diff --git a/canvas/src/lib/__tests__/runtime-names.test.ts b/canvas/src/lib/__tests__/runtime-names.test.ts
new file mode 100644
index 00000000..ed9fbe37
--- /dev/null
+++ b/canvas/src/lib/__tests__/runtime-names.test.ts
@@ -0,0 +1,48 @@
+/**
+ * Tests for `runtimeDisplayName` — the friendly-name lookup that
+ * surfaces the workspace runtime in the chat indicator, details
+ * tab, and a few component labels. Tiny but high-touch: every
+ * surface that shows "this workspace runs on X" goes through here.
+ *
+ * Issue: #1815 follow-up — `src/lib/runtime-names.ts` was at 0%
+ * coverage despite being read by 3+ rendering paths.
+ */
+import { describe, it, expect } from "vitest";
+import { runtimeDisplayName } from "../runtime-names";
+
+describe("runtimeDisplayName", () => {
+  it.each([
+    ["claude-code", "Claude Code"],
+    ["langgraph", "LangGraph"],
+    ["deepagents", "DeepAgents"],
+    ["openclaw", "OpenClaw"],
+    ["crewai", "CrewAI"],
+    ["autogen", "AutoGen"],
+  ])("known runtime %q maps to %q", (input, expected) => {
+    expect(runtimeDisplayName(input)).toBe(expected);
+  });
+
+  it("unknown runtime falls back to the input string verbatim", () => {
+    // A future runtime not yet in the lookup map should render with
+    // its own id — better than a generic placeholder for ops debugging.
+    expect(runtimeDisplayName("hermes")).toBe("hermes");
+    expect(runtimeDisplayName("custom-runtime-9000")).toBe(
+      "custom-runtime-9000",
+    );
+  });
+
+  it("empty string falls back to 'agent' (final default)", () => {
+    // Any code path that loses the runtime field still renders SOMETHING;
+    // the chat indicator never shows a blank label.
+    expect(runtimeDisplayName("")).toBe("agent");
+  });
+
+  it("is case-sensitive — uppercase variants miss the lookup", () => {
+    // The lookup keys are lowercase by convention. Pin the case
+    // sensitivity explicitly so a future refactor that lowercases
+    // the input "for safety" doesn't silently change behavior — the
+    // upstream slug is already normalized lowercase.
+    expect(runtimeDisplayName("Claude-Code")).toBe("Claude-Code");
+    expect(runtimeDisplayName("LANGGRAPH")).toBe("LANGGRAPH");
+  });
+});
diff --git a/canvas/src/lib/__tests__/utils.test.ts b/canvas/src/lib/__tests__/utils.test.ts
new file mode 100644
index 00000000..30402c2c
--- /dev/null
+++ b/canvas/src/lib/__tests__/utils.test.ts
@@ -0,0 +1,74 @@
+/**
+ * Tests for `cn` — the canvas's className-merging helper. Wraps
+ * `twMerge(clsx(inputs))` so callers can:
+ *   1. Combine class strings + arrays + objects (clsx),
+ *   2. Resolve Tailwind conflicts so the LAST value wins on the same
+ *      utility (twMerge — e.g. `cn("p-2", "p-4")` → "p-4").
+ *
+ * Tiny surface but load-bearing — every component that conditionally
+ * styles uses this. A regression that loses Tailwind-merge dedup would
+ * show as silent class duplication in the rendered DOM (cosmetic, but
+ * accumulates and breaks `:where()` rules + theme overrides).
+ *
+ * Issue: #1815 follow-up — `src/lib/utils.ts` was at 0% coverage.
+ */
+import { describe, it, expect } from "vitest";
+import { cn } from "../utils";
+
+describe("cn", () => {
+  it("returns a single class unchanged", () => {
+    expect(cn("text-red-500")).toBe("text-red-500");
+  });
+
+  it("joins multiple positional classes", () => {
+    expect(cn("text-red-500", "bg-zinc-900")).toBe("text-red-500 bg-zinc-900");
+  });
+
+  it("flattens array inputs (clsx-style)", () => {
+    expect(cn(["text-red-500", "bg-zinc-900"])).toBe(
+      "text-red-500 bg-zinc-900",
+    );
+  });
+
+  it("respects truthy / falsy conditional object syntax", () => {
+    expect(
+      cn({ "text-red-500": true, "text-blue-500": false, "bg-zinc-900": true }),
+    ).toBe("text-red-500 bg-zinc-900");
+  });
+
+  it("dedups conflicting Tailwind utilities — last wins", () => {
+    // The single load-bearing reason for twMerge over plain clsx —
+    // a regression here would silently double-apply padding tokens
+    // and confuse the visible style.
+    expect(cn("p-2", "p-4")).toBe("p-4");
+    expect(cn("text-red-500", "text-blue-500")).toBe("text-blue-500");
+  });
+
+  it("keeps non-conflicting Tailwind utilities", () => {
+    // Make sure the dedup is keyed on utility group, not blanket
+    // merge. p-2 and m-2 don't conflict; both must survive.
+    expect(cn("p-2", "m-4")).toBe("p-2 m-4");
+  });
+
+  it("handles a mix of all input shapes", () => {
+    expect(
+      cn(
+        "base-class",
+        ["array-class-1", "array-class-2"],
+        { "object-true": true, "object-false": false },
+        "trailing-class",
+      ),
+    ).toBe(
+      "base-class array-class-1 array-class-2 object-true trailing-class",
+    );
+  });
+
+  it("handles empty / nullish inputs without throwing", () => {
+    expect(cn()).toBe("");
+    expect(cn("")).toBe("");
+    expect(cn(null, undefined, false)).toBe("");
+    expect(cn("active", null, "highlighted", undefined)).toBe(
+      "active highlighted",
+    );
+  });
+});