Audited the codebase against docs/development/high-performance-go.md
and fixed the five highest-impact violations identified by scanning
internal/ and rules/.

1. rename: map[int]bool → map[int]struct{} (guideline: map[K]struct{}
   for sets). ValidRefDefBodyLines and contentBlockLines tracked
   presence-only with bool values; struct{} removes the 1-byte value
   overhead and makes the set semantics explicit. Updated callers in
   lsp/rename.go and rename_test.go.

2. export: map[int]bool → map[int]struct{} for stripLines/bodyLines
   (same guideline). stripDirectives, overlapsAny, and emitLines all
   operated on presence-only maps; changed all three sites.

3. secreview/render: fmt.Sprintf(":%d") → strconv.Itoa (guideline:
   strconv over fmt.Sprintf). strconv.Itoa is ~3× faster than
   fmt.Sprintf for integer formatting because it skips reflection and
   format-string parsing.

4. index/locate: eliminate string(lines[i]) per loop iteration in
   enclosingListKey (guideline: stay in []byte). FindSubmatch([]byte)
   replaces FindStringSubmatch(string(line)), removing one heap
   allocation per scanned line in the upward-scan loop. Only the
   matched key group is converted to string at the return point.

5. concisenessscoring: eliminate message += fmt.Sprintf pattern
   (guideline: strings.Builder over +). A single conditional
   fmt.Sprintf replaces the initial Sprintf followed by a
   string-concatenation assignment, removing one heap allocation per
   diagnostic when verbose cues are present.

All tests pass. mdsmith check . reports 0 failures.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015QYub2iGP6CeeEFSfjV3Wv

…rage

Three test improvements from code-review round 1:

- rule_test.go: replace vacuous assert.NotEmpty (which strings.Contains
  already implies non-empty) with a meaningful assert.Contains for "e.g.,"
  so the assertion can actually go red if the format string loses its
  example section

- rule_test.go: add TestCheck_NoCuesMessage to exercise the
  `if examples == ""` branch — verboseParagraph always produces cues so
  the base-message-only path was uncovered; fixes the Codecov patch check
  failure (40% → 100% on that branch)

- locate_test.go: rename TestEnclosingListKey_NoStringAllocPerLine to
  TestEnclosingListKey_FindsParentKey; the test only asserts the return
  value, not allocation behaviour, so the old name was misleading

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015QYub2iGP6CeeEFSfjV3Wv