Add CUB implementation plan spec and update project documentation

New docs/_CUB_RBPKGBUILD_IMPL_PLAN.md with full CUB package builder specification
covering RBPKGBUILD format, CLI commands, build flow, BUR repository, and AUR conversion.
Updated AGENTS.md with pkgutils extensions and CUB integration details.
Updated AMD GPU integration docs with current P2 progress.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

local/docs/P2-AMD-GPU-DISPLAY.md

@@ -25,7 +25,7 @@ DRM scheme daemon. Registers scheme:drm/card0.
 - GEM: buffer object create/mmap/close
 - Dispatches to AMD driver backend
 
-### amdgpu source (local/recipes/gpu/amdgpu-source/)
+### amdgpu C port (local/recipes/gpu/amdgpu/source/)
 AMD GPU driver source extracted from Linux 7.0-rc7:
 - drivers/gpu/drm/amd/ — full AMD driver (269k lines)
 - drivers/gpu/drm/ttm/ — TTM memory manager
@@ -38,11 +38,10 @@ Compiles AMD DC display code against linux-kpi headers with -D__redox__:
 - redox_glue.h — type compatibility, function stubs, macro replacements
 - redox_stubs.c — C implementations of Linux kernel API stubs
 - amdgpu_redox_main.c — daemon entry point replacing module_init
-- Makefile.redox — standalone build for development
 
 ## Build Integration
 
-Config: local/config/my-amd-desktop.toml
+Config: config/redbear-desktop.toml (includes desktop.toml + Red Bear GPU packages)
 - Includes redox-drm and amdgpu packages
 - filesystem_size = 8196 (8GB, needs space for firmware blobs)
 
@@ -89,9 +88,12 @@ pcid: local/config/pcid.d/amd_gpu.toml
 |------|---------|
 | local/recipes/gpu/redox-drm/ | DRM scheme daemon |
 | local/recipes/gpu/amdgpu/ | Build recipe + integration glue |
-| local/recipes/gpu/amdgpu-source/ | AMD driver source (from Linux 7.0-rc7) |
-| local/config/my-amd-desktop.toml | Build config |
-| local/config/pcid.d/amd_gpu.toml | PCI auto-detection |
+| local/recipes/gpu/amdgpu/source/ | AMD driver C port source (from Linux 7.0-rc7) |
+| config/redbear-desktop.toml | Build config |
+| local/config/pcid.d/amd_gpu.toml | PCI auto-detection (AMD) |
+| local/recipes/gpu/redox-drm/source/src/drivers/interrupt.rs | MSI-X/legacy interrupt abstraction |
+| local/config/pcid.d/intel_gpu.toml | Intel GPU PCI auto-detection |
+| local/patches/base/P0-pcid-config-endpoint.patch | pcid /config file endpoint |
 | local/scripts/build-amd.sh | Build wrapper |
 | local/scripts/test-amd-gpu.sh | Test script |
 
@@ -102,3 +104,25 @@ pcid: local/config/pcid.d/amd_gpu.toml
 | redox-driver-sys | ✅ | MmioRegion, PciDevice, IrqHandle, DmaBuffer |
 | linux-kpi | ✅ | C headers, FFI stubs (kmalloc, mutex, spinlock...) |
 | firmware-loader | ✅ | scheme:firmware daemon |
+
+## P1/P2 Changes Since Initial Implementation
+
+### pcid /config endpoint (T1)
+- Added `Config { addr: PciAddress }` handle to pcid scheme
+- Routes `/scheme/pci/{addr}/config` to raw PCI config space read/write
+- Enables redox-driver-sys PciDevice to access config space for MSI-X, BAR parsing
+
+### MSI-X interrupt support (T2-T4)
+- Created shared `InterruptHandle` enum in `redox-drm/src/drivers/interrupt.rs`
+- Tries MSI-X first (find capability → parse → map table → mask_all → enable → request_vector)
+- Falls back to legacy IRQ if MSI-X unavailable
+- Both AMD and Intel drivers use `InterruptHandle::setup()`
+
+### Dynamic PCI device info (T6)
+- Replaced hardcoded `redox_pci_find_amd_gpu()` stub with `redox_pci_set_device_info()`
+- Rust side passes real PciDeviceInfo (vendor, device, revision, IRQ, BAR0/BAR2) to C via FFI
+- C layer validates the struct is populated before `amdgpu_redox_init()` uses it
+
+### Intel GPU support (T4-T5)
+- Intel driver switched to shared `InterruptHandle` (MSI-X + legacy)
+- Added `local/config/pcid.d/intel_gpu.toml` for auto-detection (vendor 0x8086, class 0x03)