added documentation

TODO.md

@@ -16,3 +16,26 @@
 - ~fetch requested files from mirror~
 - ~DB sync from mirror~
 - ~Config file and import~
+
+Looking at what you've built and what's left on your TODO, here's how I'd think about the "done" line for a capstone:
+
+**What you already have that's impressive:**
+- Real concurrent systems work — singleflight, atomic ops, mutex
+- Custom HTTP transport with timeout tuning
+- Atomic file writes with the tmp-then-rename pattern
+- Meaningful test suite with httptest, not just trivial unit tests
+- Clean dependency injection, thoughtful package boundaries
+- Config validation with proper error wrapping
+
+**What would make it a complete capstone story:**
+- The streaming solution for large packages — this is your most interesting unsolved technical problem and directly demonstrates you understand the HTTP layer
+- At least one more meaningful feature working end-to-end, either the refresh scheduling via systemd timer or the prefetch-on-refresh logic
+- Actually deployed and serving your home network — "running in production" is a strong closer
+
+**What I'd leave out of the capstone scope:**
+- The AUR builder — that's a whole second project honestly
+- Chi middleware — nice but not substantive enough to matter
+
+The through-line you want to be able to tell is: *I built a caching reverse proxy from scratch in Go, handling concurrency, filesystem atomicity, and HTTP semantics correctly, and deployed it on real hardware.* You're close to being able to say that. The streaming piece and a working deployment are the remaining gaps.
+
+How far out is the capstone deadline?