fix(mcp): test passes timeout_seconds and check_ignore to runners that reject them #1779

Description

The MCP test tool builds a command line from its arguments without checking which runner will receive it. Two arguments are accepted by the tool schema but rejected by one of the two runners, so the call fails with exit 64 before any test runs.

The cause is visible on main (8c772f3):

• _parseTest in lib/src/mcp/mcp_server.dart appends --check-ignore and --timeout unconditionally, whichever runner dart selects.
• --timeout is registered only on very_good test (lib/src/commands/test/test.dart).
• --check-ignore is registered only on very_good dart test (lib/src/commands/dart/commands/dart_test_command.dart).
• Neither the timeout_seconds nor the check_ignore schema description says it is runner-specific.

This bites agents twice: an agent told to "always set timeout_seconds" cannot test a pure Dart package, and an agent told to pass check_ignore cannot test a Flutter one. The plugin's green-gate skill currently instructs both (VeryGoodOpenSource/vgv-ai-flutter-plugin#178).

Steps To Reproduce

1. Call the MCP test tool on a pure Dart package with {"dart": true, "timeout_seconds": 60}.
2. Observe partial_failure / validation: Could not find an option named "--timeout".
3. Call the MCP test tool on a Flutter package with {"check_ignore": true}.
4. Observe partial_failure / validation: Could not find an option named "--check-ignore".

Expected Behavior

One of the following, in order of preference:

1. Each argument works on both runners: very_good dart test gains --timeout (ideally the wall-clock kill from fix(mcp): test timeout_seconds does not kill a hung test run, which blocks every later tool call #1765 / fix(mcp): enforce wall-clock timeout for test runs #1766) and very_good test gains --check-ignore.
2. Otherwise, the handler validates combinations before running and returns a validation failure that names the argument and the runner it applies to, and the schema descriptions say which runner each argument supports.

Additional Context

• Seen in field use in 3 of 310 calls (sessions 2007f494 on 2026-10-07 and 493ade61 on 2026-10-14). Transcript excerpts are available on request.

• very_good_cli 1.5.0, Dart 3.13.5, Flutter 3.47.6, macOS 26.5 arm64, Claude Code 2.1.302.

• Related: fix(mcp): test timeout_seconds does not kill a hung test run, which blocks every later tool call #1765 (timeout does not kill a hung run), feat(mcp): expose show_uncovered on the test tool #1705 (MCP surface narrower than the CLI).

• Tracking issue: fix: very-good-cli MCP field diagnostic (310 calls) — tracking issue vgv-ai-flutter-plugin#180