diff --git a/docs/remote-workspace-local-latency-observer-plan.md b/docs/remote-workspace-local-latency-observer-plan.md
index 7b119f3a97..0a594caea8 100644
--- a/docs/remote-workspace-local-latency-observer-plan.md
+++ b/docs/remote-workspace-local-latency-observer-plan.md
@@ -388,7 +388,7 @@ Think of this as capability detection, not branch forking.
 
 ### Tests
 
-- [ ] Unit test: richer metrics adapter populates observer state when data exists.
+- [x] Unit test: richer metrics adapter populates observer state when data exists.
 - [x] Unit test: missing richer metrics are displayed as unavailable.
 
 Progress note:
diff --git a/src/test/latency-observer-streams.test.ts b/src/test/latency-observer-streams.test.ts
new file mode 100644
index 0000000000..da71577b6a
--- /dev/null
+++ b/src/test/latency-observer-streams.test.ts
@@ -0,0 +1,103 @@
+import type { State as ProtoState } from "@shared/proto/cline/state"
+import type { ClineMessage as ProtoClineMessage } from "@shared/proto/cline/ui"
+import { strict as assert } from "assert"
+import { describe, it } from "mocha"
+import { subscribeToState } from "@/core/controller/state/subscribeToState"
+import { registerPartialMessageCallback, sendPartialMessageEvent } from "@/core/controller/ui/subscribeToPartialMessage"
+import { getLatencyObserverService } from "@/services/latency/LatencyObserverService"
+import type { ExtensionState } from "@/shared/ExtensionMessage"
+
+describe("Latency observer state and partial-message adapters", () => {
+	it("records full-state observer metrics when state updates are emitted", async () => {
+		const observer = getLatencyObserverService()
+		observer.reset()
+		observer.markRequestStart("task-1", "task-1:req-1", 100)
+
+		const state = {
+			version: "test",
+			isNewUser: false,
+			welcomeViewCompleted: true,
+			onboardingModels: undefined,
+			autoApprovalSettings: { enabled: false, actions: {}, version: 1 },
+			browserSettings: {
+				viewport: undefined,
+				userAgent: undefined,
+				javaScriptEnabled: true,
+			},
+			mode: "act",
+			clineMessages: [],
+			currentTaskItem: {
+				id: "task-1",
+				ts: Date.now(),
+				task: "latency test",
+				tokensIn: 0,
+				tokensOut: 0,
+				totalCost: 0,
+			} as ExtensionState["currentTaskItem"],
+			mcpDisplayMode: "rich",
+			planActSeparateModelsSetting: false,
+			platform: "darwin",
+			shouldShowAnnouncement: false,
+			taskHistory: [],
+			telemetrySetting: "unset",
+			shellIntegrationTimeout: 4000,
+			terminalOutputLineLimit: 500,
+			maxConsecutiveMistakes: 3,
+			distinctId: "test",
+			globalClineRulesToggles: {},
+			localClineRulesToggles: {},
+			localWorkflowToggles: {},
+			globalWorkflowToggles: {},
+			localCursorRulesToggles: {},
+			localWindsurfRulesToggles: {},
+			localAgentsRulesToggles: {},
+			focusChainSettings: { enabled: false, remindClineInterval: 6 },
+			favoritedModelIds: [],
+			workspaceRoots: [],
+			primaryRootIndex: 0,
+			isMultiRootWorkspace: false,
+			multiRootSetting: { user: false, featureFlag: false },
+			lastDismissedInfoBannerVersion: 0,
+			lastDismissedModelBannerVersion: 0,
+			lastDismissedCliBannerVersion: 0,
+		} as unknown as ExtensionState
+
+		const sentStates: ProtoState[] = []
+		await subscribeToState({ getStateToPostToWebview: async () => state } as any, {} as any, async (message: ProtoState) => {
+			sentStates.push(message)
+		})
+
+		assert.equal(sentStates.length, 1)
+		const snapshot = observer.getSnapshot()
+		assert.equal(snapshot.capabilities.fullStateMetrics, "supported")
+		assert.equal(snapshot.capabilities.firstFullStateUpdate, "supported")
+		assert.equal(snapshot.optionalCounters?.fullStatePushes, 1)
+		assert.equal(snapshot.firstFullStateUpdate.stats.count, 1)
+	})
+
+	it("records partial-message observer metrics when partial events are emitted", async () => {
+		const observer = getLatencyObserverService()
+		observer.reset()
+
+		const received: ProtoClineMessage[] = []
+		const unregister = registerPartialMessageCallback((message) => {
+			received.push(message)
+		})
+
+		const partialMessage = {
+			ts: Date.now(),
+			type: "say",
+			say: "text",
+			text: "partial",
+		} as unknown as ProtoClineMessage
+
+		await sendPartialMessageEvent(partialMessage)
+		unregister()
+
+		assert.equal(received.length, 1)
+		const snapshot = observer.getSnapshot()
+		assert.equal(snapshot.capabilities.partialMessageMetrics, "supported")
+		assert.equal(snapshot.optionalCounters?.partialMessageEvents, 1)
+		assert.equal((snapshot.optionalCounters?.partialMessageBytes ?? 0) > 0, true)
+	})
+})