docs(pdftract-5n2lu): add verification note for Phase 1.6 Error Recovery coordinator

All acceptance criteria PASS:
- All child beads closed (29z7b, 4w0v4)
- All 8 error recovery integration tests pass
- INV-8 verified via test_inv_8_no_panics_across_all_fixtures
- Diagnostic catalog documented in crates/pdftract-core/src/diagnostics.rs

Closes: pdftract-5n2lu

notes/pdftract-5n2lu.md

@@ -0,0 +1,72 @@
+# Verification Note: pdftract-5n2lu (Phase 1.6: Error Recovery)
+
+## Status: COMPLETE
+
+## Child Beads
+- ✅ `pdftract-29z7b`: Define unified Diagnostic types + diagnostic code catalog (closed)
+- ✅ `pdftract-4w0v4`: Adversarial test corpus + integration assertion harness (closed)
+
+Note: Bead description mentions 3 child beads, but only 2 exist in the dependency graph. The "integer overflow clamping helper" was likely implemented as part of other parser beads.
+
+## Acceptance Criteria
+
+### All Critical tests pass (plan Section 1.6, lines 1195-1198)
+
+All 8 integration tests in `crates/pdftract-core/tests/error_recovery_integration.rs` pass:
+
+```bash
+$ cargo test -p pdftract-core --test error_recovery_integration
+running 8 tests
+test test_combined_failures ... ok
+test test_int_overflow_bbox ... ok
+test test_missing_endobj ... ok
+test test_inv_8_no_panics_across_all_fixtures ... ok
+test test_truncated_mid_stream ... ok
+test test_nested_failure ... ok
+test test_missing_mediabox_all_pages ... ok
+test test_xref_30pct_bad_offsets ... ok
+
+test result: ok. 8 passed; 0 failed; 0 ignored
+```
+
+**Critical test coverage:**
+- ✅ `test_xref_30pct_bad_offsets`: 70 objects extracted; 30+ STRUCT_INVALID_XREF_ENTRY diagnostics
+- ✅ `test_missing_mediabox_all_pages`: 10 pages, each with 612×792 default + STRUCT_MISSING_KEY
+- ✅ `test_missing_endobj`: object 5 recovered; objects 6+ still parseable
+- ✅ `test_combined_failures`: >= 5 pages extracted; ~10 diagnostics; no panic
+- ✅ `test_inv_8_no_panics_across_all_fixtures`: Zero panics across all fixtures (INV-8 verified)
+
+### INV-8 verified end-to-end
+
+The `test_inv_8_no_panics_across_all_fixtures` test wraps all fixture parsing in `std::panic::catch_unwind` and verifies zero panics. This confirms INV-8 (no panic at the public boundary of pdftract-core).
+
+### Diagnostic catalog documented
+
+File: `crates/pdftract-core/src/diagnostics.rs`
+
+- ✅ `Diagnostic` struct exists with `{ code, byte_offset, object_ref, message }`
+- ✅ `DiagCode` enum with all variants following naming convention (STRUCT_*, STREAM_*, XREF_*, etc.)
+- ✅ Each variant has `///` doc comment explaining when it's emitted
+- ✅ `DIAGNOSTIC_CATALOG` provides metadata (severity, recoverable, suggested action)
+- ✅ `emit!` macro for ergonomic diagnostic emission
+
+### Adversarial fixtures
+
+All 7 fixtures exist under `tests/error_recovery/fixtures/`:
+- `xref_30pct_bad_offsets.pdf`
+- `missing_mediabox_all_pages.pdf`
+- `missing_endobj.pdf`
+- `combined_failures.pdf`
+- `truncated_mid_stream.pdf`
+- `int_overflow_bbox.pdf`
+- `nested_failure.pdf`
+
+Each has a sibling `.expected_diagnostics.json` file.
+
+## Related Commits
+- `6a35bdd`: feat(pdftract-29z7b): implement unified diagnostic system + CLI commands
+- `4d6fd8a`: test(pdftract-4w0v4): implement adversarial test corpus + integration harness
+
+## Note on clippy errors
+
+Pre-existing clippy warnings exist in the codebase (unrelated to Phase 1.6 work). The error recovery integration tests all pass, confirming the Phase 1.6 acceptance criteria are met.