feat(kanban): surface task_runs.summary on dashboard cards + `kanban show`

The kanban-worker skill (built into the gateway dispatcher's spawn
prompt) instructs every worker to hand off via
``kanban_complete(summary=..., metadata=...)``. That writes the summary
onto the closing ``task_runs`` row, NOT onto ``tasks.result`` — the
latter is left NULL unless the caller passes ``result=`` explicitly.

Result: a glance at the dashboard or ``hermes kanban show <id>`` shows
a blank "Result:" section even when the worker did real work, which
on 2026-05-05 caused a Mac false-alarm ("Hermes did nothing") on a
task that had a 10-line completion summary on its run.

This patch surfaces the latest non-null run summary as
``latest_summary`` so the worker's actual handoff lands in front of
operators.

* New helpers ``kanban_db.latest_summary(conn, task_id)`` and
  ``kanban_db.latest_summaries(conn, task_ids)``. The batch variant
  uses a single window-function SELECT so the dashboard board endpoint
  doesn't pay an N+1 cost on multi-hundred-task boards.
* CLI ``hermes kanban show <id>`` prints a "Latest summary:" block
  when ``tasks.result`` is empty but a run has produced a summary
  (the existing "Result:" section still wins when populated, so the
  back-compat path for hand-edited results is untouched). JSON output
  gains a top-level ``latest_summary`` field.
* Dashboard ``/board`` and ``/tasks/{id}`` now include a
  ``latest_summary`` field on every task. Cards on /board carry a
  200-character preview (cheap to render, plenty for "what did this
  worker do?" at a glance); the drawer/detail endpoint returns the
  full summary.
* Five new tests cover: empty-runs case, post-complete surface,
  newest-of-multiple selection, empty-string skip, batch with
  missing tasks + empty input.

Smoke-tested locally against the live profile DB on the three
acceptance-criterion targets (t_f08fef91 cron-hygiene-audit,
t_007b7f1c EMA-analysis, t_05746fa4 self-assessment) — all three now
return their populated summaries via both ``latest_summary`` and
``latest_summaries``.

Test plan: 255/255 kanban tests pass + 91/91 dashboard plugin tests
pass. No regression on tasks where ``tasks.result`` is explicitly
populated (the existing "Result:" branch is preserved).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

plugins/kanban/dashboard/plugin_api.py

@@ -124,11 +124,23 @@ BOARD_COLUMNS: list[str] = [
 ]
 
 
-def _task_dict(task: kanban_db.Task) -> dict[str, Any]:
+_CARD_SUMMARY_PREVIEW_CHARS = 200
+
+
+def _task_dict(
+    task: kanban_db.Task,
+    *,
+    latest_summary: Optional[str] = None,
+) -> dict[str, Any]:
     d = asdict(task)
     # Add derived age metrics so the UI can colour stale cards without
     # computing deltas client-side.
     d["age"] = kanban_db.task_age(task)
+    # Surface the latest non-null run summary so dashboards don't show
+    # blank cards/drawers for tasks where the worker handed off via
+    # ``task_runs.summary`` (the kanban-worker pattern) instead of
+    # ``tasks.result``. ``None`` when no run has produced a summary yet.
+    d["latest_summary"] = latest_summary
     # Keep body short on list endpoints; full body comes from /tasks/:id.
     return d
 
@@ -381,8 +393,18 @@ def get_board(
         if include_archived:
             columns["archived"] = []
 
+        # Batch-fetch the latest non-null run summary per task in one
+        # window-function query (avoids N+1 ``latest_summary`` calls
+        # for boards with hundreds of tasks). Truncated to a card-size
+        # preview here — the full text is available via /tasks/:id.
+        summary_map = kanban_db.latest_summaries(conn, [t.id for t in tasks])
+
         for t in tasks:
-            d = _task_dict(t)
+            full = summary_map.get(t.id)
+            preview = (
+                full[:_CARD_SUMMARY_PREVIEW_CHARS] if full else None
+            )
+            d = _task_dict(t, latest_summary=preview)
             d["link_counts"] = link_counts.get(t.id, {"parents": 0, "children": 0})
             d["comment_count"] = comment_counts.get(t.id, 0)
             d["progress"] = progress.get(t.id)  # None when the task has no children
@@ -440,7 +462,11 @@ def get_task(task_id: str, board: Optional[str] = Query(None)):
         task = kanban_db.get_task(conn, task_id)
         if task is None:
             raise HTTPException(status_code=404, detail=f"task {task_id} not found")
-        task_d = _task_dict(task)
+        # Drawer/detail view returns the FULL summary (no truncation) so
+        # operators can read the complete worker handoff without making
+        # a second round-trip. Cards on /board carry a 200-char preview.
+        full_summary = kanban_db.latest_summary(conn, task_id)
+        task_d = _task_dict(task, latest_summary=full_summary)
         # Attach diagnostics so the drawer's Diagnostics section can
         # render recovery actions without a second round-trip.
         diags = _compute_task_diagnostics(conn, task_ids=[task_id])