test(mcp-server): selection requests, get_selection texts, and page screenshots that leave the view alone

Unit tests for the request plumbing (random id, one answer, timeout), the tool's texts (cells, nothing selected, external draw.io) and the shell's side (one answer per request, after draw.io is up, never during a projection); the wiring test starts a session with BROWSER=none to see the no-tab message. Shell e2e: cells selected in the editor reach get_selection; a PNG of another page differs from the page on screen, which stays.

packages/mcp-server/tests/http-server.test.ts

@@ -29,6 +29,7 @@ import {
     onStateChange,
     previewUrl,
     requestExport,
+    requestSelection,
     requestSync,
     restoreHistoryEntry,
     setDrawioDir,
@@ -37,6 +38,7 @@ import {
     shellConfig,
     shutdown,
     startHttpServer,
+    waitForSelection,
     waitForSync,
 } from "../src/http-server.ts"
 
@@ -424,6 +426,69 @@ describe("export requests", () => {
     })
 })
 
+describe("selection requests (get_selection)", () => {
+    const picked = {
+        pageId: "p1",
+        pageName: "Page-1",
+        cells: [{ id: "3", label: "Login", edge: false }],
+    }
+
+    it("shows the request to the page and takes its answer once", async () => {
+        const id = "mcp-selection"
+        setState(id, "<mxfile>x</mxfile>")
+        expect(requestSelection(id)).toBe(true)
+        const poll = JSON.parse(
+            (await request(`/api/state?sessionId=${id}`)).body,
+        )
+        expect(poll.selectionId).toMatch(/^[0-9a-f-]{36}$/)
+        // The request survives a write meanwhile
+        setState(id, "<mxfile>y</mxfile>")
+        const waiting = waitForSelection(id, 3000)
+        const answer = await postJson("/api/state", {
+            sessionId: id,
+            selectionId: poll.selectionId,
+            selection: picked,
+        })
+        expect(answer.status).toBe(200)
+        expect(await waiting).toEqual(picked)
+        // Taken: the next poll shows no request
+        const after = JSON.parse(
+            (await request(`/api/state?sessionId=${id}`)).body,
+        )
+        expect(after.selectionId).toBeNull()
+        expect(getState(id)?.xml).toBe("<mxfile>y</mxfile>")
+    })
+
+    it("ignores an answer to another request, and gives up in time", async () => {
+        const id = "mcp-selection-late"
+        setState(id, "<mxfile>x</mxfile>")
+        requestSelection(id)
+        const first = JSON.parse(
+            (await request(`/api/state?sessionId=${id}`)).body,
+        )
+        requestSelection(id)
+        await postJson("/api/state", {
+            sessionId: id,
+            selectionId: first.selectionId,
+            selection: picked,
+        })
+        expect(getState(id)?.selection).toBeUndefined()
+        expect(getState(id)?.selectionId).not.toBe(first.selectionId)
+        // A malformed answer is not taken either
+        const second = getState(id)?.selectionId
+        await postJson("/api/state", {
+            sessionId: id,
+            selectionId: second,
+            selection: { cells: "3" },
+        })
+        expect(getState(id)?.selection).toBeUndefined()
+        expect(await waitForSelection(id, 250)).toBeNull()
+        // The request is withdrawn with the timeout
+        expect(getState(id)?.selectionId).toBeUndefined()
+        expect(requestSelection("mcp-unknown-session")).toBe(false)
+    })
+})
+
 describe("a session state recreated after it was lost", () => {
     const SAVED = `<mxfile><diagram id="p" name="P"><mxGraphModel><root><mxCell id="0"/><mxCell id="1" parent="0"/><mxCell id="saved" vertex="1" parent="1"/></root></mxGraphModel></diagram></mxfile>`
     const getJson = async (id: string) =>