refactor(token-meter): simplify singleton service (round 1)

packages/compact/compact-basic/tests/compact-loop-repro.spec.ts

@@ -62,9 +62,7 @@ async function harness(toolSteps: number): Promise<{ ctx: Context; compact: Repr
   await ctx.plugin(ToolRegistry)
   await ctx.plugin(AgentRegistry)
   await ctx.plugin(AgentLoop, { agents: [] })
-  await ctx.plugin(TokenMeterService, {
-    models: { mock: { contextWindow: 64, charsPerToken: 1_000 } },
-  })
+  await ctx.plugin(TokenMeterService, { contextWindow: 400 })
   ctx.llm.registerAdapter(['mock'], new StepwiseToolAdapter(toolSteps))
   ctx.tools.register(defineTool({
     name: 'work',
@@ -74,11 +72,12 @@ async function harness(toolSteps: number): Promise<{ ctx: Context; compact: Repr
       return [{ type: 'text', text: 'work result' }]
     },
   }))
-  // Tiny window so a couple of tool steps cross the threshold and compaction
-  // fires within the runaway turn.
+  // Small window so several tool steps cross the threshold and compaction
+  // fires within the runaway turn after enough history can shrink.
   const compact = new ReproCompactService(ctx, {
     auto: true,
-    models: { mock: { thresholdRatio: 0.5, retainTokens: 20 } },
+    thresholdRatio: 0.5,
+    retainTokens: 50,
     summarizationModel: '',
     maxTokens: 8192,
     compactionRetries: 1,