Diff Procedure (Markdown Report + JSON Manifest)

Workflow

1. Load and normalize inputs

1. Parse CANDIDATE_JSON and locate lease_state, change_log, and traceability.
2. If change_log is missing, null, or empty, emit an empty diff report with reason no_change_log_entries.
3. Apply normalization rules from references/diff_rules.md before comparing values (trimmed strings, numeric epsilon, lexical date comparison).

2. Build chronological path timelines

1. Walk change_log in listed order only. Do not create a synthetic “state at date T” view.
2. For each field_path, initialize the timeline origin as the earliest observed old_value.
3. Append each change event as a transition containing:
   • from_value, to_value
   • effective_date
   • source_document
   • citation
   • impact_notes
4. Derive progression labels like OL -> A1 -> A2 using unique source documents encountered on that path.

3. Group for report readability

1. Group timelines by field_path prefix according to references/diff_rules.md.
2. Maintain stable output ordering:
   • Dates
   • Financial schedule inserts/changes
   • Financial scalar updates (for example TI allowance)
   • Remaining groups alphabetically
3. Within each group, sort paths by first appearance index in change_log.

4. Render markdown diff report

For each grouped section, emit a table with canonical columns from diff_rules.md:

• Field Path
• Progression
• Original
• Current
• Amendment Events
• Citation Pair(s)
• Notes

Display rules:

• Show null-to-value transitions explicitly (null -> 50000).
• Show type changes explicitly (string("60") -> number(60)).
• For object/array values, summarize compactly in markdown but keep full normalized values in manifest.

5. Reverse diff preview (optional)

If DRAFT_AMENDMENT is provided:

1. Flatten draft updates into dot/bracket paths.
2. For each draft path, compare against current lease_state value.
3. Emit overwrite_preview entries with:
   • field_path
   • current_value
   • draft_value
   • would_overwrite (true/false)
   • comparison_reason (equal_after_normalization, value_change, type_change, current_missing)
4. Do not mutate or merge into lease_state; preview only.

6. Emit JSON manifest

Emit one fenced json block with:

• schema_version
• change_entry_count
• groups
• field_timelines
• overwrite_preview (optional)
• warnings

Validation

Before emission, verify:

• Every change_log.field_path resolves in lease_state or is a valid append path for arrays.
• Earliest timeline value equals earliest old_value per path.
• Latest timeline value equals current lease_state value for that path.
• Every event with source_document also has citation (and vice versa).
• Grouping and column order match references/diff_rules.md.

Error Handling

• Malformed JSON: stop and return parser error.
• Missing change_log: return empty deliverable with warning missing_change_log.
• Unresolvable path: keep entry, mark path_resolution_warning, do not guess replacements.
• Null or ambiguous values: skip-don’t-guess; include canonical reason string skipped_ambiguous_or_null_input.

Prerequisites

• Upstream extraction should be conformance-checked with lease-eval when available.
• This skill depends on explicit change_log chronology and does not infer amendment deltas from prose.

Worked Example (fixture golden_ol_a1)

Expected grouped sections from 6 entries:

1. Dates (ExpirationDate, TermMonths)
2. Financials.BaseRent.Schedule[5]
3. Financials.BaseRent.Schedule[6]
4. Financials.TIAllowance (Amount + RatePerSF grouped together)

The TI allowance fields are presented as one section because they share the Financials.TIAllowance prefix and same amendment attribution.

Follow-on Work

• Optional HTML diff renderer for downstream portal embedding.
• Optional path alias map for friendlier labels without changing canonical manifest paths.