feat(review): class-first skill review prompt (#16026)

The background skill-review prompt (spawned after N user turns) now instructs
the reviewer to SURVEY existing skills first, identify the CLASS of task, and
PREFER updating/generalizing an existing skill over creating a new narrow one.

This reduces near-duplicate skill accumulation at the source. Catches the
common failure mode where repeated tasks of the same class each spawn their
own specific skill ("fix-my-tauri-error", "fix-my-electron-error") instead
of a single class-level skill ("desktop-app-build-troubleshooting").

Applied to both _SKILL_REVIEW_PROMPT and the **Skills** half of
_COMBINED_REVIEW_PROMPT. Memory-only review prompt unchanged.

Groundwork for the Curator feature (issue #7816) — the creation-side fix.
Curator handles the retirement/consolidation side in a follow-up PR.

Tests assert the behavioral instructions are present (survey, class, update-
over-create, overlap-flagging, opt-out clause) rather than snapshotting the
full prompt text.

tests/run_agent/test_review_prompt_class_first.py

@@ -0,0 +1,78 @@
+"""Behavior tests for the class-first skill review prompts.
+
+The skill review / combined review prompts steer the background review agent
+toward generalizing existing skills rather than accumulating near-duplicates.
+These tests assert the behavioral *instructions* are present — they do NOT
+snapshot the full prompt text (change-detector).
+"""
+
+from run_agent import AIAgent
+
+
+def test_skill_review_prompt_instructs_survey_first():
+    """Prompt must tell the reviewer to list existing skills before deciding."""
+    prompt = AIAgent._SKILL_REVIEW_PROMPT
+    assert "skills_list" in prompt, "must instruct the reviewer to call skills_list"
+    assert "skill_view" in prompt, "must instruct the reviewer to skill_view candidates"
+    assert "SURVEY" in prompt, "must name the survey step explicitly"
+
+
+def test_skill_review_prompt_is_class_first():
+    """Prompt must steer toward the CLASS of task, not the specific task."""
+    prompt = AIAgent._SKILL_REVIEW_PROMPT
+    assert "CLASS" in prompt, "must tell the reviewer to think about the task class"
+    assert "class level" in prompt, "must anchor naming at the class level"
+
+
+def test_skill_review_prompt_prefers_updating_existing():
+    """Prompt must prefer generalizing an existing skill over creating a new one."""
+    prompt = AIAgent._SKILL_REVIEW_PROMPT
+    assert "PREFER GENERALIZING" in prompt or "PREFER UPDATING" in prompt, (
+        "must state the update-over-create preference"
+    )
+    assert "ONLY CREATE A NEW SKILL" in prompt, (
+        "must gate new-skill creation behind a last-resort clause"
+    )
+
+
+def test_skill_review_prompt_flags_overlap_for_followup():
+    """Prompt must ask the reviewer to note overlapping skills for future review."""
+    prompt = AIAgent._SKILL_REVIEW_PROMPT
+    assert "overlap" in prompt.lower(), "must mention the overlap-flagging protocol"
+
+
+def test_skill_review_prompt_preserves_opt_out_clause():
+    """The 'Nothing to save.' escape clause must remain."""
+    prompt = AIAgent._SKILL_REVIEW_PROMPT
+    assert "Nothing to save." in prompt
+
+
+def test_combined_review_prompt_keeps_memory_section():
+    """Combined prompt must still cover memory review."""
+    prompt = AIAgent._COMBINED_REVIEW_PROMPT
+    assert "**Memory**" in prompt
+    assert "memory tool" in prompt
+
+
+def test_combined_review_prompt_skills_section_is_class_first():
+    """The **Skills** half of the combined prompt must follow the same protocol."""
+    prompt = AIAgent._COMBINED_REVIEW_PROMPT
+    assert "**Skills**" in prompt
+    assert "SURVEY" in prompt
+    assert "CLASS" in prompt
+    assert "skills_list" in prompt
+    assert "ONLY CREATE A NEW SKILL" in prompt
+
+
+def test_combined_review_prompt_preserves_opt_out_clause():
+    prompt = AIAgent._COMBINED_REVIEW_PROMPT
+    assert "Nothing to save." in prompt
+
+
+def test_memory_review_prompt_unchanged_in_structure():
+    """Memory-only review prompt stays focused on user facts — not touched by this change."""
+    prompt = AIAgent._MEMORY_REVIEW_PROMPT
+    # Guardrails: the memory-only prompt must NOT mention skills/surveys.
+    assert "skills_list" not in prompt
+    assert "SURVEY" not in prompt
+    assert "memory tool" in prompt