feat(sessions): group conversation list by project directory (closes #67) (#96)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/lib/session-grouping.test.ts

@@ -0,0 +1,43 @@
+import { test } from "node:test"
+import assert from "node:assert/strict"
+import { groupByDirectory } from "./session-grouping.ts"
+
+test("groupByDirectory: buckets items by directory, preserving item order within a bucket", () => {
+  const items = [
+    { id: "1", directory: "/a" },
+    { id: "2", directory: "/b" },
+    { id: "3", directory: "/a" },
+  ]
+  const groups = groupByDirectory(items)
+  assert.equal(groups.length, 2)
+  assert.equal(groups[0].directory, "/a")
+  assert.deepEqual(groups[0].items.map((i) => i.id), ["1", "3"])
+  assert.equal(groups[1].directory, "/b")
+  assert.deepEqual(groups[1].items.map((i) => i.id), ["2"])
+})
+
+test("groupByDirectory: orders groups by first-seen directory, not alphabetically", () => {
+  const items = [
+    { id: "1", directory: "/z" },
+    { id: "2", directory: "/a" },
+  ]
+  const groups = groupByDirectory(items)
+  assert.deepEqual(
+    groups.map((g) => g.directory),
+    ["/z", "/a"],
+  )
+})
+
+test("groupByDirectory: empty input returns no groups", () => {
+  assert.deepEqual(groupByDirectory([]), [])
+})
+
+test("groupByDirectory: single directory yields a single group with all items", () => {
+  const items = [
+    { id: "1", directory: "/a" },
+    { id: "2", directory: "/a" },
+  ]
+  const groups = groupByDirectory(items)
+  assert.equal(groups.length, 1)
+  assert.equal(groups[0].items.length, 2)
+})

src/lib/session-grouping.ts

@@ -0,0 +1,31 @@
+// Pure helpers for grouping the session list by project directory.
+// No React Native imports — unit-testable with node --test.
+
+/** A contiguous-by-directory bucket of items, in first-seen order. */
+export interface DirectoryGroup<T> {
+  directory: string
+  items: T[]
+}
+
+/**
+ * Groups items by their `directory` field, preserving both the original
+ * item order within a group and the order in which each directory was
+ * first encountered. Does not sort — callers decide presentation order.
+ */
+export function groupByDirectory<T extends { directory: string }>(items: T[]): DirectoryGroup<T>[] {
+  const order: string[] = []
+  const buckets = new Map<string, T[]>()
+
+  for (const item of items) {
+    const dir = item.directory
+    let bucket = buckets.get(dir)
+    if (!bucket) {
+      bucket = []
+      buckets.set(dir, bucket)
+      order.push(dir)
+    }
+    bucket.push(item)
+  }
+
+  return order.map((directory) => ({ directory, items: buckets.get(directory) as T[] }))
+}