feat: heph migrate-links — rewrite legacy [[Name]] links to [[id]] (§8.4)

`wikilink::to_ids` rewrites name-addressed links to the canonical id
(id-first resolve: an already-id target is left alone, a name → its id
with any label preserved). `Store::migrate_wikilinks_to_ids` runs it over
every body and re-saves through update_node (which collapses + materializes
by id); idempotent. Surfaced as the `migrate.wikilinks` RPC + RemoteStore
forward + the `heph migrate-links` CLI command (not auto-run — the owner
runs it once per store).

Name-resolution + the canonical-context hack stay for now so legacy links
keep resolving pre-migration; retiring them is a later tidy. Tests:
to_ids unit + a heph-core migrate integration (rewrite + materialize +
idempotency).

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

docs/changelog.d/v1-prototype.feature.md

@@ -28,7 +28,7 @@ Begin the v1 prototype (Phase 1, tech-spec §11.1), built in TDD slices:
 - `heph-tui` task-list visuals (§8.1): each row now leads with an attention **flag** (`⚑`, colored red/orange/blue; blank for white) and a **project-colored bullet** — the bullet's color is derived stably from the project id (so it survives projects being added/removed), letting you scan a mixed list by project at a glance. The list also grows a **scrollbar** and keeps the selected task scrolled into view when there are more tasks than fit.
 - `heph-tui` sort toggle (§8.1): **`s`** flips the task list between two orders — **default** (attention → most-overdue → project → creation) and **by-project** (grouped under dimmed `──── Project ────` separators, then the same sub-order). The view's filter still applies first. (To free `s`, **skip** moved to **`S`**.)
 - `heph.nvim` task-view rows (§8): `:Heph next`/`:Heph list` rows now show a compact **do/late date chip** (and a recurrence `↻`), so you can see scheduling at a glance; `<CR>` still jumps to a task's context doc.
-- Wiki-links by node id (§8.4): node resolution is now **id-first** (`[[NODEID]]` resolves to its node ahead of any name match, so links can't be shadowed by a like-named node), and heph.nvim grows a **`[[` picker** — type `[[` (or `:Heph link`) to search your nodes and insert a canonical `[[NODEID]]` link, with a "+ Create new doc" entry that mints one on the spot. Following such a link (`<CR>`) jumps straight by id. Those id links are kept **readable**: on read a bare `[[NODEID]]` is expanded to `[[NODEID|Current Name]]` (so it follows renames, in both the nvim buffer and the TUI preview), and on save it collapses back to the canonical bare id — a custom `|label` you write is preserved as an override. In the editor the id is **concealed** — a link renders as just its name, styled like a hyperlink, with the raw `[[id|Name]]` revealed on the line your cursor is on. (Legacy `[[Name]]` links still resolve until a one-time migration rewrites them.)
+- Wiki-links by node id (§8.4): node resolution is now **id-first** (`[[NODEID]]` resolves to its node ahead of any name match, so links can't be shadowed by a like-named node), and heph.nvim grows a **`[[` picker** — type `[[` (or `:Heph link`) to search your nodes and insert a canonical `[[NODEID]]` link, with a "+ Create new doc" entry that mints one on the spot. Following such a link (`<CR>`) jumps straight by id. Those id links are kept **readable**: on read a bare `[[NODEID]]` is expanded to `[[NODEID|Current Name]]` (so it follows renames, in both the nvim buffer and the TUI preview), and on save it collapses back to the canonical bare id — a custom `|label` you write is preserved as an override. In the editor the id is **concealed** — a link renders as just its name, styled like a hyperlink, with the raw `[[id|Name]]` revealed on the line your cursor is on. Legacy `[[Name]]` links keep working, and **`heph migrate-links`** rewrites them to the canonical id form in one pass when you're ready (idempotent).
 - Frontmatter editing in heph.nvim (§8.3): opening a node now shows an editable **YAML frontmatter** block on top of the body (`id`/`kind`/`title`/`tags`, and for a task or its context doc the task's `state`/`attention`/`do_date`/`late_on`/`recurrence`/`project`). On save, the plugin diffs the block and issues the right RPC per changed field — rename, set-attention, reschedule (dates as `YYYY-MM-DD`), move-to-project (by name), and tag add/remove — then saves the body; the store strips the block so it never persists. A mistyped `state` surfaces a validation error; a buffer with no block changes no metadata (so deleting the block can't wipe your tags). Inline **`#hashtags`** typed in the body are also added as tags on save (a `# heading` doesn't count) and are rendered in **italics** so they stand out. Link-follow and promotion are unaffected (they're content-relative, not line-absolute).
 - Frontmatter projection (§8.3): a node can now be fetched with an editable **YAML frontmatter** block prepended — `node.get {frontmatter: true}` renders `id`/`kind`/`title`/`tags`, and for a task (or its context doc) the owning task's `state`/`attention`/`do_date`/`late_on`/`recurrence`/`project` plus a `task:` ref. Dates are local `YYYY-MM-DD`. On write, the store **strips and ignores** any leading frontmatter (conservatively — a real `---` hrule in prose survives) before the CRDT diff, so frontmatter never persists and an unchanged read→write is a no-op; a naive editor can't corrupt metadata. This is the read/write groundwork for editing a node's metadata as frontmatter in heph.nvim (the diff-into-RPCs layer is next).
 - Tags (§4, §8.3): nodes can now be **tagged**. A tag is a `tag`-kind node whose id is deterministic in `(owner, name)`, so the same name is **one canonical tag** shared across everything it's applied to (and replicas converge — no duplicate tags). Tagging is an OR-set link, so adding/removing is idempotent and merge-safe. Surfaced as `tag.add`/`tag.remove`/`tag.list` RPCs and `heph tag add|rm|list` (list a node's tags, or every tag with no node). Tag names are trimmed; a canonical case/spelling normalization is deferred to the future zk import. This is the groundwork for the `tags:` line of the upcoming frontmatter edit surface.

docs/reference/tech-spec.md

@@ -338,7 +338,7 @@ Field rules: `id`/`kind` are **read-only** (display only); `title`, `attention`,
 - **At rest (target):** `[[NODEID]]`, or `[[NODEID|custom text]]` when the author wrote explicit display text. The id before the `|` is the target.
 - ✅ **Projection (same philosophy as §8.3):** `heph-core::wikilink` (pure, injected id→title) — `node.get` **expands** a bare `[[NODEID]]` → `[[NODEID|Current Name]]` (every read, so the nvim buffer *and* the TUI preview are readable), and `update_node` **collapses** a `|text` equal to the target's current name back to bare before the CRDT diff (a custom label is preserved as an override). Transform order: read = expand links → prepend frontmatter; write = strip frontmatter → collapse links → store. An unchanged read→write round-trips to the canonical bare id. *(`heph export` still emits raw ids — a later polish.)*
 - ✅ **`heph.nvim` display:** `conceal.lua` hides the `[[id|` prefix and the `]]` suffix with conceal extmarks (refreshed on edit), leaving the label as a styled `HephLink` hyperlink; `conceallevel=2` + empty `concealcursor` reveal the raw link on the cursor's line so it stays editable.
-- ⏳ **Migration:** a **one-time fixup** rewrites existing `[[Title]]` bodies to `[[NODEID]]` (resolve→id; flag the unresolvable), after which name-resolution + the canonical-context hack are removed. No special care is warranted (no critical data yet); a first-class migrations feature stays **deferred**.
+- ✅ **Migration:** **`heph migrate-links`** (the `migrate.wikilinks` RPC → `Store::migrate_wikilinks_to_ids` → `wikilink::to_ids`) rewrites legacy `[[Name]]` bodies to `[[NODEID]]` and re-materializes the `wiki` links by id; idempotent (already-id links untouched). It is **not auto-run** — the owner runs it once per store. Name-resolution and the canonical-context hack **stay for now** (legacy links keep working until the migration has been run everywhere); removing them is a later tidy. A first-class migrations feature stays **deferred**.
 
 ## 9. Testing strategy (TDD, layered)
 
@@ -470,7 +470,7 @@ See [[design]] §5–§7 for the constraints later phases impose on present choi
    - ✅ **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), and inline `#hashtags` in the body are unioned into the tag set on save.
-5. ◐ **Wiki-links by node id (§8.4) — authoring + display DONE, migration next:** ✅ id-first resolution; the `heph.nvim` `[[` picker (`search` → insert `[[NODEID|Name]]`, "+ Create" mints a doc) + id-direct follow; the **expand-on-read / collapse-on-write** projection (`heph-core::wikilink`); and **conceal display** (`conceal.lua` hides the id, shows the label as a `HephLink`, reveals on the cursor line). ⏳ Remaining: the one-time `[[Title]]`→`[[NODEID]]` migration (then retire name-resolution + the canonical-context hack). See §8.4.
+5. ✅ **Wiki-links by node id (§8.4) — DONE:** id-first resolution; the `heph.nvim` `[[` picker (`search` → insert `[[NODEID|Name]]`, "+ Create" mints a doc) + id-direct follow; the **expand-on-read / collapse-on-write** projection (`heph-core::wikilink`); **conceal display** (`conceal.lua` hides the id, shows the label as a `HephLink`, reveals on the cursor line); and the one-time **`heph migrate-links`** migration of legacy `[[Name]]`→`[[NODEID]]`. *(Follow-up tidy, once the migration is run on every store: retire name-resolution + the canonical-context hack — kept for now so legacy links work pre-migration.)* 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]]).
 8. ⏳ **Adoption refinement + multi-tenant (§13) — before v1 done, low priority:** local→authed **adoption** currently rewrites `owner_id` (`adopt_owner`) but not yet the owner-embedded deterministic ids (journal/tag) + their links; and the hub is single-tenant (one owner per store) — owner-per-token storage is a future extension.