LSP seam: async execution model, helix keymap, evaluation harness

The base every language backend plugs into. Three parts:

ASYNC. The core had no request/response shape - every effect was
fire-and-forget or instantaneous. A language query is the first thing
that answers later, so: Effect .lsp -> shell worker -> Event .lsp_resp.
tty.zig uses io.concurrent + the vaxis queue, gui.zig a detached thread
+ the mutex queue it already had for ptys; web no-ops it. The worker
never touches the core (path/source/arg are snapshotted into an LspJob),
one query in flight identified by a monotonic id so a second press makes
the first answer stale, and no rows is a legal answer.

KEYMAP. Helix's, verified against its default.rs rather than recalled.
gd/gD/gy/gi/gr and ]d/[d had no conflicts. The SPC letters did, so
pardes's own builtins moved instead of helix's: Kill k->q, Del d->wc
(closing a pane is a window op, and c is helix's own close), Dump/Restore
s?->f?, Tutor ht->T. A three-exception muscle-memory map is not a map.

RESULTS ARE +SEARCH ROWS. path:LINE:COL text, absolute. That is what
look.zig resolves and n/N step, so one row from a goto jumps and several
open a buffer - helix's multi-result picker needed no picker code.

Backends supply exactly one function (lsp.query) plus a supports set and
a name; the base has none on purpose. zig build lspbench scores them on
the same corpus: feature matrix (trusting results, not the supports
flag - a claimed-but-empty kind is reported as a false claim), cold and
warm latency, peak RSS.

Two snapshot scripts moved. leader.snap encoded the old key paths.
chordcut.snap's last two steps clicked column 5, which lands on a FILE
pane, so 'key c-b' toggled nothing and the typed text was being read as
normal-mode keys - the golden recorded no TTY pane and no cat -v output
anywhere. Pointing them at an actual shell makes both steps assert what
their comments claim, and the tty paste chord is now covered for the
first time.

1 files changed, 10 insertions, 10 deletions

diff --git a/test/snapshots/chordcut.snap b/test/snapshots/chordcut.snap
index a412b57e..a1b65a4d 100644
--- a/test/snapshots/chordcut.snap
+++ b/test/snapshots/chordcut.snap
@@ -118,18 +118,18 @@ snapstyle clickdismiss
 # tty paste chord: a mouse-listening app gets the click forwarded (SGR,
 # body-relative) then the register between bracketed-paste markers —
 # cat -v prints the received bytes visibly
-press left 5 11
-release left 5 11
+press left 35 11
+release left 35 11
 stable 400 5000
 key c-b
 stable 600 8000
 text stty -icanon -echo; printf '\x1b[?2004h\x1b[?1000h\x1b[?1006h'; cat -v
 key enter
 stable 700 8000
-press left 10 12
-press right 10 12
-release right 10 12
-release left 10 12
+press left 40 12
+press right 40 12
+release right 40 12
+release left 40 12
 stable 700 8000
 snap ttyprobe
 # a plain prompt (mouse modes off) gets no click bytes — just the paste;
@@ -139,9 +139,9 @@ stable 600 8000
 text stty sane; printf '\x1b[?1000l\x1b[?1006l'
 key enter
 stable 600 8000
-press left 10 12
-press right 10 12
-release right 10 12
-release left 10 12
+press left 40 12
+press right 40 12
+release right 40 12
+release left 40 12
 stable 700 8000
 snap ttyprompt