diff --git a/tests/test_edge_sync_journal.py b/tests/test_edge_sync_journal.py
new file mode 100644
index 00000000..a0a7cfa2
--- /dev/null
+++ b/tests/test_edge_sync_journal.py
@@ -0,0 +1,135 @@
+from __future__ import annotations
+
+from core.sync.journal import JournalDirection, JournalStatus, LocalSyncJournal
+
+
+def test_append_upload_creates_pending_entry() -> None:
+    journal = LocalSyncJournal()
+    decision = journal.append_upload(
+        entry_id="u1",
+        artifact_id="trace-1",
+        artifact_type="trace",
+        target_uri="s3://bucket/traces/trace-1.jsonl.zst",
+    )
+
+    assert decision.accepted
+    assert decision.reason == "pending"
+    assert decision.entry is not None
+    assert decision.entry.direction is JournalDirection.UPLOAD
+    assert decision.entry.status is JournalStatus.PENDING
+    assert journal.pending() == (decision.entry,)
+
+
+def test_append_download_creates_pending_entry() -> None:
+    journal = LocalSyncJournal()
+    decision = journal.append_download(
+        entry_id="d1",
+        artifact_id="pack-v1",
+        artifact_type="pack_release",
+    )
+
+    assert decision.accepted
+    assert decision.entry is not None
+    assert decision.entry.direction is JournalDirection.DOWNLOAD
+    assert decision.entry.status is JournalStatus.PENDING
+
+
+def test_duplicate_entry_rejects_without_overwrite() -> None:
+    journal = LocalSyncJournal()
+    first = journal.append_upload(entry_id="u1", artifact_id="a1", artifact_type="trace")
+    second = journal.append_upload(entry_id="u1", artifact_id="a2", artifact_type="trace")
+
+    assert first.accepted
+    assert not second.accepted
+    assert second.reason == "duplicate_entry_id"
+    assert journal.get("u1").artifact_id == "a1"  # type: ignore[union-attr]
+
+
+def test_mark_completed_preserves_entry_metadata() -> None:
+    journal = LocalSyncJournal()
+    journal.append_upload(entry_id="u1", artifact_id="trace-1", artifact_type="trace")
+    decision = journal.mark_completed("u1")
+
+    assert decision.accepted
+    assert decision.reason == "completed"
+    assert decision.entry is not None
+    assert decision.entry.status is JournalStatus.COMPLETED
+    assert decision.entry.artifact_id == "trace-1"
+    assert journal.pending() == ()
+
+
+def test_mark_failed_preserves_reason_and_increments_attempts() -> None:
+    journal = LocalSyncJournal()
+    journal.append_upload(entry_id="u1", artifact_id="trace-1", artifact_type="trace")
+    failure = journal.mark_failed("u1", "object_store_unavailable")
+
+    assert failure.accepted
+    assert failure.entry is not None
+    assert failure.entry.status is JournalStatus.FAILED
+    assert failure.entry.reason == "object_store_unavailable"
+    assert failure.entry.attempts == 1
+
+
+def test_failed_upload_does_not_clear_journal_state() -> None:
+    journal = LocalSyncJournal()
+    journal.append_upload(entry_id="u1", artifact_id="trace-1", artifact_type="trace")
+    journal.mark_failed("u1", "timeout")
+
+    entry = journal.get("u1")
+    assert entry is not None
+    assert entry.artifact_id == "trace-1"
+    assert entry.status is JournalStatus.FAILED
+
+
+def test_retry_failed_entry_returns_to_pending_without_incrementing_attempts() -> None:
+    journal = LocalSyncJournal()
+    journal.append_upload(entry_id="u1", artifact_id="trace-1", artifact_type="trace")
+    journal.mark_failed("u1", "timeout")
+    retry = journal.retry("u1")
+
+    assert retry.accepted
+    assert retry.reason == "pending"
+    assert retry.entry is not None
+    assert retry.entry.status is JournalStatus.PENDING
+    assert retry.entry.attempts == 1
+    assert retry.entry.reason is None
+
+
+def test_rejected_download_can_be_retried() -> None:
+    journal = LocalSyncJournal()
+    journal.append_download(entry_id="d1", artifact_id="pack-v1", artifact_type="pack_release")
+    journal.mark_rejected("d1", "hash_mismatch")
+    retry = journal.retry("d1")
+
+    assert retry.accepted
+    assert retry.entry is not None
+    assert retry.entry.status is JournalStatus.PENDING
+    assert retry.entry.reason is None
+
+
+def test_unknown_entry_transition_rejects() -> None:
+    journal = LocalSyncJournal()
+    decision = journal.mark_completed("missing")
+
+    assert not decision.accepted
+    assert decision.reason == "unknown_entry"
+
+
+def test_journal_serializes_to_dicts() -> None:
+    journal = LocalSyncJournal()
+    journal.append_upload(entry_id="u1", artifact_id="trace-1", artifact_type="trace")
+    journal.mark_failed("u1", "timeout")
+
+    payload = journal.as_dicts()
+    assert payload == (
+        {
+            "entry_id": "u1",
+            "direction": "upload",
+            "artifact_id": "trace-1",
+            "artifact_type": "trace",
+            "status": "failed",
+            "target_uri": None,
+            "reason": "timeout",
+            "attempts": 1,
+        },
+    )