feat(plugin): add exportTimelineData() and getProjectItems() to ExtendScript

exportTimelineData() walks all video tracks in the active sequence and
returns clip source/timeline frame positions + file paths so the panel JS
can map them back to MAM asset IDs for timeline export.

getProjectItems() enumerates all ProjectItems with paths — useful for
rebuilding the import mapping after a Premiere restart.

services/premiere-plugin/jsx/premiere.jsx

@@ -309,6 +309,130 @@ function exportSequence(outputPath, presetPath) {
     }
 }
 
+// ============================================================================
+// Timeline Export — read sequence clips for MAM round-trip
+// ============================================================================
+
+/**
+ * Reads all clips from all video tracks in the active sequence.
+ * Returns JSON with sequence settings and a flat clip array.
+ *
+ * Each clip entry contains:
+ *   filePath          – absolute OS path to source media (for MAM asset ID lookup)
+ *   fileName          – project panel display name
+ *   trackIndex        – 0-based video track index (0 = V1, 1 = V2, …)
+ *   sourceInFrames    – in-point within source media, in frames
+ *   sourceOutFrames   – out-point within source media, in frames
+ *   timelineInFrames  – clip start position on timeline, in frames
+ *   timelineOutFrames – clip end position on timeline, in frames
+ *
+ * sequence.timebase is ticks-per-frame.  Premiere uses 254,016,000,000
+ * ticks/second, so fps = 254016000000 / timebase.
+ */
+function exportTimelineData() {
+    var result = {
+        success:      false,
+        message:      "",
+        sequenceName: "",
+        frameRate:    59.94,
+        width:        1920,
+        height:       1080,
+        clips:        []
+    };
+
+    try {
+        if (!app.project) {
+            result.message = "No active project";
+            return JSON.stringify(result);
+        }
+
+        var sequence = app.project.activeSequence;
+        if (!sequence) {
+            result.message = "No active sequence";
+            return JSON.stringify(result);
+        }
+
+        result.sequenceName = sequence.name;
+
+        var TICKS_PER_SECOND = 254016000000;
+        var timebaseTicks    = parseFloat(sequence.timebase) || 4240384;
+        result.frameRate     = parseFloat((TICKS_PER_SECOND / timebaseTicks).toFixed(4));
+
+        try { result.width  = sequence.frameSizeHorizontal || 1920; } catch (e) {}
+        try { result.height = sequence.frameSizeVertical   || 1080; } catch (e) {}
+
+        var videoTracks = sequence.videoTracks;
+        for (var t = 0; t < videoTracks.numTracks; t++) {
+            var track = videoTracks[t];
+            if (!track || !track.clips) continue;
+            var numClips = track.clips.numItems;
+            for (var c = 0; c < numClips; c++) {
+                try {
+                    var clip = track.clips[c];
+                    if (!clip || !clip.projectItem) continue;
+
+                    var filePath = "";
+                    try { filePath = clip.projectItem.getMediaPath(); } catch (e) {}
+
+                    var srcIn  = Math.round(parseFloat(clip.inPoint.ticks)  / timebaseTicks);
+                    var srcOut = Math.round(parseFloat(clip.outPoint.ticks) / timebaseTicks);
+                    var recIn  = Math.round(parseFloat(clip.start.ticks)    / timebaseTicks);
+                    var recOut = Math.round(parseFloat(clip.end.ticks)      / timebaseTicks);
+
+                    // Skip degenerate clips (zero or negative duration)
+                    if (srcOut <= srcIn || recOut <= recIn) continue;
+
+                    result.clips.push({
+                        trackIndex:        t,
+                        filePath:          filePath,
+                        fileName:          clip.projectItem.name || "",
+                        sourceInFrames:    srcIn,
+                        sourceOutFrames:   srcOut,
+                        timelineInFrames:  recIn,
+                        timelineOutFrames: recOut
+                    });
+                } catch (e) { /* skip malformed clip */ }
+            }
+        }
+
+        result.success = true;
+        result.message = result.clips.length + " clip(s) across " + videoTracks.numTracks + " track(s)";
+        return JSON.stringify(result);
+    } catch (error) {
+        result.message = "Error reading timeline: " + error.message;
+        return JSON.stringify(result);
+    }
+}
+
+/**
+ * Returns all media ProjectItems in the current project with name + file path.
+ * Useful for rebuilding the asset-path lookup map after a Premiere restart
+ * when temp-file paths may have changed.
+ */
+function getProjectItems() {
+    var result = { items: [] };
+    try {
+        if (!app.project) return JSON.stringify(result);
+        _collectProjectItems(app.project.rootItem, result.items);
+    } catch (e) {}
+    return JSON.stringify(result);
+}
+
+function _collectProjectItems(bin, out) {
+    if (!bin || !bin.children) return;
+    for (var i = 0; i < bin.children.numItems; i++) {
+        var item = bin.children[i];
+        if (!item) continue;
+        if (item.type === ProjectItemType.BIN) {
+            _collectProjectItems(item, out);
+        } else {
+            var path = "";
+            try { path = item.getMediaPath(); } catch (e) {}
+            out.push({ name: item.name, path: path });
+        }
+    }
+}
+
 // ============================================================================
 // Helper Functions
 // ============================================================================