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+# NUVMAP Delta-DAG Sharding Spec
+
+## Goal
+
+Make search traces shardable, replayable, and independently verifiable.
+
+## Shard ID format
+
+```text
+famm-ddag://<problem_hash>/<shard_type>/<hash>
+```
+
+## Required hashes
+
+```json
+{
+  "problem_hash": "sha256(base instance)",
+  "rule_hash": "sha256(route rule + weights)",
+  "projection_hash": "sha256(NUVMAP projection config)",
+  "node_hash": "sha256(projected node payload)",
+  "edge_hash": "sha256(parent_hash + delta + child_hash)",
+  "receipt_hash": "sha256(final verifier payload)"
+}
+```
+
+## Edge verification
+
+Every delta-edge shard must verify:
+
+```text
+apply_delta(parent_state, delta, route_rule)
+→ child_state
+
+hash(project(child_state))
+= child_node_hash
+```
+
+## DAG merge condition
+
+Two states may share a node if their NUVMAP projections match:
+
+```math
+h_{\mathrm{NUV}}(s_a)=h_{\mathrm{NUV}}(s_b)
+```
+
+The merge is safe only for the selected projection level. Exact receipt still replays an explicit solution path.
+
+## Projection levels
+
+| Level | Meaning | Use |
+|---|---|---|
+| `exact` | raw canonical state | safest; fewer merges |
+| `frontier` | frontier + domains + scars + residual | normal FAMM use |
+| `symmetry` | frontier plus symmetry/canonical color relabeling | aggressive merge |
+| `semantic` | semantic-mass basin only | routing prior, not proof |
+
+## Receipt rule
+
+The DAG may guide and compress search, but the final solution must be verified by a domain exact gate.
+
+For graph coloring:
+
+```math
+R(c)=|\{(u,v)\in E:c_u=c_v\}|=0
+```
+
+For exact cover:
+
+```math
+R(x)=\|Ax-\mathbf 1\|_1=0
+```