Get a math problem solved with the actual decision points flagged, not just a clean final derivation

Solve this problem step by step, but I need you to explicitly flag every point where you had to choose a method or approach among real alternatives — not just show a clean derivation that makes the solution look more obvious than it actually was to arrive at.

PROBLEM
Solve the system: x^2 + y^2 = 25 and y = x + 1

WHAT METHODS WE'VE COVERED SO FAR IN CLASS
Substitution method for systems, factoring quadratics, the quadratic formula — haven't covered matrix methods yet

WHAT I'M SUPPOSED TO PRACTICE FOR
Recognizing when to substitute versus when to try factoring first on nonlinear systems, since I keep picking the slower path on the actual quiz

Solve the problem using only methods from Substitution method for systems, factoring quadratics, the quadratic formula — haven't covered matrix methods yet — if the most elegant solution uses something we haven't covered, use the approach we have covered instead, even if it's longer, since the point is practicing what I'm actually responsible for. At every step where there was a genuine choice of approach (which algebraic manipulation to try first, whether to substitute or use a formula directly, which case to check first in a multi-case problem), stop and state explicitly: what the choice point was, what the alternatives were, and why you picked the one you did over the others — not just proceeding as if there were only ever one obvious next move. Where a step is just mechanical execution of an already-chosen approach (arithmetic, simplifying an expression) with no real decision involved, don't flag it — only genuine decision points, so the flags stay meaningful rather than becoming noise on every line. After the full solution, add a short section naming the one decision point in this problem most likely to trip someone up on a similar problem under exam conditions, and what signal in the problem should have pointed toward the right choice.

WHAT NOT TO DO
Do not use a method outside Substitution method for systems, factoring quadratics, the quadratic formula — haven't covered matrix methods yet even if it's shorter. Do not flag purely mechanical steps as decision points — that dilutes the signal on what's genuinely worth learning to recognize.

OUTPUT FORMAT
1. Step-by-step solution with inline [DECISION POINT] flags only at genuine choice points, each with the alternatives considered and why this one was chosen.
2. Final answer.
3. The single most exam-relevant decision point in this problem and the signal that should cue the right choice.