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/link.lua

@@ -0,0 +1,62 @@
+--- `[[wiki-link]]` parsing and following (tech-spec §8).
+---
+--- The cursor grammar mirrors `heph-core`'s `extract.rs`: a span `[[target]]`
+--- or `[[target|display]]`, where the resolvable name is everything left of the
+--- first `|`, trimmed. Resolution goes through `node.resolve` (exact, the same
+--- mapping that materializes stored `wiki` links) — never fuzzy `search`, which
+--- would mis-jump.
+
+local rpc = require("heph.rpc")
+local util = require("heph.util")
+
+local M = {}
+
+--- The wiki target under the cursor on the current line, or nil. Scans for the
+--- `[[...]]` span that contains the cursor column.
+function M.target_under_cursor()
+  local line = vim.api.nvim_get_current_line()
+  local col = vim.api.nvim_win_get_cursor(0)[2] + 1 -- 1-based byte column
+  local from = 1
+  while true do
+    local open_s, open_e = line:find("[[", from, true)
+    if not open_s then
+      return nil
+    end
+    local close_s, close_e = line:find("]]", open_e + 1, true)
+    if not close_s then
+      return nil
+    end
+    if col >= open_s and col <= close_e then
+      local inner = line:sub(open_e + 1, close_s - 1)
+      local target = inner:match("^([^|]*)") or ""
+      target = target:gsub("^%s+", ""):gsub("%s+$", "")
+      return (#target > 0) and target or nil
+    end
+    from = close_e + 1
+  end
+end
+
+--- Follow the `[[link]]` under the cursor to its node. Unresolved links are
+--- allowed (tech-spec §5) — an INFO toast, not an error.
+function M.follow()
+  local target = M.target_under_cursor()
+  if not target then
+    util.notify("no [[link]] under cursor", vim.log.levels.WARN)
+    return
+  end
+  local node = rpc.call("node.resolve", { title = target })
+  if not node then
+    util.notify("unresolved link [[" .. target .. "]]", vim.log.levels.INFO)
+    return
+  end
+  require("heph.node").open(node.id)
+end
+
+--- Attach the buffer-local `<CR>` follow keymap (only on heph:// buffers).
+function M.attach(buf)
+  vim.keymap.set("n", "<CR>", function()
+    M.follow()
+  end, { buffer = buf, desc = "heph: follow [[link]]" })
+end
+
+return M