Add get_last_session_id() to Python and Go SDKs (github#671)

* Initial plan

* Add get_last_session_id() to Python and Go SDKs with E2E tests

Co-authored-by: patniko <26906478+patniko@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: patniko <26906478+patniko@users.noreply.github.com>

Author: Copilot

go/README.md

@@ -104,6 +104,7 @@ That's it! When your application calls `copilot.NewClient` without a `CLIPath` n
 - `ResumeSessionWithOptions(sessionID string, config *ResumeSessionConfig) (*Session, error)` - Resume with additional configuration
 - `ListSessions(filter *SessionListFilter) ([]SessionMetadata, error)` - List sessions (with optional filter)
 - `DeleteSession(sessionID string) error` - Delete a session permanently
+- `GetLastSessionID(ctx context.Context) (*string, error)` - Get the ID of the most recently updated session
 - `GetState() ConnectionState` - Get connection state
 - `Ping(message string) (*PingResponse, error)` - Ping the server
 - `GetForegroundSessionID(ctx context.Context) (*string, error)` - Get the session ID currently displayed in TUI (TUI+server mode only)

go/client.go

@@ -726,6 +726,40 @@ func (c *Client) DeleteSession(ctx context.Context, sessionID string) error {
 	return nil
 }
 
+// GetLastSessionID returns the ID of the most recently updated session.
+//
+// This is useful for resuming the last conversation when the session ID
+// was not stored. Returns nil if no sessions exist.
+//
+// Example:
+//
+//	lastID, err := client.GetLastSessionID(context.Background())
+//	if err != nil {
+//	    log.Fatal(err)
+//	}
+//	if lastID != nil {
+//	    session, err := client.ResumeSession(context.Background(), *lastID, &copilot.ResumeSessionConfig{
+//	        OnPermissionRequest: copilot.PermissionHandler.ApproveAll,
+//	    })
+//	}
+func (c *Client) GetLastSessionID(ctx context.Context) (*string, error) {
+	if err := c.ensureConnected(); err != nil {
+		return nil, err
+	}
+
+	result, err := c.client.Request("session.getLastId", getLastSessionIDRequest{})
+	if err != nil {
+		return nil, err
+	}
+
+	var response getLastSessionIDResponse
+	if err := json.Unmarshal(result, &response); err != nil {
+		return nil, fmt.Errorf("failed to unmarshal getLastId response: %w", err)
+	}
+
+	return response.SessionID, nil
+}
+
 // GetForegroundSessionID returns the ID of the session currently displayed in the TUI.
 //
 // This is only available when connecting to a server running in TUI+server mode

go/internal/e2e/session_test.go

@@ -828,6 +828,40 @@ func TestSession(t *testing.T) {
 			t.Error("Expected error when resuming deleted session")
 		}
 	})
+	t.Run("should get last session id", func(t *testing.T) {
+		ctx.ConfigureForTest(t)
+
+		// Create a session and send a message to persist it
+		session, err := client.CreateSession(t.Context(), &copilot.SessionConfig{OnPermissionRequest: copilot.PermissionHandler.ApproveAll})
+		if err != nil {
+			t.Fatalf("Failed to create session: %v", err)
+		}
+
+		_, err = session.SendAndWait(t.Context(), copilot.MessageOptions{Prompt: "Say hello"})
+		if err != nil {
+			t.Fatalf("Failed to send message: %v", err)
+		}
+
+		// Small delay to ensure session data is flushed to disk
+		time.Sleep(500 * time.Millisecond)
+
+		lastSessionID, err := client.GetLastSessionID(t.Context())
+		if err != nil {
+			t.Fatalf("Failed to get last session ID: %v", err)
+		}
+
+		if lastSessionID == nil {
+			t.Fatal("Expected last session ID to be non-nil")
+		}
+
+		if *lastSessionID != session.SessionID {
+			t.Errorf("Expected last session ID to be %s, got %s", session.SessionID, *lastSessionID)
+		}
+
+		if err := session.Destroy(); err != nil {
+			t.Fatalf("Failed to destroy session: %v", err)
+		}
+	})
 }
 
 func getSystemMessage(exchange testharness.ParsedHttpExchange) string {

go/types.go

@@ -749,6 +749,14 @@ type deleteSessionResponse struct {
 	Error   *string `json:"error,omitempty"`
 }
 
+// getLastSessionIDRequest is the request for session.getLastId
+type getLastSessionIDRequest struct{}
+
+// getLastSessionIDResponse is the response from session.getLastId
+type getLastSessionIDResponse struct {
+	SessionID *string `json:"sessionId,omitempty"`
+}
+
 // getForegroundSessionRequest is the request for session.getForeground
 type getForegroundSessionRequest struct{}
 

python/copilot/client.py

@@ -961,6 +961,30 @@ async def delete_session(self, session_id: str) -> None:
             if session_id in self._sessions:
                 del self._sessions[session_id]
 
+    async def get_last_session_id(self) -> str | None:
+        """
+        Get the ID of the most recently updated session.
+
+        This is useful for resuming the last conversation when the session ID
+        was not stored.
+
+        Returns:
+            The session ID, or None if no sessions exist.
+
+        Raises:
+            RuntimeError: If the client is not connected.
+
+        Example:
+            >>> last_id = await client.get_last_session_id()
+            >>> if last_id:
+            ...     session = await client.resume_session(last_id, {"on_permission_request": PermissionHandler.approve_all})
+        """
+        if not self._client:
+            raise RuntimeError("Client not connected")
+
+        response = await self._client.request("session.getLastId", {})
+        return response.get("sessionId")
+
     async def get_foreground_session_id(self) -> str | None:
         """
         Get the ID of the session currently displayed in the TUI.

python/e2e/test_session.py

@@ -303,6 +303,23 @@ async def test_should_delete_session(self, ctx: E2ETestContext):
                 session_id, {"on_permission_request": PermissionHandler.approve_all}
             )
 
+    async def test_should_get_last_session_id(self, ctx: E2ETestContext):
+        import asyncio
+
+        # Create a session and send a message to persist it
+        session = await ctx.client.create_session(
+            {"on_permission_request": PermissionHandler.approve_all}
+        )
+        await session.send_and_wait({"prompt": "Say hello"})
+
+        # Small delay to ensure session data is flushed to disk
+        await asyncio.sleep(0.5)
+
+        last_session_id = await ctx.client.get_last_session_id()
+        assert last_session_id == session.session_id
+
+        await session.destroy()
+
     async def test_should_create_session_with_custom_tool(self, ctx: E2ETestContext):
         # This test uses the low-level Tool() API to show that Pydantic is optional
         def get_secret_number_handler(invocation):

test/snapshots/session/should_get_last_session_id.yaml

@@ -0,0 +1,10 @@
+models:
+  - claude-sonnet-4.5
+conversations:
+  - messages:
+      - role: system
+        content: ${system}
+      - role: user
+        content: Say hello
+      - role: assistant
+        content: Hello! I'm GitHub Copilot CLI, ready to help with your software engineering tasks.