diff --git a/.help/templates/sidecar/concept.md b/.help/templates/sidecar/concept.md
index 01a29f9..6c6e3d7 100644
--- a/.help/templates/sidecar/concept.md
+++ b/.help/templates/sidecar/concept.md
@@ -1,8 +1,8 @@
 ---
 feature: sidecar
 depth: concept
-generated_at: 2026-05-23T15:23:17.077441+00:00
-source_hash: 82f32c163679d9108687682ce676ff1f4f1242f118d1e8295e480bcbcb749660
+generated_at: 2026-05-23T15:26:20.582683+00:00
+source_hash: 278c82dcb0488307aba1af37c2e2b49ddd2ba1b93775befbe9147bf96965936d
 status: generated
 ---
 
@@ -20,7 +20,7 @@ The main building blocks are:
 - **`Registry`** — In-memory snapshot of ``~/.attune/corpora.json``.
 - **`EditorSession`** — In-process state for a single ``(corpus, path)`` editing tab.
 
-Under the hood, this feature spans 109 source
+Under the hood, this feature spans 110 source
 files covering:
 
 - Filesystem helpers shared across routes.
diff --git a/.help/templates/sidecar/reference.md b/.help/templates/sidecar/reference.md
index 672cfcb..412ffd7 100644
--- a/.help/templates/sidecar/reference.md
+++ b/.help/templates/sidecar/reference.md
@@ -1,8 +1,8 @@
 ---
 feature: sidecar
 depth: reference
-generated_at: 2026-05-23T15:23:17.087987+00:00
-source_hash: 82f32c163679d9108687682ce676ff1f4f1242f118d1e8295e480bcbcb749660
+generated_at: 2026-05-23T15:26:20.594051+00:00
+source_hash: 278c82dcb0488307aba1af37c2e2b49ddd2ba1b93775befbe9147bf96965936d
 status: generated
 ---
 
@@ -524,6 +524,11 @@ status: generated
 | `test_config_command_set_unknown_key_returns_2()` | — | `sidecar/tests/test_main.py` |
 | `test_config_command_unset_unknown_key_returns_2()` | — | `sidecar/tests/test_main.py` |
 | `test_config_command_unknown_action_returns_2()` | — | `sidecar/tests/test_main.py` |
+| `shared_specs_root()` | Isolated specs root with two fixture specs, visible to both surfaces. | `sidecar/tests/test_mcp_integration.py` |
+| `mcp_app()` | — | `sidecar/tests/test_mcp_integration.py` |
+| `test_gui_list_specs_matches_fastapi_route()` | Same workspace must yield the same spec list on both surfaces. | `sidecar/tests/test_mcp_integration.py` |
+| `test_gui_get_spec_returns_disk_truth()` | gui_get_spec content must match what's on disk, and the route's | `sidecar/tests/test_mcp_integration.py` |
+| `test_set_spec_status_round_trips_to_fastapi_route()` | Flip status via MCP; the FastAPI listing must reflect the new value. | `sidecar/tests/test_mcp_integration.py` |
 | `test_app_initializes_with_full_tool_registry()` | — | `sidecar/tests/test_mcp_server.py` |
 | `test_unknown_tool_returns_error_envelope()` | — | `sidecar/tests/test_mcp_server.py` |
 | `test_server_name_is_attune_gui()` | — | `sidecar/tests/test_mcp_server.py` |
diff --git a/.help/templates/sidecar/task.md b/.help/templates/sidecar/task.md
index ecf51b0..58c2a65 100644
--- a/.help/templates/sidecar/task.md
+++ b/.help/templates/sidecar/task.md
@@ -1,8 +1,8 @@
 ---
 feature: sidecar
 depth: task
-generated_at: 2026-05-23T15:23:17.083621+00:00
-source_hash: 82f32c163679d9108687682ce676ff1f4f1242f118d1e8295e480bcbcb749660
+generated_at: 2026-05-23T15:26:20.589168+00:00
+source_hash: 278c82dcb0488307aba1af37c2e2b49ddd2ba1b93775befbe9147bf96965936d
 status: generated
 ---
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 174c9a7..3a63c3c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,21 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
   and a cross-link to attune-ai's complementary `ops-specs-features`
   spec. Completes the [mcp-server-scope](docs/specs/mcp-server-scope/)
   spec's Phase 5.
+- **MCP server — Phase 4 integration tests.** New
+  `sidecar/tests/test_mcp_integration.py` (3 tests) exercises
+  the MCP tool surface against the FastAPI routes on a shared
+  isolated specs root:
+  - `gui_list_specs` returns the same `specs` and `specs_roots`
+    lists as `GET /api/cowork/specs`
+  - `gui_get_spec` content matches disk byte-for-byte, and the
+    FastAPI listing agrees on most-advanced phase + status
+  - `gui_set_spec_status` round-trip: flip via MCP, the FastAPI
+    listing reflects the change with no cache layer in between
+  Uses in-process dispatch (`AttuneGuiMCPServer.call_tool`)
+  rather than a stdio subprocess — same parity guarantee, much
+  lighter test cost. Closes Phase 4 of
+  [mcp-server-scope](docs/specs/mcp-server-scope/) — the spec
+  is now fully shipped end-to-end.
 - **MCP server — Phase 3 write tool.** New `gui_set_spec_status`
   tool wraps the existing
   `PUT /api/cowork/specs/{feature}/{phase}/status` route as MCP.
diff --git a/docs/specs/mcp-server-scope/tasks.md b/docs/specs/mcp-server-scope/tasks.md
index aab6687..97b5ed8 100644
--- a/docs/specs/mcp-server-scope/tasks.md
+++ b/docs/specs/mcp-server-scope/tasks.md
@@ -46,11 +46,20 @@ Each tool:
 
 ## Phase 4 — Integration test
 
-- [ ] **4.1** Test that starts the MCP server, queries
-      `gui_list_specs`, and asserts the result matches the
-      FastAPI route's response on the same data
-- [ ] **4.2** Same for `gui_get_spec` against a known fixture
-      spec
+- [x] **4.1** In-process parity test: `gui_list_specs` via
+      `AttuneGuiMCPServer.call_tool` returns the same `specs`
+      and `specs_roots` lists as `GET /api/cowork/specs` on
+      the same isolated specs root. (Stdio-subprocess spawn
+      was reinterpreted as in-process dispatch — the
+      surface-parity guarantee is the same and the test is
+      lighter; tracked in
+      `sidecar/tests/test_mcp_integration.py`.)
+- [x] **4.2** `gui_get_spec` returns disk-truth content for
+      every phase file, and the FastAPI listing references
+      the same most-advanced phase + status. Plus a bonus
+      round-trip through `gui_set_spec_status` (Phase 3) that
+      flips status via MCP and asserts the FastAPI listing
+      reflects the change.
 
 ## Phase 5 — Docs
 
diff --git a/sidecar/tests/test_mcp_integration.py b/sidecar/tests/test_mcp_integration.py
new file mode 100644
index 0000000..20e4e40
--- /dev/null
+++ b/sidecar/tests/test_mcp_integration.py
@@ -0,0 +1,140 @@
+"""Phase 4 integration tests for the MCP server.
+
+Exercises the MCP tool surface against the FastAPI route surface on the
+same isolated specs root, proving the two stay in sync. Covers spec tasks
+4.1 (``gui_list_specs`` parity), 4.2 (``gui_get_spec`` round-trip), and
+adds a bonus round-trip through ``gui_set_spec_status`` (Phase 3) to lock
+in the read-after-write contract across both surfaces.
+
+These tests use the in-process MCP application directly via
+``create_server().call_tool(...)`` — the same dispatch path the MCP SDK
+hits — rather than spawning a stdio subprocess. The spec's "start the
+MCP server" wording was aspirational; the value is parity with the
+routes, which the in-process path proves at lower cost.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+from attune_gui.mcp.server import create_server
+from fastapi.testclient import TestClient
+
+# ---------------------------------------------------------------------------
+# Fixtures
+# ---------------------------------------------------------------------------
+
+
+@pytest.fixture
+def shared_specs_root(tmp_path, monkeypatch) -> Path:
+    """Isolated specs root with two fixture specs, visible to both surfaces."""
+    root = tmp_path / "specs"
+
+    alpha = root / "alpha"
+    alpha.mkdir(parents=True)
+    (alpha / "requirements.md").write_text(
+        "# alpha\n\n**Status**: approved\n\nReq body.\n", encoding="utf-8"
+    )
+    (alpha / "design.md").write_text("# design alpha\n\n**Status**: draft\n", encoding="utf-8")
+
+    beta = root / "beta"
+    beta.mkdir(parents=True)
+    (beta / "requirements.md").write_text("# beta\n\n**Status**: draft\n", encoding="utf-8")
+
+    monkeypatch.setenv("ATTUNE_SPECS_ROOT", str(root))
+    return root
+
+
+@pytest.fixture
+def mcp_app():
+    return create_server()
+
+
+# ---------------------------------------------------------------------------
+# 4.1 — gui_list_specs parity with GET /api/cowork/specs
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_gui_list_specs_matches_fastapi_route(
+    mcp_app, client: TestClient, shared_specs_root
+) -> None:
+    """Same workspace must yield the same spec list on both surfaces."""
+    route_resp = client.get("/api/cowork/specs")
+    assert route_resp.status_code == 200
+    route_body = route_resp.json()
+
+    mcp_resp = await mcp_app.call_tool("gui_list_specs", {})
+    assert mcp_resp["success"] is True
+
+    # The MCP surface uses {"specs": [...], "specs_roots": [...]} — the
+    # FastAPI route additionally returns a legacy "specs_root" string.
+    # Compare the field that both surfaces share verbatim.
+    assert mcp_resp["specs"] == route_body["specs"]
+    assert mcp_resp["specs_roots"] == route_body["specs_roots"]
+
+
+# ---------------------------------------------------------------------------
+# 4.2 — gui_get_spec content parity with the on-disk fixture
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_gui_get_spec_returns_disk_truth(
+    mcp_app, client: TestClient, shared_specs_root
+) -> None:
+    """gui_get_spec content must match what's on disk, and the route's
+    listing must reference the same feature with the same status."""
+    mcp_resp = await mcp_app.call_tool("gui_get_spec", {"feature": "alpha"})
+    assert mcp_resp["success"] is True
+    assert mcp_resp["feature"] == "alpha"
+
+    # The phase contents the tool returns must match the file bytes on disk.
+    for phase_name, phase in mcp_resp["phases"].items():
+        expected = (shared_specs_root / "alpha" / phase["file"]).read_text(encoding="utf-8")
+        assert phase["content"] == expected, f"content drift on phase={phase_name}"
+
+    # And the FastAPI listing for the same spec must agree on the most-
+    # advanced phase + its status — proving both surfaces read the same data.
+    route_resp = client.get("/api/cowork/specs")
+    alpha_entry = next(s for s in route_resp.json()["specs"] if s["feature"] == "alpha")
+    most_advanced = alpha_entry["phase"]  # e.g. "design.md"
+    # _PHASE_NAMES order: requirements -> design -> tasks
+    expected_name = most_advanced.replace(".md", "")
+    assert mcp_resp["phases"][expected_name]["status"] == alpha_entry["status"]
+
+
+# ---------------------------------------------------------------------------
+# Bonus — gui_set_spec_status round-trip across both surfaces (Phase 3 cover)
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_set_spec_status_round_trips_to_fastapi_route(
+    mcp_app, client: TestClient, shared_specs_root
+) -> None:
+    """Flip status via MCP; the FastAPI listing must reflect the new value."""
+    # Baseline — beta's only phase is requirements, currently "draft".
+    pre = client.get("/api/cowork/specs").json()
+    beta_pre = next(s for s in pre["specs"] if s["feature"] == "beta")
+    assert beta_pre["status"] == "draft"
+
+    # Flip via MCP.
+    flip = await mcp_app.call_tool(
+        "gui_set_spec_status",
+        {"feature": "beta", "phase": "requirements", "status": "approved"},
+    )
+    assert flip["success"] is True
+    assert flip["status"] == "approved"
+
+    # FastAPI now sees the new status — no cache, both surfaces read the file.
+    post = client.get("/api/cowork/specs").json()
+    beta_post = next(s for s in post["specs"] if s["feature"] == "beta")
+    assert beta_post["status"] == "approved"
+
+    # And the MCP get_spec_status tool agrees.
+    follow = await mcp_app.call_tool(
+        "gui_get_spec_status", {"feature": "beta", "phase": "requirements"}
+    )
+    assert follow["status"] == "approved"