docs(pdftract-2qw5j): add verification note for schema generation

Verified that the JSON schema generation system is fully implemented:
- xtask gen-schema produces valid JSON Schema Draft 2020-12
- Committed schema matches generated output (no diffs)
- CI gate enforces schema sync (quality-matrix/schema-gen template)
- All required enum values present (page_type with broken_vector, confidence_source, severity)
- Schema metadata correct ($id, $schema, title, description)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

notes/pdftract-2qw5j.md

@@ -0,0 +1,124 @@
+# Verification Note: pdftract-2qw5j (JSON Schema Generation)
+
+## Task Summary
+Generate docs/schema/v1.0/pdftract.schema.json via xtask + schema gen CI gate
+
+## Date
+2026-05-28
+
+## Implementation Status: COMPLETE
+
+All components of the JSON schema generation system are implemented and working correctly.
+
+## Verification Results
+
+### PASS Criteria
+
+1. **xtask gen-schema produces valid JSON Schema** ✅
+   - Binary: `xtask/src/bin/gen_schema.rs`
+   - Command: `cargo run --manifest-path=xtask/Cargo.toml --bin gen_schema`
+   - Output: `docs/schema/v1.0/pdftract.schema.json` (59,273 bytes)
+   - Schema is valid JSON Schema Draft 2020-12
+
+2. **Committed file matches generated output** ✅
+   - Running gen-schema produces byte-identical output to committed file
+   - No diffs detected: `git diff --exit-code docs/schema/v1.0/pdftract.schema.json`
+   - Stable sorting via `sort_keys_recursive()` function
+
+3. **Schema includes required metadata** ✅
+   - `$id`: "https://pdftract.com/schema/v1.0/pdftract.schema.json"
+   - `$schema`: "https://json-schema.org/draft/2020-12/schema"
+   - `title`: "pdftract Output v1.0"
+   - `description`: Full description of extraction output structure
+
+4. **Schema includes Phase 7 placeholder objects** ✅
+   - Empty arrays for Phase 7 features: `threads`, `attachments`, `signatures`, `form_fields`, `links`, `annotations`
+   - All placeholder fields documented in schema descriptions
+
+5. **Enum properties documented** ✅
+   - `page_type` includes "broken_vector" (per 5.1 + 6.1 requirement)
+   - `confidence_source` field documented with allowed values
+   - `severity` field documented with allowed values
+
+6. **CI gate implemented** ✅
+   - Workflow: `.ci/argo-workflows/pdftract-ci.yaml`
+   - Template: `schema-gen` (lines 1851-1940)
+   - Enforcement: Regenerates schema, fails build on any diff
+   - Error message includes reproduction command
+
+## Schema Coverage
+
+The generated schema includes complete definitions for:
+
+### Document-level
+- `Output` (root object)
+- `DocumentMetadata`
+- `ExtractionQuality`
+- `OutlineNode` (bookmarks)
+- `ThreadJson` (article threads)
+- `AttachmentJson` (embedded files)
+- `SignatureJson` (digital signatures)
+- `FormFieldJson` (form fields)
+- `LinkJson` (hyperlinks)
+- `JavascriptActionJson` (JS actions)
+
+### Page-level
+- `PageJson`
+- `SpanJson` (text spans)
+- `BlockJson` (structural blocks)
+- `TableJson`, `RowJson`, `CellJson` (tables)
+- `AnnotationJson` (annotations)
+
+### Diagnostics
+- `DiagnosticJson`
+- `ObjectLocationJson`
+
+## Technical Implementation
+
+### Rust Type Derives
+All relevant types have `#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]`:
+- `Output`, `PageJson`, `SpanJson`, `BlockJson`
+- `DiagnosticJson`, `AnnotationJson`, `FormFieldJson`
+- All supporting types
+
+### Stable Output
+- `sort_keys_recursive()` ensures deterministic key ordering
+- `BTreeMap` for all object keys
+- Pretty-printed with 2-space indentation
+
+### CI Integration
+The `schema-gen` template in pdftract-ci.yaml:
+1. Runs `cargo run --release -- gen-schema`
+2. Compares output to committed file via `git diff --exit-code`
+3. Fails build on any difference with clear error message
+4. Part of quality-matrix (Tier-1 hard gate)
+
+## References
+
+- Plan section: Phase 6.1 JSON Schema deliverable (line 2027-2045)
+- CI workflow: `.ci/argo-workflows/pdftract-ci.yaml` (template: schema-gen)
+- Generated schema: `docs/schema/v1.0/pdftract.schema.json`
+- xtask binary: `xtask/src/bin/gen_schema.rs`
+
+## Notes
+
+- Schema generation is fast (~12 seconds cold build)
+- No warnings or errors during generation
+- Schema is committed to repo (not generated at build time)
+- This enables schema diffs to be reviewable in PRs
+- Schema $id uses pdftract.com domain (DNS already available)
+
+## Retrospective
+
+### What worked
+- The schemars crate integrates seamlessly with existing serde derives
+- CI gate provides clear error messages with reproduction steps
+- Stable sorting ensures deterministic output for diffs
+
+### What didn't
+- No issues encountered; implementation was already complete
+
+### Reusable pattern
+- For similar schema generation tasks: use schemars + xtask + CI diff gate
+- Always use BTreeMap sorting for deterministic JSON output
+- Commit generated files (don't generate at build time) for reviewability