diff --git a/packages/app/src/pages/layout/helpers.test.ts b/packages/app/src/pages/layout/helpers.test.ts
index 5dfa543c9..a43dd15e2 100644
--- a/packages/app/src/pages/layout/helpers.test.ts
+++ b/packages/app/src/pages/layout/helpers.test.ts
@@ -321,13 +321,13 @@ describe("layout workspace helpers", () => {
   })
 
   describe("sessionListDirectories", () => {
-    test("uses opened projects when present", () => {
+    test("unions opened and server projects, opened first", () => {
       const opened = [{ worktree: "/a", sandboxes: ["/a-sbx"] }, { worktree: "/b" }]
       const server = [{ worktree: "/server", sandboxes: ["/server-sbx"] }]
-      expect(sessionListDirectories(opened, server)).toEqual(["/a", "/a-sbx", "/b"])
+      expect(sessionListDirectories(opened, server)).toEqual(["/a", "/a-sbx", "/b", "/server", "/server-sbx"])
     })
 
-    test("falls back to server projects when nothing is opened (fresh client, amicode#288)", () => {
+    test("returns only server projects when nothing is opened (fresh client, amicode#288)", () => {
       const server = [
         { worktree: "/", sandboxes: ["/staging"] },
         { worktree: "/amicode" },
@@ -336,7 +336,13 @@ describe("layout workspace helpers", () => {
       expect(sessionListDirectories([], server)).toEqual(["/", "/staging", "/amicode", "/opencode"])
     })
 
-    test("fallback dedupes and drops empty entries", () => {
+    test("dedupes across opened and server projects", () => {
+      const opened = [{ worktree: "/a", sandboxes: ["/shared"] }]
+      const server = [{ worktree: "/a" }, { worktree: "/b", sandboxes: ["/shared"] }]
+      expect(sessionListDirectories(opened, server)).toEqual(["/a", "/shared", "/b"])
+    })
+
+    test("dedupes and drops empty entries from server-only path", () => {
       const server = [
         { worktree: "/a", sandboxes: ["/a"] },
         { worktree: "/a" },
diff --git a/packages/app/src/pages/layout/helpers.ts b/packages/app/src/pages/layout/helpers.ts
index 4105a082c..e99324465 100644
--- a/packages/app/src/pages/layout/helpers.ts
+++ b/packages/app/src/pages/layout/helpers.ts
@@ -59,24 +59,33 @@ export const displayName = (project: { name?: string; worktree: string }) =>
 
 /**
  * Directories whose sessions the list surfaces (Sessions dropdown, home list)
- * aggregate over: the user's opened projects, falling back to the server's
- * registered projects when nothing has been opened yet (fresh client, empty
- * persisted registry — amicode#288). Session listing only; this must NOT feed
- * the project switcher, or closing a server-registered project becomes
- * impossible (the fallback would re-add it).
+ * — always the union of opened projects (first) and server-registered projects
+ * (deduplicated, appended). Every historical project the server knows about
+ * contributes sessions, not just the ones currently open. Session listing only;
+ * this must NOT feed the project switcher, or closing a server-registered
+ * project becomes impossible (amicode#839, replacing the fallback-only behavior
+ * from amicode#288).
  */
 export function sessionListDirectories(
   opened: { worktree: string; sandboxes?: string[] }[],
   serverProjects: { worktree: string; sandboxes?: string[] }[],
 ): string[] {
-  const dirs = opened.flatMap((p) => [p.worktree, ...(p.sandboxes ?? [])])
-  if (dirs.length > 0) return dirs
   const seen = new Set<string>()
-  return serverProjects.flatMap((p) => [p.worktree, ...(p.sandboxes ?? [])]).filter((d) => {
-    if (!d || seen.has(d)) return false
+  const result: string[] = []
+  const add = (d: string) => {
+    if (!d || seen.has(d)) return
     seen.add(d)
-    return true
-  })
+    result.push(d)
+  }
+  for (const p of opened) {
+    add(p.worktree)
+    for (const s of p.sandboxes ?? []) add(s)
+  }
+  for (const p of serverProjects) {
+    add(p.worktree)
+    for (const s of p.sandboxes ?? []) add(s)
+  }
+  return result
 }
 
 export function toggleHomeProjectSelection(
diff --git a/packages/app/src/pages/session.tsx b/packages/app/src/pages/session.tsx
index 2a81c8d63..2b0c887c0 100644
--- a/packages/app/src/pages/session.tsx
+++ b/packages/app/src/pages/session.tsx
@@ -268,11 +268,11 @@ function ResolvedTargetSessionRoute() {
   })
 
   // Notify the extension which project this session is bound to so the
-  // sidebar highlight tracks the active tab. autoExpand=false: session
-  // navigation should only change the highlight, never toggle folder state.
+  // sidebar highlight tracks the active tab. mode="expand": opening a session
+  // expands its project folder if collapsed, without collapsing others.
   createEffect(() => {
     const dir = directory()
-    if (dir) notifyProjectSelected(dir, false)
+    if (dir) notifyProjectSelected(dir, "expand")
   })
 
   return (
diff --git a/packages/app/src/pages/session/composer/session-composer-controls.ts b/packages/app/src/pages/session/composer/session-composer-controls.ts
index 3951072d9..0a553a68d 100644
--- a/packages/app/src/pages/session/composer/session-composer-controls.ts
+++ b/packages/app/src/pages/session/composer/session-composer-controls.ts
@@ -109,7 +109,7 @@ export function createPromptProjectControls() {
     if (pathKey(worktree) === pathKey(sdk().directory)) {
       const fallback = hiddenProjectWorktree()
       if (search.draftId && fallback) {
-        notifyProjectSelected(fallback, true)
+        notifyProjectSelected(fallback, "reset")
         tabs.updateDraft(search.draftId, { directory: fallback })
       }
       return
diff --git a/packages/app/src/utils/amicode-workspace-projects.test.ts b/packages/app/src/utils/amicode-workspace-projects.test.ts
index f207b6364..8f0614d96 100644
--- a/packages/app/src/utils/amicode-workspace-projects.test.ts
+++ b/packages/app/src/utils/amicode-workspace-projects.test.ts
@@ -12,34 +12,34 @@ describe("amicode workspace-projects — notifyProjectSelected (#663)", () => {
       notifyProjectSelected("/Users/jj/harmoniqs")
       expect(calls).toHaveLength(1)
       const [msg, origin] = calls[0] as [Record<string, unknown>, string]
-      expect(msg).toEqual({ source: "amicode", kind: "project-selected", path: "/Users/jj/harmoniqs", autoExpand: true })
+      expect(msg).toEqual({ source: "amicode", kind: "project-selected", path: "/Users/jj/harmoniqs", mode: "reset" })
       expect(origin).toBe("*")
     } finally {
       window.parent.postMessage = orig
     }
   })
 
-  test("explicit selection defaults to autoExpand=true", () => {
+  test("explicit selection defaults to mode 'reset'", () => {
     const calls: unknown[] = []
     const orig = window.parent.postMessage
     window.parent.postMessage = (...args: unknown[]) => { calls.push(args) }
     try {
       notifyProjectSelected("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/projects/foo")
       const [msg] = calls[0] as [Record<string, unknown>]
-      expect(msg.autoExpand).toBe(true)
+      expect(msg.mode).toBe("reset")
     } finally {
       window.parent.postMessage = orig
     }
   })
 
-  test("session navigation passes autoExpand=false", () => {
+  test("session navigation passes mode 'expand'", () => {
     const calls: unknown[] = []
     const orig = window.parent.postMessage
     window.parent.postMessage = (...args: unknown[]) => { calls.push(args) }
     try {
-      notifyProjectSelected("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/projects/foo", false)
+      notifyProjectSelected("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/projects/foo", "expand")
       const [msg] = calls[0] as [Record<string, unknown>]
-      expect(msg.autoExpand).toBe(false)
+      expect(msg.mode).toBe("expand")
     } finally {
       window.parent.postMessage = orig
     }
@@ -85,11 +85,11 @@ describe("session-composer-controls — toggle deselect (#673)", () => {
     expect(toggleBranch).toMatch(/notifyProjectSelected/)
   })
 
-  test("deselect notification passes autoExpand true so the folder collapses", () => {
+  test("deselect notification passes mode 'reset' so the sidebar collapses the old folder", () => {
     const selectFn = ctrlSrc.slice(ctrlSrc.indexOf("const selectProject"))
     // The toggle branch's notifyProjectSelected call (before the main one)
     const toggleBranch = selectFn.slice(0, selectFn.indexOf("notifyProjectSelected(worktree)"))
-    // Must NOT pass false — needs true (or default) so the sidebar collapses the old folder
-    expect(toggleBranch).not.toMatch(/notifyProjectSelected\([^)]*,\s*false/)
+    // Must NOT pass "none" — needs "reset" (or default) so the sidebar collapses the old folder
+    expect(toggleBranch).not.toMatch(/notifyProjectSelected\([^)]*,\s*["']none["']/)
   })
 })
diff --git a/packages/app/src/utils/amicode-workspace-projects.ts b/packages/app/src/utils/amicode-workspace-projects.ts
index da20fc16b..8975e0f90 100644
--- a/packages/app/src/utils/amicode-workspace-projects.ts
+++ b/packages/app/src/utils/amicode-workspace-projects.ts
@@ -29,9 +29,13 @@ export function requestAddWorkspaceProject(): void {
 }
 
 /** Notify the extension host that the user selected a project in the dropdown.
- *  The extension forwards this to the sidebar (collapse others, expand selected).
- *  autoExpand=true (default) for explicit dropdown clicks; false for session
- *  navigation (highlight only, don't toggle folder state). */
-export function notifyProjectSelected(worktree: string, autoExpand = true): void {
-  window.parent.postMessage({ source: "amicode", kind: "project-selected", path: worktree, autoExpand }, "*")
+ *  The extension forwards this to the sidebar with a three-valued mode:
+ *  - "reset"  (default) — expand selected, collapse others (project selector)
+ *  - "expand" — expand selected if collapsed, leave others alone (session open / tab switch)
+ *  - "none"   — highlight only, no folder state changes (orphan fallback, replay)
+ */
+export type ActiveProjectMode = "none" | "expand" | "reset"
+
+export function notifyProjectSelected(worktree: string, mode: ActiveProjectMode = "reset"): void {
+  window.parent.postMessage({ source: "amicode", kind: "project-selected", path: worktree, mode }, "*")
 }