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(result as Record)\n : undefined;\n}\n\n/** A list request valid on either wire, for learning who owns what. */\nfunction discoveryRequest(\n req: Request,\n revision: SpecVersion,\n list: string\n): { original: Request; body: Buffer } {\n const original = {\n method: 'POST',\n url: '/',\n protocol: req.protocol,\n query: {},\n headers: {\n host: req.headers.host ?? 'localhost',\n 'content-type': 'application/json',\n accept: 'application/json, text/event-stream',\n 'mcp-protocol-version': revision,\n 'mcp-method': list\n }\n } as unknown as Request;\n const body = Buffer.from(\n JSON.stringify({\n jsonrpc: '2.0',\n id: 1,\n method: list,\n params: {\n _meta: {\n [META_PROTOCOL_VERSION]: revision,\n [META_CLIENT_CAPABILITIES]: {}\n }\n }\n })\n );\n return { original, body };\n}\n\nexport type CompositeHandler = (\n req: Request,\n res: Response,\n runId: string,\n revision: SpecVersion,\n names: string[],\n suffix: string\n) => Promise;\n\nexport function createCompositeRoute(deps: CompositeDeps): CompositeHandler {\n // Which child owns each tool, prompt and resource. Learned by asking fresh\n // throwaway instances, never the run's cells, so no child's log records a\n // request the client did not send. Per process: each isolate learns once.\n const owners = new Map>>();\n\n function invalid(\n revision: SpecVersion,\n names: string[]\n ): { status: number; error: string } | undefined {\n if (names.length < 2) {\n return {\n status: 404,\n error: `a composite joins two or more scenarios with '${COMPOSITE_SEPARATOR}'`\n };\n }\n for (const name of names) {\n if (!hostedScenarios.has(name)) {\n return { status: 404, error: `unknown scenario '${name}'` };\n }\n const reason = notComposableReason(name);\n if (reason) {\n return {\n status: 400,\n error: `'${name}' cannot share a URL: it ${reason}`\n };\n }\n const cell = deps.matrix.cell(name, revision);\n if (!cell || cell.scoring === 'n/a') {\n return {\n status: 404,\n error: `scenario '${name}' does not apply to ${revision}${cell?.reason ? `: ${cell.reason}` : ''}`\n };\n }\n if (!cell.startable) {\n return {\n status: 501,\n error: `scenario '${name}' at ${revision} cannot be started here: ${cell.startReason}`\n };\n }\n }\n return undefined;\n }\n\n function view(\n req: Request,\n runId: string,\n revision: SpecVersion,\n names: string[]\n ): CompositeView {\n const scenarioName = names.join(COMPOSITE_SEPARATOR);\n return {\n runId,\n revision,\n url: `${deps.cellBaseUrl(req, { runId, revision, scenarioName })}${MCP_PATH}`,\n resultsUrl: deps.resultsUrlFor(req, runId, revision),\n children: names.map((name) => {\n const cell = deps.matrix.cell(name, revision)!;\n return {\n scenario: name,\n description: hostedScenarios.meta(name)!.description,\n resultsUrl: deps.resultsUrlFor(req, runId, revision, name),\n ...(cell.steps && { steps: cell.steps })\n };\n })\n };\n }\n\n function ownersOf(\n req: Request,\n revision: SpecVersion,\n names: string[],\n list: string\n ): Promise> {\n const key = `${revision}/${names.join(COMPOSITE_SEPARATOR)}/${list}`;\n let found = owners.get(key);\n if (found) return found;\n found = (async () => {\n const results: ChildResult[] = [];\n for (const name of names) {\n const scenario = freshScenario(hostedScenarios.get(name)!);\n const url = deps.cellBaseUrl(req, {\n runId: 'owners',\n revision,\n scenarioName: name\n });\n const listener = scenario.handler?.(\n () => url,\n hostedScenarioContext(revision)\n );\n if (!listener) continue;\n const { original, body } = discoveryRequest(req, revision, list);\n const reply = await replay(original, body, (r, s) => {\n r.url = scenario.mcpPath || '/';\n listener(r, s);\n });\n results.push({ child: name, result: resultOf(reply, 1) });\n }\n const learned = new Map();\n for (const [item, child] of mergeList(list, results)?.owners ?? []) {\n learned.set(ownerKey(list, item), child);\n }\n return learned;\n })();\n owners.set(key, found);\n return found;\n }\n\n return async function handleComposite(\n req,\n res,\n runId,\n revision,\n names,\n suffix\n ) {\n const problem = invalid(revision, names);\n if (problem) {\n res.status(problem.status).json({ error: problem.error });\n return;\n }\n if (deps.isPageRequest(req)) {\n // A browser opening the MCP URL itself is sent to the page about it.\n if (suffix !== '') {\n const q = req.originalUrl.indexOf('?');\n const page = deps.cellBaseUrl(req, {\n runId,\n revision,\n scenarioName: names.join(COMPOSITE_SEPARATOR)\n });\n res.redirect(303, q === -1 ? page : page + req.originalUrl.slice(q));\n return;\n }\n const v = view(req, runId, revision, names);\n if (deps.wantsHtml(req)) {\n const { renderComposite } = await import('./html.ts');\n res.type('html').send(renderComposite(v));\n } else {\n res.json(v);\n }\n return;\n }\n\n await loadCells(names.map((scenarioName) => ({ scenarioName, revision })));\n const runs: HostedRun[] = [];\n for (const scenarioName of names) {\n const run = deps.mountCell(req, { runId, revision, scenarioName }, res);\n if (!run) return;\n runs.push(run);\n }\n // All children at once: a discover (merged below from every child's\n // answer) does not wait on the store, anything else waits one round\n // trip rather than one per child.\n await deps.prepare(runs, req, true);\n const pathOf = (run: HostedRun) => run.mcpPath || '/';\n const forward = (run: HostedRun) =>\n deps.dispatch(run, run.listener, req, res, pathOf(run), true);\n\n if (req.method !== 'POST') {\n forward(runs[0]);\n return;\n }\n\n const route = async (body: Buffer | undefined) => {\n const messages = body\n ? jsonRpcMessages(body.toString('utf8'), 'application/json')\n : [];\n // A batch goes to the first child whole.\n const message = messages.length === 1 ? messages[0] : undefined;\n const where = routeFor(message);\n if (where.kind === 'first') return forward(runs[0]);\n if (where.kind === 'addressed') {\n const owner = (await ownersOf(req, revision, names, where.list)).get(\n ownerKey(where.list, where.item)\n );\n return forward(\n runs.find((run) => run.scenarioName === owner) ?? runs[0]\n );\n }\n\n // Every child sees the request exactly as the client sent it.\n // Each copy keeps the connection the client sent it over, for the\n // cells' traffic.\n const conn = connectionOf(req);\n const replies = await Promise.all(\n runs.map((run) =>\n replay(req, body ?? 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