[ivanpaghubasan]

Summary

Adds AGCFG-013 (medium, 0.6, repo scope): a committed agent guidance file contains
zero-width characters, Unicode Tags-block characters (U+E0000..U+E007F) or
bidirectional controls. It runs the AGCFG-009 code-point test, with the same
exemptions, on guidance files AGCFG-009/010 do not read: CLAUDE.md, GEMINI.md,
.cursor/rules//.mdc, .windsurfrules, .windsurf/rules/.md, .devin/rules/*.md,
.github/copilot-instructions.md, .github/instructions//*.instructions.md.
Sheet ref: AGCFG-008 remainder (live AGCFG-008 is a different rule).

Changes

• New predicate repo_guidance_file_has_hidden_text; new component kinds
  gemini_md, cursor_rule, windsurf_rule, copilot_instruction, and
  ScanManifest.GuidanceFiles. CLAUDE.md keeps its existing claude_md kind.
• Schema 38 → 39 (provisional). Rules 385 → 386.
• Corpus fixture with a PROVENANCE row (contains real Tags-block bytes spelling
  "placeholder").
• CHANGELOG, ARCHITECTURE, COVERAGE and CLAUDE.md updated.

Not built

HTML-comment, instruction-phrase and base64 markers: no source supports them, and a
scan of 305 guidance files in 27 public repos found 109 benign HTML comments in 25
files. Claude Code strips block-level HTML comments from CLAUDE.md. .cursorrules is
not read.

Verification

• go build, go vet, go test ./... pass; check-rules-sync.sh in sync.
• Corpus before/after: 0 finding changes outside the new fixture; component-only
  changes are in the new fixture. The nine repo_component_present rules are unchanged.
• The origin/main binary skips AGCFG-013 with META-005.

Related

Rules: trustabl/agent-reliability-rules#209
Rulebook: trustabl/trustabl-rulebook#160
Merge order: engine, rules, rulebook; the rules PR waits for the rulebook PR.