Restructure agent setup

.opencode/skills/prism-dag/SKILL.md

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+---
+name: prism-dag
+description: DAG / graph patterns for Prism — adjacency list rules, arena allocation, Kahn's algorithm, flat buffer layout
+license: MIT
+compatibility: opencode
+metadata:
+  domain: core
+---
+## What I do
+
+Captures the conventions for Prism's directed acyclic graph (DAG) implementation: how edges are stored, how the graph is validated, and how to avoid common pitfalls.
+
+## When to use me
+
+Use this when working on graph/DAG structures (`pr_graph.h`, `pr_graph.c`, or `scratchpad/dag.c`), adding new node types, or modifying the topological sort / cycle detection logic.
+
+## Conventions
+
+### Adjacency lists — separate edge nodes
+
+Adjacency list nodes must be **separately allocated from the vertex array**. Never use the vertex struct itself as a linked-list node in another vertex's adjacency chain — that shares the `next` pointer between two roles and corrupts the graph.
+
+```c
+// correct — per-edge copy on the arena
+static void addEdge(PrGraph *g, const WpAllocator *alloc, u64 from, u64 to) {
+	PrVertex *src = &g->vertices[from];
+	PrVertex *dst = wpMemAllocatorAlloc(alloc, sizeof(PrVertex));
+	if (!dst) { /* handle OOM */ return; }
+	dst->id    = g->vertices[to].id;
+	dst->value = g->vertices[to].value;
+	dst->next  = src->next;
+	src->next  = dst;
+}
+
+// wrong — reuses the destination vertex as the list node
+static void addEdge_bad(PrGraph *g, u64 from, u64 to) {
+	PrVertex *src  = &g->vertices[from];
+	PrVertex *dest = &g->vertices[to];
+	dest->next = src->next;
+	src->next  = dest;   // overwrites dest->next used elsewhere
+}
+```
+
+Arena bump allocation (`wpMemAllocatorAlloc`) is the natural fit for edge nodes. Always NULL-check the result — arena allocators can fail if the backing buffer is exhausted.
+
+### Flat buffer layout
+
+For hot-path graph evaluation, prefer SoA layouts and keep the DAG in contiguous arrays rather than individually allocated linked structures.
+
+### Cycle detection
+
+Use Kahn's algorithm integrated into `prGraphAddEdge` for cycle detection with rollback. When an edge would create a cycle, the edge is not added and the function returns an error.
+
+### Memory management
+
+Stack-allocate where possible; pass `WpAllocator *` explicitly for heap allocations.