Assessing impact

NO GUESSED TEST LISTS AND NO FULL-SUITE-BY-DEFAULT.
Compute the dependent set and the affected tests from the graph first.

Announce: "Using tracedecay:assessing-impact for ."

Blast radius

1. Have changed file paths already? → tracedecay_diff_context (files): modified symbols + dependents + affected tests in ONE offline call — prefer this over separate lookups. Works with no network and no PR.
2. Single symbol → resolve to node ID (tracedecay:exploring-code ladder), then tracedecay_impact (node_id, shallow max_depth first).
3. File-level fan-in → tracedecay_file_dependents.
4. Optional fragility check → tracedecay_coupling / tracedecay_dependency_depth.

Coverage intelligence (read-only)

Question	Call
Which tests reach this symbol/file	tracedecay_test_map (empty result = no indexed path, strong-not-absolute evidence of untested)
Which tests can see these changed files	tracedecay_affected (files)
Where the next test is most needed	tracedecay_test_risk (path?, limit?)
"What breaks if I change/touch this"	tracedecay_impact (node_id) for a symbol, tracedecay_affected (files) for changed files

Running the impacted tests

1. tracedecay_run_affected_tests (changed_paths, max_tests, profile, timeout_secs): pass/fail per test with covered source nodes. Cargo/Rust only — for other stacks use tracedecay_affected to get the test set, then the project's own runner on exactly that set.
2. Compile/type failures during the run → tracedecay:fixing-build-and-type-errors.

Rules

• Everything except run_affected_tests/diagnostics is read-only — preview scope freely before running toolchains; respect host approval/run-mode and avoid duplicate toolchain runs (first diagnostics build can take minutes).
• Coverage is structural: integration tests reaching code through binaries, fixtures, or IO can be missed. Say so when asserting "untested".
• Refactor checklist wanted → tracedecay:editing-safely. Whole-diff review → tracedecay:reviewing-changes.

If tools are deferred or MCP fails

• Deferred: one ToolSearch call — select:tracedecay_diff_context,tracedecay_impact,tracedecay_affected,tracedecay_test_map,tracedecay_run_affected_tests.
• MCP error: tracedecay tool diff_context --files … etc. (see tracedecay:using-the-cli). Do not degrade to running the full suite.

Deliverable

Do not end without all three: (a) impacted symbols + files, (b) the concrete test set (or pass/fail summary mapped back to source), (c) coverage gaps or hub risk worth flagging. If the graph cannot see part of the change (e.g. generated code), state that explicitly instead of widening to a full suite. Report any tracedecay_metrics: line.