heph.nvim: RPC client + buffer editing + wiki-links + journal (slice 11a)

The primary surface begins (tech-spec §8): a Neovim plugin that is a thin
client of the local hephd over its unix-socket JSON-RPC.

- node.resolve {title} → Node|null (heph-core Store + dispatch): exact,
  owner-scoped, non-tombstoned alias-then-title match — the same mapping that
  materializes wiki links, so follow-link jumps to the node the stored link
  points at (never fuzzy search). Unit + rpc_socket integration tests.
- heph.nvim/: vim.uv unix-socket JSON-RPC client (blocking call via vim.wait,
  id-demuxed, partial-line buffered, luanil so JSON null → Lua nil; isolated
  Sessions for tests). Buffer-backed nodes (heph://node/<id>, acwrite;
  BufReadCmd→node.get / BufWriteCmd→node.update, whole-buffer body round-trips
  exactly through the CRDT). [[wiki-link]] follow on <CR>. Daily journal.
  :Heph command surface + completion.
- Headless e2e (§9): a self-contained busted-style runner (tests/e2e/runner.lua)
  — no external plugins, no network, deterministic CI exit codes. Specs: journal
  round-trip, follow-link (+ unresolved no-op), link-two-docs/backlink.
  `make -C heph.nvim test` builds hephd and runs it.

Docs: heph-nvim reference card, §14 tracker (11a done; 11b/11c/11d queued),
changelog fragment.

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

heph.nvim/lua/heph/command.lua

@@ -0,0 +1,62 @@
+--- The `:Heph <subcommand>` user-command surface. Tactical/Organizational task
+--- views (next/list/capture/...) arrive with slice 11b; this is the knowledge-
+--- base core (journal, links).
+
+local M = {}
+
+--- subcommand -> handler(args: string[])
+M.subs = {
+  today = function()
+    require("heph.journal").open()
+  end,
+  journal = function(args)
+    require("heph.journal").open(args[1])
+  end,
+  follow = function()
+    require("heph.link").follow()
+  end,
+  open = function(args)
+    if args[1] then
+      require("heph.node").open(args[1])
+    end
+  end,
+}
+
+--- `:Heph` entry point.
+function M.run(opts)
+  local args = opts.fargs
+  local sub = args[1]
+  if not sub then
+    require("heph.util").notify("usage: :Heph <" .. table.concat(M.names(), "|") .. ">", vim.log.levels.WARN)
+    return
+  end
+  local handler = M.subs[sub]
+  if not handler then
+    require("heph.util").notify("unknown subcommand: " .. sub, vim.log.levels.ERROR)
+    return
+  end
+  local ok, err = pcall(handler, vim.list_slice(args, 2))
+  if not ok then
+    require("heph.util").notify(tostring(err), vim.log.levels.ERROR)
+  end
+end
+
+--- Sorted subcommand names.
+function M.names()
+  local names = vim.tbl_keys(M.subs)
+  table.sort(names)
+  return names
+end
+
+--- Completion: subcommand names at the first position.
+function M.complete(arglead, cmdline, _cursorpos)
+  -- Only complete the subcommand token (first arg after :Heph).
+  if cmdline:match("^%s*Heph%s+%S*$") then
+    return vim.tbl_filter(function(n)
+      return n:find(arglead, 1, true) == 1
+    end, M.names())
+  end
+  return {}
+end
+
+return M