF "\033[22m"
+#define CODE "\033[7m"
+
+static char out[4096], plain[4096];
+
+/* Renders md; `out` keeps the escapes, `plain` has them stripped. */
+static void render(const char *md) {
+  size_t n = 0;
+  CHECK(sashidown_convert(md, strlen(md), out, sizeof(out) - 1, &n,
+                          SASHIDOWN_FMT_ANSI_PLAIN) == 0);
+  out[n] = 0;
+  size_t o = 0;
+  for (size_t i = 0; i < n;) {
+    if (out[i] == '\033' && out[i + 1] == '[') {
+      i += 2;
+      while (i < n && !(out[i] >= 0x40 && out[i] <= 0x7e))
+        i++;
+      i++;
+      continue;
+    }
+    plain[o++] = out[i++];
+  }
+  plain[o] = 0;
+}
+
+static int has(const char *s, const char *needle) {
+  return strstr(s, needle) != NULL;
+}
+
+static void test_intraword(void) {
+  render("see test_apply_patch.c now");
+  CHECK(has(plain, "test_apply_patch.c"));
+  CHECK(!has(out, ITALIC));
+  render("snake_case_x and 中文_变量_名 and a__b__c");
+  CHECK(has(plain, "snake_case_x and 中文_变量_名 and a__b__c"));
+  CHECK(!has(out, ITALIC) && !has(out, BOLD));
+  render("foo_bar_ baz");
+  CHECK(has(plain, "foo_bar_ baz") && !has(out, ITALIC));
+}
+
+static void test_pairs(void) {
+  render("*it* and _it_");
+  CHECK(has(out, ITALIC "it" ITALIC_OFF " and " ITALIC "it" ITALIC_OFF));
+  render("**b** __b__");
+  CHECK(has(out, BOLD "b" BOLD_OFF " " BOLD "b" BOLD_OFF));
+  render("***x***");
+  CHECK(has(out, BOLD ITALIC "x" ITALIC_OFF BOLD_OFF));
+  render("*a_b* end");
+  CHECK(has(out, ITALIC "a_b" ITALIC_OFF " end"));
+  /* CommonMark: intraword '*' pairs, a standalone __init__ is bold */
+  render("2*3*4");
+  CHECK(has(out, "2" ITALIC "3" ITALIC_OFF "4"));
+  render("call __init__ now");
+  CHECK(has(out, BOLD "init" BOLD_OFF " now"));
+}
+
+static void test_unmatched(void) {
+  render("a * b and 2 * 3 * 4");
+  CHECK(has(plain, "a * b and 2 * 3 * 4") && !has(out, ITALIC));
+  render("trailing star*");
+  CHECK(has(plain, "trailing star*") && !has(out, ITALIC));
+  render("*mix_ words");
+  CHECK(has(plain, "*mix_ words") && !has(out, ITALIC));
+  render("**open bold only");
+  CHECK(has(plain, "**open bold only") && !has(out, BOLD));
+  render("a `b");
+  CHECK(has(plain, "a `b") && !has(out, CODE));
+}
+
+static void test_code(void) {
+  render("run `a_b_c` and `*x*`");
+  CHECK(has(plain, "run a_b_c and *x*"));
+  CHECK(has(out, CODE) && !has(out, ITALIC));
+}
+
+static void test_cjk(void) {
+  render("**粗体**，后文");
+  CHECK(has(out, BOLD "粗体" BOLD_OFF "，后文"));
+  render("看**“引号”**这里");
+  CHECK(has(out, BOLD "“引号”" BOLD_OFF "这里"));
+}
+
+int main(void) {
+  test_intraword();
+  test_pairs();
+  test_unmatched();
+  test_code();
+  test_cjk();
+  printf("test_markdown: ok\n");
+  return 0;
+}
diff --git a/tests/test_textsel.c b/tests/test_textsel.c
new file mode 100644
index 0000000..e10f5f6
--- /dev/null
+++ b/tests/test_textsel.c
@@ -0,0 +1,112 @@
+#include "cst_textsel.h"
+
+#include <locale.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define CHECK(c)                                                               \
+  do {                                                                         \
+    if (!(c)) {                                                                \
+      fprintf(stderr, "%s:%d: CHECK(%s) failed\n", __FILE__, __LINE__, #c);   \
+      exit(1);                                                                 \
+    }                                                                          \
+  } while (0)
+
+static char got[512];
+
+static const char *slice(const char *line, int indent, int c1, int c2,
+                         int trim) {
+  cst_selbuf_t b = {0};
+  CHECK(cst_textsel_append(&b, line, indent, c1, c2, trim) == 0);
+  snprintf(got, sizeof(got), "%s", b.s ? b.s : "");
+  cst_selbuf_free(&b);
+  return got;
+}
+
+static void test_ascii(void) {
+  CHECK(strcmp(slice("hello world", 0, 0, 4, 1), "hello") == 0);
+  CHECK(strcmp(slice("hello world", 0, 6, -1, 1), "world") == 0);
+  CHECK(strcmp(slice("hello world", 0, 3, 7, 1), "lo wo") == 0);
+  /* indent: columns before the content are blank */
+  CHECK(strcmp(slice("abc", 2, 0, 2, 1), "a") == 0);
+  CHECK(strcmp(slice("abc", 2, 0, 1, 1), "") == 0);
+  /* trailing spaces */
+  CHECK(strcmp(slice("ab   ", 0, 0, -1, 1), "ab") == 0);
+  CHECK(strcmp(slice("ab   ", 0, 0, -1, 0), "ab   ") == 0);
+  /* beyond the end of the content */
+  CHECK(strcmp(slice("ab", 0, 5, 9, 1), "") == 0);
+}
+
+static void test_ansi(void) {
+  const char *s = "\033[1;31mred\033[0m and \033[32mgreen\033[0m";
+  CHECK(strcmp(slice(s, 0, 0, -1, 1), "red and green") == 0);
+  CHECK(strcmp(slice(s, 0, 4, 6, 1), "and") == 0);
+  CHECK(strcmp(slice(s, 0, 8, 12, 1), "green") == 0);
+  int c1, c2;
+  cst_textsel_word(s, 0, 10, &c1, &c2);
+  CHECK(c1 == 8 && c2 == 12);
+}
+
+static void test_words(void) {
+  const char *s = "  open src/tui.c:42 now";
+  int c1, c2;
+  cst_textsel_word(s, 0, 9, &c1, &c2);
+  CHECK(c1 == 7 && c2 == 18);
+  CHECK(strcmp(slice(s, 0, c1, c2, 1), "src/tui.c:42") == 0);
+  cst_textsel_word(s, 0, 6, &c1, &c2); /* on a space */
+  CHECK(c1 == 6 && c2 == 6);
+  cst_textsel_word(s, 0, 40, &c1, &c2); /* past the end */
+  CHECK(c1 == 40 && c2 == 40);
+  cst_textsel_word(s, 1, 3, &c1, &c2); /* indent shifts columns */
+  CHECK(c1 == 3 && c2 == 6);
+}
+
+static void test_wide(void) {
+  /* 中文 occupies columns 0-1 and 2-3 */
+  const char *s = "中文 ok";
+  CHECK(strcmp(slice(s, 0, 1, 1, 1), "中") == 0);
+  CHECK(strcmp(slice(s, 0, 1, 2, 1), "中文") == 0);
+  CHECK(strcmp(slice(s, 0, 3, 6, 1), "文 ok") == 0);
+  int c1, c2;
+  cst_textsel_word(s, 0, 3, &c1, &c2);
+  CHECK(c1 == 0 && c2 == 3);
+  cst_textsel_word("「x」", 0, 1, &c1, &c2); /* wide punctuation */
+  CHECK(c1 == 0 && c2 == 1);
+  /* highlight edges never split a wide character */
+  c1 = 1, c2 = 2;
+  cst_textsel_snap(s, 0, &c1, &c2);
+  CHECK(c1 == 0 && c2 == 3);
+  c1 = 2, c2 = 5;
+  cst_textsel_snap(s, 0, &c1, &c2);
+  CHECK(c1 == 2 && c2 == 5);
+  c1 = 3, c2 = -1;
+  cst_textsel_snap(s, 1, &c1, &c2); /* indent 1: 中 at 1-2, 文 at 3-4 */
+  CHECK(c1 == 3 && c2 == -1);
+  c1 = 4, c2 = 1;
+  cst_textsel_snap(s, 1, &c1, &c2);
+  CHECK(c1 == 3 && c2 == 2);
+}
+
+static void test_join(void) {
+  cst_selbuf_t b = {0};
+  CHECK(cst_textsel_append(&b, "first line  ", 0, 6, -1, 1) == 0);
+  CHECK(cst_selbuf_putc(&b, '\n') == 0);
+  CHECK(cst_textsel_append(&b, "second", 2, 0, 4, 1) == 0);
+  CHECK(strcmp(b.s, "line\nsec") == 0);
+  cst_selbuf_free(&b);
+  CHECK(b.s == NULL && b.n == 0);
+}
+
+int main(void) {
+  test_ascii();
+  test_ansi();
+  test_words();
+  if (setlocale(LC_CTYPE, "C.UTF-8") || setlocale(LC_CTYPE, "en_US.UTF-8"))
+    test_wide();
+  else
+    printf("test_textsel: no UTF-8 locale, wide-character checks skipped\n");
+  test_join();
+  printf("test_textsel: ok\n");
+  return 0;
+}
diff --git a/vendor/sashidown/src/render_ansi.c b/vendor/sashidown/src/render_ansi.c
index 37cf413..72cc147 100644
--- a/vendor/sashidown/src/render_ansi.c
+++ b/vendor/sashidown/src/render_ansi.c
@@ -12,8 +12,88 @@ typedef struct {
     uint8_t code;
     uint8_t latex;
     uint8_t strike;
+    char    bold_ch;   /* '*' or '_' that opened bold / italic */
+    char    italic_ch;
 } ansi_inline_t;
 
+/* --- emphasis delimiters (CommonMark flanking rules, simplified) ---------- */
+
+/* Neighbour of a delimiter run: whitespace (also line start/end), ASCII
+ * punctuation, or anything else. Non-ASCII counts as a letter so that CJK
+ * text and its full-width punctuation behave like words. */
+enum { MD_SPACE, MD_PUNCT, MD_OTHER };
+
+static int md_class(unsigned char c)
+{
+    if (c == ' ' || c == '\t' || c == '\n' || c == '\r')
+        return MD_SPACE;
+    if ((c >= 0x21 && c <= 0x2F) || (c >= 0x3A && c <= 0x40) ||
+        (c >= 0x5B && c <= 0x60) || (c >= 0x7B && c <= 0x7E))
+        return MD_PUNCT;
+    return MD_OTHER;
+}
+
+static size_t md_run(const char *input, size_t end, size_t i)
+{
+    size_t j = i;
+    while (j < end && input[j] == input[i])
+        j++;
+    return j - i;
+}
+
+/* Flanking of the run [i, i+n) within [start, end). */
+static void md_flank(const char *input, size_t start, size_t end, size_t i,
+                     size_t n, int *left, int *right, int *pc, int *nc)
+{
+    *pc = md_class(i > start ? (unsigned char)input[i - 1] : ' ');
+    *nc = md_class(i + n < end ? (unsigned char)input[i + n] : ' ');
+    *left = *nc != MD_SPACE && (*nc != MD_PUNCT || *pc != MD_OTHER);
+    *right = *pc != MD_SPACE && (*pc != MD_PUNCT || *nc != MD_OTHER);
+}
+
+/* '_' must not open or close inside a word (snake_case, __init__). */
+static int md_can_open(const char *input, size_t start, size_t end, size_t i,
+                       size_t n)
+{
+    int l, r, pc, nc;
+    md_flank(input, start, end, i, n, &l, &r, &pc, &nc);
+    return input[i] == '*' ? l : l && (!r || pc == MD_PUNCT);
+}
+
+static int md_can_close(const char *input, size_t start, size_t end, size_t i,
+                        size_t n)
+{
+    int l, r, pc, nc;
+    md_flank(input, start, end, i, n, &l, &r, &pc, &nc);
+    return input[i] == '*' ? r : r && (!l || nc == MD_PUNCT);
+}
+
+/* Whether a run of n delimiters like input[i] that can close follows on this
+ * line, outside code spans. */
+static int md_has_closer(const char *input, size_t start, size_t end,
+                         size_t i, size_t n)
+{
+    char d = input[i];
+    size_t k = i + n;
+    while (k < end) {
+        char c = input[k];
+        if (c == '\\' && k + 1 < end) {
+            k += 2;
+        } else if (c == '`') {
+            size_t j = block_scan_until_byte(input, end, k + 1, '`');
+            k = j < end ? j + 1 : k + 1;
+        } else if (c == d) {
+            size_t m = md_run(input, end, k);
+            if (m == n && md_can_close(input, start, end, k, m))
+                return 1;
+            k += m;
+        } else {
+            k++;
+        }
+    }
+    return 0;
+}
+
 typedef struct {
     uint8_t ul;
     uint8_t ol;
@@ -100,7 +180,7 @@ static void ansi_render_inline(sashidown_ctx_t *ctx, const ansi_theme_t *th,
                                const char *input, size_t len,
                                size_t start, size_t end)
 {
-    ansi_inline_t st = {0, 0, 0, 0, 0};
+    ansi_inline_t st = {0, 0, 0, 0, 0, 0, 0};
     size_t i = start;
 
     while (i < end) {
@@ -194,10 +274,39 @@ static void ansi_render_inline(sashidown_ctx_t *ctx, const ansi_theme_t *th,
             }
         }
 
-        if ((ch == '*' || ch == '_') && i + 1 < end && input[i + 1] == (char)ch) {
-            ansi_s(ctx, st.bold ? th->strong_off : th->strong_on);
-            st.bold = !st.bold;
-            i += 2;
+        if (ch == '*' || ch == '_') {
+            /* run of 1 = italic, 2 = bold, 3 = both; others are literal */
+            size_t n = md_run(input, end, i);
+            int b = n >= 2 && n <= 3, it = n == 1 || n == 3;
+            int open_b = st.bold && st.bold_ch == (char)ch;
+            int open_i = st.italic && st.italic_ch == (char)ch;
+            if (n <= 3 && (!b || open_b) && (!it || open_i) &&
+                md_can_close(input, start, end, i, n)) {
+                if (it) {
+                    ansi_s(ctx, th->emph_off);
+                    st.italic = 0;
+                }
+                if (b) {
+                    ansi_s(ctx, th->strong_off);
+                    st.bold = 0;
+                }
+            } else if (n <= 3 && (!b || !st.bold) && (!it || !st.italic) &&
+                       md_can_open(input, start, end, i, n) &&
+                       md_has_closer(input, start, end, i, n)) {
+                if (b) {
+                    ansi_s(ctx, th->strong_on);
+                    st.bold = 1;
+                    st.bold_ch = (char)ch;
+                }
+                if (it) {
+                    ansi_s(ctx, th->emph_on);
+                    st.italic = 1;
+                    st.italic_ch = (char)ch;
+                }
+            } else {
+                fsm_append_len(ctx, input + i, n);
+            }
+            i += n;
             continue;
         }
 
@@ -208,14 +317,7 @@ static void ansi_render_inline(sashidown_ctx_t *ctx, const ansi_theme_t *th,
             continue;
         }
 
-        if (ch == '*' || ch == '_') {
-            ansi_s(ctx, st.italic ? th->emph_off : th->emph_on);
-            st.italic = !st.italic;
-            i++;
-            continue;
-        }
-
-        if (ch == '`') {
+        if (ch == '`' && block_scan_until_byte(input, end, i + 1, '`') < end) {
             ansi_s(ctx, th->code_on);
             st.code = 1;
             i++;