docs(workbench): re-measure the cost that justifies one non-isolated worker

The comment named `await import("deepagents")`, a package 0e53709 removed from
the dependencies, at a line number that had also drifted. A comment that
justifies a configuration is how that configuration stays open to question — this
one had stopped being checkable.

The cost survived the package, because it was never that factory: `runChat`
dynamically imports `./deep-agent/service`, and the graph underneath it costs
~1.25 s per worker, measured by timing the import inside a `.wb.ts`. About 0.38 s
of that is `langchain` itself. Seven of the nineteen `.wb.ts` files reach that
path, so isolating them would re-pay it six more times.

The two module-Map line numbers are corrected as well, and the guard is credited
to the harness rather than to `runScenario`.

Author: EtienneLescot

vitest.workbench.config.ts

@@ -24,16 +24,24 @@ export default defineConfig({
 		// wins and the run gets a TIMEOUT verdict instead of a dead worker.
 		testTimeout: DEFAULT_TURN_TIMEOUT_MS + 30_000,
 		reporters: ["default"],
-		// ponytail: the fixed cost of the suite is the dynamic
-		// `await import("deepagents")` in chat-service.ts:346 — hundreds of
-		// milliseconds, paid ONCE PER WORKER. One non-isolated thread makes the
-		// marginal cost of a new file its own runtime.
+		// ponytail: the fixed cost of the suite is `runChat`'s dynamic
+		// `await import("./deep-agent/service")` — measured at ~1.25 s, of which
+		// ~0.38 s is `langchain` itself and the rest is the agent graph, the tool
+		// schemas and the document model behind them. It is paid ONCE PER WORKER,
+		// and 7 of the 19 `.wb.ts` files reach that path, so isolating them would
+		// re-pay it six more times. One non-isolated thread makes the marginal
+		// cost of a new file its own runtime.
 		//
-		// The trade this accepts: `sessionsByProject` (chat-service.ts:36) and
-		// `messageCheckpointsBySession` (:48) are module Maps with no exported
-		// reset, so state now leaks between files. `runScenario` mints a unique
-		// projectId per run, which is what makes that safe — anything calling
-		// `runChat` directly would bypass the guard.
+		// (This used to name `deepagents`, which 0e53709a removed from the
+		// dependencies. The cost survived the package: it was never that factory,
+		// it was the graph underneath. Re-measure before trusting the figure —
+		// `await import(…)` timed inside a `.wb.ts` is enough.)
+		//
+		// The trade this accepts: `sessionsByProject` (chat-service.ts:38) and
+		// `messageCheckpointsBySession` (:50) are module Maps with no exported
+		// reset, so state leaks between files. The harness mints a unique
+		// projectId per run (`lib/harness.ts:239`), which is what makes that
+		// safe — anything calling `runChat` directly would bypass the guard.
 		pool: "threads",
 		maxWorkers: 1,
 		isolate: false,