test(mcp): prove tracedecay_source_edit_rollback behavior

[ScriptedAlchemy]

Summary

• Prove tracedecay_source_edit_rollback through the production MCP source-edit server, not the catalog schema.
• A completed move_symbol restores the exact preimage bytes, deletes the file the move created, and replays the same effect id.
• Stale workspace bytes, confirm=false, a reused idempotency key, a non-move effect, and a mismatched input digest are refused and leave the files untouched.

Motivation

The existing catalog test only restates the rollback input schema. Callers need a behavior test that fails when the tool stops restoring retained preimages or starts accepting a stale workspace.

Changes

• crates/tracedecay/tests/mcp_suite/mcp_handler_test/source_edit_rollback_test.rs exercises the daemon-owned MCP dispatch and asserts literal file bytes and tool payloads.
• Registers that module on the test-transport MCP suite.

Test plan

• REQUIRE_EXACT_TEST_COUNT=3 scripts/require-exact-test.sh cargo test -p tracedecay --features test-transport --test mcp_suite source_edit_rollback_test
• cargo nextest run --workspace --no-fail-fast passes
• cargo clippy has no new warnings
• No production code changed; manual MCP host session is the suite above

Checklist

• CHANGELOG.md updated (under [Unreleased] if no version bump)
• No secrets, credentials, or .env files included
• Breaking changes documented (if any)

  

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[ScriptedAlchemy]

Closing as superseded. A sibling change proving the same tool landed first as #1686.

Evidence from the triage: git log origin/master --diff-filter=A -- mcp_handler_test/source_edit_rollback_test.rs => 5e300a6 on branch cursor/prove-source-edit-rollback-7cfc; gh pr list --state merged head:cursor/prove-source-edit-rollback-7cfc => 1686 'test(mcp): prove tracedecay_source_edit_rollback behavior'; same path added in both, 3 conflict hunks

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