tests: cover m2pack cli and mcp additions

Add discovery-helper tests (env var override, PATH fallback, missing
binary) and command tests that point M2PACK_BINARY at a Python stub
script echoing canned JSON per subcommand. Cover success paths,
non-zero exit, non-JSON output, JSON-array output, and missing binary.
Extend the MCP schema mirror test to cover all 12 tools and add
dispatch tests for the new m2pack_* argv translation.

tests/mcp/test_tool_schema.py

@@ -10,6 +10,10 @@ from metin_release.commands import (
     build_manifest,
     diff_remote,
     inspect,
+    m2pack_build,
+    m2pack_diff,
+    m2pack_export_runtime_key,
+    m2pack_verify,
     promote,
     publish,
     sign,
@@ -35,17 +39,21 @@ EXPECTED_TOOL_NAMES = {
     "release_promote",
     "release_verify_public",
     "release_publish",
+    "m2pack_build",
+    "m2pack_verify",
+    "m2pack_diff",
+    "m2pack_export_runtime_key",
 }
 
 
-def test_tool_catalogue_is_exactly_the_phase_one_set():
+def test_tool_catalogue_is_exactly_the_phase_one_plus_four_set():
     assert {t.name for t in TOOL_SPECS} == EXPECTED_TOOL_NAMES
-    assert len(TOOL_SPECS) == 8
+    assert len(TOOL_SPECS) == 12
 
 
-def test_every_tool_has_release_subcommand_and_description():
+def test_every_tool_has_known_group_and_description():
     for spec in TOOL_SPECS:
-        assert spec.subcommand[0] == "release"
+        assert spec.subcommand[0] in {"release", "m2pack"}
         assert spec.description.strip()
         schema = json_schema(spec)
         assert schema["type"] == "object"
@@ -82,6 +90,10 @@ _COMMAND_MODULES = {
     "release_promote": promote,
     "release_verify_public": verify_public,
     "release_publish": publish,
+    "m2pack_build": m2pack_build,
+    "m2pack_verify": m2pack_verify,
+    "m2pack_diff": m2pack_diff,
+    "m2pack_export_runtime_key": m2pack_export_runtime_key,
 }
 
 
@@ -121,7 +133,7 @@ def test_unknown_tool_rejected_by_dispatch():
 def test_unknown_tool_name_not_in_catalogue():
     assert "release_rollback" not in TOOLS_BY_NAME
     assert "erp_reserve" not in TOOLS_BY_NAME
-    assert "m2pack_build" not in TOOLS_BY_NAME
+    assert "launcher_publish" not in TOOLS_BY_NAME
 
 
 def test_build_cli_args_rejects_missing_required():