test(mcp): owner refusal tests red since graph-tool problems always render as refusals

[ScriptedAlchemy]

Since 21552e3 ("fix(mcp): preserve parked route details", merged with #2293), settle_graph_tool_result returns every owner problem as an ApplicationRefusal. Owner-flattened argument errors used to come back as Err(TraceDecayError::Config); now they render as a problem tool result. Six mcp_suite tests that expect the error path fail on master:

cargo test -p tracedecay --features test-transport,test-helpers --test mcp_suite -- callers callees graph_query_test
test result: FAILED. 52 passed; 6 failed
mcp_handler_test::graph_analysis_test::diff_context_reports_changed_symbols_callers_and_refuses_invalid_input
mcp_handler_test::graph_query_test::test_grep_missing_pattern_errors
mcp_handler_test::graph_query_test::tracedecay_by_qualified_name_returns_the_symbol_at_that_exact_name
mcp_handler_test::graph_query_test::test_rank_invalid_direction
mcp_handler_test::graph_query_test::redundancy_reports_ranked_repository_exact_families_with_bounded_pages
mcp_handler_test::impact_behavior_test::impact_reports_callers_by_depth_and_refuses_invalid_requests

Example (tracedecay_by_qualified_name with a missing argument): the test expects JSON-RPC error -32603 tool execution failed: config error: invalid arguments for tracedecay_by_qualified_name: missing field qualified_name``. It now gets a successful result whose content is {"contract":{"schema_id":"schema.application.primitive.by-qualified-name.result",…},"problem":{…"code":"application.surface.invalid_request"…}}.

Either the tests move to the typed problem contract, or argument refusals keep their error path. Observed on a branch that only touches tracedecay-code-index-runtime, rebased on 5ad8106..f1d4e56.

[ScriptedAlchemy]

Already fixed on master by c26bf4e (#2319, "pin owner refusals as typed isError problems"): the tests moved to the typed problem contract via expect_tool_refusal, asserting kind, code and the literal argument message.

Re-verified at origin/master 061cd62:
cargo test -p tracedecay --features test-transport,test-helpers --test mcp_suite -- callers callees graph_query_test graph_analysis_test impact_behavior_test
→ test result: ok. 125 passed; 0 failed; 464 filtered out, including all six named tests (diff_context_reports_changed_symbols_callers_and_refuses_invalid_input, test_grep_missing_pattern_errors, tracedecay_by_qualified_name_returns_the_symbol_at_that_exact_name, test_rank_invalid_direction, redundancy_reports_ranked_repository_exact_families_with_bounded_pages, impact_reports_callers_by_depth_and_refuses_invalid_requests) reported ok.