fix(cli): preserve media at snapshot end boundary (#2475)

* fix(cli): preserve media at snapshot end boundary

* test(cli): cover snapshot media boundary branches

packages/cli/src/commands/snapshot.test.ts

@@ -4,6 +4,7 @@ import {
   computeSnapshotTimes,
   parseZoomScale,
   requireSnapshotFfmpeg,
+  resolveSnapshotVideoFrameTime,
   tailFrameTime,
 } from "./snapshot.js";
 
@@ -36,6 +37,106 @@ describe("transparent snapshot capture", () => {
   });
 });
 
+describe("resolveSnapshotVideoFrameTime", () => {
+  it("keeps media active at the inclusive clip end and samples its last decodable frame", () => {
+    expect(
+      resolveSnapshotVideoFrameTime({
+        globalTime: 15,
+        clipStart: 0,
+        clipDuration: 15,
+        relativeTime: 15,
+        sourceDuration: 15,
+      }),
+    ).toBeCloseTo(15 - 1 / 30, 6);
+  });
+
+  it("keeps ordinary in-window media timestamps unchanged", () => {
+    expect(
+      resolveSnapshotVideoFrameTime({
+        globalTime: 7.5,
+        clipStart: 0,
+        clipDuration: 15,
+        relativeTime: 7.5,
+        sourceDuration: 15,
+      }),
+    ).toBe(7.5);
+  });
+
+  it("does not activate media after the clip end", () => {
+    expect(
+      resolveSnapshotVideoFrameTime({
+        globalTime: 15.001,
+        clipStart: 0,
+        clipDuration: 15,
+        relativeTime: 15.001,
+        sourceDuration: 15,
+      }),
+    ).toBeNull();
+  });
+
+  it.each([
+    {
+      name: "before clip start",
+      input: {
+        globalTime: 4.9,
+        clipStart: 5,
+        clipDuration: 10,
+        relativeTime: 0,
+        sourceDuration: 10,
+      },
+      expected: null,
+    },
+    {
+      name: "negative relative time",
+      input: {
+        globalTime: 5,
+        clipStart: 5,
+        clipDuration: 10,
+        relativeTime: -0.1,
+        sourceDuration: 10,
+      },
+      expected: null,
+    },
+    {
+      name: "unknown source duration",
+      input: {
+        globalTime: 15,
+        clipStart: 5,
+        clipDuration: 10,
+        relativeTime: 10,
+        sourceDuration: 0,
+      },
+      expected: 10 - 1 / 30,
+    },
+    {
+      name: "offset clip inclusive end",
+      input: {
+        globalTime: 15,
+        clipStart: 5,
+        clipDuration: 10,
+        relativeTime: 10,
+        sourceDuration: 10,
+      },
+      expected: 10 - 1 / 30,
+    },
+    {
+      name: "clip end within floating-point tolerance",
+      input: {
+        globalTime: 15 + 5e-10,
+        clipStart: 5,
+        clipDuration: 10,
+        relativeTime: 10,
+        sourceDuration: 10,
+      },
+      expected: 10 - 1 / 30,
+    },
+  ])("handles $name", ({ input, expected }) => {
+    const result = resolveSnapshotVideoFrameTime(input);
+    if (expected === null) expect(result).toBeNull();
+    else expect(result).toBeCloseTo(expected, 6);
+  });
+});
+
 describe("computeSnapshotTimes (FINDING [7]: tail is always captured)", () => {
   it("default frames: last point is the readable tail, never exact duration", () => {
     const { times, appendedTail } = computeSnapshotTimes(8, { frames: 5 });