Addresses snap to runes, not grapheme clusters

sam and acme address runes; pardes snapped #n, line:col, dot and data's
reads to grapheme clusters, so a lone combining mark or a CRLF's \r could
not be addressed. #n, line:col, a search's match, dot (both ways) and data
now land on rune boundaries (modal.runeStart and friends), and the tty's
cell drawing is untouched. The README, fs.md and the skill say so.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 6 insertions, 3 deletions

diff --git a/src/ninep/addr.zig b/src/ninep/addr.zig
index e1d6da0f..e731ba24 100644
--- a/src/ninep/addr.zig
+++ b/src/ninep/addr.zig
@@ -94,7 +94,7 @@ pub const Addr = struct {
                     // pardes's `line:col`, Look's `file:12:5` spelling (look.zig
                     // parsePathLine): the point at that column of that line, the
                     // column in bytes from 1, clamped to the line's end and snapped
-                    // to a character's start as Look's cursor is. Not sam's.
+                    // to a rune's start, as every address is. Not sam's.
                     if (size == .line and dir == 0 and a.i + 1 < a.expr.len and a.expr[a.i] == ':' and
                         a.expr[a.i + 1] >= '0' and a.expr[a.i + 1] <= '9')
                     {
@@ -107,7 +107,7 @@ pub const Addr = struct {
                             a.err = e_range;
                             return null;
                         }
-                        const q = clip(modal.offsetAt(a.text, .{ .row = @intCast(n - 1), .col = @intCast(col - 1) }));
+                        const q = clip(modal.runeOffsetAt(a.text, .{ .row = @intCast(n - 1), .col = @intCast(col - 1) }));
                         r = .{ .q0 = q, .q1 = q };
                         continue;
                     }
@@ -162,7 +162,7 @@ pub const Addr = struct {
                 a.err = e_range;
                 return null;
             }
-            const g = clip(modal.graphemeStart(a.text, @intCast(off)));
+            const g = clip(modal.runeStart(a.text, @intCast(off)));
             return .{ .q0 = g, .q1 = g };
         }
         var line: i64 = n;
@@ -267,6 +267,9 @@ pub const Addr = struct {
             }) orelse break :found null;
             break :found Range{ .q0 = clip(m.start), .q1 = clip(m.end) };
         };
+        // A byte pattern may match inside a rune: the match covers the
+        // runes it touches.
+        if (found) |f| return .{ .q0 = clip(modal.runeStart(a.text, f.q0)), .q1 = clip(modal.runeEnd(a.text, f.q1)) };
         return found orelse {
             a.err = e_no_match;
             return null;