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+# 2026-05-18 — odd-q neighbour table aligned with axial directions
+
+## Background
+
+`mc-core` exposed two direction conventions: `AXIAL_DIRECTIONS` (canonical,
+documented in `HEX_GEOMETRY.md`) and `ODD_Q_NEIGHBORS` (the offset-coord
+projection used by climate, ecology, GPU LUT, infantry shove, courier). The
+two disagreed: an exhaustive 7×7 cross-check produced 182 direction
+mismatches. `mc-pathfinding` had its own (correct) copy of the table.
+
+## Latent symptoms
+
+- **Climate**: `wind_direction` is written as an `AXIAL_DIRECTIONS` index
+  (`mc-mapgen::assign_wind` — `dirs = [3, 0, 3, 0, 3, 0]`) and read via
+  `hex::upwind_offset` / `downwind_offset`, which routed through the
+  misaligned table. CPU and GPU climate diffusion picked the wrong upwind
+  cell for most parities.
+- **Infantry shove**: pushing "east" from an odd column resolved to the
+  NE hex instead of the actual east hex.
+- **GPU LUT** (`mc-compute::build_neighbor_lut`) inherited the same skew —
+  CPU/GPU climate were broken in lockstep with each other, so unit tests
+  comparing the two stayed green.
+
+## Fix
+
+`crates/mc-core/src/algorithms/hex.rs::ODD_Q_NEIGHBORS` rewritten to the
+axially-consistent table (the same one `mc-pathfinding` already used). A
+new `odd_q_table_agrees_with_axial_directions` test pins the invariant by
+cross-checking every entry against the axial round-trip.
+
+Two infantry shove tests (`shove_pushes_enemy_to_empty_hex`,
+`shove_blocked_when_destination_occupied`) had hardcoded the broken
+east-offset; updated to match the actual east hex in the odd-q stagger.
+
+## Verification
+
+Per-crate test runs after fix:
+
+| Crate | Tests | Result |
+|---|---|---|
+| `mc-core` | 250 | ✅ (added 1 locking test) |
+| `mc-mapgen` | 59 | ✅ |
+| `mc-compute` | 45 | ✅ |
+| `mc-climate` | 324 | ✅ |
+| `mc-ecology` | 7 | ✅ |
+| `mc-pathfinding` | 0 (lib) | ✅ |
+| `mc-turn` | 222 | ✅ (2 tests had expected values rewritten) |
+
+Unaffected subsystems (pure axial throughout — edge identity / ZOC,
+terrain blends, river generation, hydrology `flow_out`) continued to pass
+without modification.
+
+## Files touched
+
+- `src/simulator/crates/mc-core/src/algorithms/hex.rs` — table + test + doc
+- `src/simulator/crates/mc-turn/src/action_handlers/infantry.rs` — two tests
+- `public/games/age-of-dwarves/docs/HEX_GEOMETRY.md` — §13 status row