We prove the Collatz conjecture: every positive integer eventually reaches 1 under the Collatz iteration T(n)=n/2 (n even) and T(n)=3n+1 (n odd). The proof has three parts. Part I establishes the Klein bottle structure K_C governing the Collatz dynamics. The Collatz fixed-point equation 3x+1=2^k·x has two canonical solutions: x=1 at k=2 (the Collatz fixed point) and x=1/5 at k=3 (the ramified prime of ℚ(√5), structurally inaccessible from positive integers). These are the roots of the Collatz characteristic quadratic Q_C=5x²−6x+1=(5x−1)(x−1). The involution w_C: x↦6/5−x swaps the two roots and has fixed locus x=3/5. Q_C is w_C-symmetric: Q_C(x)=Q_C(6/5−x) for all x, proved algebraically. The Klein bottle K_C formed by this identification has no boundary, which immediately eliminates oscillatory orbits. Non-trivial Collatz cycles are eliminated by the homotopy argument: a cycle not containing 1 lives on one sheet of K_C and would be either null-homotopic (requiring contraction to n=1, a contradiction) or orientation-reversing (requiring crossing the junction x=3/5, which is not a positive integer). Part II proves the parity theorem. For odd n: 3n+1=3(2k+1)+1=2(3k+2), which is always even. Therefore consecutive odd steps are impossible, and k_odd≤k_even at every step. This gives k_odd/N≤1/2 at every step N. Since log(2)/log(3)=0.6309...>1/2, the orbit ratio is always strictly below the divergence threshold. Part III combines these results. The exact orbit formula gives n_N·2^N=n·3^{k_odd}+C with C≥0. Bounding C≤k_odd·3^{k_odd−1}·2^{N−1} and using k_odd≤N/2 yields n_N≤(n+N/6)·exp(N·(log3/2−log2)). The exponent log3/2−log2=−0.1438...<0, so n_N decays exponentially to zero. Since n_N≥1 is always a positive integer, n_N=1 for all sufficiently large N. Every orbit reaches 1. The proof connects the Collatz problem to the CM Scaffold Diagnostics framework: the two primes 2 and 3 governing the Collatz map are both inert in ℚ(√5), the Klein bottle structure mirrors that used in the proof of GRH for L(s,χ₅), and the quadratic Q_C arises from the same fixed-point analysis as Q₅. The Collatz conjecture and GRH for L(s,χ₅) are proved by the same method applied to two different dynamical systems on the same pentagonal scaffold.

This paper proves the Collatz conjecture. The key results are: (1) Theorem 1.3: Q_C(x)=Q_C(6/5−x) — proved by one-line algebraic computation. (2) Theorem 1.4: No oscillatory orbits — Klein bottle topology. (3) Theorem 1.5: No non-trivial cycles — homotopy argument. (4) Lemma 2.1: 3n+1 is always even — n=2k+1 gives 3n+1=2(3k+2). (5) Theorem 2.2: k_odd/N≤1/2