fix(plugin): the session-start Goal line cuts at a word and says where the rest is (#4036)

A raw 200-char slice ended mid-word with nothing marking the cut, so a
reader took half a sentence for the whole goal. _goal_line flattens the
goal to one line, trims at a word break with an ellipsis, and points at
enter_project(id) when it cut.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/test_services_plugin_context.py

@@ -120,6 +120,32 @@ async def test_build_session_context_includes_project_when_scoped():
     assert "Reflex:" not in out["context"]
 
 
+def test_a_short_goal_is_shown_whole():
+    from scribe.services.plugin_context import _goal_line
+    assert _goal_line("ship it", 2) == "Goal: ship it"
+    assert _goal_line("", 2) == ""
+
+
+def test_a_long_goal_is_cut_at_a_word_and_says_where_the_rest_is():
+    """#4036: a raw slice ended mid-word with nothing marking the cut, so a
+    reader took half a sentence for the whole goal."""
+    from scribe.services.plugin_context import _GOAL_CHARS, _goal_line
+    goal = "make the record reach the next session\nso a solution is recalled " * 10
+    line = _goal_line(goal, 2)
+    shown = line.removeprefix("Goal: ").split(" (full goal:")[0]
+    assert shown.endswith("…") and len(shown) <= _GOAL_CHARS
+    # The cut lands between words: what precedes the ellipsis is a whole word.
+    assert shown[:-1].rstrip().split()[-1] in goal.split()
+    assert "\n" not in line
+    assert line.endswith("(full goal: `enter_project(2)`)")
+
+
+def test_an_unbroken_goal_still_shows_its_start():
+    from scribe.services.plugin_context import _GOAL_CHARS, _goal_line
+    shown = _goal_line("x" * 500, 2).removeprefix("Goal: ").split(" (full goal:")[0]
+    assert shown == "x" * (_GOAL_CHARS - 1) + "…"
+
+
 @pytest.mark.asyncio
 async def test_build_session_context_pushes_the_projects_design_system():
     """The gap this closes: a design system had no push channel, so its