docs: add session break summary for 2026-07-19

docs/sessions/session-break-summary-2026-07-19-1310.md

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+# Session Break Summary - 2026-07-19 13:10
+
+## Current State
+- **Branch**: `feat/reader-inc2-caseband` (pushed to remote, maps to PR #80)
+- **Worktree**: `core-wt-inc2`
+- **What was just completed**: 
+  - Fixed `_token_in` in `generate/math_roundtrip.py` to enforce contiguous substrings when matching multi-word phrases, addressing a latent `wrong=0` hole.
+  - Successfully ran `smoke` validation suite and `holdout_dev/v1` exact measurement.
+  - Case 0148 is confirmed solved, converting 1 case while holding `wrong=0` perfectly across the full 500 cases (`correct=6 wrong=0 refused=494 (n=500)`).
+  - Graph dump for case 0148 committed to `docs/research/0148-first-conversion-proof.md` as proof of correct-for-the-right-reason binding.
+  - PR #80 is updated with these fixes and ready for merge.
+
+## Next Concrete Steps
+1. **Merge PR #80** to ratify Increment 2 (CASE-FIRST) and officially claim the first conversion of this arc.
+2. **Review/Execute next targets**:
+   - `0001` (fast-follow): Needs `than` alongside `as` + aggregate "two other harbors combined" + "each".
+   - `q:complex` decomposition direction.
+
+## Open Invariants / Hazards
+- The solver is currently fail-closed and strictly guards `wrong=0`. When introducing the 0001 capabilities (e.g. `two other harbors combined` as a 2-peer sum), ensure that aggregate logic remains defensively bounded and doesn't pollute the broader `wrong=0` baseline.
+
+## Key Files to Re-Read
+- `docs/research/increment-2-caseband-plan-2026-07-19.md` (for the planned continuation work on 0001)
+- `generate/math_roundtrip.py` (specifically `_token_in`)
+- `generate/math_candidate_parser.py`