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Review fixes to steps 1 and 2, found by an adversarial pass over the committed
chain. One is a real bug and the rest are comments that were false.
THE BUG. `waitInput` put the FUSE descriptor in the poll set whenever the mount
existed, and the `.fuse` arm ignored every revent. Linux's `fuse_dev_poll`
answers EPOLLERR once the connection is gone, and POSIX reports POLLERR whatever
the events mask asked for -- so an external `fusermount3 -u`, a sysfs abort, or
systemd taking /run/user/$UID away at final logout (exactly when a detached
session is supposed to keep running) made poll(2) return instantly, forever. The
daemon then spun the whole pump at 100% of a core for the rest of its life, and
re-offered every parked slot to the core at that rate.
Measured on the unfixed commit: 0 CPU ticks over 10 s idle, then 1000 ticks over
the next 10 s after unmounting its own mount point. Measured after the fix: 0
ticks over 8 s in the same scenario, process alive and in state S.
fuse.zig's own poll thread has carried the equivalent guard all along, which is
why the desktop shells never showed this and the daemon did.
THE COMMENTS, each checkable and each wrong:
* `Source.fuse` said the drain is not done in `dispatch` to avoid re-entering
the core. Both `pull_wait_input` and `push_poll_frame` are called from
inside `pump`, so either re-enters. The real reason is that `dispatch` is
mid-iteration over a SNAPSHOT of the descriptors, and one `push_spawn`
replaces a pane's master under it.
* `fuse.zig`'s new import said "no cycle". There is a cycle: fs_service
imports fuse.zig back and still names `*Fs` in three signatures.
* `Transport`'s rationale said tty.zig and gui.zig store one in a struct
field. Neither does; all four call sites build it inline.
* `deinit` justified its ordering against "as long as the harvest takes".
`harvest` is waitpid(WNOHANG) and blocks for nothing. The real reason to go
first is that aborting the connection wakes a parked reader while its own
shell is still alive to run its exit path.
* `harvest` claimed pane shells are the only children this process forks.
Since step 1 it also forks `fusermount3`, three times over -- reaped by its
own spawner, so the conclusion holds and the premise did not.
* docs/detached.md, docs/lsp.md and docs/design.typ still said the daemon
implements sixteen of twenty-one methods and mounts no /dev/fuse.
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Esc stops recentring
## A terminal row's ANSI colours survive being edited
The loudest colour bug this editor had: one keystroke anywhere in a coloured shell row turned EVERY
column of it grey. `EditAnchors` anchored a buffer line only when it was BYTE-IDENTICAL to the shell
row it stood over, so a single differing byte dropped the whole row's colour projection. Worst shape
is invisible: append past the pane's right edge, where the text is clipped, and the row looks the
same and only its colour goes.
Anchoring is byte-level now. An edit leaves the row's own bytes at both ends, and being the same
bytes they keep the same colours; only what was typed has no cell under it, so only that takes none.
Live, on real `fastfetch`: a 32-column blue run split into 6 + 26 around one typed character.
Three defects underneath it, all found by machinery rather than by reading:
* A JOIN removes a buffer line while the buffer's covered span grows, so `lines == covered` and both
aligned guesses — Nth line over the Nth covered row, and the same counted from the bottom —
resolved to the SAME wrong row. Every untouched row below a join went plain. Anchoring is now a
streaming monotone matching: one shell-row cursor that only ever moves forward, advanced once per
buffer line, linear in the buffer where the version before it was quadratic.
* An EMPTY line is not evidence. Splitting a row makes one, it equals every blank row in the span,
and left free to look ahead it claimed the blank row below the last output and took every coloured
row in between out of reach of the lines that owned them.
* Reflow under a scrolled viewport. `PageList.getTopLeft(.viewport)` returns the viewport pin
verbatim, x and all, while `PageList.pin` forces x to 0 — so after a reflow remapped a tracked pin
into the middle of a row, the text pass dumped row 0 from that column while the colour pass paired
the fragment with the row's FIRST cells. Row 0 wore its left half's colours until the pane snapped
back to live output. `bodyText` dumps from column zero now, which is also what ghostty's own
renderer draws.
Also here: DECSCNM (reverse video) was silently dropped whenever `tty_filter` was off, because the
raw path resolved a `.none` colour by role and never consulted the mode.
The test that found the first two is the one worth keeping: random editing against an ABSOLUTE
oracle — every row's own text names the colour it must have — because the differential oracle it
replaced was blind by construction. It skipped the edited row, which is the row the user is
complaining about.
## Esc returns to a pane without moving its view
Esc in body normal mode runs `Last`, "the pane you were in before this one", and that went through
`focusPaneLine`, which recentred a file on the target line unconditionally. So returning to a buffer
repainted the whole screen to show a line that was already on it.
`focusPaneLine` takes a landing now: `.center` for the three callers going somewhere you have not
been (a look target, a path a pane already holds, `@pN:LINE:COL`), `.keep` for Esc. `.keep` leaves
the view alone and lets `ensureCursorVisible` — which already existed and already scrolls by the
minimum into the `scroll_off` band — be the only thing that may move anything.
Not `line = 0`, which `focusPaneLine` already understands as "focus and touch nothing": a background
pane's view can move while you are away, because the wheel scrolls the pane under the POINTER and a
resize reveals no cursor, so the recorded cursor plus a minimal nudge is what actually gets you back.
Ctrl-o and Ctrl-i keep centring, and the asymmetry is structural rather than arbitrary: `Last` only
ever CROSSES panes, so the pane it lands on already holds the view you left it with, while `jumpBy`
can land in the SAME pane, where a long in-file jump would arrive on the very top or bottom row with
`scroll_off` lines of context on one side. Helix splits the same pair the same way — its jumplist
centres, its buffer switch does not.
One deliberate consequence: under `.keep` a PDF's page is not restored AT ALL, because a page reveal
IS that pane's view and a reveal of the page you are already on still snaps `document_scroll_y` to
that page's start, discarding where you had read to. When something moved the pane while you were
away — the wheel again — Esc leaves it where the wheel left it, and Ctrl-o is how you reach the
recorded page.
## host_io.zig: the machine-local half of a host, once
`host.zig` is the seam. The part of the answer that is identical on every host with an operating
system under it — fork a pane's shell, put bytes on a disk — was written FOUR times: in tty.zig,
gui.zig, macos.zig and detached/server.zig. What those copies had in common says what they were for:
all four were missing FD_CLOEXEC on the pty master, so in every shell pardes has shipped, a program
in one pane could read another pane's terminal.
One copy now, and the wire got smaller for it: `ServerMsg.spawn` is gone. A frontend never asked the
server to fork anything — the server has an operating system under it and forks through `host_io`
like every other host — and `decodeClient` lost the scratch buffer that message needed.
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