feat(tasks): task search across REST, tool, and TUI

Ranked exact/substring search: TaskSearch (all terms AND, ranked title >
key > goal > criteria > notes) over one project or the whole board via
TaskService.search. Surfaced as GET /tasks?q=, a read-only task_search tool
for agents, and a `/` filter in the TUI board.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/tui-go/internal/app/tasks_overlay.go

@@ -85,10 +85,28 @@ func (m *Model) openTasks() tea.Cmd {
 	m.taskListErr = ""
 	m.taskDetail = false
 	m.taskDetailScroll = 0
+	m.taskFilter = ""
+	m.taskFilterTyping = false
 	m.taskListLoading = true
 	return fetchTasks(m.client.HTTPBase())
 }
 
+// filteredTasks narrows the board by the `/` query — a case-insensitive substring over
+// id/title/goal. An empty query returns the whole list.
+func (m Model) filteredTasks() []TaskSummary {
+	if strings.TrimSpace(m.taskFilter) == "" {
+		return m.taskList
+	}
+	q := strings.ToLower(m.taskFilter)
+	var out []TaskSummary
+	for _, tk := range m.taskList {
+		if strings.Contains(strings.ToLower(tk.ID+" "+tk.Title+" "+tk.Goal), q) {
+			out = append(out, tk)
+		}
+	}
+	return out
+}
+
 // applyTasksLoaded folds a GET /tasks result into the board, clamping the cursor and
 // surfacing any fetch error in place of a crash.
 func (m *Model) applyTasksLoaded(msg tasksLoadedMsg) {
@@ -107,10 +125,11 @@ func (m *Model) applyTasksLoaded(msg tasksLoadedMsg) {
 // selectedTask returns the highlighted task, or false when the list is empty / the
 // cursor is out of range.
 func (m Model) selectedTask() (TaskSummary, bool) {
-	if m.taskListIndex < 0 || m.taskListIndex >= len(m.taskList) {
+	f := m.filteredTasks()
+	if m.taskListIndex < 0 || m.taskListIndex >= len(f) {
 		return TaskSummary{}, false
 	}
-	return m.taskList[m.taskListIndex], true
+	return f[m.taskListIndex], true
 }
 
 // handleTasksKey owns every key while the board is open. In list mode: navigate, r
@@ -136,15 +155,36 @@ func (m Model) handleTasksKey(k keyMsg) (tea.Model, tea.Cmd) {
 		}
 		return m, nil
 	}
+	// While editing the `/` filter, keys feed the query (esc/enter stop editing, keeping it).
+	if m.taskFilterTyping {
+		switch {
+		case k.Type == keyEnter || k.Type == keyEsc:
+			m.taskFilterTyping = false
+		case k.Type == keyBackspace:
+			if n := len(m.taskFilter); n > 0 {
+				m.taskFilter = m.taskFilter[:n-1]
+				m.taskListIndex = 0
+			}
+		case k.Type == keyRunes || k.Type == keySpace:
+			m.taskFilter += string(k.Runes)
+			m.taskListIndex = 0
+		}
+		return m, nil
+	}
 	switch {
 	case k.Type == keyEsc || runeIs(k, "T"):
 		m.overlay = OverlayNone
+	case runeIs(k, "/"):
+		m.taskFilterTyping = true
+	case runeIs(k, "c"):
+		m.taskFilter = ""
+		m.taskListIndex = 0
 	case k.Type == keyUp || runeIs(k, "k"):
 		if m.taskListIndex > 0 {
 			m.taskListIndex--
 		}
 	case k.Type == keyDown || runeIs(k, "j"):
-		if m.taskListIndex < len(m.taskList)-1 {
+		if m.taskListIndex < len(m.filteredTasks())-1 {
 			m.taskListIndex++
 		}
 	case runeIs(k, "r"):
@@ -195,11 +235,12 @@ func (m Model) tasksModal() string {
 	}
 	t := m.theme
 	w := m.modalWidth()
+	tasks := m.filteredTasks()
 
 	var b strings.Builder
 	b.WriteString(m.titleLine("tasks"))
-	if len(m.taskList) > 0 {
-		b.WriteString(mbg(t, "   ("+itoa(m.taskListIndex+1)+"/"+itoa(len(m.taskList))+")", t.P.Faint))
+	if len(tasks) > 0 {
+		b.WriteString(mbg(t, "   ("+itoa(m.taskListIndex+1)+"/"+itoa(len(tasks))+")", t.P.Faint))
 	}
 	b.WriteString("\n\n")
 
@@ -213,9 +254,19 @@ func (m Model) tasksModal() string {
 		b.WriteString("\n" + modalHints(t, [][2]string{{"T/esc", "close"}}))
 		return t.Overlay.Width(w).Render(b.String())
 	}
-	if len(m.taskList) == 0 {
-		b.WriteString(mbg(t, "  no tasks", t.P.Faint) + "\n")
-		b.WriteString("\n" + modalHints(t, [][2]string{{"r", "refresh"}, {"T/esc", "close"}}))
+
+	// Filter prompt: shown while editing the `/` query or whenever one is set.
+	if m.taskFilterTyping || m.taskFilter != "" {
+		b.WriteString(m.taskFilterLine() + "\n\n")
+	}
+
+	if len(tasks) == 0 {
+		msg := "  no tasks"
+		if m.taskFilter != "" {
+			msg = "  no tasks match \"" + m.taskFilter + "\""
+		}
+		b.WriteString(mbg(t, msg, t.P.Faint) + "\n")
+		b.WriteString("\n" + modalHints(t, m.taskListHints()))
 		return t.Overlay.Width(w).Render(b.String())
 	}
 
@@ -225,33 +276,50 @@ func (m Model) tasksModal() string {
 		bodyH = 4
 	}
 	off := 0
-	if len(m.taskList) > bodyH {
+	if len(tasks) > bodyH {
 		off = m.taskListIndex - bodyH/2
 		if off < 0 {
 			off = 0
 		}
-		if off > len(m.taskList)-bodyH {
-			off = len(m.taskList) - bodyH
+		if off > len(tasks)-bodyH {
+			off = len(tasks) - bodyH
 		}
 	}
 	end := off + bodyH
-	if end > len(m.taskList) {
-		end = len(m.taskList)
+	if end > len(tasks) {
+		end = len(tasks)
 	}
 	for i := off; i < end; i++ {
-		b.WriteString(m.taskListRow(i) + "\n")
+		b.WriteString(m.taskListRow(tasks, i) + "\n")
 	}
 
-	b.WriteString("\n" + modalHints(t, [][2]string{
-		{"↑↓", "select"}, {"enter", "detail"}, {"r", "refresh"}, {"T/esc", "close"},
-	}))
+	b.WriteString("\n" + modalHints(t, m.taskListHints()))
 	return t.Overlay.Width(w).Render(b.String())
 }
 
-// taskListRow renders one board line: marker, id, status, title, and claimant.
-func (m Model) taskListRow(i int) string {
+// taskListHints is the list-mode footer (shared by the populated and empty-filter views).
+func (m Model) taskListHints() [][2]string {
+	return [][2]string{{"↑↓", "select"}, {"enter", "detail"}, {"/", "filter"}, {"r", "refresh"}, {"T/esc", "close"}}
+}
+
+// taskFilterLine renders the `/` filter prompt over the current query, with a caret while editing.
+func (m Model) taskFilterLine() string {
 	t := m.theme
-	tk := m.taskList[i]
+	prompt := lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.BgPanel).Render("/ ")
+	caret := mbg(t, "", t.P.BgPanel)
+	if m.taskFilterTyping && m.caretVisible() {
+		caret = lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.BgPanel).Render("▏")
+	}
+	if m.taskFilter == "" {
+		return prompt + caret + mbg(t, "type to filter tasks…", t.P.Faint)
+	}
+	return prompt + mbg(t, m.taskFilter, t.P.FgStrong) + caret
+}
+
+// taskListRow renders one board line: marker, id, status, title, and claimant.
+func (m Model) taskListRow(tasks []TaskSummary, i int) string {
+	t := m.theme
+	tk := tasks[i]
 
 	marker := mbg(t, "  ", t.P.BgPanel)
 	idFg := t.P.Fg