Ring Buffer done — that's Phase 1 finished

What I got through

• Started with the full ring-buffer re-study I'd planned at the end of last session — wraparound mechanics, telling full from empty, all three disambiguation strategies compared side by side, and why "sacrifice a slot" is the real-world standard. Ended up chasing down a bunch of follow-up questions about producer/consumer concurrency, peeking vs. actually removing an item, and why the data has to move before the index advances.
• Went back and fixed the is_full/is_empty exercise I'd left hanging — turned out to be one stray brace in an if condition.
• Learned put/get on a ring_buffer_t struct fresh. Traced through it 3 out of 3 unaided, with one correction along the way (see below). The actual writing exercise took three tries before it compiled clean, but I got it through a full fill-to-max, overrun, drain-to-empty, underrun test.
• Passed the chapter test 5/5 (100%) — clean, no help, all five questions.

A mistake I made

• Mixed up is_empty's condition with is_full's while I was reasoning through put — caught it during the trace, before it turned into a real bug.

What this actually means

Ring Buffer is done. That's all of Advanced C done. That's Phase 1 done — 257 out of 257 bytes, every chapter test passed. The only thing standing between me and Phase 2 now is the Milestone Test.