heph.nvim: plug-and-play managed daemon (autostart, self-heal, client/server guardrail)

The plugin now manages its own hephd by default (autostart = true): if nothing
is serving the socket it spawns a local daemon against the default XDG paths,
kills only what it spawned on VimLeavePre, and self-heals — rpc.call retries
once through a respawn hook when the connection drops (the prior owner releases
the DB lock on exit, so a respawn can claim it).

- daemon.ensure() connects to an already-running daemon (any mode) or spawns one
  we own; stop_spawned()/is_managed() track lifecycle.
- A server/client daemon you started is always respected (spawn only when nothing
  serves the socket). autostart = false → connect-only, warns/errors if down,
  and clears the self-heal hook so it fails loudly.
- config: autostart defaults true; new `db` option; $HEPH_SOCKET / $HEPH_DB
  fallbacks isolate a dev Neovim onto a separate daemon + DB.

e2e: managed_daemon_spec covers autostart spawn, self-heal-after-kill, and
connect-only error. 10 specs green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

heph.nvim/lua/heph/daemon.lua

@@ -6,6 +6,10 @@ local uv = vim.uv or vim.loop
 
 local M = {}
 
+-- The daemon THIS nvim spawned (nil if we connected to an existing one).
+-- `{ handle, exited = { done }, socket, db, bin }`.
+M._managed = nil
+
 --- Spawn a `local`-mode hephd against `opts.db` listening on `opts.socket`.
 --- `opts.bin` defaults to `hephd` on PATH. Returns `{ handle, pid }`.
 function M.spawn(opts)
@@ -55,4 +59,71 @@ function M.wait_ready(socket, timeout)
   return true
 end
 
+--- Ensure a daemon is reachable at `opts.socket`. If one is already serving the
+--- socket (any mode — local/server/client), connect to it and do NOT spawn. Else
+--- if `opts.autostart`, spawn a local hephd we own (and manage its lifecycle).
+--- Returns `reachable, spawned_by_us`.
+function M.ensure(opts)
+  -- Already serving? A quick probe respects a daemon someone else started.
+  if M.wait_ready(opts.socket, opts.probe_ms or 400) then
+    return true, false
+  end
+  if not opts.autostart then
+    return false, false
+  end
+  local exited = { done = false }
+  local d = M.spawn({
+    bin = opts.bin,
+    socket = opts.socket,
+    db = opts.db,
+    on_exit = function()
+      exited.done = true
+    end,
+  })
+  local ok, reason = M.wait_ready(opts.socket, opts.ready_ms or 5000)
+  if not ok then
+    pcall(function()
+      if not d.handle:is_closing() then
+        d.handle:kill("sigterm")
+      end
+    end)
+    error("heph: spawned hephd but it never became ready: " .. tostring(reason))
+  end
+  M._managed = {
+    handle = d.handle,
+    exited = exited,
+    socket = opts.socket,
+    db = opts.db,
+    bin = opts.bin,
+  }
+  return true, true
+end
+
+--- True if this nvim currently owns a live spawned daemon.
+function M.is_managed()
+  return M._managed ~= nil and not M._managed.exited.done
+end
+
+--- Stop the daemon this nvim spawned (no-op if we connected to an existing one).
+function M.stop_spawned()
+  local m = M._managed
+  if not m then
+    return
+  end
+  M._managed = nil
+  if m.handle and not m.exited.done then
+    pcall(function()
+      m.handle:kill("sigterm")
+    end)
+    vim.wait(2000, function()
+      return m.exited.done
+    end, 20)
+  end
+  pcall(function()
+    if m.handle and not m.handle:is_closing() then
+      m.handle:close()
+    end
+  end)
+end
+
 return M