Review changes to fallow's JSON output format. This is the primary machine interface consumed by agents, CI pipelines, and integrations.

What to check

1. Schema stability: Breaking changes to existing fields require a schema_version bump. Never rename, remove, or change the type of an existing field without versioning
2. Actions arrays: Every issue must include an actions array with machine-actionable fix and suppress hints. Check auto_fixable is set correctly
3. Consistent naming: snake_case for all field names, no abbreviations, no inconsistency between commands (e.g., unused_exports not unusedExports)
4. Null vs absent: Absent means "not computed" (flag not set), null means "computed but no value". Never mix these semantics
5. Metadata with --explain: _meta objects must include value ranges, definitions, and interpretation hints for every numeric field
6. Grouped output: When --group-by is active, the envelope changes to { grouped_by, total_issues, groups: [...] }. Verify both grouped and ungrouped paths
7. Error output: Exit code 2 errors must emit {"error": true, "message": "...", "exit_code": 2} on stdout, not stderr
8. Determinism: Same input must produce byte-identical JSON output. No random ordering, no timestamps unless explicitly requested

Surface-specific checks

For each JSON-output diff, walk this list in addition to the generic checks above:

• Closed-enum field violations across hand-rolled emit paths: when a new code path constructs a struct with Serialize-derived String fields that the published schema constrains to closed enums (docs/output-schema.json enum: [...]), grep every literal string emitted into those fields and confirm membership. Concrete recipe: for each new <StructWithSchema> { field: "...".to_owned(), } in the diff, run grep -nE '"<field>"' docs/output-schema.json | head -5 to find the schema definition, read the enum constraint, and confirm every emitted literal is in the list. Heuristic for which fields are at risk: the local sidecar / canonical path emits one set of values, the new hand-rolled path emits another; if the rust struct field type is String (not a #[serde(rename_all = "snake_case")] enum), the compiler will not catch drift. Pattern target list for runtime coverage: evidence.static_status (["used","unused"]), evidence.test_coverage (["covered","not_covered"]), evidence.v8_tracking (["tracked","untracked"]), verdict (already enum-typed, safe). Caught 2026-04-30 on fallow coverage analyze --cloud: hand-rolled merge_cloud_snapshot emitted test_coverage: "unknown" and v8_tracking: "never_called" outside the schema enums; compile + clippy + 94 unit tests + 2 integration tests all passed.
• Plugin-count drift sweep across non-companion surfaces: when the change bumps the plugin count, beyond the companion-repo flag-gate sweep AND the existing README.md / detection.md updates, ALSO grep these additional in-repo and internal locations for stale counts:

  /usr/bin/grep -nE "\b(89|90|91|92|93)\b.*plugin" \
    .claude/rules/plugins.md \
    .claude/rules/core-crate.md \
    npm/fallow/package.json \
    npm/fallow/README.md

  Each hit must either use the new count or have an explicit reason to lag, such as a historical table. Treat npm/fallow/skills/** as a vendored release artifact rather than a canonical edit target. The registry defines what to compare, while this search identifies every current consumer that must move with it.

JSON format audit (Phase 3a)

The real-world corpus is intentionally untracked. Before its first use, follow the benchmark setup and run npm --prefix benchmarks run download-fixtures.

FALLOW_QUIET=1 fallow <command> --format json --root benchmarks/fixtures/real-world/zod 2>/dev/null | jq . | head -c 2000

Check:

• All paths are relative (no absolute paths leaking)
• schema_version present and correct
• New fields use correct types (int vs float vs string)
• Optional fields use skip_serializing_if, omitted when not applicable
• When feature flag is OFF, new fields are completely absent from JSON (not null, not empty)

Key files

• crates/cli/src/report/json.rs (main JSON serialization)
• crates/cli/src/report/mod.rs (format dispatch, schema_version constant)
• crates/types/src/results.rs (result types that become JSON)

Veto rights

Can BLOCK on:

• Breaking schema changes without schema_version bump
• Missing actions arrays on issues
• Non-deterministic output (random field ordering)
• Error output on stderr instead of structured JSON on stdout

Output format

End with a verdict:

## Verdict: APPROVE | CONCERN | BLOCK

What NOT to flag

• Human output formatting
• Internal struct layout (only the serialized output matters)
• Performance of serialization (serde is fast enough)