Slice 4: graceful project handoff (pending switch + ack)

Add pending-switch coordination to internal/activity (RequestSwitch/PendingSwitch/AckSwitch/CancelSwitch); AckSwitch atomically sets the active project and records switch-completed with Claude's summary. New MCP tools get_pending_switch and ack_switch (request is user-only via HTTP). HTTP GET/POST/DELETE /api/switch. New <handoff-bar> component (ask/waiting/cancel/completed) over SSE; activity-feed reflects switch-completed. Test covers request->ack->clear. Verified live: request/waiting/cancel over SSE.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/mcp/mcp.go

@@ -9,6 +9,7 @@ import (
 	"context"
 	"fmt"
 	"net/http"
+	"time"
 
 	mcpsdk "github.com/modelcontextprotocol/go-sdk/mcp"
 
@@ -44,6 +45,25 @@ type activityOutput struct {
 	Events []activity.Event `json:"events" jsonschema:"recent activity events, oldest first"`
 }
 
+// pendingSwitchOutput reports whether the user has asked Claude to switch projects.
+type pendingSwitchOutput struct {
+	Pending     bool      `json:"pending" jsonschema:"true if the user has requested a switch you should complete"`
+	Target      string    `json:"target,omitempty" jsonschema:"the repository path to switch to"`
+	Note        string    `json:"note,omitempty" jsonschema:"an optional note from the user"`
+	RequestedAt time.Time `json:"requestedAt,omitempty"`
+}
+
+// ackSwitchInput is the argument schema for ack_switch.
+type ackSwitchInput struct {
+	Summary string `json:"summary" jsonschema:"a short note on where you left the previous project (shown to the user)"`
+}
+
+// ackSwitchOutput reports the completed switch.
+type ackSwitchOutput struct {
+	Switched bool   `json:"switched"`
+	Target   string `json:"target,omitempty" jsonschema:"the repository now active"`
+}
+
 // NewServer builds the MCP server and registers the (currently read-only) tools.
 func NewServer(svc *service.Service, version string) *mcpsdk.Server {
 	s := mcpsdk.NewServer(&mcpsdk.Implementation{
@@ -100,6 +120,30 @@ func NewServer(svc *service.Service, version string) *mcpsdk.Server {
 		return nil, activityOutput{Events: svc.Activity(50)}, nil
 	})
 
+	// get_pending_switch — has the user asked you to switch projects? (§8.3)
+	mcpsdk.AddTool(s, &mcpsdk.Tool{
+		Name:        "get_pending_switch",
+		Description: "Check whether the user has asked you to switch to a different project. If pending is true, finish your current work to a SAFE stopping point (commit or stash so nothing is lost), then call ack_switch to complete the handoff.",
+	}, func(_ context.Context, _ *mcpsdk.CallToolRequest, _ struct{}) (*mcpsdk.CallToolResult, pendingSwitchOutput, error) {
+		p, ok := svc.PendingSwitch()
+		if !ok {
+			return nil, pendingSwitchOutput{Pending: false}, nil
+		}
+		return nil, pendingSwitchOutput{Pending: true, Target: p.Target, Note: p.Note, RequestedAt: p.RequestedAt}, nil
+	})
+
+	// ack_switch — complete a pending handoff and tell the user where you left off.
+	mcpsdk.AddTool(s, &mcpsdk.Tool{
+		Name:        "ack_switch",
+		Description: "Complete a pending project switch: makes the requested target the active project and clears the request. Call this only after reaching a safe stopping point in the current project. Pass a short summary of where you left it — the user is notified.",
+	}, func(_ context.Context, _ *mcpsdk.CallToolRequest, in ackSwitchInput) (*mcpsdk.CallToolResult, ackSwitchOutput, error) {
+		p, ok := svc.AckSwitch(in.Summary)
+		if !ok {
+			return nil, ackSwitchOutput{Switched: false}, fmt.Errorf("no pending switch to acknowledge")
+		}
+		return nil, ackSwitchOutput{Switched: true, Target: p.Target}, nil
+	})
+
 	return s
 }