Round 1 review, four P1s. All real; the first two mean the fallback did
not work at all.
**1. The latch swapped the config but never spawned or re-attached.**
Nothing re-fires an attach on a config change and `attach_buffer`
early-returns for a live attachment, so the buffer stayed bound to the
server that had just been stopped. The user got a config edit and no
language server. `fire_latch` now rebuilds through a new
`pmacs.lsp._attach_buffer` export.
Two mechanics had to be right for that rebuild to happen at all:
* It is **retried on the tick**, because `pmacs.lsp.stop` leaves the
state `shutting-down`, which `server_is_live` counts as LIVE — an
inline re-attach early-returns the stale record and the swap is a
silent no-op.
* The latch **does not stop an already-terminal server**, and this is
a substrate bug worked around rather than a style choice.
`LspManager::stop` on a `Crashed` client takes its not-initialized
branch, terminates the dead process, and sets `ShuttingDown { ..
None }` on the premise that "the next exit observation cleans up" —
but the exit already happened, which is what made it `Crashed`. No
further event arrives, so the client is stuck in `ShuttingDown`
forever: `server_is_live` reads it as live so `attach_buffer` never
rebuilds, and `forget` refuses it for not being terminal. Stopping a
dead server is what makes it un-replaceable. Named in framing §6; the
fix belongs in `stop` and changes behavior for every language.
**2. A missing `lake` bypassed probe and latch entirely** — the single
most likely real failure. `ensure_server` swallows a synchronous ENOENT
and returns nil, so there was no attachment, and the hook keyed on
`active_attachment()` returned before arming anything. The hook now keys
on the buffer's LANGUAGE and treats a Lean buffer with no attachment as
the failure itself.
**3. `waitForDiagnostics` omitted `version`.** Lean's
`WaitForDiagnosticsParams` is `{ uri, version }` (v4.9.0,
`src/Lean/Data/Lsp/Extra.lean`); the request is how a client says which
revision it wants. It looked correct only because the fake server echoes
any payload — so the fake server now validates and returns InvalidParams
without it.
**4. The ledger stated the dangerous stacking order** in one sentence
and the correct rule in the next. Fixed to say BEFORE. A safety rule
written twice with opposite senses is worse than not written.
Also (P2): the probe/latch suite now drives the production path —
`buffer.after-load` -> ticks -> probe drain -> latch -> re-attach — with
real executable stubs, and asserts the originally opened buffer ends up
on a LIVE server. Round 1's acceptance 36 asserted every server was
terminal, i.e. pinned the ABSENCE of the fallback it claimed to test.
`M.fallback` is a table so the suite can point it at a working stand-in;
the probe now spawns `cfg.command --version` rather than a hardcoded
`lake`, which is also more correct for a user who configured a wrapper.
`swap_to_fallback`'s `command ~= "lake"` guard is gone: the latch fires
only when the configured server actually failed, one visible fallback
beats no server, and `probe.latched` is what keeps it to exactly one.
Three new bites, all against the committed tree: no re-attach after the
swap -> three latch tests fail; hook keyed on the attachment -> the
missing-`lake` case fails; `waitForDiagnostics` without `version` ->
acc37 fails with the server's InvalidParams.
Levi Neuwirth
cdaea66203