selecting the displays native resolution

docs/efi.md

@@ -58,10 +58,26 @@ The comment in `boot()` says exactly this:
 ### 1. Query the framebuffer (`queryFramebuffer`)
 
 We ask the firmware for the **Graphics Output Protocol (GOP)**, which describes
-the linear framebuffer — its address, resolution, pitch, and pixel format. We
-copy those facts into our own `Framebuffer` struct. This *must* happen now,
-because after exit there's no GOP to ask. (See [framebuffer.md](framebuffer.md)
-for what those fields mean.)
+the linear framebuffer — its address, resolution, pitch, and pixel format —
+and, when we can, switch the display to its native resolution first:
+
+- Locate GOP via its *handle* (not `locateProtocol`), because the same handle
+  also carries the display's **EDID**.
+- Read the EDID (trying the `EDID_ACTIVE` then `EDID_DISCOVERED` protocol on each
+  GOP handle) and parse the first Detailed Timing Descriptor — by convention the
+  panel's preferred (native) resolution. This is best-effort: firmware installs
+  these protocols inconsistently, and OVMF with QEMU's stdvga doesn't expose them
+  at all.
+- If we got a native resolution, enumerate the GOP modes with `queryMode` and
+  `setMode` to the one that matches it (must be a linear 32bpp layout we can
+  paint into). If EDID gave us nothing, we **keep the firmware's current default
+  mode** rather than guess — with a valid EDID the firmware normally defaults to
+  the native mode itself, so its choice beats second-guessing it with, say, the
+  largest advertised mode.
+- Copy the resulting address/resolution/pitch/format into our own `Framebuffer`.
+
+All of this *must* happen now, because after exit there's no GOP to ask. (See
+[framebuffer.md](framebuffer.md) for what those fields mean.)
 
 ### 2. Load the kernel (`loadKernel` + `loadElf`)
 
@@ -149,7 +165,7 @@ power on
   -> UEFI firmware initialises hardware
   -> finds esp/EFI/BOOT/BOOTX64.efi, runs it        (our efi.zig main)
        -> grab boot services
-       -> queryFramebuffer   (via GOP)
+       -> queryFramebuffer   (via GOP: EDID native res, setMode, describe fb)
        -> loadKernel         (read danos ELF, load PT_LOAD segments to 0x100000)
        -> exitBootServices   (retry until the memory-map key holds)
        -> jump to e_entry, boot_info pointer in RDI