diff --git a/CHANGELOG.md b/CHANGELOG.md
index 02592b5c..6064064d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,11 @@
 
 - **PR #TBD** by @Michaelyklam (refs #1925) — Clarify the RuntimeAdapter Slice 3c state after #2544 shipped. The RFC now distinguishes shipped `/api/goal` routing through `RuntimeAdapter.update_goal(...)` from the still-staged `queue_message(...)` protocol method, and explicitly warns not to add a new server-side queue endpoint or queue scheduler merely for adapter symmetry while `/queue` remains browser-side queue/drain behavior.
 
+### Fixed
+
+- **PR #2563** by @Michaelyklam (closes #2554) — Align workspace-tree file rows with sibling directory rows by reserving the same expand/collapse toggle slot for files. Expanded directories now show child files stepped in at the same icon column as child folders, while directory toggles and file interactions stay unchanged.
+
+
 ## [v0.51.91] — 2026-05-18 — Release BO (stage-384 — 5-PR full sweep batch — reasoning-replay history fix + archive-extract per-session inbox + fallback streaming warnings + sanitized custom-provider env hints + Slice 3c queue/goal adapter routing)
 
 ### Fixed
diff --git a/docs/pr-media/2554/tree-indent-after.png b/docs/pr-media/2554/tree-indent-after.png
new file mode 100644
index 00000000..8137b93c
Binary files /dev/null and b/docs/pr-media/2554/tree-indent-after.png differ
diff --git a/docs/pr-media/2554/tree-indent-before.png b/docs/pr-media/2554/tree-indent-before.png
new file mode 100644
index 00000000..13173d80
Binary files /dev/null and b/docs/pr-media/2554/tree-indent-before.png differ
diff --git a/static/style.css b/static/style.css
index e4714e21..6d4bacb9 100644
--- a/static/style.css
+++ b/static/style.css
@@ -1423,6 +1423,7 @@
   .file-item:hover{background:var(--hover-bg);color:var(--text);}
   .file-item.active{background:var(--accent-bg);color:var(--accent-text);}
   .file-tree-toggle{font-size:10px;color:var(--muted);flex-shrink:0;width:10px;text-align:center;line-height:1;}
+  .file-tree-toggle-placeholder{display:inline-block;flex:0 0 10px;width:10px;line-height:1;}
   .file-item.file-empty{color:var(--muted);opacity:.5;font-style:italic;cursor:default;font-size:11px;}
   .file-item.file-empty:hover{background:none;color:var(--muted);}
   .preview-area{flex:1;overflow:auto;padding:14px;flex-direction:column;gap:8px;display:none;opacity:0;transition:opacity .15s;}
diff --git a/static/ui.js b/static/ui.js
index cb78ba09..380ef090 100644
--- a/static/ui.js
+++ b/static/ui.js
@@ -7565,6 +7565,13 @@ function _renderTreeItems(container, entries, depth){
       const isExpanded=S._expandedDirs.has(item.path);
       arrow.textContent=isExpanded?'\u25BE':'\u25B8';
       el.appendChild(arrow);
+    }else{
+      // Keep file icons aligned with sibling directories that occupy this
+      // slot with the expand/collapse toggle. #2554
+      const spacer=document.createElement('span');
+      spacer.className='file-tree-toggle-placeholder';
+      spacer.setAttribute('aria-hidden','true');
+      el.appendChild(spacer);
     }
 
     // Icon
diff --git a/tests/test_issue2554_workspace_tree_file_indent.py b/tests/test_issue2554_workspace_tree_file_indent.py
new file mode 100644
index 00000000..3908f02c
--- /dev/null
+++ b/tests/test_issue2554_workspace_tree_file_indent.py
@@ -0,0 +1,39 @@
+"""Regression coverage for #2554 — workspace tree file rows align with directories."""
+
+from pathlib import Path
+
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+UI_JS = (REPO_ROOT / "static" / "ui.js").read_text(encoding="utf-8")
+STYLE_CSS = (REPO_ROOT / "static" / "style.css").read_text(encoding="utf-8")
+
+
+def _render_tree_item_toggle_block() -> str:
+    start = UI_JS.index("if(item.type==='dir'){\n      // Toggle arrow for directories")
+    end = UI_JS.index("\n\n    // Icon", start)
+    return UI_JS[start:end]
+
+
+def test_file_rows_get_toggle_placeholder_before_icon():
+    block = _render_tree_item_toggle_block()
+
+    assert "spacer=document.createElement('span')" in block
+    assert "spacer.className='file-tree-toggle-placeholder'" in block
+    assert "spacer.setAttribute('aria-hidden','true')" in block
+    assert "el.appendChild(spacer);" in block
+
+    spacer_idx = UI_JS.index("spacer.className='file-tree-toggle-placeholder'")
+    icon_idx = UI_JS.index("const iconEl=document.createElement('span');", spacer_idx)
+    assert spacer_idx < icon_idx, "file-row spacer must be appended before the file icon"
+
+
+def test_placeholder_matches_directory_toggle_slot_width():
+    assert ".file-tree-toggle{" in STYLE_CSS
+    assert ".file-tree-toggle-placeholder{" in STYLE_CSS
+    placeholder_start = STYLE_CSS.index(".file-tree-toggle-placeholder{")
+    placeholder_end = STYLE_CSS.index("}", placeholder_start)
+    placeholder = STYLE_CSS[placeholder_start:placeholder_end]
+
+    assert "width:10px" in placeholder
+    assert "flex:0 0 10px" in placeholder
+    assert "display:inline-block" in placeholder