feat: inline add-task form in Kanban columns

apps/web/src/app/(authenticated)/kanban/page.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { useState, useEffect, useCallback, useMemo } from "react";
+import { useState, useEffect, useCallback, useMemo, useRef } from "react";
 import type { ReactElement } from "react";
 import { useSearchParams, useRouter } from "next/navigation";
 import { DragDropContext, Droppable, Draggable } from "@hello-pangea/dnd";
@@ -12,7 +12,7 @@ import type {
 } from "@hello-pangea/dnd";
 
 import { MosaicSpinner } from "@/components/ui/MosaicSpinner";
-import { fetchTasks, updateTask, type TaskFilters } from "@/lib/api/tasks";
+import { fetchTasks, updateTask, createTask, type TaskFilters } from "@/lib/api/tasks";
 import { fetchProjects, type Project } from "@/lib/api/projects";
 import { useWorkspaceId } from "@/lib/hooks";
 import type { Task } from "@mosaic/shared";
@@ -184,9 +184,47 @@ function TaskCard({ task, provided, snapshot, columnAccent }: TaskCardProps): Re
 interface KanbanColumnProps {
   config: ColumnConfig;
   tasks: Task[];
+  onAddTask: (status: TaskStatus, title: string) => Promise<void>;
 }
 
-function KanbanColumn({ config, tasks }: KanbanColumnProps): ReactElement {
+function KanbanColumn({ config, tasks, onAddTask }: KanbanColumnProps): ReactElement {
+  const [showAddForm, setShowAddForm] = useState(false);
+  const [inputValue, setInputValue] = useState("");
+  const [isSubmitting, setIsSubmitting] = useState(false);
+  const inputRef = useRef<HTMLInputElement>(null);
+
+  // Focus input when form is shown
+  useEffect(() => {
+    if (showAddForm && inputRef.current) {
+      inputRef.current.focus();
+    }
+  }, [showAddForm]);
+
+  const handleSubmit = async (e: React.SyntheticEvent): Promise<void> => {
+    e.preventDefault();
+    if (!inputValue.trim() || isSubmitting) {
+      return;
+    }
+
+    setIsSubmitting(true);
+    try {
+      await onAddTask(config.status, inputValue.trim());
+      setInputValue("");
+      setShowAddForm(false);
+    } catch (err) {
+      console.error("[KanbanColumn] Failed to add task:", err);
+    } finally {
+      setIsSubmitting(false);
+    }
+  };
+
+  const handleKeyDown = (e: React.KeyboardEvent<HTMLInputElement>): void => {
+    if (e.key === "Escape") {
+      setShowAddForm(false);
+      setInputValue("");
+    }
+  };
+
   return (
     <div
       style={{
@@ -268,6 +306,89 @@ function KanbanColumn({ config, tasks }: KanbanColumnProps): ReactElement {
           </div>
         )}
       </Droppable>
+
+      {/* Add Task Form */}
+      {!showAddForm ? (
+        <button
+          type="button"
+          onClick={() => {
+            setShowAddForm(true);
+          }}
+          style={{
+            padding: "10px 16px",
+            border: "none",
+            background: "transparent",
+            color: "var(--muted)",
+            fontSize: "0.8rem",
+            cursor: "pointer",
+            textAlign: "left",
+            transition: "color 0.15s",
+            width: "100%",
+          }}
+          onMouseEnter={(e) => {
+            e.currentTarget.style.color = "var(--text)";
+          }}
+          onMouseLeave={(e) => {
+            e.currentTarget.style.color = "var(--muted)";
+          }}
+        >
+          + Add task
+        </button>
+      ) : (
+        <form
+          onSubmit={handleSubmit}
+          style={{ padding: "8px 12px 12px", borderTop: "1px solid var(--border)" }}
+        >
+          <input
+            ref={inputRef}
+            type="text"
+            value={inputValue}
+            onChange={(e) => {
+              setInputValue(e.target.value);
+            }}
+            onKeyDown={handleKeyDown}
+            placeholder="Task title..."
+            disabled={isSubmitting}
+            style={{
+              width: "100%",
+              padding: "8px 10px",
+              borderRadius: "var(--r)",
+              border: `1px solid ${inputValue ? "var(--primary)" : "var(--border)"}`,
+              background: "var(--surface)",
+              color: "var(--text)",
+              fontSize: "0.85rem",
+              outline: "none",
+              opacity: isSubmitting ? 0.6 : 1,
+            }}
+            autoFocus
+          />
+          <div style={{ marginTop: 6, fontSize: "0.75rem", color: "var(--muted)" }}>
+            Press{" "}
+            <kbd
+              style={{
+                padding: "2px 4px",
+                background: "var(--bg-mid)",
+                borderRadius: "2px",
+                fontFamily: "var(--mono)",
+              }}
+            >
+              Enter
+            </kbd>{" "}
+            to save,{" "}
+            <kbd
+              style={{
+                padding: "2px 4px",
+                background: "var(--bg-mid)",
+                borderRadius: "2px",
+                fontFamily: "var(--mono)",
+              }}
+            >
+              Escape
+            </kbd>{" "}
+            to cancel
+          </div>
+        </form>
+      )}
     </div>
   );
 }
@@ -621,6 +742,24 @@ export default function KanbanPage(): ReactElement {
     void loadTasks(workspaceId);
   }
 
+  /* --- add task handler --- */
+
+  const handleAddTask = useCallback(
+    async (status: TaskStatus, title: string) => {
+      try {
+        const wsId = workspaceId ?? undefined;
+        const newTask = await createTask({ title, status }, wsId);
+        // Optimistically add to local state
+        setTasks((prev) => [...prev, newTask]);
+      } catch (err: unknown) {
+        console.error("[Kanban] Failed to create task:", err);
+        // Re-fetch on error to get consistent state
+        void loadTasks(workspaceId);
+      }
+    },
+    [workspaceId, loadTasks]
+  );
+
   /* --- render --- */
 
   return (
@@ -755,7 +894,12 @@ export default function KanbanPage(): ReactElement {
             }}
           >
             {COLUMNS.map((col) => (
-              <KanbanColumn key={col.status} config={col} tasks={grouped[col.status]} />
+              <KanbanColumn
+                key={col.status}
+                config={col}
+                tasks={grouped[col.status]}
+                onAddTask={handleAddTask}
+              />
             ))}
           </div>
         </DragDropContext>