Add text states and cursors to Pure modules

Module format v3 adds text states, cursors, UTF-8 constants, text inputs
and text views. A text state is a runtime-owned draft without a store, so a
large text edits as an extent tree. Cursors are byte positions the runtime
keeps on character boundaries: insertion pushes cursors at or after the
point, removal gathers cursors inside the range, and a failed event returns
every text draft and cursor to where it was. The verifier types a cursor by
the text it belongs to and rejects editing one text with another's cursor.

Operations cover constants, concatenation, shortest round-trip number text,
character, line and byte counts, character and column-keeping line moves,
insert, remove, line views, whole-text replacement and UTF-8 checked
conversion from bytes. Replies of edited documents or texts are copied before
they are finished. pure-run gains text input and text output.

test-module covers typing Korean and emoji, moves that stop at the ends,
line moves, views, rollback, invalid UTF-8 and replacement, text-specific
verifier rules, and 20,000 damaged text modules whose cursors always stay
on character boundaries under ASan/UBSan.

1 files changed, 34 insertions, 0 deletions

diff --git a/prototypes/connections/module-text.h b/prototypes/connections/module-text.h
new file mode 100644
index 0000000..4843928
--- /dev/null
+++ b/prototypes/connections/module-text.h
@@ -0,0 +1,34 @@
+#ifndef PURE_MODULE_TEXT_H
+#define PURE_MODULE_TEXT_H
+#include "flow.h"
+#include "state.h"
+#include <stdbool.h>
+#include <stddef.h>
+
+/* Text helpers of the module executor. Text is valid UTF-8; a character is a
+ * Unicode scalar value, so every position these return is a scalar boundary. */
+
+/* Strict UTF-8: no overlongs, surrogates or values past U+10FFFF. state
+ * carries a sequence split across spans; start it at 0 and finish with
+ * pure_utf8_complete. */
+bool pure_utf8_step(unsigned *state, PureSpan span);
+bool pure_utf8_complete(unsigned state);
+bool pure_utf8_valid(PureSpan span);
+
+/* Scalars (bytes that are not 10xxxxxx) and newlines in a span. */
+size_t pure_utf8_scalars(PureSpan span);
+size_t pure_utf8_newlines(PureSpan span);
+
+/* Shortest decimal that reads back to the same finite double: integers
+ * below 1e15 without a point or exponent, otherwise %g form with a trimmed
+ * exponent. -0 prints as 0. Returns the length written (at most 32). */
+size_t pure_format_number(double value, char out[32]);
+
+/* Positions in one version of a text draft (size is version.bytes). */
+size_t pure_text_step(const PureDraft *, PureVersion, size_t position, double count);
+size_t pure_text_line_step(const PureDraft *, PureVersion, size_t position, double count);
+size_t pure_text_line_start(const PureDraft *, PureVersion, size_t position);
+size_t pure_text_line_end(const PureDraft *, PureVersion, size_t position);
+/* Scalars (unit 0) or line number counting from 1 (unit 1) before position. */
+size_t pure_text_count(const PureDraft *, PureVersion, size_t position, unsigned unit);
+#endif