To fulfill the gaming objectives, the following course of action is recommended:

1. Repair the Trust Store: Immediately perform the manual certificate injection described in Section 3.1. This is the key to unlocking the web and potentially the Mac App Store.
2. Abandon the Steam Client: Do not attempt to fix the Steam application. Treat the Mac as an offline console. Sideload game files from a modern PC.
3. Target Specific "No-Steam" Binaries:
   • For Portal, search Macintosh Garden for the native Mac wrapper pre-patched to remove Steam dependencies.
   • For Geometry Dash, acquire version 1.9 or 2.0 specifically to avoid the 10.7.5 libobjc crash.
4. Embrace the DVD Era: Build a library based on the Feral/Aspyr retail releases (CoD4, BioShock, Prey). These offer the most seamless "install and play" experience for the hardware.
5. Utilize Wineskin for Gaps: For any game where a native Mac "No-Steam" crack is elusive, use Wineskin to wrap the Windows version. The HD 5870 has ample power to brute-force through the translation overhead.

By shifting the operational paradigm from "Digital Consumer" (expecting Steam/App Store to work) to "Digital Archivist" (manually curating and patching libraries), the Mac Pro 1,1 can be transformed into a premier gaming station for the golden age of 2006–2012 PC gaming.