diff --git a/test/ai-prompts.test.ts b/test/ai-prompts.test.ts
index 60f43d7a..71163662 100644
--- a/test/ai-prompts.test.ts
+++ b/test/ai-prompts.test.ts
@@ -23,4 +23,67 @@ describe("weeklyProductivityPrompt", () => {
     expect(prompt).toContain("Activity trend: +15% vs prior period");
     expect(prompt).toContain("Write a warm, concise 3-sentence weekly summary.");
   });
+
+  it("handles zero values correctly", () => {
+    const prompt = weeklyProductivityPrompt({
+      activeDays: 0,
+      currentStreak: 0,
+      totalCommits: 0,
+      prsMerged: 0,
+      prsOpen: 0,
+      avgMergeTimeDays: 0,
+      topRepoName: "none",
+      trendLabel: "0%",
+    });
+
+    expect(prompt).toContain("Active coding days: 0");
+    expect(prompt).toContain("Total commits (90d): 0");
+    expect(prompt).toContain("PRs merged: 0, open: 0");
+  });
+
+  it("handles large numbers correctly", () => {
+    const prompt = weeklyProductivityPrompt({
+      activeDays: 30,
+      currentStreak: 365,
+      totalCommits: 99999,
+      prsMerged: 500,
+      prsOpen: 50,
+      avgMergeTimeDays: 0.5,
+      topRepoName: "massive-repo",
+      trendLabel: "+999%",
+    });
+
+    expect(prompt).toContain("Total commits (90d): 99999");
+    expect(prompt).toContain("PRs merged: 500");
+  });
+
+  it("handles negative streak values", () => {
+    const prompt = weeklyProductivityPrompt({
+      activeDays: 2,
+      currentStreak: -5,
+      totalCommits: 15,
+      prsMerged: 1,
+      prsOpen: 2,
+      avgMergeTimeDays: 1.0,
+      topRepoName: "test-repo",
+      trendLabel: "-10%",
+    });
+
+    expect(prompt).toContain("Current streak: -5 days");
+  });
+
+  it("handles empty string for topRepoName", () => {
+    const prompt = weeklyProductivityPrompt({
+      activeDays: 3,
+      currentStreak: 5,
+      totalCommits: 20,
+      prsMerged: 2,
+      prsOpen: 1,
+      avgMergeTimeDays: 1.5,
+      topRepoName: "",
+      trendLabel: "+5%",
+    });
+
+    expect(prompt).toContain("Top repository: ");
+  });
 });