test(mcp): prove tracedecay_rename_symbol behavior

[ScriptedAlchemy]

Summary

• Prove tracedecay_rename_symbol through the production MCP tool dispatch, not a mock planner.
• Lock the dry-run plan, the bytes an apply writes, an idempotent replay, and the typed denials to literal expected values.

Motivation

A rename test that only checks contains or success != true still passes when the tool returns an empty payload or leaves the tree untouched. These tests call tracedecay_rename_symbol the way a host does and compare the observed source and stable response fields to literals.

Identity digests, receipt timestamps, and occurrence ids are omitted from the comparison because they change with each fixture commit. The source file, the preview diff, the site spans, and the denial hazards do not.

Changes

• crates/tracedecay/tests/mcp_suite/mcp_handler_test/rename_symbol_test.rs

Test plan

• REQUIRE_EXACT_TEST_COUNT=3 scripts/require-exact-test.sh cargo test -p tracedecay --test mcp_suite --features test-transport rename_symbol_literal -- --test-threads=1
• Confirm the summary is 3 passed; 0 failed, not a vacuous filter match
• No production code changes

Checklist

• No secrets, credentials, or .env files included
• CHANGELOG.md updated — not required for a test-only change
• Breaking changes documented — none

  

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[ScriptedAlchemy]

Closing as superseded. A sibling change proving the same tool landed first as #1679.

Evidence from the triage: git log origin/master -- mcp_handler_test/rename_symbol_test.rs shows 9776017 landed via 3062799 'merge: PR #1679 test(mcp): prove tracedecay_rename_symbol behavior'; master's file already has test_rename_symbol_dry_run_default_reports_plan_and_writes_nothing and _apply_rewrites_declaration_and_callers

Reopen if the landed version misses an assertion this branch carries; name it and it can be ported as a small follow-up.