feat: node.linkable — first-class link targets for the [[ picker (§8.4)

The picker listed every node, so each task showed up twice (itself + its
same-titled canonical-context doc) plus tag/log noise — and the new
preview made the duplicates look identical. New `Store::list_linkable_nodes`
/ `node.linkable` returns non-tombstoned nodes minus `tag`s and the docs
that are a task's canonical-context or log attachment (you link the task,
not its body). The Telescope picker now sources from it.

Tests: a socket test (5 nodes → 2 linkable: task + standalone doc).

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

crates/heph-core/src/sqlite/mod.rs

@@ -289,6 +289,10 @@ impl Store for LocalStore {
         nodes::list(&self.conn, &self.owner_id, kind)
     }
 
+    fn list_linkable_nodes(&self) -> Result<Vec<Node>> {
+        nodes::list_linkable(&self.conn, &self.owner_id)
+    }
+
     fn journal_open_or_create(&mut self, date: &str) -> Result<Node> {
         let now = self.clock.now_ms();
         nodes::open_or_create_journal(&self.conn, &self.owner_id, now, date)

crates/heph-core/src/sqlite/nodes.rs

@@ -407,6 +407,23 @@ pub(super) fn list(conn: &Connection, owner: &str, kind: Option<NodeKind>) -> Re
     Ok(rows.collect::<rusqlite::Result<Vec<_>>>()?)
 }
 
+/// First-class wiki-link targets (tech-spec §8.4): non-tombstoned nodes, minus
+/// the internal noise — `tag` nodes, and the `doc` nodes that are a task's
+/// **canonical-context** or **log** attachment (you link the task, not its
+/// auto-created body/log). Title-sorted, for the `[[` picker.
+pub(super) fn list_linkable(conn: &Connection, owner: &str) -> Result<Vec<Node>> {
+    let sql = format!(
+        "SELECT {COLUMNS} FROM nodes
+         WHERE owner_id = ?1 AND tombstoned = 0 AND kind != 'tag'
+           AND id NOT IN (SELECT dst_id FROM links
+                          WHERE type IN ('canonical-context', 'log-of') AND tombstoned = 0)
+         ORDER BY title COLLATE NOCASE"
+    );
+    let mut stmt = conn.prepare(&sql)?;
+    let rows = stmt.query_map([owner], from_row)?;
+    Ok(rows.collect::<rusqlite::Result<Vec<_>>>()?)
+}
+
 /// A node's aliases (wiki-link names), sorted. Empty until aliases are written.
 pub(super) fn aliases(conn: &Connection, id: &str) -> Result<Vec<String>> {
     let mut stmt = conn.prepare("SELECT alias FROM aliases WHERE node_id = ?1 ORDER BY alias")?;

crates/heph-core/src/store.rs

@@ -46,6 +46,11 @@ pub trait Store {
     /// (tech-spec §6 `node.list`).
     fn list_nodes(&self, kind: Option<NodeKind>) -> Result<Vec<Node>>;
 
+    /// First-class wiki-link targets (tech-spec §8.4): non-tombstoned nodes
+    /// minus the internal noise — `tag` nodes and the `doc`s that are a task's
+    /// canonical-context or log attachment. Backs the `[[` picker.
+    fn list_linkable_nodes(&self) -> Result<Vec<Node>>;
+
     /// Resolve a wiki-link target (`[[title]]`) to a node, **exactly** — an
     /// alias match first, then an exact, owner-scoped, non-tombstoned title
     /// match; `None` if nothing matches (an unresolved link is allowed, §5).