Fix environment grouping across custom sidebar sections

packages/client-core/src/sidebar/projectThreadGroups.ts

@@ -211,7 +211,24 @@ function buildSortedItems(
   compareThreads: ThreadComparator,
   groupEnvironmentThreads: boolean,
   draftThreadIds: ReadonlySet<string>,
+  respectSections = false,
 ): ProjectThreadItem[] {
+  if (groupEnvironmentThreads && respectSections) {
+    const nodesBySectionId = new Map<string | null, ProjectThreadNode[]>();
+    for (const node of nodes) {
+      const sectionId = node.thread.sectionId;
+      const bucket = nodesBySectionId.get(sectionId);
+      if (bucket) {
+        bucket.push(node);
+      } else {
+        nodesBySectionId.set(sectionId, [node]);
+      }
+    }
+    return [...nodesBySectionId.values()].flatMap((sectionNodes) =>
+      buildSortedItems(sectionNodes, compareThreads, true, draftThreadIds),
+    );
+  }
+
   if (!groupEnvironmentThreads) {
     nodes.sort((left, right) => compareThreads(left.thread, right.thread));
     return nodes.map(buildThreadItem);
@@ -353,6 +370,7 @@ function buildThreadTreeItems(
   compareThreads: ThreadComparator,
   groupEnvironmentThreads: boolean,
   draftThreadIds: ReadonlySet<string>,
+  respectSections = false,
 ): ProjectThreadItem[] {
   const projectThreads = allThreads.filter(isSidebarProjectThread);
   const projectThreadIds = new Set(projectThreads.map((thread) => thread.id));
@@ -413,6 +431,7 @@ function buildThreadTreeItems(
     compareThreads,
     groupEnvironmentThreads,
     draftThreadIds,
+    respectSections,
   );
 }
 
@@ -438,11 +457,12 @@ export function buildSectionThreadList(
   groupEnvironmentThreads = false,
 ): ProjectThreadItem[] {
   return bucketIntoSections(
-    buildChronologicalThreadList(
+    buildThreadTreeItems(
       allThreads,
       compareThreads,
-      draftThreadIds,
       groupEnvironmentThreads,
+      draftThreadIds,
+      true,
     ),
     CHRONOLOGICAL_CONTAINER_ID,
     compareThreads,

packages/client-core/test/projectThreadGroups.test.ts

@@ -669,6 +669,103 @@ describe("worktree grouping preference", () => {
     ]);
   });
 
+  it.each([false, true])(
+    "respects sections with environment grouping %s",
+    (groupEnvironmentThreads) => {
+      const threads = [
+        ...worktreeSiblings,
+        createThread({
+          id: "later",
+          environmentId: "env_wt",
+          environmentIsWorktree: true,
+          sectionId: "sec_later",
+          createdAt: 30,
+        }),
+        createThread({
+          id: "loose",
+          environmentId: "env_wt",
+          environmentIsWorktree: true,
+          createdAt: 40,
+        }),
+      ];
+      const items = buildSectionThreadList(
+        threads,
+        compareStandardThreads,
+        [...sections, { id: "sec_later", name: "Later" }],
+        new Set(),
+        groupEnvironmentThreads,
+      );
+      expect(summarizeItems(items)).toEqual([
+        {
+          section: "chronological::sec_work",
+          name: "Work",
+          items: groupEnvironmentThreads
+            ? [{ env: "env_wt", threads: ["wt-b", "wt-a"] }]
+            : ["wt-b", "wt-a"],
+        },
+        {
+          section: "chronological::sec_later",
+          name: "Later",
+          items: ["later"],
+        },
+        "loose",
+      ]);
+      expect(summarizeItems(buildProjectThreadGroups(threads))).toEqual([
+        { env: "env_wt", threads: ["loose", "later", "wt-b", "wt-a"] },
+      ]);
+    },
+  );
+
+  it("keeps separate environment groups and their descendants in each section", () => {
+    const threads = [
+      ...worktreeSiblings,
+      createThread({
+        id: "later-a",
+        environmentId: "env_wt",
+        environmentIsWorktree: true,
+        sectionId: "sec_later",
+        createdAt: 30,
+      }),
+      createThread({
+        id: "later-b",
+        environmentId: "env_wt",
+        environmentIsWorktree: true,
+        sectionId: "sec_later",
+        createdAt: 40,
+      }),
+      createThread({ id: "child", parentThreadId: "wt-a", createdAt: 50 }),
+    ];
+    const items = buildSectionThreadList(
+      threads,
+      compareStandardThreads,
+      sections,
+      new Set(),
+      true,
+    );
+    expect(summarizeItems(items)).toEqual([
+      {
+        section: "chronological::sec_work",
+        name: "Work",
+        items: [
+          {
+            env: "env_wt",
+            threads: ["wt-b", { id: "wt-a", children: ["child"] }],
+          },
+        ],
+      },
+      {
+        section: "chronological::sec_later",
+        name: "Section",
+        items: [{ env: "env_wt", threads: ["later-b", "later-a"] }],
+      },
+    ]);
+    expect(
+      items.map((item) =>
+        item.kind === "section" ? item.group.threadCount : 0,
+      ),
+    ).toEqual([3, 2]);
+  });
+
   it("keeps worktree siblings flat inside a section when disabled", () => {
     const items = buildSectionThreadList(
       worktreeSiblings,