docs(policy): amdgpu/DCN315 display-slice C exemption (operator-approved 2026-08-04)

AGENTS.md

@@ -462,6 +462,27 @@ This exemption mirrors the operator-approved linux-kpi + redbear-iwlwifi exempti
 struct layouts most reliably defined in C headers matching the Linux source, and the
 transport follows the proven bounded-C-transport pattern.
 
+### amdgpu + redbear DCN315 display-slice exemption (operator-approved 2026-08-04)
+
+This block (a) regularizes the PRE-EXISTING amdgpu C surface
+(`local/recipes/gpu/amdgpu/source/` — it predates the formal Rust-only policy; it is
+recorded here, not expanded) and (b) authorizes the DCN315 minimal display slice C
+boundary BY CATEGORY:
+
+- **Authorized C ABI surface:** register access, DMUB interface, firmware load
+  (`dcn_3_1_5_dmcub.bin`). No modeset policy, no connector state, no scheme logic in C.
+- **Reference-only Rust reimplementation:** DML math, resource-pool construction, HWSS
+  sequencing, modeset policy — ported into Rust using the Linux source as reference,
+  never compiled as C.
+
+**Sequencing:** this category-level boundary landed first (todo 24 of the
+ryzen-7000-x670e-compat program); the DCN315 closure record (derived from Linux 7.1
+`dcn315_resource.c` before any port code is written) assigns every closure unit to
+exactly one of the two classes above and is appended to this block as the concrete
+surface list. No C may be added beyond the units the closure record classifies as C ABI.
+
+Concrete surface list: **PENDING** — appended by the DCN315 closure record (todo 33).
+
 ## DURABILITY POLICY
 
 Every change to an upstream-owned source tree (anything under `recipes/*/source/`) **must** be