+Errors with no room anywhere logs its text rather than fail the Edit

Edit's p and = put their output in +Errors, and when its column had no
room the placement refusal failed the whole Edit. +Errors now tries every
column with room, the last first, and with none its text is logged as msg
records, a line each; the Edit succeeds.

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

4 files changed, 48 insertions, 3 deletions

diff --git a/docs/tags.md b/docs/tags.md
index 5c4492bc..cee8e335 100644
--- a/docs/tags.md
+++ b/docs/tags.md
@@ -240,6 +240,9 @@ that room, the column's tallest pane is halved instead; where no pane of the
 column can give it, the new pane is refused and closed, with `no space for a
 pane in that column: each keeps its tag and 2 rows` (a 9P write or open of
 `pane/new` fails with it, ENOSPC). A pane alone in its column always fits.
+A `+Errors` pane goes to any column with room, the last first; with none,
+what it would have shown (an Edit's `p` or `=`, a write to `errors`) is
+logged as `msg` records, a line each, and the Edit still succeeds.
 
 `Placement acme` is acme's makenewwindow (util.c:449-495). The core keeps
 acme's *active column* (activecol, dat.c:37): the column last typed in
diff --git a/src/exec.zig b/src/exec.zig
index 0a7e71f9..bb4309a4 100644
--- a/src/exec.zig
+++ b/src/exec.zig
@@ -851,9 +851,32 @@ pub fn placeNew(p: *Pardes, from: usize, origin: ?usize, id: usize, kind: NewPan
         layout.snapColWeights(p, f.col);
         if (!layout.splitTallest(p, f.col, id) or !layout.placedRoomy(p, id, &before)) {
             if (layout.findPane(p, id) == null) layout.insert(p, f.col, p.col_n[f.col], id);
-            p.unplaced.set(id);
-            p.reportError(from, "placement", error.NoPaneRoom);
-            return;
+            // +Errors goes wherever there is room, last column first; with
+            // none, its maker says the text some other way (appendErrors).
+            if (kind == .errors) {
+                layout.removePane(p, id);
+                var c = p.ncol;
+                while (c > 0) {
+                    c -= 1;
+                    if (c == f.col) continue;
+                    for (p.col_panes[c][0..p.col_n[c]]) |k| p.rects[k] = before[k];
+                    layout.snapColWeights(p, c);
+                    if (p.col_n[c] == 0) {
+                        layout.insert(p, c, 0, id);
+                        break;
+                    }
+                    if (layout.splitTallest(p, c, id) and layout.placedRoomy(p, id, &before)) break;
+                    if (layout.findPane(p, id) != null) layout.removePane(p, id);
+                } else {
+                    layout.insert(p, f.col, p.col_n[f.col], id);
+                    p.unplaced.set(id);
+                    return;
+                }
+            } else {
+                p.unplaced.set(id);
+                p.reportError(from, "placement", error.NoPaneRoom);
+                return;
+            }
         }
     };
     if (kind == .command) return;
diff --git a/src/ninep/ctl.zig b/src/ninep/ctl.zig
index 25abd9b5..378dd844 100644
--- a/src/ninep/ctl.zig
+++ b/src/ninep/ctl.zig
@@ -1447,3 +1447,16 @@ test "an exec line over the command limit fails the write and says the limit; a
     try testing.expect(th.logHas(p, "a command line is at most 1024 bytes"));
     try testing.expectEqual(Status.ok, wr(p, root_exec, "Msg " ++ "z" ** 1100 ++ "\n").reply.status);
 }
+
+test "Edit's p and = never fail for want of room for +Errors: the text is logged instead" {
+    const p = try withFile(testing.allocator, "one\ntwo\n");
+    defer p.deinit();
+    p.update(.{ .resize = .{ .cols = 80, .rows = 6 } });
+    const ctl_node = Node.of(serialOf(p), .ctl);
+    try testing.expectEqual(Status.ok, wr(p, ctl_node, "Edit ,p\n").reply.status);
+    try testing.expect(th.logHas(p, " one\n") and th.logHas(p, " two\n"));
+    p.sync();
+    var count: usize = 0;
+    for (p.panes) |slot| count += @intFromBool(slot != null);
+    try testing.expectEqual(@as(usize, 1), count); // the +Errors that had no room is gone
+}
diff --git a/src/ninep/pane.zig b/src/ninep/pane.zig
index 3307eb47..791cb797 100644
--- a/src/ninep/pane.zig
+++ b/src/ninep/pane.zig
@@ -649,6 +649,12 @@ pub fn appendErrors(p: *Pardes, id: usize, text: []const u8) ?usize {
         return null;
     };
     exec.placeNew(p, id, id, free, .errors);
+    // No column had room for it (it closes at the step's end): the text is
+    // logged instead, a msg a line, so it is not lost and nothing fails.
+    if (p.unplaced.isSet(free)) {
+        var lines = std.mem.splitScalar(u8, std.mem.trimEnd(u8, text, "\n"), '\n');
+        while (lines.next()) |line| events.noteMessage(p, pane.serial, line[0..@min(line.len, pardes.Messages.LoggedMessage.cap)]);
+    }
     return text.len;
 }