GUI goldens settle on the window's idle, not two captures that agree

test/gui_golden.py hashed a scene once two captures 400 ms apart agreed;
on a loaded machine a slow frame agreed with itself before the scene's
change landed and every later hash moved up a scene. A test window now
writes a status file into its capture directory each loop step (gui.zig
writeTestStatus: step, frames captured, idle — nothing owes a frame,
nothing moves, nothing waits on the core's clock), and the harness waits
for an idle step two past the one current when it asks: a 9P write has
been served by then, so the frame is the scene's. Two things kept a
window from ever going idle, both fixed:

- Look-hover re-armed forever: resting on a word with nothing to open, the
  hover wait ran its two frames, found nothing, cancelled, and the next
  present's pointer refresh started it again: a frame every other frame
  for as long as the pointer rested there, live too (CPU). The place last
  refused is remembered (Pardes.look_hover_refused) until the pointer
  moves off it.
- The virtual clock moved only on a wait that timed out, so a steady
  trickle of events held it still; it now moves to the core's wake too
  when an event cut the wait short and nothing owes a frame.

Captures go to a directory of their own, outside the session's (a file
written there every frame is a change in the directory its panes look
at). All 17 goldens match the file as recorded at oooopqyv; eight runs,
five alongside a ReleaseFast build and three with all 16 cores saturated
(load 13-19), were byte-identical, 14 s a run unloaded (was ~30).

Tests: the resting pointer lets the core go idle.

1 files changed, 31 insertions, 2 deletions

diff --git a/src/look.zig b/src/look.zig
index 4ee5a638..39f7420e 100644
--- a/src/look.zig
+++ b/src/look.zig
@@ -934,6 +934,12 @@ fn noteLookHover(p: *Pardes, col: u16, row: u16, body_hit: ?Mouse.BodyHit, tag_h
     if (p.look_hover_wait) |waiting|
         if (waiting.col == col and waiting.row == row and waiting.pane == id and waiting.serial == pane.serial and mouse.sameBodyCell(waiting.body_hit, body_hit) and tag_layer.sameCell(waiting.tag_hit, tag_hit)) return;
 
+    // Found nothing to open here a moment ago: the pointer resting on it
+    // does not start another wait (and another frame) every frame.
+    if (p.look_hover_refused) |refused|
+        if (refused.col == col and refused.row == row and refused.pane == id and refused.serial == pane.serial and mouse.sameBodyCell(refused.body_hit, body_hit) and tag_layer.sameCell(refused.tag_hit, tag_hit)) return;
+    p.look_hover_refused = null;
+
     cancelLookHover(p);
     p.look_hover_wait = .{ .col = col, .row = row, .pane = id, .serial = pane.serial, .body_hit = body_hit, .tag_hit = tag_hit };
 }
@@ -958,8 +964,10 @@ pub fn advanceLookHover(p: *Pardes) void {
     if (waiting.frames < delay) return;
     const pane = p.panes[waiting.pane] orelse return cancelLookHover(p);
     if (pane.serial != waiting.serial) return cancelLookHover(p);
-    const pointed = edit.pointerTextSelection(p, waiting.pane, waiting.col, waiting.row, waiting.body_hit, waiting.tag_hit) orelse
+    const pointed = edit.pointerTextSelection(p, waiting.pane, waiting.col, waiting.row, waiting.body_hit, waiting.tag_hit) orelse {
+        p.look_hover_refused = waiting.*;
         return cancelLookHover(p);
+    };
     if (comptime pdf_enabled) if (!pointed.on_tag and panes.Pdf.paneNativeReady(p, pane)) {
         const probe = panes.Pdf.probeAt(p, pane, waiting.col, waiting.row) orelse
             return cancelLookHover(p);
@@ -976,7 +984,10 @@ pub fn advanceLookHover(p: *Pardes) void {
         return;
     };
     const operand = exec.pointerOperand(p, pane, pointed.sel);
-    if (operand.text == null or operand.text.?.len == 0) return cancelLookHover(p);
+    if (operand.text == null or operand.text.?.len == 0) {
+        p.look_hover_refused = waiting.*;
+        return cancelLookHover(p);
+    }
     var preview = operand.preview;
     if (preview) |*sel| sel.state = .done;
     p.look_hover_preview = .{
@@ -1727,3 +1738,21 @@ test "Look ignores missing and out of bounds pane addresses" {
         try std.testing.expect(pane.body.vsel.active); // a miss changes nothing, the selection included
     }
 }
+
+test "a pointer resting where a look-hover found nothing does not wake the core every frame" {
+    const p = try Pardes.init(std.testing.allocator, .{ .cols = 80, .rows = 24 });
+    defer p.deinit();
+    _ = try p.setTestFile("     \n" ** 30);
+    p.sync();
+    const r = p.rects[p.active];
+    // Resting on blanks in the body: a wait, then nothing to open.
+    p.update(.{ .mouse = .{ .button = .none, .kind = .motion, .col = r.x + 20, .row = r.y + 5 } });
+    var frames: usize = 0;
+    while (p.nextWake() != null and frames < 20) : (frames += 1) {
+        p.update(.tick);
+        // What a shell's present does after every frame.
+        p.acknowledgePanelPresentation(&.{});
+    }
+    try std.testing.expect(frames < 20);
+    try std.testing.expect(p.look_hover_wait == null and p.look_hover_preview == null);
+}