fix(cli): don't run unbounded ffprobe on remote snapshot inputs

VP9-alpha detection (shouldUseVp9AlphaDecoder -> extractMediaMetadata)
spawns ffprobe with no timeout. For the new remote http(s) fallback that
ran before the bounded extractVideoFrameToBuffer, so a stalled remote host
could wedge `hyperframes snapshot` in ffprobe before the 30s extract timer
ever started. Probe only local files; for remote URLs skip it (pass false).
Local alpha behavior is unchanged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/cli/src/commands/snapshot.ts

@@ -361,6 +361,7 @@ async function captureSnapshots(
             // — FFmpeg reads http(s) input directly, and Chrome-headless can't seek
             // it either, so without this those videos render blank in snapshots.
             let ffmpegInput: string | null = null;
+            let inputIsLocal = false;
             try {
               const url = new URL(v.src);
               const decodedPath = decodeURIComponent(url.pathname).replace(/^\//, "");
@@ -368,6 +369,7 @@ async function captureSnapshots(
               const rel = relative(projectDir, candidate);
               if (!rel.startsWith("..") && !isAbsolute(rel) && existsSync(candidate)) {
                 ffmpegInput = candidate;
+                inputIsLocal = true;
               } else if (url.protocol === "http:" || url.protocol === "https:") {
                 ffmpegInput = url.href;
               }
@@ -375,10 +377,19 @@ async function captureSnapshots(
               /* unresolvable src (e.g. blob:, data:) — skip */
             }
             if (!ffmpegInput) continue;
+            // VP9-alpha detection shells out to ffprobe, which has no timeout.
+            // Only probe local files (filesystem-bounded); for remote URLs skip it
+            // (pass false) so a stalled host can't wedge snapshot in ffprobe before
+            // the bounded extractVideoFrameToBuffer below ever runs. Remote
+            // VP9-alpha overlays aren't a current path — revisit with a bounded
+            // ffprobe if one appears.
+            const useVp9AlphaDecoder = inputIsLocal
+              ? await shouldUseVp9AlphaDecoder(ffmpegInput)
+              : false;
             const png = await extractVideoFrameToBuffer(
               ffmpegInput,
               Math.max(0, v.relTime),
-              await shouldUseVp9AlphaDecoder(ffmpegInput),
+              useVp9AlphaDecoder,
             );
             if (!png) continue;
             updates.push({