feat(tasks): markdown export projection

A disposable Markdown view of the board, grouped by status with checkboxes
and claimants — rendered from the event log, never a source of truth.
TaskMarkdown.render (pure) backs GET /tasks/export[?project=].

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

core/tasks/src/main/kotlin/com/correx/core/tasks/TaskMarkdown.kt

@@ -0,0 +1,54 @@
+package com.correx.core.tasks
+
+/**
+ * Renders the task board to Markdown — a *disposable projection* of the event log, grouped by
+ * status. It is never a source of truth: regenerate it, don't hand-edit it. Pure and store-free
+ * so it can render either [TaskService.list] or [TaskService.listAll] and be unit tested directly.
+ */
+object TaskMarkdown {
+
+    // Active work first, terminal states last.
+    private val ORDER = listOf(
+        TaskStatus.IN_PROGRESS,
+        TaskStatus.IN_REVIEW,
+        TaskStatus.BLOCKED,
+        TaskStatus.TODO,
+        TaskStatus.DONE,
+        TaskStatus.CANCELLED,
+    )
+
+    fun render(tasks: List<Task>): String = buildString {
+        appendLine("# Tasks")
+        appendLine()
+        appendLine("_Generated from the correx event log — disposable; regenerate, don't edit._")
+        appendLine()
+        if (tasks.isEmpty()) {
+            appendLine("_No tasks._")
+            return@buildString
+        }
+        val byStatus = tasks.groupBy { it.state.status }
+        for (status in ORDER) {
+            val group = byStatus[status]?.sortedBy { it.taskId.value }.orEmpty()
+            if (group.isEmpty()) continue
+            appendLine("## ${heading(status)} (${group.size})")
+            appendLine()
+            group.forEach { appendLine(item(it)) }
+            appendLine()
+        }
+    }.trimEnd() + "\n"
+
+    private fun item(task: Task): String {
+        val check = if (task.state.status == TaskStatus.DONE) "x" else " "
+        val claim = task.state.claimant?.let { " _(@$it)_" }.orEmpty()
+        return "- [$check] **${task.taskId.value}** ${task.state.title.orEmpty()}$claim".trimEnd()
+    }
+
+    private fun heading(status: TaskStatus): String = when (status) {
+        TaskStatus.TODO -> "To do"
+        TaskStatus.IN_PROGRESS -> "In progress"
+        TaskStatus.IN_REVIEW -> "In review"
+        TaskStatus.BLOCKED -> "Blocked"
+        TaskStatus.DONE -> "Done"
+        TaskStatus.CANCELLED -> "Cancelled"
+    }
+}

core/tasks/src/test/kotlin/com/correx/core/tasks/TaskMarkdownTest.kt

@@ -0,0 +1,33 @@
+package com.correx.core.tasks
+
+import com.correx.core.events.types.TaskId
+import org.junit.jupiter.api.Assertions.assertTrue
+import org.junit.jupiter.api.Test
+
+class TaskMarkdownTest {
+
+    private fun task(id: String, status: TaskStatus, title: String, claimant: String? = null) =
+        Task(TaskId(id), TaskState(key = id, status = status, title = title, claimant = claimant))
+
+    @Test
+    fun `renders grouped sections with checkboxes and claimants`() {
+        val md = TaskMarkdown.render(
+            listOf(
+                task("auth-1", TaskStatus.IN_PROGRESS, "JWT refresh", claimant = "claude-opus"),
+                task("auth-2", TaskStatus.DONE, "Login form"),
+            ),
+        )
+
+        assertTrue(md.startsWith("# Tasks"))
+        assertTrue(md.contains("disposable"))
+        assertTrue(md.contains("## In progress (1)"))
+        assertTrue(md.contains("- [ ] **auth-1** JWT refresh _(@claude-opus)_"))
+        assertTrue(md.contains("## Done (1)"))
+        assertTrue(md.contains("- [x] **auth-2** Login form"))
+    }
+
+    @Test
+    fun `empty board renders a placeholder`() {
+        assertTrue(TaskMarkdown.render(emptyList()).contains("_No tasks._"))
+    }
+}