feat(nvim): inline #hashtags become tags on save (§8.3)

On save, whitespace-prefixed `#hashtags` in a node's body are unioned
into its tag set (via `frontmatter.hashtags` + the existing tag diff), so
you can tag a note by writing `#kitchen` inline. A markdown `# heading`
has a space after the `#`, so it never matches. e2e covers it.

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

docs/reference/tech-spec.md

@@ -302,12 +302,12 @@ Project-subtree resolution needs the **parent-project links** ([[design]] §6.2.
 
 ## 8.3 Frontmatter as an edit surface (built)
 
-> **Status: built** (inline `#hashtags` on save are a small deferred follow-up). When a node is opened in `heph.nvim`, its structured metadata (id, title, project, do-date, tags, …) is visible and editable as a YAML frontmatter block atop the body — without that metadata ever becoming a second, drifting source of truth in the body.
+> **Status: built.** When a node is opened in `heph.nvim`, its structured metadata (id, title, project, do-date, tags, …) is visible and editable as a YAML frontmatter block atop the body — without that metadata ever becoming a second, drifting source of truth in the body.
 
 The resolving principle is a **two-layer split** that keeps the store safe against *any* client while making `heph.nvim` a rich editor:
 
 - ✅ **The store is dumb and safe.** Frontmatter is a **projection generated on read** and **stripped + silently ignored on write**. `heph-core::frontmatter::strip(body)` runs inside `update_node` **before** the `yrs` CRDT diff (conservative — it only removes a leading `---` block whose first line is a YAML key, so a leading `---` thematic break in prose survives; idempotent). The **render** side lives in `hephd` (`hephd::frontmatter::render`, since formatting `do_date`/`late_on` for humans needs the local timezone via `datespec::fmt_iso`); `node.get {frontmatter: true}` prepends it. Invariants: the at-rest body and the CRDT doc **never** contain frontmatter; an unchanged read→write round-trips to a no-op. Because inbound frontmatter is always discarded, a naive editor (or the future web UI) **cannot corrupt metadata** — at worst it sends stale frontmatter and the store drops it; the canonical block regenerates on the next read.
-- ✅ **`heph.nvim` is the smart client.** `node.lua` reads with `frontmatter: true` (the buffer opens with the block on top) and caches the rendered block; on `BufWriteCmd`, `frontmatter.lua` parses the buffer's block, **diffs it against the cached one**, and translates each changed field into the **correct structured RPC**: `title` → rename, `attention` → `set_attention`, `do_date`/`late_on`/`recurrence` → `set_schedule` (dates parsed `YYYY-MM-DD` → local-midnight ms; a removed line clears via `null`), `project` → **`set_project`** (resolved by name, §8.1), `tags` → `tag.add`/`tag.remove` (§14 tags); a mistyped `state` surfaces the daemon's validation error. Then it sends the (frontmatter-less) body. A buffer with **no** block touches no metadata — only deleting individual fields edits them — so removing the whole block can't accidentally wipe tags. (Body-position features — `[[link]]` follow, promote — are content-relative, so the prepended block doesn't disturb them.) **Remaining:** inline `#hashtags` detected on save.
+- ✅ **`heph.nvim` is the smart client.** `node.lua` reads with `frontmatter: true` (the buffer opens with the block on top) and caches the rendered block; on `BufWriteCmd`, `frontmatter.lua` parses the buffer's block, **diffs it against the cached one**, and translates each changed field into the **correct structured RPC**: `title` → rename, `attention` → `set_attention`, `do_date`/`late_on`/`recurrence` → `set_schedule` (dates parsed `YYYY-MM-DD` → local-midnight ms; a removed line clears via `null`), `project` → **`set_project`** (resolved by name, §8.1), `tags` → `tag.add`/`tag.remove` (§14 tags); a mistyped `state` surfaces the daemon's validation error. Then it sends the (frontmatter-less) body. A buffer with **no** block touches no metadata — only deleting individual fields edits them — so removing the whole block can't accidentally wipe tags. Inline **`#hashtags`** in the body are unioned into the tag set on save (a `# heading` has a space after `#`, so it doesn't match). (Body-position features — `[[link]]` follow, promote — are content-relative, so the prepended block doesn't disturb them.)
 
 **The schema** (a curated, *editable* subset — not the full export snapshot). `id`/`kind` are read-only; `title` and `tags` edit the opened node; when the node **is** a task or backs one (its canonical-context doc), the owning task's scalars are rendered and a read-only `task:` id says where those edits route:
 
@@ -468,7 +468,7 @@ See [[design]] §5–§7 for the constraints later phases impose on present choi
    - ✅ **(b) sort toggle `s` — DONE:** **default**: attention (red→orange→white→blue) → days-overdue (descending; no-date = 0) → project (name) → `created_at` (FIFO). **project mode**: project is primary, with dimmed **`──── Name ────` separators** riding atop each group's first task (the cursor only lands on real tasks). View filtering always runs **before** the sort. (`skip` moved to `S` to free `s`.)
    - ✅ **nvim task-navigation polish (§8) — DONE:** `:Heph next`/`list` rows now carry a compact **do/late date chip** (and a recurrence `↻`); `<CR>` already jumps to a row's canonical-context doc (read/navigate, not field-edit).
 3. ✅ **Tags (§4, §8.3) — DONE:** a tag is a `tag`-kind node whose id is **deterministic in `(owner, name)`** (`tag:<owner>:<name>`, like the journal), so a name is one canonical tag and replicas converge — no duplicate tag nodes. Tagging is an **OR-set `tagged` link** (mirroring `in-project`): `Store::add_tag` (get-or-create the tag node, idempotent link), `remove_tag` (tombstone the link), `tags_of` (sorted names); enumerate all tags via `list_nodes(Tag)`. RPCs `tag.add`/`tag.remove`/`tag.list` (+ RemoteStore forward); CLI `heph tag add|rm|list`. Names are trimmed, case preserved (canonical normalization deferred to the zk import). Unblocks the `tags:` line of the frontmatter surface (§8.3) and the eventual zk import; inline `#hashtags` remain a heph.nvim concern (§8.3).
-4. ✅ **YAML frontmatter as an edit surface (§8.3) — DONE:** the projection — `heph-core::frontmatter::strip` (conservative, runs in `update_node` before the CRDT diff) + `hephd::frontmatter::render` (local-tz dates via `datespec::fmt_iso`) behind `node.get {frontmatter: true}`; a task's context-doc surfaces the owning task's scalars + a `task:` ref; round-trip is a no-op and inbound frontmatter is always stripped (safe vs any client). And the `heph.nvim` smart client (`frontmatter.lua`): the buffer opens with the editable block, and `BufWriteCmd` diffs it → `title`→rename / `attention`→set_attention / dates→set_schedule / `project`→set_project / `tags`→tag.add·remove (a no-block buffer touches no metadata). **Deferred follow-up:** inline `#hashtags` detected on save.
+4. ✅ **YAML frontmatter as an edit surface (§8.3) — DONE:** the projection — `heph-core::frontmatter::strip` (conservative, runs in `update_node` before the CRDT diff) + `hephd::frontmatter::render` (local-tz dates via `datespec::fmt_iso`) behind `node.get {frontmatter: true}`; a task's context-doc surfaces the owning task's scalars + a `task:` ref; round-trip is a no-op and inbound frontmatter is always stripped (safe vs any client). And the `heph.nvim` smart client (`frontmatter.lua`): the buffer opens with the editable block, and `BufWriteCmd` diffs it → `title`→rename / `attention`→set_attention / dates→set_schedule / `project`→set_project / `tags`→tag.add·remove (a no-block buffer touches no metadata), and inline `#hashtags` in the body are unioned into the tag set on save.
 5. ⏳ **Wiki-links by node id (§8.4) — docs-first C1 (maybe C2):** canonical `[[NODEID]]` at rest, expanded/concealed for display; a `[[` picker; no name-links in the DB. Includes a one-time body fixup. See §8.4.
 6. ⏳ **`heph.nvim` slice 11d (§6/§8) — DEFERRED, post-parity:** daemon **server-push** notification framing (no-`id` lines on the socket; the client read-loop already demuxes them) + the **dirty-buffer reconcile** (the §8 "known-hard" case) + the "update-arrives-while-open" e2e (§9).
 7. ⏳ **Split `heph.nvim` to its own forge repo (§8) — UX polish:** generated from this monorepo (subtree-split in CI) so the lazy spec becomes `{ "eblume/heph.nvim" }` instead of a local-clone `dir` (see [[install-heph]]).