feat(v1.8.0): 稳定性修复 + AI Agent 体验增强

稳定性修复:

- 修复 cache.py SQLite 连接泄漏（contextlib.closing 包装）

- 修复 fetch.py requests stream=True 连接泄漏（try/finally resp.close()）

- RETRYABLE_STATUS 新增 403，激活 UA fallback 切换逻辑

- --cache-stats 移至实例解析前，无需实例即可查询

- classify_error 从错误消息提取 HTTP 状态码，正确分类 E_AUTH/E_RATE_LIMIT

- --stream 与 --queries-file 互斥检查，违规报 E_INPUT

- batch 退出码语义统一（0=有结果 / 1=全部错误 / 2=全部空结果）

AI Agent 体验增强:

- 错误码体系完善：E_CONFIG/E_AUTH/E_NETWORK/E_RATE_LIMIT/E_PARSE/E_EMPTY/E_INPUT/E_INTERNAL

- recovery_hint 恢复提示字段，AI Agent 可程序化决策恢复策略

- stream 模式新增 error 事件类型（含 error_code + recovery_hint）

- 进度事件扩展：instance_try/instance_ok/instance_fail

- batch 模式统一 schema（status 字段区分 success/failed）

- JSON 输出含 schema_version 字段确保版本兼容

测试与文档:

- 测试覆盖：330 -> 352

- SKILL.md / README.md 同步更新

tests/test_cli_e2e.py

@@ -23,7 +23,7 @@ from types import SimpleNamespace
 
 import pytest
 
-from search import _run_single_query, _emit_error, _build_params
+from search import _run_single_query, _emit_error, _build_params, _format_results
 import cache as cache_module
 
 PROJECT_ROOT = Path(__file__).resolve().parent.parent
@@ -256,7 +256,7 @@ def test_cli_version_prints_version():
     """`--version` exits 0 and prints the version string."""
     r = _run_cli("--version")
     assert r.returncode == 0
-    assert "1.7.0" in r.stdout
+    assert "1.8.0" in r.stdout
     assert "searxng-cli" in r.stdout
 
 
@@ -294,3 +294,117 @@ def test_cli_cache_stats_outputs_json(tmp_path):
     data = json.loads(r.stdout)
     assert "entries" in data
     assert "path" in data
+
+
+# ===== --dump-schema (v1.8.0) =====
+
+def test_cli_dump_schema_outputs_valid_json():
+    """`--dump-schema` prints valid JSON with schema_version/title/properties.
+
+    The schema dump is a non-search operation: it exits 0 and does NOT
+    require --query or -i (it short-circuits before instance resolution).
+    """
+    r = _run_cli("--dump-schema")
+    assert r.returncode == 0
+    data = json.loads(r.stdout)
+    assert data["schema_version"] == "1.0"
+    assert data["title"] == "SearXNG CLI Search Result"
+    assert "properties" in data
+    assert isinstance(data["properties"], dict)
+
+
+def test_cli_dump_schema_does_not_require_query():
+    """`--dump-schema` exits 0 without --query (non-search operation)."""
+    r = _run_cli("--dump-schema")
+    assert r.returncode == 0
+    # The --query-required check must not fire for --dump-schema.
+    assert "required" not in r.stderr.lower()
+
+
+# ===== --stream mutual exclusion (v1.8.0) =====
+
+def test_cli_stream_with_queries_file_rejected(tmp_path):
+    """--stream + --queries-file is rejected with E_INPUT on stdout.
+
+    Batch mode emits a JSON array, not JSON Lines; the combination is
+    explicitly rejected so AI agents don't silently get the wrong format.
+    """
+    qf = tmp_path / "queries.txt"
+    qf.write_text("query\n", encoding="utf-8")
+    r = _run_cli("--stream", "--queries-file", str(qf),
+                 "--format", "json", "-i", "https://x.example.com")
+    assert r.returncode == 1
+    data = json.loads(r.stdout)
+    assert data["error_code"] == "E_INPUT"
+
+
+def test_cli_stream_with_csv_format_rejected():
+    """--stream + --format csv is rejected with E_INPUT.
+
+    csv is a non-json format, so _emit_error routes the error to stderr
+    (as a ``[E_INPUT]`` prefixed log line) rather than stdout JSON.
+    """
+    r = _run_cli("--stream", "--format", "csv", "-q", "test",
+                 "-i", "https://x.example.com")
+    assert r.returncode == 1
+    assert "E_INPUT" in r.stderr
+
+
+# ===== schema_version in single-query JSON (v1.8.0) =====
+
+def test_format_results_json_includes_schema_version():
+    """Single-query JSON output includes schema_version: '1.0'."""
+    results = {"results": [{"title": "T", "url": "https://example.com"}]}
+    args = SimpleNamespace(format="json")
+    out = _format_results(results, args)
+    parsed = json.loads(out)
+    assert parsed["schema_version"] == "1.0"
+
+
+# ===== _fallback field must not leak to JSON output (v1.8.0) =====
+
+def test_run_single_query_html_fallback_pops_underscore_fallback(monkeypatch):
+    """HTML-fallback's internal _fallback field is removed before output.
+
+    _run_single_query pops _fallback at the end so it never appears in
+    the JSON payload; fetched_source (the public field) is set separately
+    on the --fetch path.
+    """
+    args = _make_args(format="json")
+    fake = {"results": [{"url": "https://a.com/1", "title": "A"}],
+            "_fallback": "html"}
+    monkeypatch.setattr("search.search_multi", lambda *a, **kw: fake)
+
+    results, err, _ = _run_single_query("test", args,
+                                        ["https://x.example.com"], {}, 0)
+    assert err is None
+    # _fallback must be popped so it doesn't leak into JSON output
+    assert "_fallback" not in results
+    # And the serialized JSON also omits it
+    out = _format_results(results, args)
+    parsed = json.loads(out)
+    assert "_fallback" not in parsed
+
+
+def test_run_single_query_fetch_sets_fetched_source_from_html_fallback(monkeypatch):
+    """--fetch path sets fetched_source from _fallback (or 'json').
+
+    When the search came via HTML fallback (_fallback='html'), the
+    fetched_source field reflects that origin, while _fallback itself is
+    cleaned up and never reaches JSON output.
+    """
+    args = _make_args(fetch=1)
+    fake = {"results": [{"url": "https://a.com/1"}], "_fallback": "html"}
+    monkeypatch.setattr("search.search_multi", lambda *a, **kw: fake)
+    monkeypatch.setattr("search.fetch_top_results", lambda *a, **kw: [
+        {"url": "https://a.com/1", "status": "ok", "text": "page A",
+         "text_length": 6, "truncated": False},
+    ])
+
+    results, err, _ = _run_single_query("test", args,
+                                        ["https://x.example.com"], {}, 0)
+    assert err is None
+    # fetched_source reflects the HTML fallback origin
+    assert results["fetched_source"] == "html"
+    # _fallback still cleaned up
+    assert "_fallback" not in results