diff --git a/app/lib/__tests__/aggregator.test.ts b/app/lib/__tests__/aggregator.test.ts
new file mode 100644
index 0000000..148c0f8
--- /dev/null
+++ b/app/lib/__tests__/aggregator.test.ts
@@ -0,0 +1,111 @@
+import { describe, it, expect } from "vitest"
+import { processActivities, getDaySummary } from "../aggregator"
+
+function makeActivity(source: string, hour: number, type = "event", extra: Record<string, any> = {}) {
+  const timestamp = new Date(`2026-03-15T${String(hour).padStart(2, "0")}:30:00Z`)
+  return { source, type, timestamp, ...extra }
+}
+
+function makeSpanningActivity(source: string, startHour: number, endHour: number) {
+  const timestamp = new Date(`2026-03-15T${String(startHour).padStart(2, "0")}:00:00Z`)
+  const endTime = new Date(`2026-03-15T${String(endHour).padStart(2, "0")}:00:00Z`)
+  return { source, type: "event", timestamp, endTime }
+}
+
+describe("processActivities", () => {
+  it("buckets a single activity into the correct hour", () => {
+    const activities = [makeActivity("calendar", 9)]
+    const result = processActivities(activities, 6, 23, "UTC")
+    expect(result[9].primaries).toHaveLength(1)
+    expect(result[9].primaries[0].source).toBe("calendar")
+  })
+
+  it("drops activities outside work hours", () => {
+    const activities = [makeActivity("calendar", 5), makeActivity("calendar", 23)]
+    const result = processActivities(activities, 6, 23, "UTC")
+    // Neither hour 5 nor hour 23 should have activities
+    expect(result[6]?.primaries).toHaveLength(0)
+    expect(result[22]?.primaries).toHaveLength(0)
+  })
+
+  it("separates calendar (primaries) from other sources (communications)", () => {
+    const activities = [
+      makeActivity("calendar", 10),
+      makeActivity("slack", 10),
+      makeActivity("gmail", 10),
+    ]
+    const result = processActivities(activities, 6, 23, "UTC")
+    expect(result[10].primaries).toHaveLength(1)
+    expect(result[10].communications).toHaveLength(2)
+  })
+
+  it("spans calendar events across multiple hours", () => {
+    const activities = [makeSpanningActivity("calendar", 9, 11)]
+    const result = processActivities(activities, 6, 23, "UTC")
+    expect(result[9].primaries).toHaveLength(1)
+    expect(result[10].primaries).toHaveLength(1)
+    // The original event starts at 9, so hour 10 should be a spanning entry
+    expect(result[10].primaries[0].isSpanning).toBe(true)
+  })
+
+  it("creates empty buckets for all work hours", () => {
+    const result = processActivities([], 6, 23, "UTC")
+    for (let h = 6; h < 23; h++) {
+      expect(result[h]).toBeDefined()
+      expect(result[h].primaries).toHaveLength(0)
+      expect(result[h].communications).toHaveLength(0)
+    }
+  })
+
+  it("deduplicates emails by normalized subject", () => {
+    const activities = [
+      makeActivity("gmail", 10, "email", { subject: "Re: Project update", from: "alice@example.com" }),
+      makeActivity("gmail", 10, "email", { subject: "Sv: Project update", from: "bob@example.com" }),
+    ]
+    const result = processActivities(activities, 6, 23, "UTC")
+    // Both emails normalize to "project update", so only one should remain
+    expect(result[10].communications).toHaveLength(1)
+  })
+
+  it("filters calendar notification emails", () => {
+    const activities = [
+      makeActivity("gmail", 10, "email", { subject: "Meeting invite", from: "calendar-notification@google.com" }),
+      makeActivity("gmail", 10, "email", { subject: "Real email", from: "colleague@example.com" }),
+    ]
+    const result = processActivities(activities, 6, 23, "UTC")
+    expect(result[10].communications).toHaveLength(1)
+    expect(result[10].communications[0].subject).toBe("Real email")
+  })
+})
+
+describe("getDaySummary", () => {
+  it("counts activities by source", () => {
+    const activities = [
+      makeActivity("calendar", 9),
+      makeActivity("calendar", 10),
+      makeActivity("slack", 9),
+      makeActivity("gmail", 9, "email", { subject: "Hello", from: "user@example.com" }),
+      makeActivity("docs", 11),
+      makeActivity("trello", 11),
+      makeActivity("github", 12),
+      makeActivity("jira", 12),
+    ]
+    const hourly = processActivities(activities, 6, 23, "UTC")
+    const summary = getDaySummary(hourly)
+    expect(summary.totalMeetings).toBe(2)
+    expect(summary.totalSlackMessages).toBe(1)
+    expect(summary.totalEmails).toBe(1)
+    expect(summary.totalDocEdits).toBe(1)
+    expect(summary.totalTrelloActivities).toBe(1)
+    expect(summary.totalGitHubActivities).toBe(1)
+    expect(summary.totalJiraActivities).toBe(1)
+  })
+
+  it("returns zero counts for an empty day", () => {
+    const hourly = processActivities([], 6, 23, "UTC")
+    const summary = getDaySummary(hourly)
+    expect(summary.totalMeetings).toBe(0)
+    expect(summary.totalSlackMessages).toBe(0)
+    expect(summary.totalEmails).toBe(0)
+  })
+})
diff --git a/app/lib/ai/__tests__/parse.test.ts b/app/lib/ai/__tests__/parse.test.ts
new file mode 100644
index 0000000..b3ef08e
--- /dev/null
+++ b/app/lib/ai/__tests__/parse.test.ts
@@ -0,0 +1,104 @@
+import { describe, it, expect } from "vitest"
+import { parseSuggestions } from "../parse"
+
+describe("parseSuggestions", () => {
+  it("parses a valid JSON array", () => {
+    const input = JSON.stringify([
+      {
+        projectId: "123",
+        activityTypeId: "456",
+        hours: 2,
+        description: "Worked on feature X",
+        confidence: "high",
+        sourceActivities: [
+          { source: "calendar", title: "Planning meeting", timestamp: "2026-03-15T09:00:00Z" },
+        ],
+      },
+    ])
+    const result = parseSuggestions(input)
+    expect(result).toHaveLength(1)
+    expect(result[0].projectId).toBe("123")
+    expect(result[0].activityTypeId).toBe("456")
+    expect(result[0].hours).toBe(2)
+    expect(result[0].description).toBe("Worked on feature X")
+    expect(result[0].confidence).toBe("high")
+    expect(result[0].status).toBe("pending")
+    expect(result[0].sourceActivities).toHaveLength(1)
+  })
+
+  it("extracts JSON array from markdown-wrapped response", () => {
+    const input = "Here are the suggestions:\n```json\n" + JSON.stringify([
+      { projectId: "1", activityTypeId: "2", hours: 1, description: "Test" },
+    ]) + "\n```"
+    const result = parseSuggestions(input)
+    expect(result).toHaveLength(1)
+    expect(result[0].projectId).toBe("1")
+  })
+
+  it("rounds hours to nearest 0.5, minimum 0.5", () => {
+    const input = JSON.stringify([
+      { projectId: "1", activityTypeId: "2", hours: 0.3, description: "Short task" },
+      { projectId: "1", activityTypeId: "2", hours: 1.7, description: "Medium task" },
+      { projectId: "1", activityTypeId: "2", hours: 0.1, description: "Tiny task" },
+    ])
+    const result = parseSuggestions(input)
+    expect(result[0].hours).toBe(0.5) // 0.3 rounds to 0.5 (minimum)
+    expect(result[1].hours).toBe(1.5) // 1.7 rounds to 1.5
+    expect(result[2].hours).toBe(0.5) // 0.1 rounds to 0.5 (minimum)
+  })
+
+  it("defaults confidence to medium for invalid values", () => {
+    const input = JSON.stringify([
+      { projectId: "1", activityTypeId: "2", hours: 1, description: "Test", confidence: "invalid" },
+      { projectId: "1", activityTypeId: "2", hours: 1, description: "Test" },
+    ])
+    const result = parseSuggestions(input)
+    expect(result[0].confidence).toBe("medium")
+    expect(result[1].confidence).toBe("medium")
+  })
+
+  it("handles truncated JSON response by salvaging complete objects", () => {
+    const complete = { projectId: "1", activityTypeId: "2", hours: 1, description: "First" }
+    const input = "[" + JSON.stringify(complete) + ",{\"projectId\":\"2\",\"activ"
+    const result = parseSuggestions(input)
+    expect(result).toHaveLength(1)
+    expect(result[0].projectId).toBe("1")
+  })
+
+  it("throws on completely unparseable input", () => {
+    expect(() => parseSuggestions("not json at all")).toThrow()
+  })
+
+  it("assigns unique IDs to each suggestion", () => {
+    const input = JSON.stringify([
+      { projectId: "1", activityTypeId: "2", hours: 1, description: "A" },
+      { projectId: "1", activityTypeId: "2", hours: 1, description: "B" },
+    ])
+    const result = parseSuggestions(input)
+    expect(result[0].id).toBeTruthy()
+    expect(result[1].id).toBeTruthy()
+    expect(result[0].id).not.toBe(result[1].id)
+  })
+
+  it("parses internalNote when present", () => {
+    const input = JSON.stringify([
+      {
+        projectId: "1",
+        activityTypeId: "2",
+        hours: 1,
+        description: "Client-facing text",
+        internalNote: "Technical context here",
+      },
+    ])
+    const result = parseSuggestions(input)
+    expect(result[0].internalNote).toBe("Technical context here")
+  })
+
+  it("handles empty sourceActivities gracefully", () => {
+    const input = JSON.stringify([
+      { projectId: "1", activityTypeId: "2", hours: 1, description: "Test", sourceActivities: null },
+    ])
+    const result = parseSuggestions(input)
+    expect(result[0].sourceActivities).toEqual([])
+  })
+})
diff --git a/app/lib/ai/__tests__/preprocess.test.ts b/app/lib/ai/__tests__/preprocess.test.ts
new file mode 100644
index 0000000..cb7b9c5
--- /dev/null
+++ b/app/lib/ai/__tests__/preprocess.test.ts
@@ -0,0 +1,119 @@
+import { describe, it, expect } from "vitest"
+import { preprocessActivities } from "../preprocess"
+
+function makeHourData(primaries: any[] = [], communications: any[] = []) {
+  return { primaries, communications }
+}
+
+function makeCalendarEvent(hour: number, durationMinutes: number, title = "Meeting") {
+  const timestamp = `2026-03-15T${String(hour).padStart(2, "0")}:00:00Z`
+  const endTime = new Date(new Date(timestamp).getTime() + durationMinutes * 60000).toISOString()
+  return { source: "calendar", type: "event", title, timestamp, endTime }
+}
+
+function makeSlackMessage(hour: number, channel: string, isDm = false) {
+  return {
+    source: "slack",
+    type: "message",
+    channel,
+    isDm,
+    timestamp: `2026-03-15T${String(hour).padStart(2, "0")}:15:00Z`,
+  }
+}
+
+function makeGmailActivity(hour: number, subject: string, from = "user@example.com") {
+  return {
+    source: "gmail",
+    type: "email",
+    subject,
+    from,
+    timestamp: `2026-03-15T${String(hour).padStart(2, "0")}:20:00Z`,
+  }
+}
+
+describe("preprocessActivities", () => {
+  it("flattens activities from hour buckets into a sorted list", () => {
+    const hours = {
+      "9": makeHourData([makeCalendarEvent(9, 60)], [makeSlackMessage(9, "general")]),
+      "10": makeHourData([], [makeSlackMessage(10, "dev")]),
+    }
+    const result = preprocessActivities(hours)
+    expect(result.activities).toHaveLength(3)
+    // Should be sorted by timestamp
+    expect(result.activities[0].source).toBe("calendar")
+    expect(result.activities[1].source).toBe("slack")
+    expect(result.activities[2].source).toBe("slack")
+  })
+
+  it("calculates calendar minutes from events with duration", () => {
+    const hours = {
+      "9": makeHourData([makeCalendarEvent(9, 60)]),
+      "10": makeHourData([makeCalendarEvent(10, 30)]),
+    }
+    const result = preprocessActivities(hours)
+    expect(result.calendarMinutes).toBe(90)
+  })
+
+  it("skips spanning entries to avoid double-counting", () => {
+    const event = makeCalendarEvent(9, 120)
+    const hours = {
+      "9": makeHourData([{ ...event, isSpanning: false, spanStart: true }]),
+      "10": makeHourData([{ ...event, isSpanning: true }]),
+    }
+    const result = preprocessActivities(hours)
+    // Only the non-spanning entry should be counted
+    expect(result.activities).toHaveLength(1)
+  })
+
+  it("filters out calendar invite emails", () => {
+    const hours = {
+      "9": makeHourData([], [
+        makeGmailActivity(9, "Meeting invite from John"),
+        makeGmailActivity(9, "Real email about project"),
+      ]),
+    }
+    const result = preprocessActivities(hours)
+    expect(result.activities).toHaveLength(1)
+    expect(result.activities[0].title).toContain("Real email")
+  })
+
+  it("generates correct titles for different sources", () => {
+    const hours = {
+      "9": makeHourData(
+        [makeCalendarEvent(9, 30, "Sprint Planning")],
+        [
+          makeSlackMessage(9, "general"),
+          makeSlackMessage(9, "Alice", true),
+          { source: "docs", type: "Edited", title: "Design Doc", timestamp: "2026-03-15T09:30:00Z" },
+          { source: "github", repoName: "my-repo", title: "Fix bug #123", timestamp: "2026-03-15T09:35:00Z" },
+          { source: "jira", issueKey: "PROJ-42", issueSummary: "Implement login", timestamp: "2026-03-15T09:40:00Z" },
+        ]
+      ),
+    }
+    const result = preprocessActivities(hours)
+    const titles = result.activities.map((a) => a.title)
+    expect(titles).toContain("Sprint Planning")
+    expect(titles).toContain("#general")
+    expect(titles).toContain("DM: Alice")
+    expect(titles).toContain("Edited: Design Doc")
+    expect(titles.find((t) => t.includes("my-repo"))).toBeTruthy()
+    expect(titles.find((t) => t.includes("PROJ-42"))).toBeTruthy()
+  })
+
+  it("deduplicates activities by source+timestamp+title key", () => {
+    const slack = makeSlackMessage(9, "general")
+    const hours = {
+      "9": makeHourData([], [slack, slack]),
+    }
+    const result = preprocessActivities(hours)
+    expect(result.activities).toHaveLength(1)
+  })
+
+  it("returns zero values for empty input", () => {
+    const result = preprocessActivities({})
+    expect(result.activities).toHaveLength(0)
+    expect(result.calendarMinutes).toBe(0)
+    expect(result.gapMinutes).toBe(0)
+    expect(result.totalActiveMinutes).toBe(0)
+  })
+})
diff --git a/vitest.config.ts b/vitest.config.ts
new file mode 100644
index 0000000..241bfac
--- /dev/null
+++ b/vitest.config.ts
@@ -0,0 +1,13 @@
+import { defineConfig } from "vitest/config"
+import path from "path"
+
+export default defineConfig({
+  resolve: {
+    alias: {
+      "@": path.resolve(__dirname, "."),
+    },
+  },
+  test: {
+    environment: "node",
+  },
+})