A listing says what is left of the disk, and what will fit

dir said what was there and nothing about what was left. SplitDisk has
printed the free figure since it was written, so the machine's own
listing was the poorer of the two implementations at describing the same
disk.

  43 files, 3 directories
  46 of 64 entries, 1893 blocks free

Entries first, because they are the ceiling nobody notices until they hit
it: a disk of small files runs out of directory slots long before it runs
out of blocks.

COUNTED RATHER THAN ASKED. The superblock keeps a free count and this
file calls it "a note rather than the truth" in three places. sbfsSpace
reads the whole directory table instead, which costs a read per directory
block and is the answer rather than a guess. SplitDisk goes on reading
the note and saying when it is stale, which is the right place for that
check - the host tool is what you audit a disk with.

---- And it is a fact about the disk, not about where you are ----

The first version added the blocks up as the LISTING walked past them,
which cost no extra read and was wrong: that walk stops only on entries
in the working directory, so the same disk came out as 1,996 blocks free
from the root and 2,025 from /Apps. Comparing against SplitDisk is what
said so, which is what having two implementations is for.

---- The longest run, which is what decides whether a file fits ----

  4 of 16 entries, 37 blocks free
  the longest run is 25

Files are laid down contiguously, so the free total does not say whether
a file will fit. Both implementations learn it, from one specification.

Said only when it differs from the free total. Deleting is what fragments
a contiguous store, and a disk that has only been appended to has one gap
at the end - so on a healthy disk this is silent, and a line that appears
only when something is wrong is a line somebody reads.

There is no sort on this machine and the entries are in no order, so a
candidate walks the disk: each pass finds the used extent nearest at or
after it, and anything the candidate stands inside pushes it to the far
end and starts the pass again. The same trick allocating uses. So it
costs a pass per gap rather than per file - nearly nothing on a disk with
one gap, more the more fragmented the disk is, which is the right way
round.

holes.img is six files with the second and fourth deleted, because no
other disk here can show any of this: none of them has ever had anything
deleted from it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW

Tests/manifest

@@ -1033,6 +1033,24 @@ cosmosWhere          | CosmOS/Source/cosmos.asm           | run      | cosmosWhe
 # a name twice. Then the same walk in /Apps, because a walk that only ever ran at the root
 # would not have proved it walks where you are.
 cosmosWalk           | CosmOS/Source/cosmos.asm           | run      | cosmosWalk.in      | 200000000 | disks/cosmos.img
+# ---- What a listing says about the disk it is listing ----
+#
+# dir said what was there and nothing about what was left. SplitDisk has printed the free
+# figure since it was written, so the machine's own listing was the poorer of the two
+# implementations at describing the same disk.
+#
+# COUNTED RATHER THAN ASKED. The superblock keeps a free count and sbfs.asm calls it "a note
+# rather than the truth" in three places; this reads the whole directory table instead. The
+# first version added the blocks up as the LISTING walked past them, which cost nothing extra
+# and was wrong - that walk stops only on entries in the working directory, so the same disk
+# came out as 1,996 blocks free from the root and 2,025 from /Apps. Listing both directories
+# here is what would say so again.
+#
+# And then a disk with holes in it, which is the case the longest run exists for: thirty seven
+# blocks free in three pieces, so the largest file that will fit is twenty five. Said only
+# when it differs from the free total, so the first listing is silent about it and the second
+# is not - a line that appears only when something is wrong is a line somebody reads.
+cosmosSpace          | CosmOS/Source/cosmos.asm           | run      | cosmosSpace.in     | 200000000 | disks/cosmos.img+disks/holes.img
 # ---- Starting itself ----
 #
 # /System/Boot/startup.sh runs before anybody can type. This one is also the check on #quiet