term: move the term core to subprojects/term

The core now builds, tests, and benchmarks alone, as a Meson subproject
with no dependency on the main tree.

- include/term/ holds term.h and the header-only unicode/. src/ holds
  the core and its private headers. The main tree gets only
  include/term through term_dep, so it cannot reach a private header.
- The term tests, the term benchmarks, the Kitty parser suite, and
  tools/amalgamate.py and tools/generate_unicode.py move with it. The
  tests run as term:<name>.
- The main build passes its -march (arch_flag) and b_ndebug to the
  subproject. A directory configured before this commit needs
  meson configure -Dterm:arch_flag=-march=... once.
- The term tests compile with -UNDEBUG. They do work inside assert.
- The subproject exports term_test_dep with term_api.h, for the main
  tree's render, thumbnail, color, and selection tests.
- The Kitty bridge used struct vector2i and has not compiled since the
  public API redesign. It builds again. 2 of its 14 tests fail: REP
  after a tab, and a cursor report after a resize.
- dirgraph.py drops the term and unicode layers. Its self-test uses pty.
- The symbols test ignores the __odr_asan symbols that ASan adds.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 2369 insertions, 0 deletions

diff --git a/tests/term_test.c b/tests/term_test.c
new file mode 100644
index 0000000..02c050e
--- /dev/null
+++ b/tests/term_test.c
@@ -0,0 +1,2369 @@
+#include "term_api.h"
+#include "term/unicode/unicode.h"
+#include "term/unicode/utf8.h"
+#include <assert.h>
+#include <limits.h>
+#include <pthread.h>
+#include <stdatomic.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static char response[64];
+static size_t response_len;
+static void respond(void *ud, const char *data, size_t len)
+{
+    (void)ud;
+    assert(len < sizeof(response));
+    memcpy(response, data, len);
+    response[len] = 0;
+    response_len = len;
+}
+static char title[128];
+static void capture_title(void *ud, const char *s)
+{
+    (void)ud;
+    snprintf(title, sizeof(title), "%s", s);
+}
+static const struct term_callbacks reply_cb = { .reply = respond };
+static const struct term_callbacks title_cb = { .reply = respond, .title = capture_title };
+
+static void write_seq(struct term *t, const char *s)
+{
+
+    for (; *s; s++) tt_write(t, s, 1);
+}
+static void feed_seq(struct term *t, const char *s, unsigned flags)
+{
+    for (; *s; s++) term_feed(t, s, 1, flags);
+}
+static const char *row_text(struct term *t, int r, char *buf)
+{
+    const struct term_cell *cells = term_snapshot_row(tt_snapshot_for(t), r);
+    int n = 0;
+    for (int c = 0; c < tt_cols(t); c++) {
+        uint32_t cp = tt_cell_cp(t, &cells[c]);
+        /* '?' stands for any code point outside ASCII. */
+        buf[n++] = !cp ? ' ' : cp < 0x80 ? (char)cp : '?';
+    }
+    while (n > 0 && buf[n - 1] == ' ') n--;
+    buf[n] = 0;
+    return buf;
+}
+static bool row_eq(struct term *t, int r, const char *want)
+{
+    char *got = malloc((size_t)tt_cols(t) + 1);
+    assert(got);
+    bool equal = !strcmp(row_text(t, r, got), want);
+    free(got);
+    return equal;
+}
+static bool row_is(struct term *t, int r, const char *want)
+{
+    char *got = malloc((size_t)tt_cols(t) + 1);
+    assert(got);
+    bool equal = !strcmp(row_text(t, r, got), want);
+    if (!equal)
+        fprintf(stderr, "row %d: got \"%s\" want \"%s\"\n", r, got, want);
+    free(got);
+    return equal;
+}
+
+static void write_both(struct term *whole, struct term *bytes, const char *s)
+{
+    tt_write(whole, s, strlen(s));
+    write_seq(bytes, s);
+}
+
+/* The view version of s after it copies t. A renderer redraws when the
+ * version changes. */
+static uint64_t view_version(struct term_snapshot *s, struct term *t)
+{
+    term_snapshot_update(s, t);
+    return term_snapshot_view(s)->version;
+}
+
+/*
+ * Regression: diff renderers (Claude Code, Ink) skip unchanged spaces with
+ * CUF. Cells the cursor skips must read as blanks, even on a row whose cells
+ * still hold old glyphs: a row recycled by scrolling, or a row whose tail
+ * an erase dropped without filling. Stale glyphs showed up in place of
+ * every skipped space.
+ */
+static void test_skipped_cells_read_blank(void)
+{
+    static const char *const lines[] = {
+        "ab\033[1Ccd\033[3Cef",
+        "a…b\033[1Cc",
+        "\033[1m\033[38;2;1;2;3mab\033[0m\033[2Ccd",
+    };
+    /* row_text() reads U+2026 as '?'. */
+    static const char *const want[] = { "ab cd   ef", "a?b c", "ab  cd" };
+    for (size_t k = 0; k < sizeof(lines) / sizeof(lines[0]); k++) {
+        struct term *whole = tt_new(20, 4);
+        struct term *bytes = tt_new(20, 4);
+        for (int i = 0; i < 12; i++)
+            write_both(whole, bytes, "XXXXXXXXXXXXXXXXXXXX\r\n");
+        write_both(whole, bytes, lines[k]);
+        for (struct term *t = whole; t; t = t == whole ? bytes : NULL) {
+            char *got = malloc((size_t)tt_cols(t) + 1);
+            assert(got);
+            row_text(t, 3, got);
+            if (strcmp(got, want[k])) {
+                fprintf(stderr, "line %zu (%s): got \"%s\" want \"%s\"\n", k,
+                        t == whole ? "whole" : "bytes", got, want[k]);
+                assert(0);
+            }
+            free(got);
+        }
+        term_free(whole);
+        term_free(bytes);
+    }
+
+    struct term *whole = tt_new(20, 4);
+    struct term *bytes = tt_new(20, 4);
+    write_both(whole, bytes, "abcdefgh\r\033[2C\033[K\033[2CZ");
+    assert(row_is(whole, 0, "ab  Z"));
+    assert(row_is(bytes, 0, "ab  Z"));
+    term_free(whole);
+    term_free(bytes);
+}
+
+/* Compare the first rows of both viewports cell by cell. Each terminal gets
+ * its own snapshot. A cluster has a different handle in each snapshot, so
+ * the test compares its code points. */
+static void assert_same_rows(struct term *a, struct term *b, int rows)
+{
+    struct term_snapshot *sa = term_snapshot_new();
+    struct term_snapshot *sb = term_snapshot_new();
+    bool copied = sa && sb && term_snapshot_update(sa, a) && term_snapshot_update(sb, b);
+    assert(copied);
+    int cols = term_snapshot_view(sa)->size.x;
+    assert(cols == term_snapshot_view(sb)->size.x);
+    for (int y = 0; y < rows; y++) {
+        const struct term_cell *ra = term_snapshot_row(sa, y);
+        const struct term_cell *rb = term_snapshot_row(sb, y);
+        assert(ra && rb);
+        for (int x = 0; x < cols; x++) {
+            const struct term_cell *ac = &ra[x], *bc = &rb[x];
+            uint32_t acp[32], bcp[32];
+            int an = term_snapshot_cluster(sa, ac->text, acp, 32);
+            int bn = term_snapshot_cluster(sb, bc->text, bcp, 32);
+            bool same = an == bn && an <= 32 &&
+                        !memcmp(acp, bcp, (size_t)an * sizeof(*acp)) &&
+                        ac->fg == bc->fg && ac->bg == bc->bg &&
+                        ac->attrs == bc->attrs && ac->width == bc->width;
+            if (!same) {
+                fprintf(stderr, "x=%d y=%d: a(cp=%x fg=%x bg=%x attrs=%x width=%d) "
+                        "b(cp=%x fg=%x bg=%x attrs=%x width=%d)\n", x, y,
+                        an ? acp[0] : 0, ac->fg, ac->bg, ac->attrs, ac->width,
+                        bn ? bcp[0] : 0, bc->fg, bc->bg, bc->attrs, bc->width);
+                assert(0);
+            }
+        }
+    }
+    term_snapshot_free(sa);
+    term_snapshot_free(sb);
+}
+
+static void assert_same_screen(struct term *a, struct term *b)
+{
+    assert(tt_cursor_x(a) == tt_cursor_x(b));
+    assert(tt_cursor_y(a) == tt_cursor_y(b));
+    assert(tt_history(a) == tt_history(b));
+    assert(term_modes(a).synchronized == term_modes(b).synchronized);
+    assert(tt_rows(a) == tt_rows(b));
+    assert_same_rows(a, b, tt_rows(a));
+}
+
+static void test_read_boundaries(void)
+{
+    static const char input[] =
+        "ASCII 1234567890\r\nT\xc3\xbc" "rk\xe2\x94\x80"
+        "\033[31mred\033[m\033(0lqqk\033(B"
+        "\033[2;3H!\033[2b\033[1D?\033[K"
+        "\033[?1049halt\033[?1049lZ"
+        "\033]11;?\007\033Pignored\033\\"
+        "\xf0\x9f\x98\x80\xc3XQ©️界\033[2G\033[P";
+    struct term *expected = tt_new(16, 4);
+    tt_write(expected, input, sizeof(input) - 1);
+    for (size_t split = 0; split < sizeof(input); split++) {
+        struct term *actual = tt_new(16, 4);
+        tt_write(actual, input, split);
+        tt_write(actual, input + split, sizeof(input) - 1 - split);
+        assert_same_screen(actual, expected);
+        term_free(actual);
+    }
+
+    /* The byte that ends an unfinished sequence is not lost. */
+    struct term *t = tt_new(16, 4);
+    write_seq(t, "\xc3XQ");
+    assert(tt_cell_cp(t, tt_cell(t, 0, 0)) == 0xFFFD);
+    assert(tt_cell_cp(t, tt_cell(t, 1, 0)) == 'X');
+    assert(tt_cell_cp(t, tt_cell(t, 2, 0)) == 'Q');
+    term_free(t);
+    term_free(expected);
+}
+
+static void test_ascii_controls(void)
+{
+    static const char *separators[] = {"\n", "\r", "\b", "\t", "\033[31m", "\177", "é界"};
+    for (int bottom = 0; bottom < 2; bottom++) {
+        for (size_t c = 0; c < sizeof(separators) / sizeof(separators[0]); c++) {
+            char input[256];
+            memset(input, 'a', 29);
+            size_t n = strlen(separators[c]);
+            memcpy(input + 29, separators[c], n);
+            memset(input + 29 + n, 'b', 173);
+            input[202 + n] = '\0';
+            struct term *bulk = tt_new(120, 6);
+            struct term *bytes = tt_new(120, 6);
+            const char *setup = bottom ? "\033[6;1H\033[1;3;4;38;2;12;34;56m"
+                                       : "\033[1;3;4;38;2;12;34;56m";
+            write_seq(bulk, setup);
+            write_seq(bytes, setup);
+            tt_write(bulk, input, strlen(input));
+            write_seq(bytes, input);
+            assert_same_screen(bulk, bytes);
+            term_scroll(bulk, 6);
+            term_scroll(bytes, 6);
+            assert_same_screen(bulk, bytes);
+            term_free(bulk);
+            term_free(bytes);
+        }
+    }
+}
+
+static void test_esc_control_strings_and_designators(void)
+{
+    struct term *t = tt_new(32, 2);
+    assert(t);
+
+    write_seq(t, "A\033_payload ignored\033\\B");
+    write_seq(t, "\033^privacy message\007C");
+    write_seq(t, "\033Xsos ignored\033\\D");
+    assert(row_is(t, 0, "ABCD"));
+
+    write_seq(t, "\033%Gx\033%@y\033%/z");
+    assert(row_is(t, 0, "ABCDxyz"));
+    write_seq(t, "\033%qx");
+    assert(row_is(t, 0, "ABCDxyz%qx"));
+
+    write_seq(t, "\033.Am\033*0n");
+    assert(row_is(t, 0, "ABCDxyz%qxmn"));
+    term_free(t);
+
+    t = tt_new(8, 2);
+    write_seq(t, "A\033_ignored\033DB");
+    assert(row_is(t, 0, "A"));
+    assert(row_is(t, 1, " B"));
+    term_free(t);
+}
+
+static void test_random_read_boundaries(void)
+{
+    static const char embedded[] =
+        "\033\\\033(B\r\nA\xc3\xbc\xe7\x95\x8c" "e\xcc\x81"
+        "\033[31mR\033[m\tX\bY\033]0;title\007\033Pignored\033\\"
+        "\033[?2026hS\033[?2026l\xc3XQ\xe0\x80\x80\xf4\x90\x80\x80";
+    static const size_t chunks[] = {1, 2, 7, 31, 127};
+    for (unsigned seed = 1; seed <= 4; seed++) {
+        char input[1024];
+        unsigned random = seed;
+        for (size_t i = 0; i < sizeof(input); i++) {
+            random = random * 1103515245u + 12345u;
+            input[i] = (char)(random >> 16);
+        }
+        memcpy(input + 400, embedded, sizeof(embedded) - 1);
+        struct term *whole = tt_new(32, 8);
+        tt_write(whole, input, sizeof(input));
+        for (size_t c = 0; c < sizeof(chunks) / sizeof(chunks[0]); c++) {
+            struct term *a = tt_new(32, 8);
+            struct term *b = tt_new(32, 8);
+            for (size_t block = 0; block < sizeof(input); block += 128) {
+                tt_write(a, input + block, 128);
+                for (size_t i = block; i < block + 128;) {
+                    size_t n = chunks[c];
+                    if (n > block + 128 - i) n = block + 128 - i;
+                    tt_write(b, input + i, n);
+                    i += n;
+                }
+                assert_same_screen(a, b);
+            }
+            assert_same_screen(whole, a);
+            write_seq(a, "\033\\\033(B\r\nEND");
+            write_seq(b, "\033\\\033(B\r\nEND");
+            assert_same_screen(a, b);
+            int history = tt_history(a);
+            for (int i = 0; i < history; i += 8) {
+                term_scroll(a, 8);
+                term_scroll(b, 8);
+                assert_same_screen(a, b);
+            }
+            term_free(a);
+            term_free(b);
+        }
+        term_free(whole);
+    }
+}
+
+static void test_csi_recovery(void)
+{
+    static const struct { const char *input, *first, *second; } cases[] = {
+        /* CR and LF run inside the CSI; B ends it as CUD (ECMA-48 5.5). */
+        {"A\033[\r\nB!", "A", ""},
+        /* 0xFF cancels the CSI and prints U+FFFD. */
+        {"A\033[\xff" "BC", "A?BC", ""},
+        {"A\033[\033[2JZ", " Z", ""},
+        {"\033[ 31mX", "X", ""},
+        {"\033[31$mX", "X", ""},
+        {"\033[31;?mX", "X", ""},
+        {"\033[31;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0;0mX", "X", ""},
+        {"\033[31\030X", "X", ""},
+        {"\033[31\032X", "X", ""},
+        {"\033[1$ A X", " X", ""},
+        {"AB\033[?2JX", "ABX", ""},
+        {"AB\r\033[>4hX", "XB", ""},
+    };
+    for (size_t c = 0; c < sizeof(cases) / sizeof(cases[0]); c++) {
+        size_t len = strlen(cases[c].input);
+        for (size_t split = 0; split <= len; split++) {
+            struct term *t = tt_new(20, 4);
+            tt_write(t, cases[c].input, split);
+            tt_write(t, cases[c].input + split, len - split);
+            assert(row_is(t, 0, cases[c].first));
+            assert(row_is(t, 1, cases[c].second));
+            for (int x = 0; x < 20; x++) assert(tt_cell(t, x, 0)->fg == TERM_COLOR_FG);
+            term_free(t);
+        }
+    }
+}
+
+static void test_csi_byte_boundaries(void)
+{
+    static const char *prefixes[] = {"\033[", "\033[31;", "\033[?", "\033[1 ", "\033[1$ "};
+    for (size_t p = 0; p < sizeof(prefixes) / sizeof(prefixes[0]); p++) {
+        for (unsigned byte = 0; byte < 256; byte++) {
+            char input[64];
+            size_t n = strlen(prefixes[p]);
+            memcpy(input, prefixes[p], n);
+            input[n++] = (char)byte;
+            static const char suffix[] = "mX\033[6n\033[?25l\033[?25h\033[0mY";
+            memcpy(input + n, suffix, sizeof(suffix) - 1);
+            n += sizeof(suffix) - 1;
+            struct term *whole = tt_new_opts(20, 4, &reply_cb);
+            response_len = 0;
+            tt_write(whole, input, n);
+            char expected_response[64];
+            size_t expected_len = response_len;
+            memcpy(expected_response, response, expected_len);
+            for (size_t split = 0; split <= strlen(prefixes[p]) + 2; split++) {
+                struct term *parts = tt_new_opts(20, 4, &reply_cb);
+                response_len = 0;
+                tt_write(parts, input, split);
+                tt_write(parts, input + split, n - split);
+                assert_same_screen(whole, parts);
+                assert(term_cursor(whole).visible == term_cursor(parts).visible);
+                assert(response_len == expected_len);
+                assert(!memcmp(response, expected_response, expected_len));
+                term_free(parts);
+            }
+            term_free(whole);
+        }
+    }
+}
+
+static void test_parameter_limits(void)
+{
+    struct term *t = tt_new(10, 4);
+    write_seq(t, "\033[2;4r\033[?6h\033[999999999999999999999;1H");
+    assert(tt_cursor_y(t) == 3 && tt_cursor_x(t) == 0);
+    write_seq(t, "\033[?6l\033[r");
+    write_seq(t, "\033[2;2H\033[999999999999999999999B\033[2147483647C!");
+    assert(tt_cursor_y(t) == 3 && tt_cursor_x(t) == 9);
+    assert(tt_cell(t, 9, 3)->text == '!');
+    write_seq(t, "\033[999999999999999999999A\033[999999999999999999999D");
+    assert(tt_cursor_y(t) == 0 && tt_cursor_x(t) == 0);
+    write_seq(t, "\033[38;5;999999999999999999999mX");
+    assert(tt_cell(t, 0, 0)->fg == TERM_COLOR_FG);
+
+    /* A renderer sees the cursor move to another row. */
+    struct term_snapshot *snap = term_snapshot_new();
+    uint64_t version = view_version(snap, t);
+    write_seq(t, "\033[3d");
+    assert(tt_cursor_y(t) == 2 && view_version(snap, t) != version);
+    term_snapshot_free(snap);
+
+    write_seq(t, "\033[4;8H\0337");
+    tt_resize(t, 5, 2);
+    write_seq(t, "\0338Z");
+    assert(tt_cursor_y(t) == 1 && tt_cursor_x(t) == 3);
+    assert(tt_cell(t, 2, 1)->text == 'Z');
+    term_free(t);
+}
+
+static void test_unterminated_control_strings_do_not_swallow_text(void)
+{
+    struct term *t = tt_new(20, 4);
+    assert(t);
+
+    write_seq(t, "A\033]0;random bytes\tgit\r\nstatus");
+    assert(row_is(t, 0, "A       git"));
+    assert(row_is(t, 1, "status"));
+
+    write_seq(t, "\033Prandom bytes\tbranch\r\nnext");
+    assert(row_is(t, 1, "status  branch"));
+    assert(row_is(t, 2, "next"));
+
+    term_free(t);
+
+    char overlong[1200];
+    for (int intro = 0; intro < 2; intro++) {
+        int n = snprintf(overlong, sizeof(overlong), intro ? "\033P" : "\033]0;");
+        memset(overlong + n, 'T', 1024);
+        overlong[n + 1024] = '\0';
+
+        struct term *u = tt_new(20, 4);
+        write_seq(u, overlong);
+        write_seq(u, "\r\n[sudo] password:");
+        assert(row_is(u, 0, ""));
+        assert(row_is(u, 1, "[sudo] password:"));
+        term_free(u);
+
+        struct term *d = tt_new(20, 4);
+        write_seq(d, overlong);
+        write_seq(d, "\033\\after");
+        assert(row_is(d, 0, "after"));
+        term_free(d);
+    }
+}
+
+static void test_c0_controls_after_esc_are_executed(void)
+{
+    struct term *t = tt_new(20, 4);
+    assert(t);
+
+    write_seq(t, "A\033\tB");
+    assert(row_is(t, 0, "A       B"));
+
+    term_free(t);
+}
+
+static void test_resize_reflow(void)
+{
+    struct term *t = tt_new(8, 4);
+    write_seq(t, "abcdefghijkl");
+    tt_resize(t, 16, 4);
+    assert(row_is(t, 0, "abcdefghijkl") && row_is(t, 1, ""));
+    assert(tt_cursor_y(t) == 0 && tt_cursor_x(t) == 12);
+    write_seq(t, "M");
+    assert(row_is(t, 0, "abcdefghijklM"));
+    tt_resize(t, 5, 4);
+    assert(row_is(t, 0, "abcde") && row_is(t, 1, "fghij") && row_is(t, 2, "klM"));
+    assert(tt_cursor_y(t) == 2 && tt_cursor_x(t) == 3);
+    tt_select(t, 0, 0, 2, 2);
+    char *text = tt_selection_text(t);
+    assert(text && !strcmp(text, "abcdefghijklM"));
+    free(text);
+    tt_resize(t, 20, 4);
+    assert(row_is(t, 0, "abcdefghijklM"));
+    term_free(t);
+
+    t = tt_new(6, 6);
+    write_seq(t, "\033[31mab  cdef\033[m\r\nnext");
+    term_color red = tt_cell(t, 0, 0)->fg;
+    tt_resize(t, 12, 6);
+    assert(row_is(t, 0, "ab  cdef") && row_is(t, 1, "next"));
+    assert(tt_cell(t, 7, 0)->fg == red);
+    assert(tt_cell(t, 0, 1)->fg == TERM_COLOR_FG);
+    term_free(t);
+
+    t = tt_new(4, 2);
+    write_seq(t, "abcdefghijkl");
+    assert(tt_history(t) == 1);
+    tt_resize(t, 12, 2);
+    assert(tt_history(t) == 0 && row_is(t, 0, "abcdefghijkl"));
+    assert(tt_cursor_y(t) == 0 && tt_cursor_x(t) == 11);
+    write_seq(t, "M");
+    assert(row_is(t, 1, "M"));
+    tt_resize(t, 4, 2);
+    assert(tt_history(t) == 2);
+    assert(row_is(t, 0, "ijkl") && row_is(t, 1, "M"));
+    tt_resize(t, 20, 2);
+    assert(row_is(t, 0, "abcdefghijklM"));
+    term_free(t);
+
+    t = tt_new(4, 3);
+    write_seq(t, "abcd");
+    tt_resize(t, 8, 3);
+    write_seq(t, "E");
+    assert(row_is(t, 0, "abcdE"));
+    tt_resize(t, 5, 3);
+    write_seq(t, "F");
+    assert(row_is(t, 0, "abcdE") && row_is(t, 1, "F"));
+    term_free(t);
+
+    t = tt_new(4, 4);
+    write_seq(t, "abcdefghijkl\033[?1049h12345678");
+    tt_resize(t, 8, 4);
+    assert(row_is(t, 0, "1234") && row_is(t, 1, "5678"));
+    tt_resize(t, 16, 4);
+    write_seq(t, "\033[?1049lM");
+    assert(row_is(t, 0, "abcdefghijklM"));
+    assert(tt_cursor_y(t) == 0 && tt_cursor_x(t) == 13);
+    term_free(t);
+
+    t = tt_new(4, 2);
+    write_seq(t, "abcd");
+    tt_resize(t, 4, 3);
+    write_seq(t, "E");
+    assert(row_is(t, 0, "abcd") && row_is(t, 1, "E"));
+    term_free(t);
+
+    t = tt_new(80, 4);
+    for (int i = 0; i < 1000; i++) write_seq(t, "abcdefgh");
+    tt_resize(t, 1, 4);
+    assert(tt_history(t) == 1000 * 8 - 4);
+    assert(tt_cursor_y(t) == 3 && tt_cursor_x(t) == 0);
+    assert(row_is(t, 0, "e") && row_is(t, 3, "h"));
+    tt_resize(t, 80, 4);
+    assert(tt_cursor_x(t) < 80 && tt_cursor_y(t) < 4);
+    write_seq(t, "Z");
+    assert(tt_cell(t, 0, 3)->text == 'Z');
+    term_free(t);
+
+}
+
+static void test_resize_exposes_blank_rows(void)
+{
+    struct term *t = tt_new(20, 2);
+    write_seq(t, "kept");
+    for (int pass = 0; pass < 2; pass++) {
+        tt_resize(t, 20, 6);
+        assert(row_is(t, 0, "kept"));
+        for (int y = 2; y < 6; y++) {
+            for (int x = 0; x < 20; x++) {
+                const struct term_cell *cell = tt_cell(t, x, y);
+                assert(cell->text == ' ' && cell->fg == TERM_COLOR_FG);
+                assert(cell->bg == TERM_COLOR_BG && cell->attrs == 0 && cell->width == 1);
+            }
+        }
+        write_seq(t, "\033[6;1H\tfile/");
+        assert(row_is(t, 5, "        file/"));
+        write_seq(t, "\033[1;1H");
+        tt_resize(t, 20, 2);
+    }
+    term_free(t);
+}
+
+static void test_prompt_resize(void)
+{
+    struct term *t = tt_new(80, 6);
+    const char *prompt = "~/Documents/GitHub/clernen_pi main> ";
+    write_seq(t, "\033]133;A;click_events=1\033\\");
+    write_seq(t, prompt);
+    write_seq(t, "\033]133;B\033\\");
+
+    const struct { int cols; const char *text; bool newline; } cases[] = {
+        {40, "~/Documents/GitHub/clernen_pi main> ", false},
+        {20, ".b/clernen_pi main> ", true},
+        {12, ".n_pi main> ", true},
+        {30, "~/GitHub/clernen_pi> ", false},
+        {80, "~/Documents/GitHub/clernen_pi main> ", false},
+    };
+    bool newline = false;
+    for (size_t i = 0; i < sizeof(cases) / sizeof(cases[0]); i++) {
+        tt_resize(t, cases[i].cols, 6);
+        write_seq(t, "\r\r");
+        if (newline) write_seq(t, "\033[A");
+        write_seq(t, "\033]133;A;click_events=1\033\\");
+        write_seq(t, cases[i].text);
+        write_seq(t, "\033]133;B\033\\");
+        if (cases[i].newline) write_seq(t, "\r\n");
+        write_seq(t, "\033[J");
+        char expected[80];
+        snprintf(expected, sizeof(expected), "%s", cases[i].text);
+        expected[strlen(expected) - 1] = 0;
+        assert(row_is(t, 0, expected));
+        for (int y = 1; y < 6; y++) assert(row_is(t, y, ""));
+        assert(tt_history(t) == 0);
+        newline = cases[i].newline;
+    }
+
+    write_seq(t, "\033]133;C\033\\");
+    tt_resize(t, 20, 6);
+    assert(row_is(t, 0, "~/Documents/GitHub/c"));
+    assert(row_is(t, 1, "lernen_pi main>"));
+    term_free(t);
+
+    t = tt_new(20, 6);
+    write_seq(t, "abcdefghijklmnop\r\n\033]133;A\007prompt> input\033]133;B\007");
+    tt_resize(t, 8, 6);
+    assert(row_is(t, 0, "abcdefgh") && row_is(t, 1, "ijklmnop"));
+    assert(row_is(t, 2, "prompt>"));
+    tt_resize(t, 30, 6);
+    assert(row_is(t, 0, "abcdefghijklmnop") && row_is(t, 1, "prompt>"));
+    term_free(t);
+}
+
+static void test_cursor_line_motion(void)
+{
+    struct term *t = tt_new(80, 9);
+    assert(t);
+    const char *lines = "one\r\ntwo\r\nthree\r\nfour\r\nfive\r\nsix\r\nseven\r\n";
+    tt_write(t, lines, strlen(lines));
+    const char *rewrite = "\033[6Ftwo revised\033[K\033[2Efour revised\033[K\033[3Fone revised\033[K";
+    tt_write(t, rewrite, strlen(rewrite));
+    assert(row_is(t, 1, "two revised"));
+    assert(row_is(t, 3, "four revised"));
+    assert(row_is(t, 0, "one revised"));
+    term_free(t);
+}
+
+static void test_relative_cursor_motion(void)
+{
+    struct term *t = tt_new(10, 5);
+    assert(t);
+    const char *text = "0123456789\r\nabcdefghij\r\nklmnopqrst";
+    tt_write(t, text, strlen(text));
+    const char *sequence = "\033[3`X\033[2aY\033[1eZ\033[2dW";
+    tt_write(t, sequence, strlen(sequence));
+    assert(tt_cell(t, 2, 2)->text == 'X');
+    assert(tt_cell(t, 5, 2)->text == 'Y');
+    assert(tt_cell(t, 6, 3)->text == 'Z');
+    assert(tt_cell(t, 7, 1)->text == 'W');
+    term_free(t);
+}
+
+static void test_top_region_scrollback(void)
+{
+    static const struct {
+        const char *scroll;
+        int lines;
+    } cases[] = {
+        {"\n", 1},
+        {"\033D", 1},
+        {"\033E", 1},
+        {"\033[S", 1},
+        {"\033[2S", 2},
+        {"\033[99S", 4},
+    };
+    for (size_t i = 0; i < sizeof(cases) / sizeof(cases[0]); i++) {
+        struct term *t = tt_new(12, 6);
+        write_seq(t, "one\r\ntwo\r\nthree\r\nfour\r\nPROMPT\r\nSTATUS");
+        write_seq(t, "\033[1;4r\033[4;1H");
+        write_seq(t, cases[i].scroll);
+        assert(tt_history(t) == cases[i].lines);
+        assert(row_is(t, 0, cases[i].lines == 1 ? "two" :
+                            cases[i].lines == 2 ? "three" : ""));
+        assert(row_is(t, 3, ""));
+        assert(row_is(t, 4, "PROMPT") && row_is(t, 5, "STATUS"));
+        term_scroll(t, cases[i].lines);
+        assert(tt_view_offset(t) == cases[i].lines);
+        assert(row_is(t, 0, "one") && row_is(t, 1, "two"));
+        term_free(t);
+    }
+
+    /* Retain the same history as a full screen after the ring wraps. */
+    struct term *t = tt_new(12, 6);
+    struct term *reference = tt_new(12, 4);
+    const char *footer = "\033[5;1H\033[31mPROMPT\r\nSTATUS\033[m\033[1;4r";
+    tt_write(t, footer, strlen(footer));
+    for (int i = 0; i < 2 * TEST_SCROLLBACK; i++) {
+        char line[32];
+        int len = snprintf(line, sizeof(line), "line %04d\r\n", i);
+        tt_write(t, line, (size_t)len);
+        tt_write(reference, line, (size_t)len);
+    }
+    assert(tt_history(t) == tt_history(reference));
+    assert(tt_cursor_x(t) == tt_cursor_x(reference));
+    assert(tt_cursor_y(t) == tt_cursor_y(reference));
+    assert(row_is(t, 4, "PROMPT") && row_is(t, 5, "STATUS"));
+    assert(tt_cell(t, 0, 4)->fg == tt_cell(t, 0, 5)->fg);
+    assert(tt_cell(t, 0, 4)->fg != TERM_COLOR_FG);
+    for (int i = 0; i <= tt_history(reference); i++) {
+        assert_same_rows(t, reference, tt_rows(reference));
+        term_scroll(t, 1);
+        term_scroll(reference, 1);
+    }
+    term_free(t);
+    term_free(reference);
+}
+
+static void test_editor_scrolling(void)
+{
+    struct term *t = tt_new(80, 24);
+    write_seq(t, "\033[?1049hTITLE");
+    for (int i = 1; i <= 20; i++) {
+        char line[64];
+        snprintf(line, sizeof(line), "\033[%d;1Hline %02d", i + 1, i);
+        write_seq(t, line);
+    }
+    write_seq(t, "\033[23;1HHELP\033[24;1HFOOTER");
+
+    write_seq(t, "\033[4;22r\033[22;1H\n\033[1;24r"
+                 "\033[21;1Hline 21\033[K\r\033[4d");
+    assert(row_is(t, 0, "TITLE") && row_is(t, 2, "line 02"));
+    assert(row_is(t, 3, "line 04") && row_is(t, 19, "line 20"));
+    assert(row_is(t, 20, "line 21") && row_is(t, 21, ""));
+    assert(row_is(t, 22, "HELP") && row_is(t, 23, "FOOTER"));
+    assert(tt_cursor_x(t) == 0 && tt_cursor_y(t) == 3);
+    assert(tt_history(t) == 0);
+    term_free(t);
+
+    t = tt_new(12, 6);
+    write_seq(t, "old\r\nHEAD\r\nA\r\nB\r\nC\r\nD\r\nFOOT");
+    assert(tt_history(t) == 1);
+    write_seq(t, "\033[2;5r\033[3;2H\033[M");
+    assert(row_is(t, 0, "HEAD") && row_is(t, 1, "A"));
+    assert(row_is(t, 2, "C") && row_is(t, 3, "D") && row_is(t, 4, ""));
+    assert(row_is(t, 5, "FOOT"));
+    /* DL moves the cursor to the left margin (xterm). */
+    assert(tt_cursor_x(t) == 0 && tt_cursor_y(t) == 2);
+    write_seq(t, "\033[L");
+    assert(row_is(t, 2, "") && row_is(t, 3, "C") && row_is(t, 4, "D"));
+    write_seq(t, "\033[2;1H\033M");
+    assert(row_is(t, 1, "") && row_is(t, 2, "A") && row_is(t, 4, "C"));
+    write_seq(t, "\033[5;1H\033D");
+    assert(row_is(t, 1, "A") && row_is(t, 3, "C") && row_is(t, 4, ""));
+    write_seq(t, "\033[T\033[S");
+    assert(row_is(t, 1, "A") && row_is(t, 3, "C"));
+
+    write_seq(t, "\033[5;2r\033[1;999999999999r\033[44m\033[999999999999S");
+    assert(row_is(t, 0, "HEAD") && row_is(t, 5, "FOOT"));
+    for (int r = 1; r <= 4; r++) {
+        assert(row_is(t, r, ""));
+        assert(tt_cell(t, 0, r)->bg == tt_cell(t, 11, r)->bg);
+        assert(tt_cell(t, 0, r)->bg != TERM_COLOR_BG);
+    }
+    assert(tt_history(t) == 1);
+
+    write_seq(t, "\033[6;1H\033[M\033[L");
+    assert(row_is(t, 5, "FOOT"));
+
+    tt_resize(t, 12, 4);
+    write_seq(t, "\033[4;1H\033[2Kend\n");
+    assert(tt_cursor_y(t) == 3 && row_is(t, 2, "end"));
+    term_free(t);
+}
+
+static bool pending_decsca_decsed_decsel(void)
+{
+    struct term *d = tt_new(20, 3);
+    write_seq(d, "\033[H" "AB" "\033[1\"q" "CD" "\033[0\"q" "EF");
+    write_seq(d, "\033[?2J");
+    bool ok = row_eq(d, 0, "  CD");
+    term_free(d);
+
+    struct term *l = tt_new(20, 3);
+    write_seq(l, "\033[H" "GH" "\033[1\"q" "IJ" "\033[0\"q" "KL");
+    write_seq(l, "\033[H\033[?0K");
+    ok = ok && row_eq(l, 0, "  IJ");
+    term_free(l);
+    return ok;
+}
+
+static bool pending_decfra_decera(void)
+{
+    struct term *f = tt_new(20, 3);
+    write_seq(f, "\033[88;1;2;2;4$x");
+    bool ok = row_eq(f, 0, " XXX") && row_eq(f, 1, " XXX");
+    term_free(f);
+
+    struct term *e = tt_new(20, 3);
+    write_seq(e, "\033[Habcde\r\nfghij");
+    write_seq(e, "\033[1;2;2;3$z");
+    ok = ok && row_eq(e, 0, "a  de") && row_eq(e, 1, "f  ij");
+    term_free(e);
+    return ok;
+}
+
+static bool pending_deccra(void)
+{
+    struct term *t = tt_new(20, 3);
+    write_seq(t, "\033[HAB\r\nCD");
+    write_seq(t, "\033[1;1;2;2;1;1;5;1$v");
+    bool ok = row_eq(t, 0, "AB  AB") && row_eq(t, 1, "CD  CD");
+    term_free(t);
+    return ok;
+}
+
+static bool pending_decrara(void)
+{
+    struct term *t = tt_new(20, 3);
+    write_seq(t, "\033[H\033[1mAB\033[mCD");
+    write_seq(t, "\033[1;1;1;4;1$t");
+    bool ok = !(tt_cell(t, 0, 0)->attrs & TERM_ATTR_BOLD) &&
+              (tt_cell(t, 2, 0)->attrs & TERM_ATTR_BOLD);
+    term_free(t);
+    return ok;
+}
+
+static bool pending_decsera(void)
+{
+    struct term *t = tt_new(20, 3);
+    write_seq(t, "\033[H\033[0\"qAB\033[1\"qCD");
+    write_seq(t, "\033[1;1;1;4${");
+    bool ok = row_eq(t, 0, "  CD");
+    term_free(t);
+    return ok;
+}
+
+static bool pending_deccolm(void)
+{
+    struct term *t = tt_new(80, 4);
+    write_seq(t, "\033[?40h" "keep" "\033[?3h");
+    bool ok = tt_cols(t) == 132 && row_eq(t, 0, "") &&
+              tt_cursor_x(t) == 0 && tt_cursor_y(t) == 0;
+    write_seq(t, "\033[?3l");
+    ok = ok && tt_cols(t) == 80;
+    term_free(t);
+    return ok;
+}
+
+static bool pending_decic_decdc(void)
+{
+    struct term *i = tt_new(10, 2);
+    write_seq(i, "\033[Habcdef\033[H\033[2'}");
+    bool ok = row_eq(i, 0, "  abcdef");
+    term_free(i);
+
+    struct term *d = tt_new(10, 2);
+    write_seq(d, "\033[Habcdef\033[H\033[2'~");
+    ok = ok && row_eq(d, 0, "cdef");
+    term_free(d);
+    return ok;
+}
+
+static bool pending_sl_sr(void)
+{
+    struct term *l = tt_new(10, 2);
+    write_seq(l, "\033[Habcdef\033[2 @");
+    bool ok = row_eq(l, 0, "cdef");
+    term_free(l);
+
+    struct term *r = tt_new(10, 2);
+    write_seq(r, "\033[Habcdef\033[2 A");
+    ok = ok && row_eq(r, 0, "  abcdef");
+    term_free(r);
+    return ok;
+}
+
+static bool pending_sixel(void)
+{
+    struct term *t = tt_new(20, 6);
+    write_seq(t, "\033[H\033Pq#0;2;100;100;100#0~~~~\033\\");
+    bool ok = tt_cursor_y(t) > 0;
+    term_free(t);
+    return ok;
+}
+
+static void test_unimplemented_da_features(void)
+{
+    static const struct {
+        const char *name;
+        bool (*run)(void);
+    } cases[] = {
+        { "DECSCA/DECSED/DECSEL selective erase (DA1 6)", pending_decsca_decsed_decsel },
+        { "DECFRA/DECERA rectangle fill, erase (DA1 28)", pending_decfra_decera },
+        { "DECCRA rectangle copy (DA1 28)",               pending_deccra },
+        { "DECRARA rectangle attributes (DA1 28)",        pending_decrara },
+        { "DECSERA rectangle selective erase (DA1 28)",   pending_decsera },
+        { "DECCOLM 132 columns (DA1 1)",                  pending_deccolm },
+        { "DECIC/DECDC column insert, delete (DA1 21)",   pending_decic_decdc },
+        { "SL/SR scroll left, right (DA1 21)",            pending_sl_sr },
+        { "sixel graphics, cursor advance (DA1 4)",       pending_sixel },
+    };
+    size_t total = sizeof(cases) / sizeof(cases[0]), ready = 0;
+    for (size_t i = 0; i < total; i++) {
+        if (!cases[i].run()) continue;
+        printf("  %s now passes: assert it and add its DA1 parameter\n", cases[i].name);
+        ready++;
+    }
+    printf("unimplemented features: %zu pending, %zu ready to promote\n",
+           total - ready, ready);
+}
+
+static void test_device_attributes(void)
+{
+    struct term *t = tt_new_opts(80, 24, &reply_cb);
+
+    write_seq(t, "\033[c");
+    assert(!strcmp(response, "\033[?62;22c"));
+    response_len = 0;
+    write_seq(t, "\033[0c");
+    assert(!strcmp(response, "\033[?62;22c"));
+
+    write_seq(t, "\033[>c");
+    assert(!strcmp(response, "\033[>0;10;0c"));
+
+    response_len = 0;
+    write_seq(t, "\033[=c");
+    assert(response_len == 0);
+
+    term_free(t);
+}
+
+static void expect_flags(struct term *t, const char *commands, const char *reply)
+{
+    write_seq(t, commands);
+    write_seq(t, "\033[?u");
+    assert(!strcmp(response, reply));
+}
+static void test_keyboard_negotiation(void)
+{
+    struct term *t = tt_new_opts(80, 24, &reply_cb);
+    assert(!term_modes(t).app_cursor);
+    write_seq(t, "\033[?1h");
+    assert(term_modes(t).app_cursor);
+    write_seq(t, "\033[?1l");
+    assert(!term_modes(t).app_cursor);
+    expect_flags(t, "", "\033[?0u");
+    expect_flags(t, "\033[=1u", "\033[?1u");
+    expect_flags(t, "\033[>3u\033[>31u", "\033[?31u");
+    expect_flags(t, "\033[<u", "\033[?3u");
+    expect_flags(t, "\033[=4;2u", "\033[?7u");
+    expect_flags(t, "\033[=2;3u", "\033[?5u");
+    expect_flags(t, "\033[=31;99u", "\033[?5u");
+    expect_flags(t, "\033[<u", "\033[?1u");
+    expect_flags(t, "\033[<999999999999999999999999u", "\033[?0u");
+    expect_flags(t, "\033[>1:2u\033[=3;1;4u\033[1>31u", "\033[?0u");
+    expect_flags(t, "\033[=255u", "\033[?31u");
+    expect_flags(t, "\033[>u", "\033[?0u");
+    expect_flags(t, "\033[<u", "\033[?31u");
+    expect_flags(t, "\033[>1u\033[>2u\033[<2u", "\033[?31u");
+    expect_flags(t, "\033[?1049h", "\033[?0u");
+    expect_flags(t, "\033[>3u", "\033[?3u");
+    expect_flags(t, "\033[?1049l", "\033[?31u");
+
+    for (int i = 0; i < 1000; i++) write_seq(t, "\033[>1u");
+    expect_flags(t, "\033[<u", "\033[?1u");
+    expect_flags(t, "\033[<2147483647u", "\033[?0u");
+    write_seq(t, "hello");
+    assert(row_is(t, 0, "hello"));
+    term_free(t);
+}
+
+static void expect_selection(struct term *t, int x1, int y1, int x2, int y2, const char *want)
+{
+    tt_select(t, x1, y1, x2, y2);
+    char *text = tt_selection_text(t);
+    if (!text || strcmp(text, want))
+        fprintf(stderr, "selection: got '%s', want '%s'\n", text ? text : "NULL", want);
+    assert(text && !strcmp(text, want));
+    free(text);
+}
+
+static void test_wide_characters(void)
+{
+    struct term *t = tt_new(8, 4);
+    write_seq(t, "A😀界B");
+    assert(tt_cursor_x(t) == 6);
+    assert(tt_cell(t, 1, 0)->text == 0x1f600 && tt_cell(t, 3, 0)->text == 0x754c);
+    expect_selection(t, 2, 0, 2, 0, "😀");
+    write_seq(t, "\033[3Gx\033[4GX");
+    assert(row_is(t, 0, "A xX B"));
+    write_seq(t, "\033[2J\033[HA😀BC\033[2G\033[@");
+    expect_selection(t, 0, 0, 7, 0, "A 😀BC");
+    write_seq(t, "\033[3G\033[P");
+    expect_selection(t, 0, 0, 7, 0, "A  BC");
+    write_seq(t, "\033[2J\033[HA😀BC\033[3G\033[X");
+    assert(row_is(t, 0, "A  BC"));
+
+    write_seq(t, "\033[4;1H😀\r \033[4;1H😀\033[4;2H\033[38;2;1;2;3mX");
+    assert(row_is(t, 3, " X"));
+    term_free(t);
+
+    t = tt_new(5, 8);
+    write_seq(t, "abcd😀Z");
+    assert(tt_cursor_y(t) == 1 && tt_cursor_x(t) == 3);
+    expect_selection(t, 0, 0, 4, 1, "abcd😀Z");
+    tt_resize(t, 3, 8);
+    assert(tt_cell(t, 1, 1)->text == 0x1f600 && tt_cell(t, 0, 2)->text == 'Z');
+    assert(tt_cursor_y(t) == 2 && tt_cursor_x(t) == 1);
+    expect_selection(t, 0, 0, 2, 2, "abcd😀Z");
+    tt_resize(t, 12, 8);
+    assert(tt_cursor_x(t) == 7 && tt_cursor_y(t) == 0);
+    expect_selection(t, 0, 0, 11, 0, "abcd😀Z");
+    tt_resize(t, 1, 8);
+    tt_resize(t, 12, 8);
+    expect_selection(t, 0, 0, 11, 0, "abcd😀Z");
+    assert(tt_cursor_x(t) == 7);
+    term_free(t);
+
+    t = tt_new(4, 3);
+    write_seq(t, "abc©️)");
+    assert(tt_cursor_y(t) == 1 && tt_cursor_x(t) == 3);
+    expect_selection(t, 0, 0, 3, 1, "abc©️)");
+    write_seq(t, "\033[2J\033[H😀︎x");
+    assert(tt_cursor_x(t) == 2 && tt_cell(t, 1, 0)->text == 'x');
+    expect_selection(t, 0, 0, 3, 0, "😀︎x");
+    write_seq(t, "\033[2J\033[H\033[?7labc😀");
+    assert(tt_cursor_y(t) == 0 && tt_cursor_x(t) == 3);
+    term_free(t);
+
+    t = tt_new(4, 2);
+    write_seq(t, "😀😀界界AB");
+    term_scroll(t, 1);
+    expect_selection(t, 0, 0, 3, 1, "😀😀界界");
+    term_scroll_to(t, 0);
+    tt_resize(t, 10, 2);
+    expect_selection(t, 0, 0, 9, 0, "😀😀界界AB");
+    term_free(t);
+}
+
+static void test_wide_runs(void)
+{
+    static const char *const runs[] = {
+        "日本語漢字仮名交じり文中文測試終端輸出性能比較日本語漢字仮名交じり文",
+        "    日本語漢字仮名交じり文中文測試終端輸出性能比較",
+        "┌─────────────────────┬─────────────────────┐",
+        "日本語漢字仮名交じり文abc中文測試終端輸出性能比較",
+        "日本語漢字仮名交じり文̈中文測試終端輸出性能比較",
+        "한국어를테스트하는줄을적습니다한국어를테스트하는줄을적습니다",
+        "！＂＃＄％＆＇（）＊＋，－．／０１２３４５６７８９",
+        "日本語漢字仮名交じり文😀中文測試終端輸出性能比較",
+    };
+    for (size_t k = 0; k < sizeof(runs) / sizeof(*runs); k++) {
+        char text[512];
+        snprintf(text, sizeof(text), "\033[999;1H%s", runs[k]);
+        struct term *bulk = tt_new(120, 6);
+        struct term *split = tt_new(120, 6);
+        tt_write(bulk, text, strlen(text));
+        write_seq(split, text);
+        assert_same_screen(bulk, split);
+
+        expect_selection(bulk, 0, 5, 119, 5, runs[k]);
+        term_free(bulk);
+        term_free(split);
+    }
+}
+
+static void test_invalid_utf8_runs(void)
+{
+    static const unsigned char invalid[][3] = {
+        {0xe0, 0x82, 0xa1}, {0xed, 0xa0, 0x80}, {0xe0, 0x9f, 0xbf},
+    };
+    for (size_t k = 0; k < sizeof(invalid) / sizeof(*invalid); k++) {
+        char input[128];
+        size_t n = 0;
+        for (int i = 0; i < 32; i++) {
+            memcpy(input + n, invalid[k], 3);
+            n += 3;
+        }
+        memcpy(input + n, "END", 3);
+        n += 3;
+        struct term *bulk = tt_new(120, 4);
+        struct term *split = tt_new(120, 4);
+        write_seq(bulk, "\033[4;1H\n");
+        write_seq(split, "\033[4;1H\n");
+        tt_write(bulk, input, n);
+        for (size_t i = 0; i < n; i++) tt_write(split, input + i, 1);
+        /* Each byte is a maximal invalid subpart: one U+FFFD each. */
+        for (int c = 0; c < 96; c++)
+            assert(tt_cell_cp(bulk, tt_cell(bulk, c, 3)) == 0xFFFD);
+        for (int c = 0; c < 3; c++)
+            assert(tt_cell_cp(bulk, tt_cell(bulk, 96 + c, 3)) == (uint32_t)"END"[c]);
+        assert_same_screen(bulk, split);
+        term_free(bulk);
+        term_free(split);
+    }
+}
+
+static void test_recycled_scrollback_blanks(void)
+{
+    for (int mode = 0; mode < 3; mode++) {
+        struct term *t = tt_new(32, 3);
+        write_seq(t, "\033[3;1H");
+        const char *line = mode == 2 ? "abcdefghijklmnopqrstuvwxyz\r\033[S" :
+                                       "abcdefghijklmnopqrstuvwxyz\r\n";
+        for (int i = 0; i < TEST_SCROLLBACK + 10; i++) {
+            if (mode == 1) write_seq(t, line);
+            else tt_write(t, line, strlen(line));
+        }
+        write_seq(t, "\tfile/");
+        assert(row_is(t, 2, "        file/"));
+        term_free(t);
+    }
+}
+
+/* Scrolling the view by any amount lands inside the scrollback, and a
+ * scroll that cannot move leaves the frame alone. */
+static void test_scroll_view_clamps_extreme_deltas(void)
+{
+    struct term *t = tt_new(20, 3);
+    for (int i = 0; i < 10; i++)
+        write_seq(t, "line\r\n");
+    int max = tt_history(t);
+    assert(max > 1);
+    struct term_snapshot *snap = term_snapshot_new();
+    term_scroll(t, 1);
+    term_scroll(t, INT_MAX);
+    assert(tt_view_offset(t) == max);
+    uint64_t version = view_version(snap, t);
+    term_scroll(t, 1);
+    assert(view_version(snap, t) == version);
+    term_scroll(t, -1);
+    term_scroll(t, INT_MIN);
+    assert(tt_view_offset(t) == 0);
+    version = view_version(snap, t);
+    term_scroll(t, -1);
+    assert(view_version(snap, t) == version);
+    term_snapshot_free(snap);
+    term_free(t);
+}
+
+static void test_batched_recycled_lines(void)
+{
+    static const char *const endings[] = {
+        "short\r\nx\r\nyz\r\n",
+        "short\r\nx\r\nyz\r\n\tfile/",
+        "abcdefghijklmnopqrstuvwxyz012345more\r\nx\r\nyz\r\n\033[2CZ",
+        "short\r\nx\r\nyz\r\n界\xcc\x81",
+        "short\r\nx\r\nyz\r\npartial\r",
+    };
+    for (size_t k = 0; k < sizeof(endings) / sizeof(endings[0]); k++) {
+        struct term *bulk = tt_new(32, 3);
+        struct term *bytes = tt_new(32, 3);
+        const char *old = "\033[31;44mabcdefghijklmnopqrst界界界\r\n";
+        for (int i = 0; i < TEST_SCROLLBACK + 10; i++) {
+            tt_write(bulk, old, strlen(old));
+            write_seq(bytes, old);
+        }
+        write_seq(bulk, "\033[0;1;3m");
+        write_seq(bytes, "\033[0;1;3m");
+        tt_write(bulk, endings[k], strlen(endings[k]));
+        write_seq(bytes, endings[k]);
+
+        assert_same_screen(bulk, bytes);
+        for (int i = 0; i < tt_history(bulk); i += 3) {
+            term_scroll(bulk, 3);
+            term_scroll(bytes, 3);
+            assert_same_screen(bulk, bytes);
+        }
+        term_free(bulk);
+        term_free(bytes);
+    }
+}
+
+static void test_full_width_line_endings(void)
+{
+    static const char *const feeds[] = {
+        "aaaa\r\nbbbb\r\ncccc\r\ndddd\r\neeee\r\nffff",
+        "aaaa\r\nbbbb\r\ncccc\r\ndddd\neeee",
+        "aaaa\r\nbbbb\r\ncccc\r\ndddd\re",
+        "aaaa\r\nbbbb\r\ncccc\r\nddddeeeeff",
+        "aa\r\nbb\r\ncc\r\nd中d\r\nef",
+    };
+    for (size_t k = 0; k < sizeof(feeds) / sizeof(feeds[0]); k++) {
+        struct term *bulk = tt_new(4, 3);
+        struct term *bytes = tt_new(4, 3);
+        tt_write(bulk, feeds[k], strlen(feeds[k]));
+        write_seq(bytes, feeds[k]);
+        assert_same_screen(bulk, bytes);
+        term_free(bulk);
+        term_free(bytes);
+    }
+
+    struct term *t = tt_new(4, 3);
+    tt_write(t, feeds[0], strlen(feeds[0]));
+    assert(tt_history(t) == 3);
+    assert(row_is(t, 0, "dddd") && row_is(t, 1, "eeee") && row_is(t, 2, "ffff"));
+    term_free(t);
+}
+
+/* Compare the screen, cursor, and scrollback for each input mode.
+ *
+ * Input mode          | Byte-wise | 64 KiB bulk | 512 KiB single write
+ * Raw LF              | Reference | Must match  | Must match
+ * Newline conversion  | Reference | Must match  | Must match
+ *
+ * The input length selects the stream path. The 512 KiB write also has
+ * enough newlines to test the backward scan when newline conversion is
+ * active.
+ */
+static void test_bulk_line_flood(void)
+{
+    static const struct term_vector2i geoms[] = {
+        {.x = 80, .y = 24}, {.x = 27, .y = 8}, {.x = 10, .y = 5}, {.x = 120, .y = 80},
+    };
+    for (size_t g = 0; g < 2 * sizeof(geoms) / sizeof(geoms[0]); g++) {
+        int cols = geoms[g / 2].x, rows = geoms[g / 2].y;
+        size_t cap = 1u << 19;
+        char *buf = malloc(cap);
+        assert(buf);
+        size_t n = 0;
+        unsigned state = 12345;
+        while (n < cap / 2) {
+            state = state * 1103515245u + 12345u;
+            unsigned pick = (state >> 16) % 27;
+            buf[n++] = pick == 26 ? '\n' : (char)('a' + pick);
+        }
+        for (int k = -1; k <= 1; k++) {
+            memset(buf + n, 'x', (size_t)(cols + k));
+            n += (size_t)(cols + k);
+            buf[n++] = '\n';
+            memset(buf + n, 'y', (size_t)(2 * cols + k));
+            n += (size_t)(2 * cols + k);
+            buf[n++] = '\n';
+        }
+        while (n < cap) {
+            state = state * 1103515245u + 12345u;
+            unsigned pick = (state >> 16) % 27;
+            buf[n++] = pick == 26 ? '\n' : (char)('a' + pick);
+        }
+
+        struct term *bulk = tt_new(cols, rows);
+        struct term *stream = tt_new(cols, rows);
+        struct term *bytes = tt_new(cols, rows);
+        unsigned flags = g % 2 != 0 ? TERM_FEED_ONLCR : 0;
+        for (size_t i = 0; i < n; i += 65536)
+            term_feed(bulk, buf + i, n - i < 65536 ? n - i : 65536, flags);
+        /* One large write has enough newlines to discard old output. */
+        term_feed(stream, buf, n, flags);
+        for (size_t i = 0; i < n; i++) term_feed(bytes, buf + i, 1, flags);
+
+        assert_same_screen(bulk, bytes);
+        assert_same_screen(stream, bytes);
+        for (int i = 0; i < tt_history(bulk); i += 7) {
+            term_scroll(bulk, 7);
+            term_scroll(stream, 7);
+            term_scroll(bytes, 7);
+            assert_same_screen(bulk, bytes);
+            assert_same_screen(stream, bytes);
+        }
+        term_free(bulk);
+        term_free(stream);
+        term_free(bytes);
+        free(buf);
+    }
+}
+
+/* Dense LF input must keep its text through edits and buffer moves. */
+static void test_ascii_flood_edits(void)
+{
+    static const int widths[] = {1, 2, 7, 120};
+    char input[65536];
+    unsigned state = 43;
+    for (size_t i = 0; i < sizeof(input); i++) {
+        state = state * 1103515245u + 12345u;
+        unsigned pick = (state >> 16) % 5;
+        input[i] = pick == 4 ? '\n' : (char)('a' + pick);
+    }
+    memset(input + 1024, '\n', 256);
+    static const char edit[] =
+        "\033[1;1Hé漢x̂\033[T\033[2;1HEND"
+        "\033[?1049hALT\033[?1049l\033[6;1Htail\n";
+    for (size_t w = 0; w < sizeof(widths) / sizeof(widths[0]); w++) {
+        for (size_t chunk = 4096; chunk <= sizeof(input); chunk *= 16) {
+            struct term *bulk = tt_new(widths[w], 6);
+            struct term *bytes = tt_new(widths[w], 6);
+            for (size_t i = 0; i < sizeof(input); i += chunk)
+                term_feed(bulk, input + i, chunk, TERM_FEED_ONLCR);
+            for (size_t i = 0; i < sizeof(input); i++)
+                term_feed(bytes, input + i, 1, TERM_FEED_ONLCR);
+            assert_same_screen(bulk, bytes);
+            term_feed(bulk, edit, sizeof(edit) - 1, TERM_FEED_ONLCR);
+            for (size_t i = 0; i < sizeof(edit) - 1; i++)
+                term_feed(bytes, edit + i, 1, TERM_FEED_ONLCR);
+            assert_same_screen(bulk, bytes);
+            for (int i = 0; i < tt_history(bulk); i += 6) {
+                term_scroll(bulk, 6);
+                term_scroll(bytes, 6);
+                assert_same_screen(bulk, bytes);
+            }
+            term_scroll_to(bulk, 0);
+            term_scroll_to(bytes, 0);
+            assert(tt_resize(bulk, widths[w] + 3, 7));
+            assert(tt_resize(bytes, widths[w] + 3, 7));
+            assert_same_screen(bulk, bytes);
+            term_free(bulk);
+            term_free(bytes);
+        }
+    }
+}
+
+/* Newline modes: 0 is a plain line feed, 1 is LNM (CSI 20 h), and 2 is
+ * newline conversion on the feed. */
+static void test_margin_linefeed_bursts(void)
+{
+    static const char *bursts[] = {
+        "\n\n", "\n\n\n\n\n", "\n\n\n\n\n\n\n\n",
+        "\r\n\r\n", "\r\n\r\n\r\n\r\n\r\n\r\n",
+        "\n\n\r\n\r\n\n\n",
+    };
+    for (size_t k = 0; k < sizeof(bursts) / sizeof(bursts[0]); k++) {
+        for (int mode = 0; mode < 3; mode++) {
+            struct term *bulk = tt_new(8, 8);
+            struct term *bytes = tt_new(8, 8);
+            const char *setup = "\033[1;1Htop\033[2;1Ha\033[3;1Hb\033[4;1Hc"
+                                "\033[5;1Hd\033[6;1He\033[7;1Hf\033[8;1Hfoot"
+                                "\033[2;7r\033[7;3H";
+            tt_write(bulk, setup, strlen(setup));
+            tt_write(bytes, setup, strlen(setup));
+            if (mode == 1) {
+                write_seq(bulk, "\033[20h");
+                write_seq(bytes, "\033[20h");
+            }
+            unsigned flags = mode == 2 ? TERM_FEED_ONLCR : 0;
+            term_feed(bulk, bursts[k], strlen(bursts[k]), flags);
+            feed_seq(bytes, bursts[k], flags);
+            assert_same_screen(bulk, bytes);
+            assert(row_is(bulk, 0, "top"));
+            assert(row_is(bulk, 7, "foot"));
+            term_free(bulk);
+            term_free(bytes);
+        }
+    }
+}
+
+static void test_alt_linefeed_burst_after_resize(void)
+{
+    struct term *bulk = tt_new(8, 5);
+    struct term *bytes = tt_new(8, 5);
+    const char *setup = "\033[?1049h\033[5;1H\n\n\n\n";
+    tt_write(bulk, setup, strlen(setup));
+    write_seq(bytes, setup);
+    tt_resize(bulk, 8, 3);
+    tt_resize(bytes, 8, 3);
+    const char *burst = "\n\n\n\n\r\n\r\n";
+    tt_write(bulk, burst, strlen(burst));
+    write_seq(bytes, burst);
+    assert_same_screen(bulk, bytes);
+    tt_resize(bulk, 12, 4);
+    tt_resize(bytes, 12, 4);
+    assert_same_screen(bulk, bytes);
+    term_free(bulk);
+    term_free(bytes);
+}
+
+/*
+ * Regression: the alternate screen scrolls by moving its top row. A resize
+ * changed the row count but kept that top row, so rows came back out of
+ * order, and further line feeds indexed past the row tables.
+ */
+static void test_alt_resize_keeps_row_order(void)
+{
+    const char *setup = "\033[?1049h\033[5;1H\n\n\n"
+                        "\033[1;1HA\033[2;1HB\033[3;1HC\033[4;1HD\033[5;1HE";
+
+    struct term *grow = tt_new(20, 5);
+    write_seq(grow, setup);
+    tt_resize(grow, 20, 8);
+    assert(row_is(grow, 0, "A") && row_is(grow, 4, "E"));
+    assert(row_is(grow, 5, "") && row_is(grow, 7, ""));
+    term_free(grow);
+
+    /* The cursor is on the last row, so shrinking scrolls A and B off. */
+    struct term *shrink = tt_new(20, 5);
+    write_seq(shrink, setup);
+    tt_resize(shrink, 20, 3);
+    assert(row_is(shrink, 0, "C") && row_is(shrink, 2, "E"));
+    term_free(shrink);
+}
+
+static void test_alt_shrink_then_flood(void)
+{
+    struct term *t = tt_new(80, 40);
+    tt_write(t, "\033[?1049h\033[40;1H", 16);
+    for (int i = 0; i < 35; i++)
+        tt_write(t, "x\n", 2);
+    tt_resize(t, 80, 10);
+    /* More lines than the ring holds, one write per line. */
+    char line[32];
+    for (int i = 0; i < 6000; i++) {
+        int len = snprintf(line, sizeof(line), "\rline %04d\n", i);
+        tt_write(t, line, (size_t)len);
+    }
+    assert(row_is(t, 8, "line 5999") && row_is(t, 0, "line 5991"));
+    term_free(t);
+}
+
+/* Regression: ED 3 on the alternate screen kept the history count, so the
+ * normal screen came back with blank history rows. */
+static void test_alt_erase_scrollback(void)
+{
+    struct term *t = tt_new(20, 5);
+    for (int i = 0; i < 30; i++)
+        tt_write(t, "line\r\n", 6);
+    assert(tt_history(t) > 0);
+    write_seq(t, "\033[?1049h\033[3J\033[?1049l");
+    assert(tt_history(t) == 0);
+    term_free(t);
+}
+
+/* Regression: a snapshot knew its terminal by address. A new terminal that
+ * reused a freed one's memory then showed the old terminal's rows. */
+static void test_snapshot_follows_new_terminal(void)
+{
+    struct term_snapshot *s = term_snapshot_new();
+    for (int i = 0; i < 8; i++) {
+        struct term *t = tt_new(10, 2);
+        char text[2] = { (char)('a' + i), 0 };
+        tt_puts(t, text);
+        assert(term_snapshot_update(s, t));
+        assert(term_snapshot_row(s, 0)[0].text == (uint32_t)text[0]);
+        term_free(t);
+    }
+    term_snapshot_free(s);
+}
+
+static void test_string_payloads(void)
+{
+    static const char *prefixes[] = {"\033]0;", "\033]7;file://host/", "\033P"};
+    static const char *ends[] = {"\007", "\033\\"};
+    static const size_t chunks[] = {1, 7, 4096};
+    for (size_t p = 0; p < 3; p++) {
+        for (size_t e = 0; e < 2; e++) {
+            for (int large = 0; large < 2; large++) {
+                char input[1024];
+                size_t n = (size_t)snprintf(input, sizeof(input), "%s⠋ çalışma/clernen_pi", prefixes[p]);
+                if (large) {
+                    memset(input + n, 'a', 600);
+                    n += 600;
+                }
+                n += (size_t)snprintf(input + n, sizeof(input) - n, "%sOK", ends[e]);
+                for (size_t c = 0; c < 3; c++) {
+                    title[0] = 0;
+                    response_len = 0;
+                    struct term *t = tt_new_opts(80, 4, &title_cb);
+                    for (size_t i = 0; i < n;) {
+                        size_t take = n - i < chunks[c] ? n - i : chunks[c];
+                        tt_write(t, input + i, take);
+                        i += take;
+                    }
+                    assert(row_is(t, 0, "OK"));
+                    assert(tt_cursor_x(t) == 2 && tt_cursor_y(t) == 0);
+                    assert(response_len == 0);
+                    if (p == 0 && !large)
+                        assert(!strcmp(title, "⠋ çalışma/clernen_pi"));
+                    if (large) {
+                        if (p == 0) {
+                            assert(!strncmp(title, "⠋ çalışma/clernen_pi",
+                                            strlen("⠋ çalışma/clernen_pi")));
+                            assert(title[sizeof(title) - 1] == 0);
+                        } else {
+                            assert(title[0] == 0);
+                        }
+                    }
+                    term_free(t);
+                }
+            }
+        }
+    }
+}
+
+static void test_newline_policy_survives_reset(void)
+{
+    static const char *const resets[] = { "\033c", "\033[!p", "\033[20l" };
+    for (size_t i = 0; i < sizeof(resets) / sizeof(resets[0]); i++) {
+        struct term *t = tt_new(20, 6);
+        term_feed(t, "a\n", 2, TERM_FEED_ONLCR);
+        assert(tt_cursor_x(t) == 0);
+        write_seq(t, resets[i]);
+        term_feed(t, "b\nc", 3, TERM_FEED_ONLCR);
+        assert(tt_cursor_x(t) == 1);
+        assert(row_is(t, tt_cursor_y(t), "c"));
+        term_free(t);
+    }
+}
+
+static void test_lnm_mode_alone_is_not_sticky(void)
+{
+    struct term *t = tt_new(20, 6);
+    write_seq(t, "\033[20h\033c");
+    tt_write(t, "b\nc", 3);
+    assert(tt_cursor_x(t) == 2);
+    term_free(t);
+}
+
+/* A C0 control ends an unfinished UTF-8 sequence, which prints U+FFFD. A
+ * lone continuation byte prints U+FFFD too. */
+static void test_c0_ends_utf8_sequence(void)
+{
+    static const char input[] = "\xc3\n\xa9z";
+    for (size_t split = 0; split < sizeof(input) - 1; split++) {
+        struct term *t = tt_new(20, 4);
+        tt_write(t, input, split);
+        tt_write(t, input + split, sizeof(input) - 1 - split);
+        assert(tt_cell_cp(t, tt_cell(t, 0, 0)) == 0xFFFD);
+        assert(tt_cell_cp(t, tt_cell(t, 1, 1)) == 0xFFFD);
+        assert(tt_cell_cp(t, tt_cell(t, 2, 1)) == 'z');
+        term_free(t);
+    }
+}
+
+/* A bulk stream of long lines must behave like byte-wise input after every
+ * later operation that touches those rows: overwriting, scroll-region
+ * rotation, reflow, alternate-screen round trips, and selection. */
+static void test_bulk_rows_survive_edits(void)
+{
+    enum { COLS = 40, ROWS = 6 };
+    static char flood[1 << 16];
+    for (size_t i = 0; i < sizeof(flood); i++)
+        flood[i] = (char)('a' + (i * 7 + i / COLS) % 26);
+
+    struct term *bulk = tt_new(COLS, ROWS);
+    struct term *bytes = tt_new(COLS, ROWS);
+    write_seq(bulk, "\033[1;4;38;2;9;8;7;48;2;1;2;3m");
+    write_seq(bytes, "\033[1;4;38;2;9;8;7;48;2;1;2;3m");
+    tt_write(bulk, flood, sizeof(flood));
+    for (size_t i = 0; i < sizeof(flood); i++) tt_write(bytes, flood + i, 1);
+    assert_same_screen(bulk, bytes);
+
+    /* Overwrite the middle of a streamed row, then erase part of another. */
+    const char *edit = "\033[m\033[2;5HXYZ\033[3;1H\033[K\033[4;10H\033[1K";
+    write_seq(bulk, edit);
+    write_seq(bytes, edit);
+    assert_same_screen(bulk, bytes);
+    assert(tt_view_cell(bulk, 4, 1)->text == 'X');
+
+    /* Scroll region rotation moves row pointers between ring slots. */
+    const char *region = "\033[2;5r\033[5;1H\n\n\033[T\033[r";
+    write_seq(bulk, region);
+    write_seq(bytes, region);
+    assert_same_screen(bulk, bytes);
+
+    /* Alternate screen and back, then view history. */
+    write_seq(bulk, "\033[?1049hALT\033[?1049l");
+    write_seq(bytes, "\033[?1049hALT\033[?1049l");
+    assert_same_screen(bulk, bytes);
+    for (int i = 0; i < 3; i++) {
+        term_scroll(bulk, 100);
+        term_scroll(bytes, 100);
+        assert_same_screen(bulk, bytes);
+    }
+    term_scroll_to(bulk, 0);
+    term_scroll_to(bytes, 0);
+
+    /* Selection text reads rows straight from history. */
+    term_scroll(bulk, 50);
+    term_scroll(bytes, 50);
+    tt_select(bulk, 0, 0, COLS - 1, 2);
+    tt_select(bytes, 0, 0, COLS - 1, 2);
+    char *a = tt_selection_text(bulk), *b = tt_selection_text(bytes);
+    assert(a && b && !strcmp(a, b) && strlen(a) >= COLS);
+    free(a);
+    free(b);
+    term_scroll_to(bulk, 0);
+    term_scroll_to(bytes, 0);
+
+    /* Reflow narrower and wider keeps history identical. */
+    tt_resize(bulk, 29, ROWS);
+    tt_resize(bytes, 29, ROWS);
+    assert_same_screen(bulk, bytes);
+    tt_resize(bulk, 61, ROWS + 2);
+    tt_resize(bytes, 61, ROWS + 2);
+    assert_same_screen(bulk, bytes);
+    term_scroll(bulk, 20);
+    term_scroll(bytes, 20);
+    assert_same_screen(bulk, bytes);
+
+    term_free(bulk);
+    term_free(bytes);
+}
+
+static void test_erase_keeps_used_rows(void)
+{
+    for (int row = 0; row < 40; row++) {
+        struct term *t = tt_new(20, 40);
+        char seq[64];
+        int len = snprintf(seq, sizeof(seq), "\033[%d;1Hsaved\033[2J", row + 1);
+        tt_write(t, seq, (size_t)len);
+        assert(tt_history(t) == row + 1);
+        for (int y = 0; y < 40; y++)
+            assert(row_eq(t, y, ""));
+        term_scroll(t, 1);
+        assert(row_eq(t, 0, "saved"));
+        term_free(t);
+    }
+}
+
+static void test_blank_rows(void)
+{
+    /* ED 2 pushes used rows to scrollback; the erased screen reads as
+     * default-color blanks through every accessor. */
+    struct term *t = tt_new(10, 4);
+    write_seq(t, "one\r\ntwo\r\nthree");
+    write_seq(t, "\033[2J");
+    assert(tt_history(t) == 3);
+    for (int y = 0; y < 4; y++)
+        for (int x = 0; x < 10; x++) {
+            const struct term_cell *c = tt_view_cell(t, x, y);
+            assert(c->text == ' ' && c->fg == TERM_COLOR_FG &&
+                   c->bg == TERM_COLOR_BG);
+            assert(tt_cell(t, x, y)->text == ' ');
+        }
+    term_scroll(t, 3);
+    assert(row_is(t, 0, "one") && row_is(t, 1, "two") && row_is(t, 2, "three"));
+    term_scroll_to(t, 0);
+
+    /* A scrolled-in blank row reads as blanks, then accepts new text. */
+    write_seq(t, "\033[4;1Hlast\r\n\r\n\r\n");
+    for (int x = 0; x < 10; x++)
+        assert(tt_view_cell(t, x, 3)->text == ' ');
+    write_seq(t, "\033[4;6Hhi");
+    assert(row_is(t, 3, "     hi"));
+    term_free(t);
+
+    /* A spaces-only row does not extend ED 2 history. */
+    t = tt_new(10, 6);
+    write_seq(t, "top\033[6;1H     ");
+    assert(tt_history(t) == 0);
+    write_seq(t, "\033[2J");
+    assert(tt_history(t) == 1);
+    term_scroll(t, 1);
+    assert(row_is(t, 0, "top"));
+    term_scroll_to(t, 0);
+
+    /* Blank rows survive a resize and still read as blanks. */
+    tt_resize(t, 20, 6);
+    for (int x = 0; x < 20; x++)
+        assert(tt_cell(t, x, 5)->text == ' ' &&
+               tt_cell(t, x, 5)->bg == TERM_COLOR_BG);
+    term_free(t);
+
+    /* Erasing a blank row with a color still produces a colored row. */
+    t = tt_new(10, 4);
+    write_seq(t, "\033[2J\033[41m\033[2K");
+    assert(tt_cell(t, 0, 0)->bg != TERM_COLOR_BG);
+    assert(tt_cell(t, 9, 0)->bg == tt_cell(t, 0, 0)->bg);
+    term_free(t);
+}
+
+static void test_csi_text_chunks(void)
+{
+    static const char *cases[] = {
+        "\033[2;3Hhello\033[2DXY\033[K\033[1A\033[3C!\r\n",
+        "\033[H日本語\033[2GXY\033[7mabc\033[m!\033[2Knext",
+        "\033[Hscreen\033[2J\033[Hnext\033[2K\r\n",
+        "\033[H012345678901234567890123\033[2DXY\033[J!",
+        "\033[?7l\033[H012345678901234567890123\033[1CXY",
+        "\033[41m\033[2J\033[Htext\033[0Jtail\033[1Jend",
+        "\033[2;3Htext\033[3Jnext\033[0K\033[1K\033[2K!",
+        "\033[?6h\033[2;3Htext\033[Jnext",
+        "\033[16;1Ha\033[17;1Hb\033[32;1Hc\033[40;1Hd\033[2J",
+        "\033[40;1H \033[17;1Ha\033[2J\033[Hnext",
+        "\033[?1049h\033[40;1H\n\033[17;1Htext\033[2J",
+    };
+    for (size_t c = 0; c < sizeof(cases) / sizeof(cases[0]); c++) {
+        const char *seq = cases[c];
+        size_t len = strlen(seq);
+        struct term *expected = tt_new(20, 40);
+        write_seq(expected, seq);
+        for (size_t split = 0; split <= len; split++) {
+            struct term *actual = tt_new(20, 40);
+            tt_write(actual, seq, split);
+            tt_write(actual, seq + split, len - split);
+            assert(tt_cursor_x(actual) == tt_cursor_x(expected));
+            assert(tt_cursor_y(actual) == tt_cursor_y(expected));
+            assert(tt_history(actual) == tt_history(expected));
+            int history = tt_history(expected);
+            term_scroll(actual, history);
+            term_scroll(expected, history);
+            for (int page = 0; page <= history; page++) {
+                assert_same_rows(actual, expected, 40);
+                term_scroll(actual, -1);
+                term_scroll(expected, -1);
+            }
+            term_free(actual);
+        }
+        term_free(expected);
+    }
+}
+
+/* A terminal grows past its first reservation: taller than 256 rows and
+ * wider than 2048 columns, on both screens. History and the saved screen
+ * keep their text. */
+static void test_grow_past_reservation(void)
+{
+    struct term *t = tt_new(40, 10);
+    for (int i = 0; i < 30; i++) {
+        char line[32];
+        int len = snprintf(line, sizeof(line), "hist %02d\r\n", i);
+        tt_write(t, line, (size_t)len);
+    }
+    int history = tt_history(t);
+    assert(history > 0);
+
+    tt_resize(t, 40, 700);
+    assert(tt_rows(t) == 700);
+    tt_write(t, "\033[700;1Hbottom", 14);
+    assert(row_is(t, 699, "bottom"));
+
+    tt_resize(t, 3000, 700);
+    assert(tt_cols(t) == 3000);
+    tt_write(t, "\033[698;2995Hedge!", 16);
+    assert(tt_cell(t, 2994, 697)->text == 'e' && tt_cell(t, 2998, 697)->text == '!');
+
+    tt_write(t, "\033[700;1H", 8);
+    for (int i = 0; i < 1000; i++) {
+        char line[32];
+        int len = snprintf(line, sizeof(line), "\r\nfill %04d", i);
+        tt_write(t, line, (size_t)len);
+    }
+    int history_before = tt_history(t);
+    assert(history_before > 0);
+
+    tt_write(t, "\033[?1049h", 8);
+    tt_write(t, "alt", 3);
+    tt_resize(t, 3000, 2500);
+    assert(tt_rows(t) == 2500);
+    assert(row_is(t, 0, "alt"));
+    tt_write(t, "\033[?1049l", 8);
+
+    bool found = false;
+    term_scroll(t, tt_history(t));
+    for (int y = 0; y < tt_rows(t) && !found; y++)
+        found = row_eq(t, y, "hist 00");
+    assert(found);
+    term_scroll(t, -tt_history(t));
+    bool last = false;
+    for (int y = 0; y < tt_rows(t) && !last; y++)
+        last = row_eq(t, y, "fill 0999");
+    assert(last);
+    term_free(t);
+}
+
+struct concurrent_worker_args {
+    struct term *t;
+    _Atomic bool done;
+};
+
+static void *concurrent_feed_worker(void *arg)
+{
+    struct concurrent_worker_args *w = arg;
+    static const char stream[] =
+        "The quick brown fox jumps over the lazy dog.\r\n"
+        "\033[31mRed text\033[0m and \033[32mgreen text\033[0m.\r\n"
+        "Some unicode: 漢字, ひらがな, and emojis: 😀🚀🎉\r\n"
+        "\033[2J\033[HCleared and reset\r\n"
+        "Line 1\r\nLine 2\r\nLine 3\r\nLine 4\r\nLine 5\r\n"
+        "\033]7;file:///tmp/dir\007\033]22;pointer\007"
+        "\033]8;;https://example.com\007link\033]8;;\007\r\n";
+    size_t len = strlen(stream);
+
+    for (int i = 0; i < 2000; i++) {
+        term_feed(w->t, stream, len, 0);
+    }
+    atomic_store(&w->done, true);
+    return NULL;
+}
+
+static void test_concurrent_feed_and_snapshot(void)
+{
+    struct term *t = term_new(&(struct term_options){
+        .size = { .x = 80, .y = 24 },
+        .scrollback = 1000,
+    });
+    assert(t != NULL);
+
+    struct concurrent_worker_args w = { .t = t, .done = false };
+    pthread_t th;
+    int err = pthread_create(&th, NULL, concurrent_feed_worker, &w);
+    assert(err == 0);
+
+    struct term_snapshot *snap = term_snapshot_new();
+    assert(snap != NULL);
+
+    while (!atomic_load(&w.done)) {
+        bool ok = term_snapshot_update(snap, t);
+        assert(ok);
+        struct term_vector2i sz = term_size(t);
+        assert(sz.x > 0 && sz.y > 0);
+        term_scroll(t, 2);
+        term_scroll_to(t, 0);
+        struct term_modes m = term_modes(t);
+        (void)m;
+        struct term_cursor c = term_cursor(t);
+        (void)c;
+
+        /* Every reader is safe while another thread feeds. */
+        char buf[256];
+        term_select_start(t, (struct term_vector2i){ .x = 0, .y = 0 }, false, TERM_SELECT_WORD);
+        term_select_extend(t, (struct term_vector2i){ .x = 40, .y = 10 }, false);
+        (void)term_has_selection(t);
+        (void)term_selection_text(t, buf, sizeof(buf));
+        (void)term_link_at(t, (struct term_vector2i){ .x = 1, .y = 1 }, buf, sizeof(buf));
+        (void)term_cwd(t, buf, sizeof(buf));
+        (void)term_pointer_shape(t, buf, sizeof(buf));
+        (void)term_history_rows(t);
+        (void)term_history_text(t, 5, buf, sizeof(buf));
+        struct term_scrollback sb = term_scrollback(t);
+        assert(sb.offset >= 0 && sb.total >= 0);
+    }
+
+    pthread_join(th, NULL);
+    bool ok = term_snapshot_update(snap, t);
+    assert(ok);
+
+    term_snapshot_free(snap);
+    term_free(t);
+}
+
+int main(void)
+{
+    test_concurrent_feed_and_snapshot();
+    test_grow_past_reservation();
+    test_skipped_cells_read_blank();
+    test_csi_text_chunks();
+    test_erase_keeps_used_rows();
+    test_blank_rows();
+    test_lnm_mode_alone_is_not_sticky();
+    test_newline_policy_survives_reset();
+    test_esc_control_strings_and_designators();
+    test_string_payloads();
+    test_recycled_scrollback_blanks();
+    test_scroll_view_clamps_extreme_deltas();
+    test_batched_recycled_lines();
+    test_invalid_utf8_runs();
+    test_c0_ends_utf8_sequence();
+    test_full_width_line_endings();
+    test_bulk_line_flood();
+    test_ascii_flood_edits();
+    test_margin_linefeed_bursts();
+    test_alt_linefeed_burst_after_resize();
+    test_alt_resize_keeps_row_order();
+    test_alt_shrink_then_flood();
+    test_alt_erase_scrollback();
+    test_snapshot_follows_new_terminal();
+    test_bulk_rows_survive_edits();
+
+    assert(!strcmp(UNICODE_DATA_VERSION, "18.0.0"));
+    assert(!strcmp(term_unicode_version(), UNICODE_DATA_VERSION));
+    assert(unicode_width('A') == 1);
+    assert(unicode_width(0x0301) == 0);
+    assert(unicode_width(0x754C) == 2);
+    assert(unicode_width(0x1FAE0) == 2);
+    assert(unicode_emoji_presentation(0x1FAE0));
+    assert(unicode_width(0x1FAEB) == 2);
+    assert(unicode_emoji_presentation(0x1FAEB));
+    {
+        /* A Jamo Extended-B vowel draws inside its leading consonant. */
+        struct term *t = term_new(&(struct term_options){ .size = { .x = 10, .y = 2 } });
+        term_feed(t, "\xe1\x84\x80\xed\x9e\xb0", 6, 0);
+        assert(term_cursor(t).pos.x == 2);
+        term_free(t);
+    }
+
+    test_wide_characters();
+    test_wide_runs();
+    test_editor_scrolling();
+    test_top_region_scrollback();
+    test_device_attributes();
+    test_unimplemented_da_features();
+    test_keyboard_negotiation();
+    test_resize_reflow();
+    test_resize_exposes_blank_rows();
+    test_prompt_resize();
+    test_cursor_line_motion();
+    test_relative_cursor_motion();
+    test_read_boundaries();
+    test_ascii_controls();
+    test_random_read_boundaries();
+    test_csi_recovery();
+    test_csi_byte_boundaries();
+    test_parameter_limits();
+    test_unterminated_control_strings_do_not_swallow_text();
+    test_c0_controls_after_esc_are_executed();
+    struct term *t = tt_new_opts(10, 4, &reply_cb);
+    write_seq(t, "\033(Babc\r\nD");
+    assert(tt_cell(t, 0, 0)->text == 'a');
+    assert(tt_cell(t, 0, 1)->text == 'D');
+    write_seq(t, "\033[H/tmp/proj\r\n$ ");
+    assert(tt_cell(t, 0, 1)->text == '$');
+    assert(tt_cursor_x(t) == 2 && tt_cursor_y(t) == 1);
+    write_seq(t, "\r>");
+    assert(tt_cell(t, 0, 1)->text == '>');
+    assert(tt_cursor_x(t) == 1 && tt_cursor_y(t) == 1);
+    write_seq(t, "\r\n$");
+    assert(tt_cell(t, 0, 2)->text == '$');
+    assert(tt_cursor_x(t) == 1 && tt_cursor_y(t) == 2);
+    write_seq(t, "\033[H\033(0lqqk\033(B");
+    assert(tt_cell(t, 0, 0)->text == 0x250c);
+    assert(tt_cell(t, 3, 0)->text == 0x2510);
+    write_seq(t, "\033[3d\rX\033[4bY");
+    assert(tt_cell(t, 4, 2)->text == 'X');
+    assert(tt_cell(t, 5, 2)->text == 'Y');
+    write_seq(t, "\033[3;3H\033[2X");
+    assert(tt_cell(t, 2, 2)->text == ' ' && tt_cell(t, 3, 2)->text == ' ');
+    assert(tt_cell(t, 4, 2)->text == 'X' && tt_cursor_x(t) == 2);
+
+    write_seq(t, "\033[2J\033[H1234567890");
+    assert(tt_cell(t, 9, 0)->text == '0');
+    assert(tt_cursor_x(t) == 9 && tt_cursor_y(t) == 0);
+    write_seq(t, "A");
+    assert(tt_cell(t, 0, 1)->text == 'A');
+    assert(tt_cursor_x(t) == 1 && tt_cursor_y(t) == 1);
+
+    write_seq(t, "\033[2J\033[Habcdefghij\r\nX");
+    assert(tt_cell(t, 9, 0)->text == 'j');
+    assert(tt_cell(t, 0, 1)->text == 'X' && tt_cursor_y(t) == 1);
+
+    write_seq(t, "\033[2J\033[H\033[99GZ");
+    assert(tt_cell(t, 9, 0)->text == 'Z' && tt_cursor_x(t) == 9);
+    write_seq(t, "\033[2J\033[9;99HY");
+    assert(tt_cursor_y(t) == 3 && tt_cell(t, 9, 3)->text == 'Y');
+
+    write_seq(t, "\033[2J\033[H\033[?7l1234567890AB");
+    assert(tt_cell(t, 9, 0)->text == 'B' && tt_cursor_y(t) == 0);
+    write_seq(t, "\033[?7h");
+
+    write_seq(t, "\033[2J\033[Habcd\033[2G\033[4hX\033[4l");
+    assert(row_is(t, 0, "aXbcd"));
+
+    write_seq(t, "\033[2;4r\033[?6h\033[2;3H@");
+    assert(tt_cell(t, 2, 2)->text == '@');
+    write_seq(t, "\033[?6l\033[r");
+
+    write_seq(t, "\033[2J\033[H\033[3g\033[4G\033H\r\tT");
+    assert(tt_cell(t, 3, 0)->text == 'T');
+
+    write_seq(t, "\033[3;5H\033[5n");
+    assert(!strcmp(response, "\033[0n"));
+    write_seq(t, "\033[6n");
+    assert(!strcmp(response, "\033[3;5R"));
+
+    write_seq(t, "\033[2J\033[?69h\033[3;6s\033[?6h\033[Habcdef");
+    assert(tt_cell(t, 2, 0)->text == 'a' && tt_cell(t, 5, 0)->text == 'd');
+    assert(tt_cell(t, 2, 1)->text == 'e' && tt_cell(t, 3, 1)->text == 'f');
+    write_seq(t, "\033[?6;69l");
+
+    write_seq(t, "\033[?1;5;1004;2026h\033[!p");
+    struct term_modes modes = term_modes(t);
+    assert(!modes.app_cursor && !modes.focus_events);
+    assert(!modes.synchronized && !modes.reverse_video);
+    write_seq(t, "kept\033c");
+    assert(row_is(t, 0, ""));
+
+    write_seq(t, "\033[2J\033[Hz\033[11b");
+    assert(tt_cell(t, 9, 0)->text == 'z' && tt_cell(t, 1, 1)->text == 'z');
+    assert(tt_cell(t, 2, 1)->text == ' ');
+    assert(tt_cursor_x(t) == 2 && tt_cursor_y(t) == 1);
+    write_seq(t, "\033[2J\033[H1234567890\rA");
+    assert(tt_cell(t, 0, 0)->text == 'A');
+    write_seq(t, "\033[2;4H\033[2J");
+    assert(tt_cursor_x(t) == 3 && tt_cursor_y(t) == 1);
+    assert(term_modes(t).mouse == TERM_MOUSE_OFF);
+    write_seq(t, "\033[?1000;1006h");
+    assert(term_modes(t).mouse == TERM_MOUSE_NORMAL);
+    assert(term_modes(t).mouse_encoding == TERM_MOUSE_ENC_SGR);
+    write_seq(t, "\033[?1002h");
+    assert(term_modes(t).mouse == TERM_MOUSE_BUTTON);
+    assert(term_modes(t).mouse_encoding == TERM_MOUSE_ENC_SGR);
+    write_seq(t, "\033[?1003h");
+    assert(term_modes(t).mouse == TERM_MOUSE_ANY);
+    write_seq(t, "\033[?1006l");
+    assert(term_modes(t).mouse_encoding == TERM_MOUSE_ENC_X10);
+    write_seq(t, "\033[?1015h");
+    assert(term_modes(t).mouse_encoding == TERM_MOUSE_ENC_URXVT);
+    write_seq(t, "\033[?1016h");
+    assert(term_modes(t).mouse_encoding == TERM_MOUSE_ENC_SGR_PIXELS);
+    write_seq(t, "\033[?1004h");
+    term_focus(t, false);
+    assert(!strcmp(response, "\033[O"));
+    term_focus(t, true);
+    assert(!strcmp(response, "\033[I"));
+    write_seq(t, "\033[?1003l");
+    assert(term_modes(t).mouse == TERM_MOUSE_OFF);
+    response_len = 0;
+    write_seq(t, "\033]10;?\007");
+    assert(!strcmp(response, "\033]10;rgb:ffff/ffff/ffff\033\\"));
+    write_seq(t, "\033P+q696e646e\033\\");
+    assert(!strcmp(response, "\033P0+r696e646e\033\\"));
+    write_seq(t, "\033P+q6b696e64\033\\");
+    assert(!strcmp(response, "\033P1+r6b696e64=1b5b313b3242\033\\"));
+    term_free(t);
+    t = tt_new(40, 4);
+    write_seq(t, "hello 世界  \r\nsecond line\r\nhttps://example.com/path.");
+    tt_select(t, 9, 0, 0, 0);
+    char *text = tt_selection_text(t);
+    assert(text && !strcmp(text, "hello 世界"));
+    free(text);
+    tt_select(t, 5, 1, 0, 0);
+    text = tt_selection_text(t);
+    assert(text && !strcmp(text, "hello 世界\nsecond"));
+    free(text);
+    assert(tt_selected(t, 0, 0) && tt_selected(t, 5, 1));
+    assert(!tt_selected(t, 6, 1));
+    text = tt_link_at(t, 10, 2);
+    assert(text && !strcmp(text, "https://example.com/path"));
+    free(text);
+    assert(!tt_link_at(t, 10, 1));
+    write_seq(t, "\033[?2004h");
+    assert(term_modes(t).bracketed_paste);
+    text = tt_selection_text(t);
+    assert(text && !strcmp(text, "hello 世界\nsecond"));
+    free(text);
+    write_seq(t, "\033[?2004l\r\nlast\r\n");
+    assert(!term_modes(t).bracketed_paste);
+    term_scroll(t, 1);
+    tt_select(t, 0, 0, 9, 0);
+    text = tt_selection_text(t);
+    assert(text && !strcmp(text, "hello 世界"));
+    free(text);
+    tt_resize(t, 50, 4);
+    text = tt_selection_text(t);
+    assert(text && !strcmp(text, "hello 世界"));
+    free(text);
+    term_free(t);
+    t = tt_new(40, 4);
+    write_seq(t, "\033[31;44mA\033[>4;0mB\033[>4;1m\033[31mC");
+    assert(tt_cell(t, 0, 0)->fg == tt_cell(t, 1, 0)->fg);
+    assert(tt_cell(t, 0, 0)->bg == tt_cell(t, 1, 0)->bg);
+    assert(tt_cell(t, 0, 0)->fg == tt_cell(t, 2, 0)->fg);
+    assert(tt_cell(t, 0, 0)->bg == tt_cell(t, 2, 0)->bg);
+    assert(tt_cursor_x(t) == 3 && tt_cursor_y(t) == 0);
+    write_seq(t, "\033[0mD");
+    assert(tt_cell(t, 3, 0)->fg == TERM_COLOR_FG);
+    assert(tt_cell(t, 3, 0)->bg == TERM_COLOR_BG);
+    term_free(t);
+
+    t = tt_new(10, 4);
+    write_seq(t, "ABCDEFGHIJ\r\n\r\n\r\n\r\n");
+    term_scroll(t, 1);
+    assert(tt_view_cell(t, 0, 0)->text == 'A');
+    assert(tt_view_cell(t, 9, 0)->text == 'J');
+    term_scroll_to(t, 0);
+
+    for (int i = 0; i < TEST_SCROLLBACK; i++)
+        write_seq(t, "xy\r\n");
+    term_scroll(t, 1);
+    assert(tt_view_cell(t, 0, 0)->text == 'x');
+    for (int c = 2; c < 10; c++) {
+        assert(tt_view_cell(t, c, 0)->text == ' ');
+        assert(tt_view_cell(t, c, 0)->bg == TERM_COLOR_BG);
+    }
+    term_free(t);
+
+    t = tt_new(10, 4);
+    write_seq(t, "\033[41m\033[2K");
+    term_color erased_bg = tt_cell(t, 0, 0)->bg;
+    assert(erased_bg != TERM_COLOR_BG);
+    assert(tt_cell(t, 9, 0)->bg == erased_bg);
+    write_seq(t, "\033[m\n\n\n\n");
+    term_scroll(t, 1);
+    assert(tt_view_cell(t, 9, 0)->bg == erased_bg);
+    assert(tt_view_cell(t, 10, 0)->bg == TERM_COLOR_BG);
+    term_free(t);
+
+    t = tt_new(10, 4);
+    write_seq(t, "\033[Hnormal");
+    write_seq(t, "\033[?1049h");
+    for (int c = 0; c < 10; c++) {
+        assert(tt_cell(t, c, 0)->text == ' ');
+        assert(tt_cell(t, c, 0)->bg == TERM_COLOR_BG);
+    }
+    write_seq(t, "\033[Halt\n\033[2J");
+    write_seq(t, "\033[?1049l");
+    assert(tt_cell(t, 0, 0)->text == 'n' && tt_cell(t, 5, 0)->text == 'l');
+    term_free(t);
+
+    t = tt_new(20, 8);
+    write_seq(t, "one\r\ntwo\r\nthree\r\nfour\r\nfive\r\n$ ");
+    assert(tt_cursor_y(t) == 5 && tt_history(t) == 0);
+    tt_resize(t, 20, 3);
+    assert(tt_cursor_y(t) == 2 && tt_history(t) == 3);
+    assert(row_is(t, 0, "four") && row_is(t, 1, "five") && row_is(t, 2, "$"));
+    term_scroll(t, 3);
+    assert(row_is(t, 0, "one") && row_is(t, 1, "two") && row_is(t, 2, "three"));
+    term_scroll_to(t, 0);
+    tt_resize(t, 20, 8);
+    assert(tt_cursor_y(t) == 5 && tt_history(t) == 0);
+    assert(row_is(t, 0, "one") && row_is(t, 2, "three") && row_is(t, 5, "$"));
+    assert(row_is(t, 6, "") && row_is(t, 7, ""));
+
+    tt_resize(t, 20, 6);
+    assert(tt_cursor_y(t) == 5 && tt_history(t) == 0);
+    assert(row_is(t, 0, "one") && row_is(t, 5, "$"));
+    term_free(t);
+
+    t = tt_new(20, 6);
+    write_seq(t, "a\r\nb\r\nc\r\nd\r\ne\r\n");
+    write_seq(t, "\033[?1049h\033[6;1Hbottom");
+    int before = tt_history(t);
+    tt_resize(t, 20, 3);
+    assert(tt_history(t) == before);
+    tt_resize(t, 20, 6);
+    assert(tt_history(t) == before);
+    write_seq(t, "\033[?1049l");
+    assert(row_is(t, 0, "a") && row_is(t, 4, "e"));
+    term_free(t);
+
+    t = tt_new(40, 6);
+    write_seq(t, "\033[?1049h\033[1;38Hxy");
+    tt_resize(t, 12, 6);
+    write_seq(t, "\033[?1049l");
+    assert(tt_cursor_x(t) < tt_cols(t));
+    write_seq(t, "Q");
+    assert(tt_cell(t, tt_cursor_x(t) - 1, tt_cursor_y(t))->text == 'Q');
+    term_free(t);
+
+    t = tt_new(8, 4);
+    write_seq(t, "abcdefghijkl");
+    tt_select(t, 0, 0, 3, 1);
+    text = tt_selection_text(t);
+    assert(text && !strcmp(text, "abcdefghijkl"));
+    free(text);
+    write_seq(t, "\033[2J\033[Habcd\r\nefgh");
+    tt_select(t, 0, 0, 3, 1);
+    text = tt_selection_text(t);
+    assert(text && !strcmp(text, "abcd\nefgh"));
+    free(text);
+    term_free(t);
+
+    t = tt_new(10, 4);
+    write_seq(t, "abcdef");
+    write_seq(t, "\033[1;3H\033[P");
+    assert(row_is(t, 0, "abdef"));
+    assert(tt_cursor_x(t) == 2 && tt_cursor_y(t) == 0);
+    write_seq(t, "\033[2P");
+    assert(row_is(t, 0, "abf"));
+    assert(tt_cursor_x(t) == 2 && tt_cursor_y(t) == 0);
+    write_seq(t, "\033[10P");
+    assert(row_is(t, 0, "ab"));
+    assert(tt_cursor_x(t) == 2 && tt_cursor_y(t) == 0);
+    term_free(t);
+
+    t = tt_new(8, 4);
+    write_seq(t, "abcdef");
+    write_seq(t, "\033[1;3H\033[@");
+    assert(row_is(t, 0, "ab cdef"));
+    assert(tt_cursor_x(t) == 2 && tt_cursor_y(t) == 0);
+    write_seq(t, "\033[2@");
+    assert(row_is(t, 0, "ab   cde"));
+    term_free(t);
+
+    t = tt_new(10, 4);
+    assert(term_cursor(t).style == TERM_CURSOR_BLOCK);
+    assert(term_cursor(t).blink == true);
+
+    write_seq(t, "\033[2 q");
+    assert(term_cursor(t).style == TERM_CURSOR_BLOCK);
+    assert(term_cursor(t).blink == false);
+
+    write_seq(t, "\033[3 q");
+    assert(term_cursor(t).style == TERM_CURSOR_UNDERLINE);
+    assert(term_cursor(t).blink == true);
+
+    write_seq(t, "\033[4 q");
+    assert(term_cursor(t).style == TERM_CURSOR_UNDERLINE);
+    assert(term_cursor(t).blink == false);
+
+    write_seq(t, "\033[5 q");
+    assert(term_cursor(t).style == TERM_CURSOR_BAR);
+    assert(term_cursor(t).blink == true);
+
+    write_seq(t, "\033[6 q");
+    assert(term_cursor(t).style == TERM_CURSOR_BAR);
+    assert(term_cursor(t).blink == false);
+
+    write_seq(t, "\033[0 q");
+    assert(term_cursor(t).style == TERM_CURSOR_BLOCK);
+    assert(term_cursor(t).blink == true);
+
+    write_seq(t, "\033[5 q");
+    write_seq(t, "\033[ q");
+    assert(term_cursor(t).style == TERM_CURSOR_BLOCK);
+    assert(term_cursor(t).blink == true);
+
+    write_seq(t, "\033[6 q");
+    assert(term_cursor(t).style == TERM_CURSOR_BAR && !term_cursor(t).blink);
+    write_seq(t, "\033[?1049h");
+    write_seq(t, "\033[3 q");
+    assert(term_cursor(t).style == TERM_CURSOR_UNDERLINE && term_cursor(t).blink);
+    write_seq(t, "\033[?1049l");
+    assert(term_cursor(t).style == TERM_CURSOR_BAR && !term_cursor(t).blink);
+
+    term_set_cursor_default(t, TERM_CURSOR_UNDERLINE, true);
+
+    write_seq(t, "\033[5 q");
+    assert(term_cursor(t).style == TERM_CURSOR_BAR && term_cursor(t).blink);
+    write_seq(t, "\033[0 q");
+    assert(term_cursor(t).style == TERM_CURSOR_UNDERLINE && !term_cursor(t).blink);
+
+    write_seq(t, "\033[2 q");
+    assert(term_cursor(t).style == TERM_CURSOR_BLOCK && !term_cursor(t).blink);
+    write_seq(t, "\033[ q");
+    assert(term_cursor(t).style == TERM_CURSOR_UNDERLINE && !term_cursor(t).blink);
+
+    write_seq(t, "\033[1 q");
+    assert(term_cursor(t).style == TERM_CURSOR_BLOCK && term_cursor(t).blink);
+    write_seq(t, "\033[!p");
+    assert(term_cursor(t).style == TERM_CURSOR_UNDERLINE && !term_cursor(t).blink);
+    term_free(t);
+
+    t = tt_new(20, 4);
+    write_seq(t, "\033[1;2;3;4;9;53mA\033[21mB\033[4:2mC\033[22;24mD\033[0mE");
+    const uint16_t styles = TERM_ATTR_BOLD | TERM_ATTR_FAINT | TERM_ATTR_ITALIC |
+                            TERM_ATTR_STRIKE | TERM_ATTR_OVERLINE;
+    assert((tt_cell(t, 0, 0)->attrs & styles) == styles);
+    assert(term_attr_underline(tt_cell(t, 0, 0)->attrs) == TERM_UNDERLINE_SINGLE);
+    assert(term_attr_underline(tt_cell(t, 1, 0)->attrs) == TERM_UNDERLINE_DOUBLE);
+    assert(term_attr_underline(tt_cell(t, 2, 0)->attrs) == TERM_UNDERLINE_DOUBLE);
+    assert(!(tt_cell(t, 3, 0)->attrs & (TERM_ATTR_BOLD | TERM_ATTR_FAINT)));
+    assert(term_attr_underline(tt_cell(t, 3, 0)->attrs) == TERM_UNDERLINE_NONE);
+    assert(tt_cell(t, 4, 0)->attrs == 0);
+    term_free(t);
+
+    t = tt_new(20, 4);
+    write_seq(t, "\033[30mA\033[0;1;30mB\033[0;90mC");
+    assert(tt_cell(t, 0, 0)->fg == tt_cell(t, 1, 0)->fg);
+    assert(tt_cell(t, 1, 0)->fg != tt_cell(t, 2, 0)->fg);
+    assert(!(tt_cell(t, 0, 0)->attrs & TERM_ATTR_BOLD));
+    assert(tt_cell(t, 1, 0)->attrs & TERM_ATTR_BOLD);
+    term_free(t);
+
+    const char *colon_rgb = "\033[48;2;145;2;34m\033[38;2;12;34;56mA"
+                            "\033[38:2::12:34:56mB\033[;mC";
+    for (size_t split = 0; split <= strlen(colon_rgb); split++) {
+        t = tt_new(20, 4);
+        tt_write(t, colon_rgb, split);
+        tt_write(t, colon_rgb + split, strlen(colon_rgb) - split);
+        assert(row_is(t, 0, "ABC"));
+        for (int x = 0; x < 2; x++) {
+            assert(tt_cell(t, x, 0)->fg == 0xFF0C2238);
+            assert(tt_cell(t, x, 0)->bg == 0xFF910222);
+        }
+        assert(tt_cell(t, 2, 0)->fg == TERM_COLOR_FG);
+        assert(tt_cell(t, 2, 0)->bg == TERM_COLOR_BG);
+        term_free(t);
+    }
+
+    t = tt_new(20, 4);
+    write_seq(t, "\033[38;2;246;226;183;49mX");
+    assert(tt_cell(t, 0, 0)->fg == 0xFFF6E2B7);
+    assert(tt_cell(t, 0, 0)->bg == TERM_COLOR_BG);
+    term_free(t);
+
+    t = tt_new(20, 4);
+    const char *clusters = "(\xc2\xa9\xef\xb8\x8f)\xe2\x98\xba\xef\xb8\x8e"
+                           "\xf0\x9f\x91\xa8\xe2\x80\x8d\xf0\x9f\x8c\xbe";
+    write_seq(t, clusters);
+
+    assert(tt_cursor_x(t) == 7);
+    assert((tt_cell(t, 1, 0)->attrs & TERM_ATTR_EMOJI) && tt_cell(t, 1, 0)->width == 2);
+    assert(tt_cell(t, 2, 0)->width == 0);
+    assert((tt_cell(t, 4, 0)->attrs & TERM_ATTR_TEXT) && tt_cell(t, 4, 0)->width == 1);
+    assert((tt_cell(t, 5, 0)->attrs & TERM_ATTR_EMOJI) && tt_cell(t, 5, 0)->width == 2);
+    assert(tt_cell(t, 6, 0)->width == 0);
+
+    tt_select(t, 0, 0, 6, 0);
+    text = tt_selection_text(t);
+    assert(text && !strcmp(text, clusters));
+    free(text);
+    term_free(t);
+
+    /* BS with a pending wrap clears the wrap and moves left from the last
+     * column, as in xterm and the VT100. */
+    t = tt_new(5, 2);
+    write_seq(t, "12345");
+    assert(row_is(t, 0, "12345"));
+    assert(tt_cursor_x(t) == 4 && tt_cursor_y(t) == 0);
+    write_seq(t, "\b");
+    assert(tt_cursor_x(t) == 3 && tt_cursor_y(t) == 0);
+    write_seq(t, "X");
+    assert(row_is(t, 0, "123X5"));
+    assert(tt_cursor_x(t) == 4 && tt_cursor_y(t) == 0);
+    write_seq(t, "\b \b");
+    assert(row_is(t, 0, "123 5"));
+    assert(tt_cursor_x(t) == 3 && tt_cursor_y(t) == 0);
+    term_free(t);
+
+    /* A renderer sees each cursor move within the row. */
+    t = tt_new(10, 2);
+    struct term_snapshot *snap = term_snapshot_new();
+    write_seq(t, "abc");
+    uint64_t version = view_version(snap, t);
+    write_seq(t, "\b");
+    assert(tt_cursor_x(t) == 2 && view_version(snap, t) != version);
+    version = view_version(snap, t);
+    write_seq(t, "\r");
+    assert(tt_cursor_x(t) == 0 && view_version(snap, t) != version);
+    version = view_version(snap, t);
+    write_seq(t, "\t");
+    assert(tt_cursor_x(t) == 8 && view_version(snap, t) != version);
+    term_snapshot_free(snap);
+    term_free(t);
+
+    t = tt_new(20, 2);
+    tt_write(t, "hello world", 11);
+    assert(row_is(t, 0, "hello world"));
+    assert(tt_cursor_x(t) == 11 && tt_cursor_y(t) == 0);
+    term_free(t);
+
+    title[0] = 0;
+    t = tt_new_opts(10, 4, &title_cb);
+    write_seq(t, "\033]0;My Shell\007");
+    assert(!strcmp(title, "My Shell"));
+    write_seq(t, "\033]2;Second Title\033\\");
+    assert(!strcmp(title, "Second Title"));
+    write_seq(t, "\033]1;Icon Name\007");
+    assert(!strcmp(title, "Icon Name"));
+    term_free(t);
+
+    t = tt_new(20, 4);
+    write_seq(t, "$ /mnt/work");
+    const char *round_trip = "\033[?1049h\033[?1049l";
+    tt_write(t, round_trip, strlen(round_trip));
+    assert(row_is(t, 0, "$ /mnt/work"));
+    term_free(t);
+
+    /* A renderer sees both switches between the screens. */
+    t = tt_new(20, 4);
+    snap = term_snapshot_new();
+    write_seq(t, "$ /mnt/work");
+    version = view_version(snap, t);
+    write_seq(t, "\033[?1049h");
+    assert(view_version(snap, t) != version);
+    version = view_version(snap, t);
+    write_seq(t, "\033[?1049l");
+    assert(view_version(snap, t) != version);
+    assert(row_is(t, 0, "$ /mnt/work"));
+    term_snapshot_free(snap);
+    term_free(t);
+
+    t = tt_new(20, 4);
+    write_seq(t, "output");
+    write_seq(t, "\r\033[K../");
+    assert(row_is(t, 0, "../"));
+    term_free(t);
+
+    t = tt_new(80, 24);
+    assert(!term_modes(t).alternate);
+    write_seq(t, "\033[?1049h");
+    assert(term_modes(t).alternate);
+    write_seq(t, "\033[?1049l");
+    assert(!term_modes(t).alternate);
+    term_free(t);
+
+    const char *color_runs[] = {
+        "\033[1;1H\033[48;2;10;20;30m\033[38;2;200;210;220ma"
+        "\033[48;2;100;110;120m\033[38;2;230;240;250mb",
+        "\033[1;1H\033[38;2;200;210;220m\033[48;2;10;20;30ma"
+        "\033[38;2;230;240;250m\033[48;2;100;110;120mb",
+    };
+    for (size_t run = 0; run < sizeof(color_runs) / sizeof(color_runs[0]); run++) {
+        const char *seq = color_runs[run];
+        size_t len = strlen(seq);
+        for (size_t split = 0; split <= len; split++) {
+            t = tt_new(100, 2);
+            tt_write(t, seq, split);
+            tt_write(t, seq + split, len - split);
+            assert(row_is(t, 0, "ab"));
+            assert(tt_cursor_x(t) == 2 && tt_cursor_y(t) == 0);
+            assert(tt_cell(t, 0, 0)->fg == 0xffc8d2dc);
+            assert(tt_cell(t, 0, 0)->bg == 0xff0a141e);
+            assert(tt_cell(t, 1, 0)->fg == 0xffe6f0fa);
+            assert(tt_cell(t, 1, 0)->bg == 0xff646e78);
+            for (int col = 2; col < 100; col++)
+                assert(tt_cell(t, col, 0)->bg == TERM_COLOR_BG);
+            assert(row_is(t, 1, ""));
+            term_free(t);
+        }
+    }
+
+    puts("PASS: terminal regression tests");
+    return 0;
+}