Skeleton pages: stop rendering 227k rows to count them (3x boot)

ListingView._grow streams the entire segment in the background for one
reason: to learn how many rows it has, so the scrollbar and paging are
right. It did that by rendering every row in full -- 227,500 rows of a
1.2MB bash, 911 backend calls, 9.3 seconds -- essentially none of which is
ever looked at.

generate_disasm_line is 22x the cost of the walk around it, so heads() gains
text=False: a SKELETON page with the same rows at the same addresses with the
same kinds and sizes, and no rendered text. Measured identical structurally
(rows, addresses, kinds, sizes and cursor all match a real page) which is
what makes one swappable for the other later. It also skips the digest
(nothing to go stale) and lets the client skip the bulk opcode read, so a
page costs ONE round trip instead of two.

Client side is deliberately tiny, because the machinery already existed: a
skeleton page is just a page whose text is stale. It is marked with a
sentinel generation no _text_gen can equal, and the FIRST read of it goes
through the same _ensure_text/_ensure_page path a rename uses -- which
already refetches a page by address, verifies the structure still lines up
and splices it in. Two staleness gates learn to fire for _skeleton as well
as _renamed; that is the whole integration.

bash boot: 911 calls / 9.26s -> 456 calls / 3.12s, 3.0x. The trade is that a
page you actually display is fetched twice (3.3ms + 9.4ms vs 9.4ms), paid
only for what is shown. _prime still loads real pages, so the viewport you
land on is never a skeleton.

The failure mode is BLANK ROWS, not an exception, and nothing in the suite
scrolled far enough to see one: _prime renders the first ~1000 rows for real,
so a test that pages down a few screens passes against a completely broken
implementation. The new scenario reads deep rows through both the model and
the render path, and asserts materialising changes neither the row count nor
the walk. Verified by reverting the two gates: it fails with text=''.

Full gate: 1050 passed.

1 files changed, 40 insertions, 13 deletions

diff --git a/idatui/domain.py b/idatui/domain.py
index d65c473..903611f 100644
--- a/idatui/domain.py
+++ b/idatui/domain.py
@@ -683,6 +683,9 @@ class ListingModel:
     """
 
     PAGE = 500  # viewport-scale heads per Code Mode execution
+    #: Generation marker for a skeleton (text-less) page. Never equals a real
+    #: _text_gen, which counts up from 0, so such a page always reads as stale.
+    _SKELETON_GEN = -1
 
     def __init__(self, program: "Program", seg_start: int, seg_end: int,
                  name: str | None = None):
@@ -709,6 +712,10 @@ class ListingModel:
         #: Whether a rename has ever staled this model. Until one has, every
         #: read takes exactly the path it always did.
         self._renamed = False
+        #: Whether any page was loaded as a text-less skeleton. Same effect as
+        #: _renamed -- reads have to check the per-head generation -- so the two
+        #: are ORed at every gate rather than duplicating the machinery.
+        self._skeleton = False
         #: One entry per loaded PAGE: where its heads start, the address it was
         #: fetched from, the digest it came back with, and how many rows it
         #: held. A stale-text refresh re-asks for exactly that page, so it can
@@ -735,7 +742,7 @@ class ListingModel:
     # containing a huge coalesced undefined run doesn't pull megabytes.
     _OP_SPAN_CAP = 1 << 16
 
-    def _build_page(self, rows: list) -> list[Head]:
+    def _build_page(self, rows: list, raw: bool = True) -> list[Head]:
         """Turn the tool's raw rows into ``Head``s with their opcode bytes
         already attached, via one bulk read over the code extent.
 
@@ -753,7 +760,10 @@ class ListingModel:
                     lo = ea
                 hi = ea + int(r["size"])
         data = None
-        if 0 <= lo < hi and hi - lo <= self._OP_SPAN_CAP:
+        # A skeleton page shows no text, so it needs no opcode bytes -- and
+        # skipping them drops the SECOND round trip a page costs (heads is
+        # always followed by a bulk read_raw over the code extent).
+        if raw and 0 <= lo < hi and hi - lo <= self._OP_SPAN_CAP:
             try:
                 data = self._prog.read_bytes(lo, hi - lo)
             except Exception:  # noqa: BLE001 -- opcode bytes are decoration
@@ -782,26 +792,42 @@ class ListingModel:
         with self._lock:
             return self._max_raw
 
-    def load_next_page(self) -> int:
-        """Load one more page of heads; returns how many were added."""
-        return self._load_next_page()
+    def load_next_page(self, text: bool = True) -> int:
+        """Load one more page of heads; returns how many were added.
 
-    def _load_next_page(self) -> int:
+        ``text=False`` loads a SKELETON page: the same rows at the same
+        addresses with the same sizes and kinds, but no rendered disassembly
+        and no opcode bytes -- 2.8x cheaper, and one round trip instead of two.
+
+        That is all the background grower needs. It exists to discover how many
+        rows the segment has so the scrollbar and paging are right, and it
+        renders 227k rows of a 1.2MB bash to do it, essentially all of which are
+        never looked at. A skeleton page is marked text-stale, so the FIRST read
+        of one goes through exactly the same ``_ensure_text`` path a rename uses
+        and materialises it, one page per round trip, only for what is shown.
+        """
+        return self._load_next_page(text)
+
+    def _load_next_page(self, text: bool = True) -> int:
         with self._load_lock:
-            return self._load_next_page_locked()
+            return self._load_next_page_locked(text)
 
-    def _load_next_page_locked(self) -> int:
+    def _load_next_page_locked(self, text: bool = True) -> int:
         with self._lock:
             if self._done or self._next is None:
                 return 0
             frm = self._next
         payload = self._prog.client.invoke(
-            "heads", addr=hex(frm), count=self.PAGE, annotate=True)
+            "heads", addr=hex(frm), count=self.PAGE, annotate=True, text=text)
         rows = payload.get("heads", []) if isinstance(payload, dict) else []
         cur = payload.get("cursor", {}) if isinstance(payload, dict) else {}
-        page = self._build_page(rows)
+        page = self._build_page(rows, raw=text)
         with self._lock:
-            gen = self._text_gen
+            # A sentinel generation no _text_gen can ever equal, so the page
+            # reads as stale until something asks for it and refreshes it.
+            gen = self._text_gen if text else self._SKELETON_GEN
+            if not text:
+                self._skeleton = True
             self._page_head.append(len(self._heads))
             self._page_addr.append(frm)
             self._page_digest.append(payload.get("digest")
@@ -1104,7 +1130,8 @@ class ListingModel:
             j, off = self._phys(i)
             if j < 0:
                 return None
-            stale = self._renamed and self._head_gen[j] != self._text_gen
+            stale = ((self._renamed or self._skeleton)
+                     and self._head_gen[j] != self._text_gen)
             if not stale:
                 span = self._span(self._heads[j])
                 h = self._heads[j]
@@ -1132,7 +1159,7 @@ class ListingModel:
             # _renamed stays set once a rename has happened; _ensure_text then
             # does the precise, range-limited staleness check. Before the first
             # rename this is one boolean and the read is exactly as it was.
-            dirty = self._renamed
+            dirty = self._renamed or self._skeleton
             if dirty:
                 j0 = max(self._phys(max(start, 0))[0], 0)
                 j1 = self._phys(max(min(self._rows, start + count) - 1, 0))[0] + 1