Merge terminal scheduler fixture correction

Co-authored-by: npub1jh9wn95s0472h86ahapupaf7m6kx4v9sx2n0atj2hltcfer8k06s5n3pyf <95cae996907d7cab9f5dbf43c0f53edeac6ab0b032a6feae4abfd784e467b3f5@buzz.block.builderlab.xyz>

Signed-off-by: npub1jh9wn95s0472h86ahapupaf7m6kx4v9sx2n0atj2hltcfer8k06s5n3pyf <95cae996907d7cab9f5dbf43c0f53edeac6ab0b032a6feae4abfd784e467b3f5@buzz.block.builderlab.xyz>

* commit 'd67b99a3dd611f0c239d9bce13552417acaba622':
  refactor(terminal): delete the slice-sizing function nothing calls

Signed-off-by: npub1jh9wn95s0472h86ahapupaf7m6kx4v9sx2n0atj2hltcfer8k06s5n3pyf <95cae996907d7cab9f5dbf43c0f53edeac6ab0b032a6feae4abfd784e467b3f5@buzz.block.builderlab.xyz>

desktop/src-tauri/crates/buzz-terminal/src/fences.rs

@@ -34,53 +34,29 @@ pub const OSC_BUDGET: usize = 256 << 10;
 /// spent to the last unit.
 pub const WORK_BUDGET: u64 = 250_000;
 
-/// Bounds on how many bytes are handed to the parser at once.
+/// Widest slice handed to the parser at once.
 ///
-/// The budget is checked *between* slices, so the slice is what actually
-/// bounds one lock hold, and a fixed byte count cannot do it: `ESC#8` is
-/// three bytes and costs a full grid, so 256 bytes of it is 1.6 ms at 200x50
-/// and 14 ms at 1600x50. [`slice_bytes`] therefore derives the size from the
-/// grid, and these two clamp it -- `MAX` at the throughput plateau (measured:
-/// plain-char parsing saturates by 64 bytes and is flat to 64 KiB), `MIN`
-/// where a slice stops being able to hold a whole escape sequence: 4 bytes
-/// covers `ESC#8` and `ESC c` intact, so the floor never splits the densest
-/// atoms across slices for no benefit. Measured throughput at the floor is
-/// ~74% of the plateau on plain text and ~77% on SGR, which is the price of
-/// bounding a grid whose worst atom exceeds the budget outright.
-pub const MIN_SLICE: usize = 4;
+/// The floor is 1 byte and lives in [`slice_bytes_remaining`] rather than
+/// here: on a grid whose worst atom exceeds the whole budget -- RIS at any
+/// real scrollback depth -- no wider slice can promise to stop after the
+/// callback that crosses. This cap is the other end, set at the throughput
+/// plateau: plain-char parsing saturates by 64 bytes and is flat to 64 KiB
+/// measured, so nothing above it buys anything and a larger value only
+/// coarsens the cut.
 pub const MAX_SLICE: usize = 256;
 
-/// Bytes to hand the parser at once on a `columns x lines` grid.
+/// Bytes to hand the parser next.
 ///
-/// Sized against the **densest atom the grid admits**, so the bound holds on
-/// the first byte of a cold feeder for any payload: two bytes of `ESC c` buy
-/// [`max_atom_work`], which is the most work per byte upstream offers, and
-/// `budget / (atom / 2)` is the widest slice that cannot exceed one budget.
+/// The **only** slice-sizing function, deliberately: an earlier version of
+/// this module also exported a `slice_bytes(columns, lines, scrollback)` that
+/// the scheduler stopped calling when slices became remaining-aware, and the
+/// fixtures went on asserting against it. The two disagreed exactly where the
+/// floor bound -- reporting 4 where the engine used 1 -- so the preconditions
+/// were describing a function no longer in the path. One function, one
+/// answer, and every test asserts on what `drain` actually calls.
 ///
-/// Deliberately *derived rather than learned*. An earlier version sized
-/// slices from the density of preceding slices, which is strictly worse where
-/// it matters: a fresh feeder has observed nothing, so its first slice is
-/// wide, and a first wide slice of RIS spends many budgets before anything
-/// looks. A bound that has to be taught is not a bound on the lesson.
-///
-/// [`MIN_SLICE`] floors it, and on any grid with real scrollback the floor is
-/// what binds -- RIS at the default 10k depth is worth more than the entire
-/// budget on its own, so no slice size can keep a drain inside the budget and
-/// the floor stops the arithmetic from asking for fractions of a byte. That
-/// residual is not hidden: it is exactly [`max_drain_work`], and it is the
-/// honest cost of an indivisible callback that upstream can be asked to make
-/// smaller only by not calling it.
-pub fn slice_bytes(columns: usize, lines: usize, scrollback: usize) -> usize {
-    let densest = (max_atom_work(columns, lines, scrollback) / 2).max(1);
-    ((WORK_BUDGET / densest) as usize).clamp(MIN_SLICE, MAX_SLICE)
-}
-
-/// Bytes to hand the parser when `spent` of the budget is already gone.
-///
-/// The scheduling rule in one place so the fixtures can assert on it rather
-/// than on a copy of the arithmetic: a slice of `N` bytes holds at most
-/// `N / atom_bytes` atoms, so `remaining / densest` bytes cannot carry a
-/// drain past the budget.
+/// The rule: a slice of `N` bytes holds at most `N / atom_bytes` atoms, so
+/// `remaining / densest` bytes cannot carry a drain past the budget.
 ///
 /// `next_escape` is how far the next `ESC` is from the front of the tail.
 /// This is the difference between a correct bound and an unusable one. Only

desktop/src-tauri/crates/buzz-terminal/tests/slicing.rs

@@ -10,8 +10,8 @@
 //! `> 0` is satisfied by a seam that executed exactly one unit.
 
 use buzz_terminal::fences::{
-    max_atom_work, max_drain_work, slice_bytes, slice_bytes_remaining, Fences, MAX_SLICE,
-    MIN_SLICE, SYNC_CAP, TAIL_CAP, WORK_BUDGET,
+    max_atom_work, max_drain_work, slice_bytes_remaining, Fences, MAX_SLICE, SYNC_CAP, TAIL_CAP,
+    WORK_BUDGET,
 };
 use buzz_terminal::{Size, Terminal};
 
@@ -339,26 +339,26 @@ fn a_resize_mid_tail_reprices_the_remainder() {
 /// serves both.
 #[test]
 fn slice_size_shrinks_as_the_worst_atom_grows() {
-    let small = slice_bytes(80, 24, 0);
-    let large = slice_bytes(1600, 50, 0);
+    let small = slice_bytes_remaining(80, 24, 0, 0, 0);
+    let large = slice_bytes_remaining(1600, 50, 0, 0, 0);
     assert!(
         small > large,
         "a bigger grid makes each byte more expensive, so slices must shrink: \
          80x24 -> {small}, 1600x50 -> {large}",
     );
     assert!(
-        slice_bytes(200, 50, 10_000) <= slice_bytes(200, 50, 0),
+        slice_bytes_remaining(200, 50, 10_000, 0, 0) <= slice_bytes_remaining(200, 50, 0, 0, 0),
         "scrollback makes RIS more expensive, so it may only shrink slices",
     );
     for (columns, lines, scrollback) in [(80, 24, 0), (200, 50, 0), (400, 100, 0), (1600, 50, 0)] {
-        assert!((MIN_SLICE..=MAX_SLICE).contains(&slice_bytes(columns, lines, scrollback)));
+        assert!((1..=MAX_SLICE).contains(&slice_bytes_remaining(columns, lines, scrollback, 0, 0)));
         // One slice holds at most N/2 of the densest atom. Either that fits a
         // budget, or the floor binds -- and then the overshoot is stated by
         // `max_drain_work` rather than being an accident.
-        let worst = (slice_bytes(columns, lines, scrollback) as u64 / 2)
-            * max_atom_work(columns, lines, scrollback);
+        let width = slice_bytes_remaining(columns, lines, scrollback, 0, 0);
+        let worst = (width as u64 / 2) * max_atom_work(columns, lines, scrollback);
         assert!(
-            worst <= WORK_BUDGET || slice_bytes(columns, lines, scrollback) == MIN_SLICE,
+            worst <= WORK_BUDGET || width == 1,
             "{columns}x{lines}: a slice buys {worst} work against a \
              {WORK_BUDGET} budget without the MIN clamp to excuse it",
         );
@@ -923,12 +923,18 @@ fn a_scrollback_change_reprices_the_densest_atom_and_the_slicing() {
     //   depth, so a conforming repair would show work identical to the
     //   control and the assertions here would invert into false failures.
     assert!(
-        slice_bytes(shallow.columns, shallow.screen_lines, shallow.scrollback) > MIN_SLICE,
+        slice_bytes_remaining(
+            shallow.columns,
+            shallow.screen_lines,
+            shallow.scrollback,
+            0,
+            0
+        ) > 1,
         "geometry cannot discriminate: the shallow arm is already floored",
     );
     assert_eq!(
-        slice_bytes(deep.columns, deep.screen_lines, deep.scrollback),
-        MIN_SLICE,
+        slice_bytes_remaining(deep.columns, deep.screen_lines, deep.scrollback, 0, 0),
+        1,
     );
 
     // How a terminal at `size` retires 200 RIS: work, and how many
@@ -1151,8 +1157,8 @@ fn extreme_dimensions_saturate_instead_of_wrapping() {
     // most expensive. Wrapping inverts the fence. So: the widest possible
     // atom must give the narrowest possible slice.
     assert_eq!(
-        slice_bytes(huge, huge, huge),
-        MIN_SLICE,
+        slice_bytes_remaining(huge, huge, huge, 0, 0),
+        1,
         "an overflowing grid must clamp to the smallest slice; a wrapped \
          `max_atom_work` would hand back a generous one",
     );
@@ -1173,10 +1179,10 @@ fn extreme_dimensions_saturate_instead_of_wrapping() {
     for (axis, at) in [
         (
             "scrollback",
-            (|n| slice_bytes(200, 50, n)) as fn(usize) -> usize,
+            (|n| slice_bytes_remaining(200, 50, n, 0, 0)) as fn(usize) -> usize,
         ),
-        ("columns", |n| slice_bytes(n.max(1), 50, 0)),
-        ("lines", |n| slice_bytes(200, n.max(1), 0)),
+        ("columns", |n| slice_bytes_remaining(n.max(1), 50, 0, 0, 0)),
+        ("lines", |n| slice_bytes_remaining(200, n.max(1), 0, 0, 0)),
     ] {
         let mut previous = usize::MAX;
         for exponent in 0..60 {
@@ -1186,7 +1192,7 @@ fn extreme_dimensions_saturate_instead_of_wrapping() {
                 "slice widened from {previous} to {width} at {axis} \
                  2^{exponent}: more expensive grid, more generous slice",
             );
-            assert!(width >= MIN_SLICE);
+            assert!(width >= 1);
             previous = width;
         }
     }