test(consolidation): add regression tests for tiktoken truncation path and history char cap

Cover two untested boundaries from #3412:
- _truncate_to_token_budget with positive budget exercises tiktoken
- _MAX_HISTORY_CHARS caps Recent History section in system prompt

Made-with: Cursor

tests/agent/test_context_prompt_cache.py

@@ -116,6 +116,20 @@ def test_recent_history_capped_at_max(tmp_path) -> None:
     assert f"entry-{builder._MAX_RECENT_HISTORY + 19}" in prompt
 
 
+def test_recent_history_truncated_at_max_chars(tmp_path) -> None:
+    """Recent History section must be truncated at _MAX_HISTORY_CHARS."""
+    workspace = _make_workspace(tmp_path)
+    builder = ContextBuilder(workspace)
+
+    big_entry = "x" * (builder._MAX_HISTORY_CHARS + 5_000)
+    builder.memory.append_history(big_entry)
+
+    prompt = builder.build_system_prompt()
+    history_section = prompt.split("# Recent History\n\n", 1)
+    assert len(history_section) == 2
+    assert len(history_section[1]) < builder._MAX_HISTORY_CHARS + 200
+
+
 def test_no_recent_history_when_dream_has_processed_all(tmp_path) -> None:
     """If Dream has consumed everything, no Recent History section should appear."""
     workspace = _make_workspace(tmp_path)