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.

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

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+---
+name: prism-rhi
+description: RHI (Rendering Hardware Interface) patterns — compile-time dispatch, by-value desc structs, wapp array aliases, backend file layout
+license: MIT
+compatibility: opencode
+metadata:
+  domain: rendering
+---
+## What I do
+
+Captures the RHI conventions for Prism: how backends are dispatched, how descriptor structs and arrays are handled, and how the files are organized.
+
+## When to use me
+
+Use this when working on any file in `scratchpad/rhi/` or `src/prism/rhi/`, or when creating a new backend (Vulkan, D3D12, Metal).
+
+## Conventions
+
+### Backend dispatch
+
+Backend selection is compile-time via `-D PR_RHI_VULKAN` / `-D PR_RHI_D3D12` / `-D PR_RHI_METAL`. The umbrella header `pr_rhi.h` includes the appropriate alias file:
+
+```c
+#if defined(PR_RHI_VULKAN)
+#  include "vulkan/pr_rhi_vk_aliases.h"
+#elif defined(PR_RHI_D3D12)
+#  include "d3d12/pr_rhi_d3d12_aliases.h"
+#elif defined(PR_RHI_METAL)
+#  include "metal/pr_rhi_metal_aliases.h"
+#else
+#  error "Define one of: PR_RHI_VULKAN, PR_RHI_D3D12, PR_RHI_METAL"
+#endif
+```
+
+Each `_aliases.h` file maps generic names to backend-specific names:
+
+```c
+#define prRhiCreateDevice       prRhiCreateDeviceVk
+#define prRhiCreateSwapchain    prRhiCreateSwapchainVk
+#define prRhiCreateBuffer       prRhiCreateBufferVk
+// …
+```
+
+Backend implementations are suffixed with the backend name: `pr_rhi_vk_device.c`, `pr_rhi_vk_swapchain.c`, etc.
+
+### Desc structs
+
+All descriptor structs are passed **by value**, not `const *`:
+
+```c
+// correct
+PrRhiDevice *prRhiCreateDevice(PrRhiPhysicalDevice *pdev, PrRhiSurface *surface,
+                                PrRhiDeviceDesc desc, WpAllocator *alloc);
+
+// wrong
+PrRhiDevice *prRhiCreateDevice(PrRhiPhysicalDevice *pdev, PrRhiSurface *surface,
+                                const PrRhiDeviceDesc *desc, WpAllocator *alloc);
+```
+
+### File layout
+
+```
+scratchpad/rhi/
+├── pr_rhi.h              ← umbrella header (API declarations + backend dispatch)
+├── pr_rhi_types.h        ← shared types (enums, element types, array aliases, desc structs, opaque handles)
+├── vulkan/
+│   ├── pr_rhi_vk.h       ← Vulkan backend header (opaque struct defs + Vk-suffixed decls)
+│   └── pr_rhi_vk_aliases.h ← #define alias mapping
+├── d3d12/
+│   └── …
+└── metal/
+    └── …
+```
+