test(lsp): name acc32 for what it pins; label the unpinned guard

Two corrections found by bite-testing the suite rather than by reading
it.

**Acceptance 32 was mis-named.** It claimed to pin "the one-shot is
removed BEFORE invocation". Biting that — moving the removal after the
`pcall` — still passes, because `pcall` catches the raise either way and
the removal runs regardless. The before/after ordering is unobservable
unless a handler re-enters the drain, and nothing does. What the test
actually pins is that removal is **unconditional**: the bite that gates
it on `if ok then` fails 2 != 1, because the surviving registration is
invoked a second time by the purge. Renamed and re-commented to say so.
The implementation still removes before invoking, which is the right
defensive order; it is simply not what the assertion proves.

**The purge's generation check is defensive and untested**, now labelled
in place instead of reading as covered. Reaching it needs a crash and
its restart to both land in a gap with no `_async.tick`; the backoff is
500ms, so any tick in that window sees `crashed` and the
absent-or-terminal test fires first. Every attempt to stage it
deterministically exercised the `crashed` path instead. It stays as
insurance for a stalled editor, and says that about itself.

Bites recorded, all against the committed tree:
- removal gated on a clean return -> acc32 fails (2 != 1).
- purge driven by a `crashed`/`stopped` event seen in the drain, the
  design the framing originally implied -> the no-attachment case fails
  ("never called"), while the attached case still passes. That is the
  discrimination acceptance 34's second half exists for.
- a resolver without `pmacs.fs.canonicalize` -> two servers, pinned as
  34b's own falsification.

builtin/runtime/lsp.lua

@@ -1683,6 +1683,18 @@ local function purge_dead_pending()
     for rid, entry in pairs(pend) do
       -- Absent or terminal, or the same sid running a NEW generation:
       -- in every case the request this entry awaits is unanswerable.
+      --
+      -- The generation half is **defensive and not covered by the
+      -- acceptance suite**, stated plainly rather than left to look
+      -- tested. Reaching it requires a crash and its restart to both
+      -- fall inside a gap with no `_async.tick` — the crash backoff is
+      -- 500ms (`src/lsp.rs:1007`), so any tick during that window sees
+      -- `crashed` and the absent-or-terminal test above fires first. A
+      -- stalled or idle editor can produce such a gap, and then this is
+      -- the only thing standing between a one-shot and waiting forever
+      -- on a reply the dead generation owed. Every attempt to stage it
+      -- deterministically ended up exercising the `crashed` path
+      -- instead, so it is kept as insurance and labelled as such.
       if attempt == nil or attempt ~= entry.attempt then
         dead[#dead + 1] = rid
       end

tests/lsp_dispatch_seams_acceptance.rs

@@ -336,16 +336,22 @@ fn acc33_raising_response_handler_does_not_stop_the_drain() {
 }
 
 // ---------------------------------------------------------------------------
-// Acceptance 32 — the one-shot is removed BEFORE invocation.
+// Acceptance 32 — the one-shot is removed exactly once, whether or not
+// the handler raises.
 //
-// Observed rather than asserted structurally: the handler raises, and
-// the server is then stopped. If removal happened only on a clean
-// return — or not at all — the purge below would invoke the same handler
-// a second time with an error. The count is what pins it.
+// Named for what it pins rather than for the framing's wording. Q#LN9
+// specifies removal *before* invocation, and the implementation does
+// that — but bite-testing showed the before/after ordering is not
+// observable on its own: `pcall` catches the raise either way, so
+// removal after the call is behaviorally identical unless a handler
+// re-enters the drain, which nothing does. What IS observable, and what
+// this pins, is that removal is **unconditional**: the bite that moves
+// it inside `if ok then` fails here 2 != 1, because the surviving
+// registration gets invoked a second time by the purge.
 // ---------------------------------------------------------------------------
 
 #[test]
-fn acc32_response_one_shot_is_removed_before_invocation() {
+fn acc32_response_one_shot_is_removed_even_when_the_handler_raises() {
     let fx = Fixture::new();
     let mut state = editor();
     attached_rust(&mut state, &fx);
@@ -375,8 +381,8 @@ fn acc32_response_one_shot_is_removed_before_invocation() {
     assert_eq!(
         eval::<i64>(&state, "return _G.calls"),
         1,
-        "a delivered one-shot must not be re-invoked by the purge — it \
-         was removed before the raising handler ran, not after"
+        "a delivered one-shot must not be re-invoked by the purge — \
+         removal is unconditional, not gated on a clean return"
     );
 }